WO2021186157A2

WO2021186157A2 - Method and apparatus for monomolecular layers

Info

Publication number: WO2021186157A2
Application number: PCT/GB2021/050643
Authority: WO
Inventors: Igor VOZYAKOV; Aleksandr SHCHEBLANOV
Original assignee: Vozyakov Igor; Shcheblanov Aleksandr
Priority date: 2020-03-16
Filing date: 2021-03-16
Publication date: 2021-09-23
Also published as: GB202013079D0; GB202016345D0; WO2021186159A1; WO2021186155A1; GB2593242B; GB2593256A; GB2593242A; GB202013075D0; WO2021186157A3; GB2593241B; GB2593241A; WO2021186168A1; CH717232A1; GB202018405D0; GB202013078D0; GB2593955A; GB2593243B; GB2593955B; GB2593243A

Abstract

A method of flaking nano-platelets from particles of a laminar material is provided. The method comprises steps of providing a suspension of the particles of the laminar material in a liquid; and forming a flow with toroidal vortices in the suspension of the particles such that the particles are exposed to alternating flow velocities and alternating pressures. A method of separating a mixture of graphite and nano-platelets including graphene is also provided. A method of aligning nano-platelets in a suspension is also provided.

Description

Method and Apparatus for Monomolecular Lavers

The present invention relates to the field of monomolecular layers of a solid 2D substance, such as boron, graphite, and other compounds. In particular, embodiments of the invention relate to a method of producing monomolecular layers of a solid 2D substance by separating it from a 3D (multi-monolayer) material at its structural defects and stress concentration points. For example, producing graphene in the form of platelets, nano-sized particles, and such like using source materials derived from graphite and other laminated graphite compounds.

Graphene is single layer of planar carbon whose atoms are covalently bonded into a bidimensional hexagonal lattice. It ranks among the strongest and most promising materials presently known, yet reliable manufacturing of graphene such that it can be used in modern technologies poses a number of challenges. At present, graphene can be obtained using one of a number of various methods including, but not limited to, the following:

Preparation of graphene by destroying/delaminating graphite through its chemical intercalation with halogen compounds, metal salts, etc., followed by subjecting it to thermal stress, ultrasound, or mechanical shearing. (KR 20110089625; KR 20100116399; US 2005271574; US 2009026086; US 2009155578; US 3885007).

These methods are complex and can be inefficient; they involve chemicals, high temperatures, and pressures while requiring complex equipment, such as ultrasound units and super centrifuges which can be hazardous.

Preparation of graphene by treating graphite with strong acids and thereafter reducing the graphite oxide using strong reducing agents, such as hydrazine, NaBH4, hydroquinone, etc. (US 2013197256; US 20100303706) is also known.

These methods involve the use of strong acids with the result that a substantial amount of water is required to wash unreacted products and neutralize the strong acids; they may be used in industrial operations to a limited extent. The resultant graphene has a defective crystalline structure that reduces the material’s electric conductivity, heat conductivity, wear resistance, and other characteristics.

Conventional mechanical exfoliation methods using adhesive tape are difficult to reproduce, particularly on a large scale. They typically produce exceedingly tiny amounts of graphene, under 0.001 mg, and require the use of special graphite grade, i.e. natural highly oriented pyrolytic graphite.

Graphene can be obtained from a process wherein graphite powder is wet ball-milled in an organic solvent with a surface tension of 30-45 Nnr¹. Surfaces of milling balls in use are coated with soft polymer. By coating the hard milling balls with soft polymer, damage to graphite crystal structure from rigid collisions among the milling balls is effectively decreased. Such ball-milling can improve the productivity of graphene preparation; uniform graphene product thickness of 1-2 carbon atom layers may be obtained; and industrialized production can be easily implemented (WO 2011054305), but the resultant graphene fragments are often too small, as the balls largely operate by milling the source material.

A further method to obtain graphene flakes can be performed by exfoliating a layered material, which includes dispersing graphite in a liquid medium containing therein a surfactant; and exposing the suspension or slurry to ultrasonic waves at an energy level for a sufficient length of time to produce separated nano-scaled platelets. Such ultrasound treatment is combined with mechanical shear treatment, such as using an air mill, ball mill, rotating shear blade or a combination thereof (US 2008279756).

This method’s deficiency arises from uncontrolled milling of the material, effectively throughout its volume, whereas subsequent separation of graphene from the solution containing surfactants is a highly labour-intensive process, and the use of ultrasound in operation is hazardous.

A further method for producing graphene particles or flakes comprises rubbing solid graphite against a rough grainy surface, e.g., a glass surface with roughness between 0.01 and 10 pm. Such rubbing transfers graphite onto the rough surface and leaves traces of graphene material. The said surface is then subjected to sonication in order to collect the graphene material from the same (WO 2011055039). This method is inefficient; it requires repeated interruption of the process for collecting graphene layers from the rubbing surface as to restore its roughness and continue the process of solid graphite rubbing.

An additional method for producing graphene particulates that includes dispersion of source graphite material comprises a nanotomy process in which graphene blocks are cut from a source of graphite; the tool used for this purpose is a diamond blade with its cutting edge radius ranging from 1 to 5 nanometers, while the blocks are cut out by passing the blade in separate strokes in two mutually intersecting dimensions. After the blocks are cut out, they are delaminated into numerous graphene particles using acids, such as chlorosulfonic acid, sulfuric acid, or a mixture thereof. Once graphene elements are dispersed in liquid, the same are separated from the liquid by way of filtration (US 2012272868). This method is inefficient; numerous passes have to be made using a single blade to obtain the required number of blocks; the operation is hazardous, since subsequent delamination of blocks into graphene elements is achieved using strong acids. The method is also expensive given the high cost of nanotomy diamond blades and the use of expensive precision equipment.

A further method for obtaining graphene includes dispersion of a source graphite material by way of brushing graphite with a brush to obtain a product containing graphene and graphite elements, whereby graphene is separated from the resultant product by centrifuge treatment in liquid to facilitate the product’s layering into graphite and graphene (CN 102602914). According to this method, after graphene is separated away, graphite elements that have not been separated into graphene flakes remain.

There is a need for a method of producing graphene in both large quantities and high quality. A further need exists to obtain the maximum number of sheets of 2D pre-formed layers of graphene from a 3D layered material such as graphite. Summary

Aspects of the invention are set out in the independent claims and preferred features are set out in the dependent claims.

According to a first aspect there is provided a method of flaking nano-platelets from particles of a laminar material, comprising steps of: providing a suspension of the particles of the laminar material in a liquid; and forming a flow with toroidal vortices in the suspension of the particles such that the particles are exposed to alternating flow velocities and alternating pressures.

Preferably the alternating flow velocities and alternating pressures cause the flaking of nano-platelets from the particles. Preferably neither ultrasound treatment nor cavitation effects cause the flaking of nano-platelets from the particles.

For effective flaking the flow may comprise local pressures of at least 10 MPa, preferably at least 25 MPa, further preferably at least 50 MPa. The flow may comprise local pressures of up to 1 mPa, preferably up to 0.1 mPa, further preferably up to 0.01 mPa. The method may comprise forming a turbulent flow in a suspension. The turbulent flow may be a flow with toroidal vortices.

For effective flaking the flow may comprise local velocities of at least 100 meters per second, preferably at least 150 meters per second, further preferably at least 200 meters per second. The flow may comprise local velocities of 200-400 meters per second. The flow may comprise local velocities of 2-4 meters per second. The peripheral flow velocity in a toroidal vortex may be greater than the flow velocity in the fluid outside the toroidal vortex by a factor of at least 10, preferably by a factor of at least 16, further preferably by a factor of at least 20.

For effective flaking the flow may comprise high-frequency alternating flow velocities. The flow may comprise high-frequency alternating pressures. The flow may comprise alternating flow velocities produced at a frequency of at least 500 Hz, preferably 1000 Hz, further preferably 3000 Hz. The flow may comprise alternating pressures produced at a frequency of at least 500 Hz, preferably at least 1000 Hz, further preferably at least 2000 Hz. The flow may comprise high-frequency alternating flow velocities and/or high- frequency alternating pressures produced at a frequency of 600 to 2500 Hz or 640 to 2520 Hz.

For effective flaking the toroidal vortices may have a typical diameter of at least 10 pm, preferably at least 20 pm, further preferably at least 40 pm. For effective flaking the toroidal vortices may have a typical diameter of up to 500 pm, preferably up to 100 pm, further preferably up to 50 pm. Preferably the toroidal vortices are micrometer-scale toroidal vortices.

The flow may include at least 150, preferably at least 200, further preferably at least 500 toroidal vortices per litre of suspension. The flow may include 200 to 3000 toroidal vortices per litre of suspension or 190-2940 toroidal vortices per litre of suspension.

For effective flaking the suspension of the particles may comprise at least 1 , preferably at least 2, further preferably at least 3 parts fluid per 1 part particles by mass. The suspension of the particles may comprise up to 50, preferably up to 10, further preferably up to 5 parts fluid per 1 part particles by mass. The suspension may be a suspension in water, de-ionised water, de-mineralised water, surfactant-free water, ultrapure water, ethanol, tetrahydrofurane, chloroform, acetone or toluene. Ultrapure water may have a resistivity of at least 18.1 MW-crn or at least 18.1 MW-crn at 25°C. The particles may be graphite, and the nano-platelets may include graphene.

The method may further comprise a step of dispersing particles of a laminar material in a liquid to form a suspension.

The flow may be formed by a notched rotor rotating in cooperation with a notched stator to block and open cyclically a plurality of passages for a fluid.

The method may further comprise a step of separating a mixture of graphite and nano platelets including graphene, comprising suspending the mixture of graphite and nano platelets including graphene in a liquid with 1.5-2.5 g/cm³ density for selective movement of a component part of the mixture toward a specific portion of the liquid under the influence of gravity.

According to another aspect there is provided apparatus for flaking nano-platelets from particles of a laminar material, comprising a flow generator adapted to form a flow with toroidal vortices in a suspension of the particles of the laminar material such that the particles are exposed to alternating flow velocities and alternating pressures. Apparatus may further comprising a separator for separating a mixture of graphite and nano-platelets including graphene, comprising a liquid with a density of 1.5-2.5 g/cm³ for selective movement of at least one of the graphite and the nano-platelets toward a specific portion of the liquid under the influence of gravity.

Apparatus may further comprise an aligner for aligning nano-platelets in a suspension, the aligner comprising an arrangement for bubbling a gas through the suspension for vertical orientation of the nano-platelets; and a layer of a further liquid that is immiscible with the liquid of the suspension, such that the nano-platelets move at least partially into the further liquid under the influence of gas bubbles.

According to another aspect there is provided a method of separating a mixture of graphite and nano-platelets including graphene, comprising a step of: suspending the mixture of graphite and nano-platelets including graphene in a liquid with a density of 1.5-2.5 g/cm³ for selective movement of at least one of the graphite and the nano platelets toward a specific portion of the liquid under the influence of gravity.

The movement may be settling of the graphite toward a bottom portion of the liquid. The movement may be flotation of the graphene nano-platelets (or nano-platelets including graphene) toward a top portion of the liquid.

The liquid may have a density in the range of 1.7-2.4 g/cm³. For effective separation the liquid may have a density selected based on the density of the graphite. The liquid may have a density of up to 99.9% the density of the graphite, preferably up to 99.5% the density of the graphite, further preferably up to 99% or 98.5% the density of the graphite. The liquid may have a density of at least 90% the density of the graphite, preferably at least 95% the density of the graphite, further preferably at least 98% or 98.5% the density of the graphite. The liquid may have a density in the range of 98-99% the density of the graphite, preferably approximately 98.5% the density of the graphite.

The liquid may be an aqueous solution. The liquid may be a solution of a chlorine salt, optionally NaCI, CaC or KCI.

For effective separation the method may further comprise bubbling a gas through the liquid. The gas may be introduced at or near a bottom portion of the liquid. The gas may be highly dispersed in the liquid. For effective delivery the gas may be introduced from an outlet having a size of at least 0.05 mm, preferably at least 0.1 mm, further preferably at least 0.2 mm. For effective dispersion the gas may be introduced from an outlet having a size of up to 1 mm, preferably up to 0.7 mm, further preferably up to 0.5 mm. The gas may be nitrogen. The gas may be air. The gas may be a chemically inert gas. For effective separation a flow rate of the gas into the liquid may be up to 0.004 m³/sec per 1 m² of a top surface of the liquid, or up to 0.002 m³/sec per 1 m² of a top surface of the liquid. The gas may be bubbled into the liquid at a pressure of up to 10 kPa in excess of the liquid column pressure, preferably up to 5 kPa in excess of the liquid column pressure, further preferably up to 4 kPa in excess of the liquid column pressure.

For stabilisation the method may further comprise providing a layer of a further liquid that is immiscible with the liquid of the mixture, such that one of graphite and the nano platelets move toward and into the further liquid. The further liquid may be less dense than the liquid of the mixture. The further liquid may be hydrophobic.

For collection of a component part of the mixture the method may further comprise flowing the further liquid relative to the liquid of the mixture for entrainment of a component part of the mixture by the further liquid. The method may further comprise continuously flowing the further liquid over a surface of the liquid of the mixture. The method may further comprise recovering the further liquid for collection of the nano platelets of graphene. The fluid containing the graphite may also be recovered for cycling back into the input flow. The method may further comprise flaking nano-platelets from particles of a laminar material. Flaking nano-platelets from particles of a laminar material may comprise steps as aforementioned.

According to another aspect there is provided apparatus for separating a mixture of graphite and nano-platelets including graphene, comprising a liquid with a density of 1.5- 2.5 g/cm³ for selective movement of at least one of the graphite and the nano-platelets toward a specific portion of the liquid under the influence of gravity.

Apparatus may further comprise an aligner for aligning nano-platelets in a suspension, the aligner comprising an arrangement for bubbling a gas through the suspension for vertical orientation of the nano-platelets; and a layer of a further liquid that is immiscible with the liquid of the suspension, such that the nano-platelets move at least partially into the further liquid under the influence of gas bubbles. According to another aspect there is provided a method of aligning nano-platelets in a suspension, comprising steps of: providing a suspension of the nano-platelets in a liquid; bubbling a gas through the suspension for orientation of the nano-platelets; and providing a layer of a further liquid that is immiscible with the liquid of the suspension, such that the nano-platelets move at least partially into the further liquid under the influence of gas bubbles.

The gas bubble can help orientate the nano-platelets and promote movement into the further liquid. The further liquid can help localize and stabilize the flakes in their orientation at the phase interface. The orientated nano-platelets may self-assemble in an ordered structure at an interface of the liquid the suspension under the influence of gas bubbles. The orientation of the nano-platelets may be a vertical orientation or a horizontal orientation. The liquid is preferably a water-insoluble liquid.

The liquid of the suspension may be water or an aqueous solution. The further liquid may be or may include at least one of: kerosene, petroleum oils, mineral oils, tetrachloroethylene, trichloroethylene, white spirit, organosilicon compounds, dibutoxymethane and food oils. The food oils may be waste food oils. Food oils may have low solubility in water. The further liquid may be less dense than the liquid of the suspension. This can enable the further liquid to float on top of the suspension. The further liquid may be partially soluble in the liquid of the suspension, provided it is not fully soluble such that it forms an immiscible phase.

The method may further comprise flowing the further liquid relative to the liquid of the suspension for entrainment of nano-platelets by the further liquid. The method may further comprise continuously flowing the further liquid over a surface of the liquid of the suspension.

The method may further comprise recovering the further liquid for collection of the nano platelets. The method may further comprise drawing off the further liquid at an aperture arranged at or near a phase interface between the further liquid and the liquid of the suspension. The aperture may be a slot, preferably a horizontal slot. The slot may be formed by flaps arranged to adapt to fluid flowing through the slot. The method may further comprise fixing the orientated nano-platelets relative to one another to form a meta-material of ordered nano-platelets. Fixing may consist of linking nano-platelets to one another, embedding nano-platelets in a matrix, or linking nano platelets to one another with a linking agent. The nano-platelets may be graphene and linking with a linking agent may consist of linking with 1-aminopyrene disuccinimidyl suberate. 1-aminopyrene disuccinimidyl suberate is preferably a conjugated molecule of 1-aminopyrene and disuccinimidyl suberate. 1-aminopyrene disuccinimidyl suberate can cross-link adjacent graphene nanosheets via p-p interfacial interactions.

The meta-material may be a film, an arrangement of films, a mat, a filament or an arrangement of filaments. The meta-material may be formed continuously. The meta material may comprise nano-platelets arranged in one or more layers in a regular arrangement, preferably in a fish scale pattern, a pattern with triangular packing, or a chainmail pattern. The meta-material may be formed by coating an object with the orientated nano-platelets and/or moulding a cast formed of the orientated nano-platelets. For effectiveness the gas may be introduced at or near a bottom portion of the liquid of the suspension. The gas may be highly dispersed in the liquid of the suspension. For effective delivery the gas may be introduced from an outlet having a size of at least 0.05 mm, preferably at least 0.1 mm, further preferably at least 0.2 mm. For effective dispersion the gas may be introduced from an outlet having a size of up to 1 mm, preferably up to 0.7 mm, further preferably up to 0.5 mm. The gas may be nitrogen. The gas may be air. The gas may be a chemically inert gas. For effective separation a flow rate of the gas into the liquid may be up to 0.004 m³/sec per 1 m² of a top surface of the liquid, or up to 0.002 m³/sec per 1 m² of a top surface of the liquid. The gas may be bubbled into the liquid at a pressure of up to 10 kPa in excess of the liquid column pressure, preferably up to 5 kPa in excess of the liquid column pressure, further preferably up to 4 kPa in excess of the liquid column pressure.

The method may further comprise flaking nano-platelets from particles of a laminar material. Flaking nano-platelets from particles of a laminar material may comprise steps as aforementioned. The method may further comprise separating a mixture of graphite and nano-platelets including graphene. Separating a mixture of graphite and nano-platelets including graphene may comprise steps as aforementioned. According to another aspect there is provided apparatus for aligning nano-platelets in a suspension, comprising an arrangement for bubbling a gas through the suspension for orientation of the nano-platelets; and a layer of a further liquid that is immiscible with the liquid of the suspension, such that the nano-platelets move at least partially into the further liquid under the influence of gas bubbles.

The nano-platelets may be as aforementioned. The suspension may be as aforementioned. The gas may be as aforementioned. The further liquid may be as aforementioned.

According to another aspect there is provided a meta-material formed by aligning nano platelets in an orientation in a suspension, and fixing the orientated nano-platelets relative to one another to form a meta-material of ordered nano-platelets.

The meta-material may be formed as aforementioned. The nano-platelets may be as aforementioned. The suspension may be as aforementioned.

According to further aspects there may be provided:

• A method of producing monomolecular layers of a solid substance by way of flaking at its structural defects and stress concentration points, as exemplified by flaky graphene, whereby source graphite is flaked in a generator thanks to high- frequency alternating flow velocities produced thereby, plus pressure changes in the stream of the flaking material, to obtain a flaking product containing graphene plus graphite elements.

• A method of separating flaky graphene out of the resultant flaking product, whereas flaky graphene is separated out of the flaking product by availing of graphene’s hydrophobic properties and using an aquatic phase of 1.7-2.4 g/cm³ density

• A method whereas, to improve the efficiency of separating flaky graphene from graphite and to protect flaky graphene from oxidation in atmospheric air, such aquatic phase of 1.7-2.4 g/cm³ density is injected with highly dispersed gaseous nitrogen at a pressure exceeding the column pressure of such aquatic phase by no more than 50 - 100 g/cm², while the gaseous nitrogen flow rate does not exceed 0.2 cm³/sec per 1 cm² of the aquatic phase’s free surface.

• A method whereas strict spatial orientation of the graphene flakes is achieved through vertical upward movement of the highly dispersed gaseous nitrogen as the graphene flakes raise at the interface between the nitrogen bubble and the dense aquatic phase, and also thanks to the planar form of the graphene flakes.

• A method whereas, to align graphene flakes vertically to the aquatic phase surface, a hydrophobic liquid is poured on the same and then continuously removed from the aquatic phase surface along with separated graphene through a horizontal slot whose dimensions define the meta-surface size. The volume ratio of the aquatic phase to the hydrophobic liquid is maintained between 100:2 and 100:4.

• A method whereas, in case such hydrophobic liquid is bled off above the liquid phase separation line, we obtain a meta-surface where graphene flakes are oriented vertically.

• A method whereas, in case the aquatic phase containing graphene flakes is bled off below the phase separation line, we obtain a meta-surface where graphene flakes are oriented horizontally parallel to the phase separation line.

• A method whereas, to prevent graphene particles from clumping into micelles and druses within the aquatic phase, and to make sure that graphene is continuously separated from graphite, a hydrophobic liquid is continuously poured onto the surface of the dense aquatic phase and then continuously removed from the surface of the aquatic phase along with separated graphene.

Brief Description of the Drawinqs

Example embodiments are illustrated in the accompanying figures in which:

Figure 1 illustrates a schematic diagram comprising apparatus used to perform nano platelet flaking and separation according to the present disclosure;

Figure 2 illustrates a cross-section of a generator according to an embodiment of the present invention;

Figure 3 illustrates a perspective view of a rotor disc of a generator;

Figure 4 illustrates a perspective view of a stator disc of a generator;

Figure 5 shows a cross sectional view of a portion of the generator of Figure 2;

Figure 6 shows a cross sectional view along the section A-A of Figure 5;

Figure 7 shows a cross sectional view of a generator with outlet duct;

Figures 8 illustrates a perspective view of a permanent flow generated by conditions in a generator;

Figure 9 illustrates a perspective view of a periodical flow generated by conditions in a generator; Figure 10 shows a sectional and plan view schematic of flows when a stator notch is aligned with a rotor notch;

Figure 11 shows a sectional and plan view schematic of flows when a rotor notch has no overlap with a stator notch;

Figure 12 shows a sectional and plan view schematic of flows when a stator notch has no overlap with a rotor notch;

Figures 13a, 13b and 13c illustrate graphs of local flow velocity, acceleration and absolute pressure in flow in a generator during different phases of operation;

Figure 14 shows a cross sectional side view of a generator with a nozzle;

Figure 15 shows a cross sectional front view of the generator with a nozzle of Figure 14; Figure 16 shows another nozzle;

Figure 17 shows a schematic illustration of another rotor ring;

Figure 18 shows a perspective drawing of flows with the rotor ring of Fig. 17;

Figure 19 shows a schematic view of another rotor ring;

Figure 20 shows another view of the rotor ring of Fig. 19;

Figure 21 shows a perspective drawing of another rotor ring and stator ring;

Figure 22 shows a schematic illustration of an alternative generator with axial flow; Figure 23 illustrates a schematic diagram for achieving horizontally aligned graphene flakes on a surface of a dense fluid;

Figure 24 illustrates a schematic diagram for achieving vertically aligned graphene flakes;

Figures 25a, 25b, 25c, 25d, 25e, 25f, 25g and 25h illustrate schematic diagrams of different arrangements of horizontally orientated nano-platelets; and Figure 26 illustrates stages of a method to produce aligned graphene meta-material according to the present disclosure.

In the drawings, like reference numerals are used to indicate like elements.

Detailed Description

An objective of the presently described method is to obtain nano-platelets using a simple and affordable zero-waste flaking method that produces a minimal amount of a laminar source material left unseparated. The method provides a highly productive, continuous, and efficient method, that avoids excessive fragmentation whilst retaining the spatial and planar structure of its nanoplatelets, for example by encouraging separation of the nanoplatelets at natural structural defects rather than by force as seen in some other techniques.

A method of obtaining graphene from source graphite is described as an example of the presently described zero-waste flaking method. It will be appreciated that the method can be performed on other multi-monomolecular laminar source materials such as boron nitride, molybdenum disulfide and other layered crystals. In such layered crystals the layers are stacked in a three-dimensional crystalline long-range order. The bonds between layers are substantially weaker than the bonds within a layer. The chemical bonds within a layer are for example covalent; the bonds between layers are for example metallic with a strength comparable to van der Waals bonds.

As used herein, the term ‘nano-platelets’ is synonymous with the terms ‘nano-sized platelets’ and ‘nano-scale platelets’ and preferably includes: monomolecular layers such as individual graphene sheets; bilayer structures formed of 2 monomolecular layers; few-layer structures formed of e.g. 2-10 monomolecular layers such as so-called ‘few- layer graphene’; and structures formed of multiple monomolecular layers, e.g. with a thickness smaller than 100 nm or typically smaller than 15 nm or 10 nm. Nano-platelets may have a length ranging from sub-micrometre to 100 micrometres, or less; nano platelets with a length less than 100 nm may also be referred to as nanofragments or quantum dots.

As used herein, the term ‘laminar material’ preferably designates a material formed of molecular sheets stacked in a three-dimensional regular order, such as graphite. The molecular sheets may have a quasi-infinite size. In graphite planar sheets of carbon atoms, each atom bound to three neighbours in a honeycomb-like structure, are stacked in a three-dimensional regular order. Other laminar materials include 2D materials, including boron nitride, Molybdenum disulfide and other layered crystals.

Laminar materials can be processed by highly efficient mechanical appliances using the below described method without using any aggressive chemicals, strong acids, surfactants, high temperatures, high pressures, complicated equipment, ultrasound units, super centrifuges, or large amounts of water.

A further objective is to obtain so called “meta-materials”, also referred to as “meta surfaces”, comprising aligned layers of nano-platelets, wherein a meta-material comprises an artificially produced material having a defined spatial structure. A meta- material represents a man-made and spatially structured form of nano-platelets, such as graphene, in a specifically designed arrangement for interactions amongst nanoplatelets orientated and/or aligned horizontally or vertically.

Three distinct stages of the zero-waste flaking method can be described as: nanoplatelet flaking from laminar source material, separation of the nanoplatelets from laminar source material, and preparation of nanoplatelet layers for use in industry, for example formation of a meta-material of the nano-platelets. These three distinct stages are discussed herein below as an illustrative example of how they can be used together to achieve a comprehensive method for producing aligned graphene layers from source graphite. However, the skilled person will appreciate that each of the stages can be performed individually, without the other stages, and/or that alternative methods for performing one or more of the stages can be substituted.

Figure 1 illustrates a schematic diagram of apparatus used to perform nano-platelet flaking and separation according to the three stages of the present disclosure. A method according to the present disclosure is described below.

Nano-platelet flaking from laminar source material

A first stage of the method is nano-platelet flaking from laminar source material. A three dimensional (3D) solid product or laminar material, such as graphite, to be separated into two dimensional (2D) monomolecular layers or nanoplatelets, such as graphene, is added to a first fluid solution in a first tank 1.

In the example described, any type of graphite can be used; graphite sources could include such materials as natural graphite, electrode graphite, and others comprising materials made up of numerous carbon layers. Graphite comprising defects, or solid impurities such as silicates, carbonates, etc. may be particularly helpful due to these impurities serving as stress centres for flaking. It will be appreciated that the same is true for non-carbon based laminar source materials. Typical densities of graphite are in the range of 2.08 to 2.23 gram/cm³.

Graphite 10 is introduced into a first tank 1 along with a fluid or liquid 9 such as water, for example demineralized water, such that the graphite 10 is suspended in a fluid, forming a suspension. The suspension fills the first tank 1 between the bottom of the tank and a water level 11. The suspension in the first tank 1 is in fluid connection with a generator 2. The fluid connection may be, for example, via a circulation loop that runs between the first tank 1 and the generator 2. A circulation loop allows un-flaked product from the suspension to be re-circulated back through the first tank 1 for a further round of flaking by the generator 2. The circulation of fluid through the circulation loop supplies the generator 2 with a fluid comprising a controlled proportion of graphite to be separated 10 into graphene flakes. The graphite 10 can be fed into the first tank 1 when the generator 2 is operating in circulation mode in order to control the fluid to graphite ratio. A mass ratio of liquid 9 to graphite 10 of between 3: 1 to 5: 1 has been found to work well for supplying to the generator 2, although other ratios may be similarly effective. The flaking process can take place in an aquatic system free from additives (organic and inorganic) other than the graphite 10.

The generator 2 acts to separate graphene flakes from the graphite 10 in the aqueous suspension. The generator 2 is configured to produce high-frequency alternating flow velocities and pressure oscillations to create conditions in the suspended graphite solution to split the graphite 10 at its naturally occurring structural defects and stress concentration points to produce graphene flakes. The generator itself is described in more detail in relation to Figures 2 to 22 below.

The flaking process induced by the generator 2 takes place once a guiding flow has been established in the generator 2, along with high-pressure zones applying alternating pressure and flow dynamics in the aquatic system. A pressure drop from 500 bar (50,000 kPa) to vacuum, see Figure 13c, and pressure increase from vacuum to 500 bar (50,000 kPa) created by the generator 2 split the source laminar material along its inherent nano defects into flaked nano-platelet product. In principle, a method is utilized to separate the nanoplatelets from the laminar source material. The method comprises decrease in strength of a solid body caused by adsorption of water observed when water is applied on the material surface, which reduces the strength of material due to reduction in surface energy. The stress concentration points, such as micro-fissures and structural defects naturally present in the source laminar material, serve as flaking centres in the laminar material to produce nano-platelet flakes under the -pressure variation zones created by the generator 2 in the aquatic solution.

In an example, the generator 2 impacts an incoming suspended mix of graphite and water by controlling the fluid dynamics of the suspended mix to produce localised controlled currents, for example toroidal vortices (also referred to herein as toroid vortices). Alternating accelerations of the suspended mix, along with pressure spikes, create high pressure zones and high shear turbulence zones with a force great enough to split the source graphite 10 to separate into flaked graphene segments. External high pressures and sheer stress experienced at naturally occurring defects and points of stress inherent in the graphite structure determine the resulting graphene flake geometry and structure. The stress experienced at the various defect sites and stress concentration points induced by the conditions of the generator 2 will be felt to an individual degree at each defect or stress location. As such, the conditions in the generator 2 can be tuned to create different size flakes of graphene by increasing or decreasing the pressure and stress created in the high-pressure high-shear zones.

Pre-set sizes of graphene, or nanoplatelets more generally, can be obtained by adjusting the pressure and turbulence in flow created by the generator (as described in more detail below) by altering the distance between the generator’s rotor ring and stator ring. Higher pressures and greater sheer stress experienced in the high-pressure zones of turbulence created by the generator 2 could be used to obtain a greater number of flaked nanoplatelets having a smaller but potentially more regular size and shape, whilst lower pressures and lower sheer stress could result in larger nanoplatelets potentially having less regular size and shape. It will be appreciated that the defects and stress centres, and therefore the resulting nano-platelets, are defined by the nano-structure of the laminar source material. Defects and stress centres are present in the source material before being suspended in the solution in the first tank 1, so choice of source material may affect the resulting nano-platelet geometry.

During one operating cycle, the generator 2 has been shown to separate between 8% to 25% (by mass) of source graphite into nano-platelets. Similar performance is observed for flaking of crystalline sulphur into nano-platelets.

Generator

The following description of the generator 2 used to separate the laminar source material into nano-platelets will be discussed below with reference to Figures 2 to 22. Figure 2 illustrates a cross sectional view of a generator 2 for generating toroid and spatial vortices in a liquid 102. As used herein, the term ‘spatial vortex’ is used to distinguish non-toroid vortices from toroid vortices, and includes vortices where the axis of rotation does not form a closed loop (e.g. tubular vortices, cone-shaped vortices). The generator 2 comprises: a substantially rotationally symmetrical stator housing 103, symmetrical about axis 107; an axial inlet opening 104, an eccentric outlet opening 105 directed in a plane 106 that is normal to axis 107, and a rotor 108 rotatable around axis 107 in the stator housing 103, the rotor 108 comprising radially outwardly extending channels 109 in constant fluid connection to the inlet opening 104. In an example, the rotor 108 has an outer diameter of about 30 cm ± 20%.

The generator further comprises a rotor disc 110 (also referred to as a rotor ring) rotatable about axis 107 and a stator disc 114 (also referred to as a stator ring). Figures 3 and 4 illustrate a perspective view of a rotor disc 110 and a stator disc 114 of a generator 2 respectively. Inner notches 112 are arranged periodically about the rotor disc 110, and notches 116 are arranged periodically about the stator disc 114.

The rotor disc 110, shown in Figure 3, is attached to the rotor 108 in a rotationally fixed manner radially outside the rotor 108. The rotor disc 110 comprises a side surface 111 normal to axis 107 with inner notches 112, spaced apart from one another and equidistant from the axis 107 for channelling a liquid 102 comprising a suspension of a laminar material to be flaked. The rotor disc 110 may additionally comprise outer notches 113 on the same surface 111 as the inner notches 112. These outer notches 113 can also be spaced apart from one another and equidistant from the axis 107. It should be appreciated that the rotor disc 110 may be provided as a separate part that is distinct from the rotor 108, or it may equally be provided as an integral feature or portion of the rotor 108.

The rotor disc 110 also includes outer notches 113. By virtue of the outer notches 113 the building of toroid vortices within the periodical liquid flow 119 is further increased before the liquid 102 exits the rotor disc 110.

The stator disc 114, shown in Figure 4, is attached with torque proof connection to the stator housing 103. The stator disc 114 comprises a side surface 115 configured to face the side surface 111 of the rotor disc 110 as well as stator notches 116 spaced apart from one another and spaced equidistantly around axis 107. It should be appreciated that the stator disc 114 may be provided as a separate part that is distinct from the stator housing 103, or it may equally be provided as an integral feature or portion of the stator housing 103. The number of each kind of notch 112, 113, 116 determines the throughput of liquid and is preferably between 16 and 42, although it will be appreciated that any number of notches can be used. It is not necessary for the notches 112, 113, 116 to be arranged equidistant from one another on the discs 110, 114, but it is preferred. The number of the inner notches 112 may equal the number of the outer notches 113 and/or the number of the stator notches 116. This is the case illustrated in Figures 3 and 4.

The generator 2 may further comprise a guide vane 121 inside the stator housing 103 radially outside the stator disc 114 and rotor disc 110 for guiding a total liquid flow 120 to the eccentric outlet opening 105. Passages radially outside of the stator disc 114 to the outlet opening 105 are provided by the spiral guide vane 121 , with blades bent in the opposite direction to the impeller blades. At the nearest point to the rotor and stator discs the guide vanes leave only a very small gap.

Figures 5 and 6 show the vanes 121 arranged in the stator housing 103 providing passages 123 for the flow downstream of the stator disc 114 and rotor disc 110. Figure 7 shows the guide vanes 121 feeding into the pump’s spiral discharge duct 124 leading to the outlet opening 105, as is well known in the art. The liquid exiting the stator disc 114 and rotor disc 110 passes through the passages 123 between the evenly spaced guide vanes 121 to enter the pump’s spiral discharge duct 124 and exits the generator via the outlet opening 105.

The guide vanes 121 are intended to reduce the velocity of liquid exiting the stator disc 114 and rotor disc 110. In this context, the stream’s kinetic energy is partially converted into pressure energy, with the pressure at the guide vane exit greater than the pressure at the entry thereto. The vanes can be optimized to meet specific desired operating parameters for a pump. The vanes can promote vortices staying intact downstream of the rotor/stator discs, for up to 3 to 5 meters within the discharge pipeline.

Figures 8 and 9 illustrate perspective views of a permanent flow 118 and a periodic flow 119 generated by conditions in a generator 2 respectively. In particular, Figures 8 and 9 illustrate how the conditions change as the rotor disc 110 and the stator disc 114 move relative to one another. A permanent flow 118 flows in a direction illustrated by arrows in Figure 8 and flows perpendicular to a periodic flow 119 illustrated by an arrow in Figure 9. Manipulation of these flows helps to create toroid vortices in the liquid 102. A permanent liquid flow 118 between the discs 110, 114 flows between the flat parallel side surface 111 , 115 of rotor disc 110 and stator disc 114 and moves in a constant radial direction, independent of the positioning of the notches 112, 116. The rotor disc 110 and the stator disc 114 are spaced apart by a gap 117. This gap 117 allows a liquid flow, defined as the permanent flow 118, through from the inner notches 112 to the outlet opening 105. The gap 117 provides for spatial vortices to be generated in the liquid flow, in use, due to the velocity difference between the opposing side surfaces 111 , 115, which define the gap 117, and due to periodical disruptions by the portioned liquid 102 passing through the gap 117 in an axial direction from the centre of the discs outward as illustrated by arrows 118 in Figure 8. This permanent liquid flow 118 contributes between 5% and 30% of the total liquid flow 120 through the generator 2 depending on the size of the gap 117. In some examples, such as when separating graphene layers from graphite, the gap 117 between the rotor disc 110 and stator disc 114 is preferably between 0.8 mm and 1.2 mm wide. In other examples the gap 117 between the rotor disc 110 and stator disc 114 is between 1 mm and 1.8 mm wide. This permanent liquid flow 118 is independent of the actual position of the rotor 108.

Inner and outer notches 112, 113 of the rotor disc 110 and stator notches 116 of the stator disc 114 provide volumes in which to form a periodic liquid flow 119 of liquid 102. The periodic liquid flow 119 flows between the inner notches 112 and the stator notches 116 as illustrated, for example, in Figure 9. When the inner notches 112 and stator notches 116 are aligned, the liquid 102 flows from the inner notches 112 to the stator notches 116, forming the periodic flow 119. Portions of liquid 102 pass back and forth from the inner notches 112 to the stator notches 116 caused by a change in volume as the rotor 108 rotates and the notches 112, 113, 116 successively align and misalign with each other. The periodic flow 119 helps to generate toroid vortices in the portioned liquid 102 by shear stress.

Liquid 102 leaves the rotor 108 to enter the inner notches 112 of rotor disc 110 when it is opposite the stator notch 116 of stator disc 114; it has roughly the same linear peripheral speed until the rotor disc 110 rotates to a position opposite the enclosed space between the notches 112, 113, 116. At that point, the passage for liquid 102 to exit the chamber of the rotor disc notch 112 closes off. This produces a pressure spike in liquid in the inner notch 112 of rotor disc 110 until an exit for the liquid 102 via a notch 116 in the stator ring 114 opens again, due to rotation, and the liquid 102 is able to flow into the stator notch 116. Figure 8 illustrates the case after the closure point of the flow from an inner notch 112 to a stator notch 116. The periodical flow becomes further accelerated; a portion of the flow turns 180° and begins to move in the opposite direction to the principal flow within the inner notches 112, taking the shape of a twisted flow and forming a stable vortex braid 122 along the full length of the inner notches 112, which partially enters the stator notch 116.

Further rotation of the rotor disc 110 partially opens the flow passage from the inner notches 112 into the stator notches 116. Given that the opening is still very narrow, the space for the vortex braid flow 122 becomes tight, and the braid begins to break up into toroid vortex pieces. The toroid vortices so generated enter the stator notches 116, where the shape of the notches shapes the vortices into separate toroid vortices.

As the flow passage from the inner notches 112 to the stator notches 116 then gradually widens, each stator notch 116 is filled with a screw-like vortex braid that, once the total flow of liquid reverses its direction 180°, breaks up into portions, generating similar toroid vortices.

The time period when the stator notches 116 are fully aligned with the inner notches 112 is very brief, as the rotor disc 110 rotates at around 3000 revolutions per minute (50 Hz). The frequency of rotation can be adjusted to achieve variations in pressure experienced by the liquid 102. The rotor’s continued rotation tightens the spaces for the vortex braid, as the inner notches 112 gradually close. This promotes continued breakup of the vortex braid into toroid vortices.

As the rotor disc 110 rotates and the stator notches 116 are closed off from the inner notches 112 again, the entire process repeats, submitting the liquid 102 to high frequency alternating flow velocities and pressures. Rotation of the rotor ring creates a suction effect and draws fluid in.

The generator 2 can be used for generating toroid and spatial vortices in a liquid 102, by: guiding the liquid 102 to the inlet opening 104 and rotating the rotor 108 with the attached rotor disc 110 to produce a permanent liquid flow 118 and a periodical liquid flow 119 between the stator disc 114 and the rotor disc 110 as described above.

Toroid vortices are generated in the portioned liquid 102 of the periodic liquid flow 119 by shear stress as the portions of liquid 102 pass from the inner notches 112 to the stator notches 116 and move back and forth therebetween. Further, spatial vortices are generated in the permanent liquid flow 118 in the gap 117 between the side surfaces 111 , 115 due to the velocity difference of the side surfaces 111, 115 and due to periodical disruptions by the portioned liquid 102 passing the gap 117 in the axial direction. Figures 10, 11 and 12 illustrate the flows between the stator disc 110 and the rotor disc 114 in different configurations in more detail. Figure 10 shows the flows when a stator notch is aligned with a rotor notch, in sectional and plan views. Figure 11 shows the flows when a rotor notch has no overlap with a stator notch, in sectional and plan views. Figure 12 shows the flows when a stator notch has no overlap with an inner rotor notch, in sectional and plan views. In the configuration shown in Figure 12 it can be seen that in the sections between inner rotor notches fluid is blocked from entering the gap between rotor ring and stator ring. Liquid flow can only exit via an inner rotor notch, as illustrated in Figures 10 and 11.

Figure 10 shows a number of vortices being formed in the periodic flow 19 due to shear along the various notch surfaces of the rotor and stator rings. Liquid flows into the inner rotor notch 112, is redirected in the inner rotor notch 112 toward the stator 114, enters the stator notch 114, and is redirected in the stator notch 114. In the illustrated example the flow can enter the outer rotor notch 113 but in other examples the outer rotor notch

113 is omitted and the flow is redirected out of the stator notch 114. In the illustrated examples the notches provide curved surfaces to redirect the flow in the inner rotor notches 112 by approximately 60-90°, and also to redirect the flow in the stator notches

114 by 60-120° or by approximately 60-90° depending on whether or not outer rotor notches 113 are provided. As the flow moves through the notches a number of toroid vortices are formed perpendicular to the liquid flow. The redirections in the notches cause flow shearing and produce vortex zones within the notches.

Figure 11 shows the permanent liquid flow 118 between the discs 110, 114 that gets squeezed up between the flat parallel side surface 111 , 115 of rotor disc 110 and stator disc 114 and moves radially. The permanent liquid flow 118 is affected by shear stresses the rotor disc 110 generates as it moves vis-a-vis the stator disc 114. The outer notches 112 continuously disrupt the linear nature of the inter-disc flow 118 and generate spatial vortices therein. The permanent liquid flow 118 is further disturbed by vortex flows as the inner notches 112 start to line up with the stator notches 116 and provide a flow path that passes from the inner notches 112 to the stator notches 116 perpendicular to that permanent liquid flow 118.

Figures 13a, 13b and 13c show graphs of local flow velocity, acceleration and absolute pressure in flow in an exemplary generator during different phases of operation.

Some of the details of the exemplary generator are as follows:

Pump capacity, Q = 200 m³/hour

Pressure head, H = 12 atmospheres (1216 kPa)

Impeller speed, n = 3,000 revolutions per minute Outer diameter of the impeller, D = 0.32 m Impeller width, h = 0.025 m Number of impeller blades, a = 6 Guide vane channel 0.040 m by 0.035 m

Rotor ring parameters:

Number of rotor inner notches, N_p = 18 Rotor inner notch width, h_p = 0.025 m Rotor inner notch height, L_p = 0.015 m Rotor inner notch depth, a_p = 0.025 m

Stator ring parameters:

Number of stator notches, n_c = 18 Stator notch width, h_c= 0.025 m Stator notch height, L_c = 0.020 m Stator notch depth, a_c = 0.020 m

Gap between the frontal surfaces of the rotor and stator rings, B = 0.001 m

The graphs in Figures 13a, 13b and 13c show flow conditions immediately downstream from the rotor ring / stator ring passage, from t=0 just before a rotor ring inner notch 112 starts to line up with a stator notch 116, continuing until the rotor ring notch fully opens (i.e. is in alignment with a stator notch) and further until the rotor ring notch closes.

As the notch 112 starts to open up, over a duration of 0.000092 seconds (0.092 milliseconds), flow velocity increase from 10 to 160-200 meters per second (m/sec). As the rotor ring notch then comes into full alignment, over a duration of 0.00023 seconds, flow velocity drops to 30 m/sec. Subsequent movements of the rotor ring result in continued progressive closure of the notch, boosting the flow velocity to 160-200 m/sec. With further rotation of the rotor ring, the notch closes (i.e. it no longer is located at a stator notch), and the flow velocity (from flow through the gap 117) drops to 10 m/sec. As the rotor ring continues to rotate, the notch 112 is in its closed configuration (with only flow through the gap 117) for 0.00064 second. The notch 112 remains in its open configuration (fully or partially lined up with a stator notch) for 0.00046 second.

Such rapid changes in flow velocity occasioned by rotor ring rotation within the same time period produce significant alternating accelerations of the flow that change from +16,000,000 to -16,000,000 m/sec². Such accelerations affect the liquid within the rotor ring notch and the slot-like gap between the rotor and stator rings.

The forces that develop in the process produce pressure in a portion of liquid flow, which varies from 500 bar (50 Megapascal MPa or 510 atmosphere atm) overpressure to 0.1 bar (0.01 MPa) vacuum over a period of 0.00046 seconds. In a 0.000092 second timespan the pressure drops from 500 bar (50 MPa) overpressure to 0.7 bar (0.07 MPa) vacuum. Such rapid pressure changes, from overpressure to vacuum and back, can be very effective at flaking particles that may be in the flow along stress lines and structural defects.

In some examples, depending on the generator design, the maximum local pressure in a toroid vortex may reach 200-400 kg/cm² (around 20-40 MPa) and flow velocity change per unit of time (acceleration) is 50,000 G (around 490,000 m/sec²).

The permanent liquid flow 118 is disturbed by vortex flows that pass from the inner notches 112 to the stator notches 116 perpendicular to the permanent liquid flow 118. In this context, the permanent liquid flow 118 is affected by shear stresses the rotor disc 110 generates as it moves in relation to the freely attached stator disc 114 that is blocked to prevent its rotation. The notches 112, 113 in the rotor disc’s side surface 111 continuously disrupt the linear nature of inter-disc flow along the permanent liquid flow 118 and generate spatial vortices therein.

A conical funnel-shaped spatial vortex forms in at a rotor ring notch as the stator ring blocks the flow exit from the rotor ring. As the rotor ring exit is closed off, the outside portion of the vortex braid produces a maximum diameter funnel and unfolds towards the rotor ring entrance. As those spatial vortices come into contact with toroid vortices, first from the inner notches 112 and then from the stator notches 116, they morph into yet smaller and more intense toroid vortices and, along with toroid vortices from the stator disc notches 112, are dispersed in total flow 120 and carried out into a discharge system. Alternating flow velocities may be produced using this technique at a frequency of at least 500 Hz, for example. Alternating pressures may also be produced using this technique at a frequency of at least 500 Hz, for example.

Contact between spatial vortices in the permanent liquid flow 118 and the spatial vortex braid for the periodical flow 119 exiting the stator notches 116 as they fully open help to cause the toroid vortices to stabilise. As the two flows 118, 119 mix, they generate a total liquid flow 120 featuring an internal volume comprising a plurality of toroid vortices.

Peripheral liquid flow velocity in a toroid vortex is greater than that of the fluid outside the toroid vortex. For example, peripheral flow velocity in a toroid vertex may be between 5 and 10 times that of the flow velocity outside the toroid vertex. Peripheral flow velocities of liquid flow in a toroid vortex may be at least 100 m/s, for example, 200 m/s to 400 m/s. Pressure of a toroid vortex may also be greater than the pressure in the fluid outside the toroid vortex. Local pressures of at least 500 kPa may be achieved.

At 3000 revolutions of the rotor ring per minute, and from 12 to 48 notches on the rotor ring, the vortex braid generation process is near enough continuous to be effectively continuous. The spatial vortexes formed in the chamber comprised by rotor ring notches and stator ring notches may be deemed stable, and their number deemed consistent with the number of notches, i.e. , 12 to 48; in their turn, the spatial vortexes produce a large number of smaller toroid vortexes with a typical torus diameter of 20-40 micrometers. The vortex braid breaks down into toroid vortexes typically ranging from 20 to 40 micrometers in diameter. Larger and smaller toroid vortexes are present as well, but in lower numbers. As the toroid vortexes travel in the flow they gradually dissipate and shrink. In an example at a distance of 3 meters from the outlet port of the generator 20-40 micrometer vortexes are still found in the pipeline. At that point smaller vortexes may have dissipated and may not be observed, whereas larger vortexes may have split into smaller ones and coincide in the 20-40 micrometer size. The toroidal vortices may have a typical diameter of at least 10 pm, preferably at least 20 pm, further preferably at least 40 pm. The toroidal vortices may have a typical diameter of up to 100 pm, preferably up to 70 pm, further preferably up to 50 pm. Preferably the toroidal vortices are micrometer-scale toroidal vortices.

In an example the rotor ring rotates at 40-60 Hz and has 16-42 notches to generate toroid vortices at 640 to 2520Hz. In this example 256-1764 vortices are produced per revolution. In addition to such primary vortexes formed at a primary frequency, secondary vortexes are formed with an integral multiple frequency (integer N = 2, 4, 6, 8), but the efficiency of those secondary vortexes is significantly less compared to efficiency of the primary vortexes. In an example where the generator throughput is about 160-240 m³/hour, a density of around 190-3000 primary vortices may be generated per litre of fluid. The flow may include at least 150, preferably at least 200, further preferably at least 500 toroidal vortices per litre of suspension. The flow may include 200 to 3000 toroidal vortices per litre of suspension or 190-2940 toroidal vortices per litre of suspension.

As described above, under such conditions, in particular due to the liquid in the permanent liquid flow 118 and the sudden change of direction in the periodical liquid flow 119 (in a direction perpendicular to the permanent liquid flow 118), a vortex is built and the liquid 102 forms toroid currents therein. The liquid 102 is subjected to resulting high frequency alternating pressures and flow velocities. Forces experienced by the suspended laminar material in the liquid 102 causes flaking of the laminar material into layers of nano-platelets.

Compared to other processes for flaking nano-platelets, the method described here is easier, cheaper and more reliable.

The generator’s design is intended to avoid generation of ultra-sound frequency fluctuations (over 20,000 Hz). Materials from which rotor and stator rings are made, along with the shape of the notches, block phenomena leading to creation and development of cavitation. Cavitation and ultrasonication are uncontrolled processes and, as they develop, they can lead to an unstable result with other effects being favoured instead of flaking of graphene. Cavitation and ultrasonication effects can be influenced by the external environment, such as atmospheric pressure and atmospheric magnetism, which it may not be convenient to control. Over-milling is avoided to prevent deformation of the flake structure, but with the generator even over-milled particles primarily consist of graphite structures. In a variant a nozzle is included in a generator in order to introduce a second fluid into the primary flow. For example air or water vapour or other gases, or a fluid that is heterogenous in respect to the primary flow, or a dispersion of a solid in a liquid, or a flowable solid such a powder can by introduced into the primary flow by way of the nozzle. Figures 14 and 15 show an example of a nozzle 212 in a generator otherwise as described with reference to Figures 2-13.

As described above, the liquid enters the generator 2 at the inlet of the generator. Gas, e.g. air, can be introduced to the liquid via a special nozzle that can be provided for this purpose in the generator. The nozzle serves to deliver gas to the generator such that the gas contacts liquid as the latter leaves the stator and rotor ring structures. The end of the nozzle 212 that delivers gas to the flow is situated in proximity to the rotor ring 108 and stator ring 114 assembly such that gas leaving the nozzle 212 contacts liquid as it leaves the rotor ring 108 and stator ring 114 assembly. Nozzles of various design and configuration may be used. Movement of the rotor ring’s upper portion creates suction within the generator, which draws fluid through the nozzle 212 and into the fluid flow.

A guide vane 202 is seen in Figures 14 and 15; such guide vanes are fixed relative to the housing and can define fluid flows from the pump’s impeller to its discharge line. A guide vane is not an essential element and it may be omitted. In the illustrated example the nozzle 212 passes through a guide vane 202; the nozzle 212 is not connected to the guide vane 202 and the nozzle can be provided in the absence of a guide vane.

In the illustrated example one nozzle is provided on the circumference of the rotor/stator ring assembly. In other examples two or more nozzles are distributed around the circumference of the rotor/stator ring assembly. The diameter of the nozzle outlet is less than the width of an outer notch of the rotor ring. The centre of the nozzle outlet is aligned with the centre of the outer notches of the rotor ring.

The nozzle outlet is located 2-3 mm from the external blades of the rotor ring to enable this suction effect to act on the gas in the nozzle. Movement of the rotor ring’s upper portion creates an atmospheric vacuum zone of 0.2-0.6 atm, which ensures continuous suction of gas into the flow. Figure 16 illustrates another configuration of a nozzle 212, with an angled outlet plane. Figure 16 also indicates two speeds at different positions in the housing outside the rotor/stator rings: Vi outside the rotor ring but prior to the nozzle, and v₂ between the nozzle outlet and the rotor ring. As the nozzle obstructs flow outside the rotor ring and only permits flow to pass in the gap between the nozzle and the rotor ring, in those different positions the flow speed is different, due to the different flow cross section areas. In an example it is calculated that Vi = 10 m/sec and v₂ = 133 m/sec. The different flow speeds give rise to the Venturi effect, and the zone in the gap between the nozzle outlet and the rotor ring is at a relatively lower pressure, causing entrainment of the gas from the nozzle into the flow.

The outer surface of the rotor ring moves at a greater speed than Vi. As the rotor ring rotates, vortexes are generated and destroyed within the stator ring notches and outer rotor notches with high intensity. This too can cause a low-pressure zone near the nozzle, similar to a vortex pump with the rotor ring acting as a vortex impeller; the rotation of the rotor also assists in drawing gas from the nozzle into the flow. In an example water from the depth of 5 to 8 meters could be lifted through the nozzle thanks to a vacuum of about 200-500 mm Hg or about 50-80 kPa at the nozzle outlet, which is generated by the synergy between the Venturi effect and the operation of the rotor ring notches.

In general gas is provided (or, equivalently “injected”) at a pressure below the average pressure of the liquid flow at the nozzle outlet, to prevent disruption of the flow produced by the generator and to prevent formation of gas bubbles in the liquid stream.

The nozzle delivers gas to the flow; in the conditions created by the generator dissociation of oxygen molecules provides a source of singlet oxygen as described above.

The example provided above discusses a rotor rotating with 3000 revolutions per minute (RPM) ± 20%, and having an outer diameter of the rotor and the rotor disc and stator disc of about 30 cm ± 20%. It should be appreciated that a toroid vortex dispersion can similarly be created at lower or higher RPM provided the rotor’s diameter is suitably increased or decreased. For instance, in a generator with an outer diameter of the rotor and the rotor disc and stator disc of about 45 cm, a suitable rotor rotation speed is around 2000 revolutions per minute. In a generator with an outer diameter of the rotor and the rotor disc and stator disc of about 90 cm, a suitable rotor rotation speed is around 1000 revolutions per minute. In all of these examples, the peripheral speed (tangential speed) of the rotating rotor, at the rotor disc (e.g. at an inlet to the rotor disc, or at an outer edge of the rotor disc), is around 47 m/sec. For a generator to produce a toroid vortex dispersion effectively, the peripheral speed of the rotor, at the rotor disc, is preferably 30 m/sec or more. A peripheral speed in the range from 20-29 m/sec is borderline and may be unstable or ineffective, though it may permit formation of a toroid vortex dispersion. A peripheral speed in the range from 15-19 m/sec may in some configurations (e.g. in otherwise particularly effective configurations) permit formation of a toroid vortex dispersion.

In some of the examples provided above the inner notches and the outer notches of the rotor ring are aligned with one another, e.g. as seen in Figures 8 and 9; in others they are not aligned, e.g. as seen in Figure 3, or some are aligned and others are not. In some of the examples provided above the inner notches and the outer notches of the rotor ring have the same or similar widths; in other examples the inner notches and the outer notches of the rotor ring do not have the same widths, e.g. as seen in Figure 6 where the inner notches are narrow than the outer notches.

Figure 17 shows another arrangement of notches that is observed to be particularly effective at creating a flow of toroid vortexes. Figure 18 illustrates the rotor ring of Figure 17 with a stator ring 114 in a generator. In this rotor ring 110, one outer notch 113 spans two inner notches 112. In the stator ring 114 the stator notches 116 are such that a stator notch 116 spans two inner notches 112. A stator notch 116 may be same or similar width as an outer rotor notch 113.

Figure 18 illustrates some flow paths in the generator with the rotor ring 110 of Figure 17. Flow from a pair of inner notches 112 of the rotor ring 110 is directed to a common rotor notch 116 of rotor ring 114. Each inner notch 112 is formed to channel liquid at an angle to its neighboring notch, such that a pair of inner notches 112 that face the same outer notch 113 channel fluid toward a common area. The central flow axes of a pair of inner notches are at a converging angle to one another; the angle is such that a point of intersection of the two flow axis is inside the volume of the notch of the stator ring, as illustrated in Figure 18.

Movement of the rotor ring 110 is now considered, starting from when two inner rotor notches 112 of the rotor ring 110 are fully aligned with a stator notch 116 of the stator ring 116, as seen in Figure 18. As the rotor ring moves, one of the pair of inner notches remains fully open, while the other of the pair of inner notches becomes partially closed. In this instant, the flow speed via the partially obstructed inner notch is significantly higher than the flow speed via the fully open inner notch. The two flows interact in the stator notch. The presence of an angle between these flows causes the faster flow to accelerate the slower flow.

With the notch design of Figures 17 and 18, the points of maximum speeds are shifted compared against the velocity plot shown in Figure 13a. What is more, the maximum flow velocity is significantly increased due to the cumulative effect of contact between two vortex braids with subsequent significant positive and negative acceleration. The number of toroid vortexes generated in the system increases exponentially, and their total peripheral speed significantly increases compared to those described above with reference to Figures 13a, 13b and 13c.

The examples illustrated in Figures 17 and 18 provide stator notches spanning two inner notches so as to commingle the periodic flows from two inner notches in a stator notch. It should be appreciated that a stator notch need not span exactly two inner notches; it may for example be sized to span more, or less, than two inner notches. In an alternative one stator notch spans one inner notch as illustrated in e.g. Figures 3 and 4, but the outer notches 116 are sized so as to span two stator notches. In this way the periodic flow from two stator notches is commingled in an outer notch. Flow interactions are promoted, and the number of toroid vortices generated is increased.

Figures 19 and 20 show plan and front view schematics of outer rotor notches 113 with a bottleneck design. In the examples previously illustrated, the outer notches of the rotor ring have approximately parallel sidewalls, as seen e.g. in Figure 8. As shown in Figures 19 and 20 the exit section of the outer notches 113 of the rotor ring 110 may be formed to provide channels that are progressively narrower and with smaller flow area and that resemble a bottleneck. The liquid is compressed as it moves along these channels. Flow speeds are increased as are flow interactions, and the number of toroid vortices generated is increased.

Figure 21 shows a variant where the rotor ring 110 does not provide outer notches. Instead, the outside part of the rotor ring constitutes an outer surface 28 shaped like a carved-out toroid with a certain curvature; the cross section of the outer surface 28 is same as or similar to the cross section of an outer notch, such that the outer surface 28 can provide a redirection of the flow similar to the outer notches as described above. The stator 114 includes prongs 29 between the stator notches 116 that project toward the outer surface 28 of the rotor ring 110. In this variant the gap 117 between the opposing side surfaces of the rotor disc and stator disc extends further between the prongs 29 and the outer surface 28 of the rotor, to permit movement of liquid along the outer surface 28 of the stator ring 110 and provide a passage via the gap 117 for a permanent liquid flow. The prongs 29 also form a notch-like channel for fluid to pass between the prongs 29 after exiting the stator notches, similar to the outer rotor notches in the other variants.

The features described with reference to Figures 17 to 21 can be combined for particularly effective formation of toroid vortexes in the flow. While the examples provided above are concerned with a centrifugal pump moving fluid in radial direction toward the rotor/stator discs, it should be appreciated that a toroid vortex dispersion can similarly be created in a pump that pumps fluid in an axial direction toward suitably adapted rotor/stator discs.

Figure 22 provides a schematic illustration of an alternative generator with a rotor disc and a stator disc adapted for axial flow, rather than radial flow, with an axial flow impeller 27 instead of a radial flow impeller as described above.

In this configuration, the stator ring 26 is arranged concentrically outside the rotor ring 25 with a gap between the inner cylindrical surface of the stator ring 26 and the outer cylindrical surface of the rotor ring 25. The rotor ring 25 has inner rotor notches on a flow-facing side such that flow from the impeller can enter the inner rotor notches. The stator ring 26 has stator notches arranged on its inner cylindrical surface, facing the rotor ring. The flow is redirected by the inner rotor notches toward the stator ring, either entering the gap between the rings (in the configuration illustrated in the lower half of the cross section in Figure 22) or entering a stator notch (in the configuration illustrated in the upper half of the cross section in Figure 22). The stator notches redirect the fluid further.

For efficient formation of toroidal vortices, the flow entering the inner rotor notches has a tangential velocity (tangential to the rotational motion of the rotor) of e.g. at least 15- 25 m/sec. Suitable guide vanes can be provided upstream of the rotor ring, to ensure that the flow entering the inner rotor notches has a suitable tangential velocity, while ensuring that the generator creates a pressure of at least 5 to 7 atmospheres (506-709 kPa). In the absence of a tangential velocity component the rotor ring causes such a tangential velocity component to be produced in the flow, which can result in a relevant loss of energy and less efficient formation of toroidal vortices.

Example: Graphene separation from graphite

In one example, the liquid 102 brought to the inlet opening 104 is water suspended with graphite, and the total liquid flow 120 conducted away from the outlet opening 5 comprises the suspended graphite along with graphene flakes which have been separated from the graphite under the high pressure high shear zones created by the generator 2.

In this example, the rotor 108 rotates with a frequency of between 2400 revolutions per minute (40 Hz) and 3600 revolutions per minute (60 Hz), preferably around 3000 revolutions per minute (50 Hz). The capacity of the generator 2 is about 200 m³/hour, ± 20%.

While in operation, rotor 108 and rotor disc 110 rotate at around 3000 revolutions per minute +/- 20%; the rotor disc’s outer diameter ranges from 0.25 to 0.40 meter +/- 20%. Its linear peripheral speed averages between 170 to 450 kilometres per hour (47 to 125 metres per second). In case of such device with a rotor disc 110 of 0.3 metre outer diameter, its linear peripheral speed would amount to 340 kilometres per hour (94 metres per second).

The following modes of generator operation are suitable for obtaining large graphene particles (often considered to be the most useful in further manufacturing): temperature of the suspension between 4°C and 25°C; pressure in the generator 2 between 8 and 12 atmosphere (between 0.81 Pa and 1.216 MPa pressure in the fluid outside a toroid vortex, or average pressure in the flow generated by the generator); - ratio of liquid 102 to source graphite 3:1 to 5:1 (by mass); gap 117 between the generator’s rotor disc 110 and stator disc 114 0.8 mm to 1.2 mm.

More stressful modes of generator operation such as using elevated temperatures, reduced gap 117 between its rotor and stator discs, or higher content of source graphite in the liquid flow, can result in undesired oxidation of the graphene product and undesired production of graphene conglomerates, such as micelles and druses.

Alternatives

Graphite and resulting graphene are used in the example describe above, however other source materials can be similarly used.

Water is described as the fluid for suspending graphite in. However, other fluids such as ethanol, tetrahydrofurane, chloroform, acetone or toluene may be suitable, particularly for other laminar materials subject to ensuring air-tightness of the process installation.

While the generator 2 is described as producing a turbulent flow suitable for flaking nano- platelets, a suitable similar turbulent flow may be generated by other arrangements and devices subject to observing the principles claimed.

Separation of flaked nano-platelets from laminar material

A second stage of the method is to separate flaked nano-platelets, for example graphene, from laminar material, for example graphite 10. The resulting solution created in the generator 2 comprises a suspended mixture of laminar material and nano-platelets. It will be appreciated that such a mixture can be created by other means than in a turbulent flow as described above with reference to the generator 2.

In the example illustrated in Figure 1 a suspended mixture of laminar material and nano- platelets is produced by the generator 2, and subsequently flows via a fluid connection to a separator tank 3.

In the example illustrated in Figure 1 graphene is separated from any remaining graphite particles in the separator tank 3. The mixture could instead be continuously looped through the circular loop between the first tank 1 and the generator 2, but this could lead to damaging of the graphene’s crystalline lattice and potentially break it into fragments that are smaller than desired. Therefore, the mixture of graphene and the remaining graphite particles, is preferably directed from the generator 2 to a separator tank 3 to be separated before recycling only the graphite particles back to the generator 2.

In the separator tank 3, source laminar material and nano-platelets are separated from each other such that they can be removed from the separator tank 3 via different outlets; a laminar material outlet at the bottom of the separator tank 3 can be looped back to the first tank 1 for further flaking, whilst the nano-platelets can be removed via a nano platelet outlet or nano-platelet offtake line 8 positioned away from the bottom of the separator tank 3. Nano-platelets removed via the nano-platelet outlet 8 can be directed away from the separator tank 3 for further processing if required.

The separator tank 3 can have a combination of fluids therein, including liquids and gasses, having different properties for different purposes. The separator tank 3 comprises a dense fluid 15 that assists in separating the laminar materials from the flaked nano-platelets and can optionally further comprise an immiscible liquid 16 that forms a separate phase and/or a gas 4. The dense fluid 15 in the separator tank 3 fills the tank from the bottom up to a dense fluid level 13 and aids separation of the laminar material from the nano-platelets. The additional immiscible fluid(s) can serve to preserve nano-platelet structure (e.g. against oxidation caused by interaction with atmospheric air) and/or to aid separation and collection of nano-platelets.

A first fluid comprises a dense fluid 15, for example a water-based fluid or a dense aquatic solution. For example, the dense fluid 15 comprises water combined with water- soluble substances such as NaCI, CaCI, KCI, and/or other salts. Any desired density of the dense fluid 15 can be achieved by appropriate addition of solutes; different densities may be required for different laminar materials and nano-platelets. Selection of fluid density is performed based on actual density of the laminar material. In the case of graphite, which has a typical density between 2.08 to 2.23 gram/cm³, the fluid density is in an example adjusted to be about 1.5% less than actual density of graphite used. Selection of a suitably dense fluid is discussed in more detail below.

Surface interactions of 2D materials, nano-platelets and nanomaterials more generally, are complex due to their size. Nano-platelets are extremely thin by definition and exhibit unique electrical properties as a result of this. Graphene, as well as many other 2D materials, is known to be inherently hydrophobic as a result of this very thin structure.

The flaked graphene produced in the generator 2 can be separated from the graphite by utilizing intrinsic hydrophobic properties of graphene. Due to the graphene flakes having a sheet-like shape, they may settle more slowly than the graphite particles. By selecting the density of the liquid such that it is slightly denser than the graphite, the graphite can settle to the bottom while the graphene remains suspended. In order to separate the flaked graphene from the graphite elements 10, a dense fluid 15, for example a dense aqueous solution as described above, is present in the separator tank 3. A density of the dense fluid 15 required for graphene produced using the described method is preferably within a range of between 1.7 to 2.4 g/cm³, depending on the actual density of the graphite used. Given its greater density, any remaining graphite material 10 not processed into graphene flakes by the generator 2 settles at the bottom of the separator tank 3 and can be removed back to the generator 2 for a further round of flaking. Once the graphite particles have settled the flaking product can be separated. The actual specific gravity of the dense fluid 15 in the example described is defined by the source graphite 10 density and is typically within a range of 1.7 to 2.4 g/cm³. The specific gravity of an object is defined as the ratio between the density of an object to a reference liquid, usually water, which has a density of 1 g/ml_ or 1 g/cm³.

Flotation of the nano-platelets to the top of the dense fluid 15 at a first surface 13, away from the laminar material, can be further aided by a stream of gas 14, for example a stream of gas bubbles, introduced into the separator tank 3 via a gas aerator 4. A highly dispersed gas 14, such as gaseous nitrogen, can be fed into the bottom of the separator tank 3. The gas 14 is fed into the separator tank 3 at a pressure exceeding the column pressure of the fluid above it by, for example, 0.05 to 0.10 kg/cm³. Column pressure is defined as the pressure exerted by a column of liquid of height, h, and density, p, and is given by the hydrostatic pressure equation p = pgh, where g is the gravitational acceleration.

Use of a gas 14 such as nitrogen stimulates efficient upward lift of graphene flakes to aid their flotation and separation from the graphite particles. The addition of nitrogen to the graphene flotation process speeds up graphene separation from the graphite elements 10 while also protecting the resultant graphene from oxidation in the presence of atmospheric air. The rate of the gas introduction may, for example, be equal to or less than 0.2 cm³/sec per 1 cm² of free surface of dense liquid phase. An example flow rate of gaseous nitrogen of 0.2 cm³/sec per 1 cm² of the dense fluid’s free surface has been shown to provide quick and non-damaging conditions for separation of the graphene. Bubbles of the gas 14 rise straight up vertically in the dense fluid 15, for example in a stream of bubbles rising in columns or in a chaotic distribution. Graphene flakes, or other nano-platelets, move among the bubbles or gas stream. The graphene flakes are buoyed upward by the gas bubbles. When the gas 14 and floating nano-platelet(s) reach the surface of the dense fluid 13, a bubble of the gas is released into the atmosphere at the top of the separation tank. The nano-platelets assume a horizontally orientated position on the surface of the dense fluid 15 when they reach the dense fluid surface 13. An illustration of this is depicted in Figure 23 and described in more detail below.

The gas is released to the dense fluid 15 through an aerator 4 through an outlet opening having a diameter that affects the bubble diameter. For example, a diameter of less than 1 mm may be suitable. In other examples, the diameter may be in the range of 0.1 to 0.8 mm, further preferably in the range of 0.2 to 0.5 mm (which has been shown to be particularly useful in separating graphite from graphene). The remaining unreacted laminar material, which is too dense to float in the dense fluid 15 and not substantially moved upwards by the gas streams of bubbles, can be removed from the separator tank 3 through a laminar material outlet at the bottom of the separator tank 3. The removed laminar material elements can be recycled back to the generator 2 for further flaking along with fresh components to be added into the first tank 1. In this way most, if not all, of the initial source laminar material can be turned into nano-platelets such that none of the source product is wasted. The process described above combining flaking and selective recycling of the graphite particles has been shown to attain an overall 97% yield of graphene from source graphite 10.

Nano-platelets separated from the laminar material can be removed via a nano-platelet outlet 8 in the separator tank 3. In the illustrated example in Figure 1 , the nano-platelet outlet 8 is in fluid connection to a filter tank 5 where the separated nano-platelets are filtered from the fluid by which they are transported.

The nano-platelet outlet 8 preferably comprises a horizontal slot, although other shapes and alignments may be used. A horizontal slot may be particularly beneficial for controlling the output of the nano-platelets as they pass through the outlet 8. The height of the slot may further be controlled to define a thickness of a layer that passes through the slot, and accordingly the number of flakes, n, of the nano-platelets that can pass through the slot. The slot can provide a first or preliminary stage in isolating separated and aligned nano-platelets from the liquid environment so as to form a film. The slot may be formed of flaps that can adapt to fluid flowing through the slot. For example, the lower flap may be selected such that it is suspended at a particular level in the flow (e.g. just above or below a liquid phase interface, or at a liquid phase interface), and the upper flap likewise. The slot may be formed of flaps that can be controlled to provide a slot with a desired height, e.g. in a louvre-arrangement where the angle of the flaps is controlled to change the slot height. In an example the horizontal slot extends horizontally along one third the circumference of the separator tank 3. The slot may include features to prevent material from adhering to the slot, for example a PTFE film portion at the slot rim.

To prevent the nano-platelets from clumping, for example into micelles and druses, when they have floated to the top of the dense aquatic solution 15, and to additionally aid nano-platelet removal when it reaches the surface of the dense fluid 13, a further fluid can also be present in the separator tank 3.

In a first example, the fluid can be a gas, for example gaseous nitrogen. This gas can be fed into the separator tank 3 through streams of bubbles introduced through the dense fluid 15 as described above. Alternatively or additionally, gas can be pumped into the top of the separator tank 3 above the liquid surface(s) in the separator tank 3. In some examples, gas can be pumped into the separator tank 3 via both described mechanisms; the gas may be the same gas type in both instances.

In a second example, the fluid can be an immiscible liquid 16, for example a hydrophobic liquid that can form an immiscible phase on the dense fluid 15. This immiscible liquid 16 can be chosen to prevent oxidation or other contamination of the separated nano platelets at the surface of the dense fluid 13 (which forms a liquid phase interface). An immiscible liquid 16 such as kerosene, petroleum oils, chlorine-based organic household liquids for dry cleaning purposes, or waste food oils of low solubility can be used. The liquid may be insoluble in water. The immiscible liquid is such that it forms an immiscible phase with the dense fluid 15 in the separator tank 3 (i.e. floats on top of the dense fluid 13) and fills the separator tank 3 between the dense fluid surface 13 (which forms a liquid phase interface) and an immiscible liquid level 12. The volume ratio between the dense fluid 15 and the immiscible liquid 16 is in an example between 100:4 and 100:2 to ensure efficient operation.

In one example, an immiscible liquid 16 is poured onto the surface of the dense fluid 13 and removed from the surface of the dense fluid 15 in a continuous manner along with the nano-platelets that have been separated. By continuous pouring of such a liquid, for example in a closed loop between the separator tank 3 and a filter tank 5, nano-platelets that have been separated from the laminar material by floating to the top surface of the dense liquid 13 can be entrained and removed. The immiscible liquid 16 can be filtered from the nano-platelets by a filter element 7 in a filter tank 5, leaving the nano-platelets as the final product.

Continuous pouring of the immiscible liquid 16 is not necessary; however, it does provide the advantage of continually removing nano-platelets from the surface of the dense fluid 13. lt is possible to adjust or vary the rate and volume of the immiscible liquid 16 flowing into the separator tank 3 depending on factors such as: nano-platelet separation rate; desired number of nano-platelet layers to be removed from the separator tank 3 at once, for example through the nano-platelet outlet 8; positioning of the nano-platelet outlet 8; and volume and/or cross-sectional area of the separator tank 3. In some examples, the flow rate and volume of the immiscible liquid 16 into the separator tank 3 can be controlled such that a determined flow of immiscible fluid over the dense fluid is achieved and a desired coverage of nano-platelets on the dense fluid 15 at the dense fluid surface 13 can be achieved. The number of layers of nano-platelets stacked on the dense fluid surface 13 can be monitored and controlled as well as surface area coverage of nano- platelets on the dense fluid surface 13. Monitoring apparatus may be installed to monitor these variables.

The slot of the nano-platelet outlet 8 is above the dense fluid surface 13 and below the immiscible liquid level 12, so that the graphene flakes in the immiscible liquid are propelled by flow of the immiscible liquid into the nano-platelet outlet 8. In case a portion of the dense fluid 15 is entrained with the immiscible liquid and enters the nano-platelet outlet 8, it can be subsequently separated in filter tank 5 and returned for recirculation via line 9.

As illustrated in Figure 1 , fluid flowing through the nano-platelet outlet 8 from the separator tank 3 is filtered from the nano-platelets in a filter tank 5 by a filter element 7 and removed back to the separator tank 3. A pump 6, such as a booster micro-pump, can be installed along a closed loop between the filter tank 5 and the separator tank 3 such that the fluid can be pumped back up to be reused in the separator tank 3 once the nano-platelet content has been filtered out.

Alternatives The dense fluid may be made from any constituent materials suitable to achieve the required density relative to the laminar source material and flaked nano-platelets.

Preparation of nano-platelet layers and meta-materials Nano-platelet layers for use in industry are widely sought after. Graphene is a single atom layer of carbon atoms and is particularly sought after because it possesses unique electronic and mechanical properties. However, films formed of graphene may be weak and exhibit a tendency towards fracture generation and proliferation and, respectively, to dust formation ultimately followed by its destruction.

Provided the graphene flakes are aligned to one another, various bonds between graphene planes, such as hydrogen bonds, ionic bonds, or PP interaction and covalent bonds, can improve strength characteristics of a multilayer graphene material without it losing the special properties of graphene. Such inter-planar effects prevent fracturing of the graphene film and/or flakes individually and improve its plastic deformation qualities without losing its salient properties.

Many previous efforts have been made to reliably and cost effectively produce graphene sheets having large areas for use in industry. A method and apparatus for aligning nano platelets, for example graphene, is described herein. A method for obtaining graphene sheets, for example aligned graphene sheets, from flaked graphene pieces is described herein. A method for obtaining meta-materials, for example graphene meta-materials, from nano-platelets is described herein.

In the illustrated example shown in Figure 1 , floating nano-platelets separated from the laminar material elements can be removed from the dense fluid surface 13 and into a filter tank 5 via a nano-platelet outlet 8. It will be appreciated that the flaking and separation of the method described above provides oneway of obtaining nano-platelets and that in other examples nano-platelets can be obtained using a number of available technologies and techniques.

According to the example disclosed herein, separated nano-platelets 4 can be directed out of the separator tank 3 via a nano-platelet outlet 8 comprising, for example a horizontal slot connecting to a filter tank 5. The filter tank 5 comprises, for example, a vacuum filter drum. In practice, whilst a separate filter tank 5 is used, it will be understood that it is an optional feature, and the fluid may remain with the nano-platelet or separated otherwise. In some examples, the nano-platelets may be aligned before they are removed from the separator tank 3. This alignment is described further below in relation to Figures 23 and 24. To stabilised aligned nano-platelets further, a film-forming agent can be applied to aligned nano-platelets, and fix their relative spatial arrangement. The nano-platelet outlet 8 is configured to direct fluid out of the separator tank 3 above or below the surface 15 of the dense fluid 13 (also referred to the liquid phase interface) to achieve an output of vertically or horizontally aligned nano-platelets respectively. Alignment can depend on the both the rate of the nano-platelets arriving at the surface 15 of the dense liquid and the fluid offtake rate through the nano-platelet outlet 8.

Parameters can be designed such that the nano-platelet structure offtake is aligned in a dense structure or in separate flaked pieces, depending on the desired structure. The number, orientation, and density of nano-platelets for determining a meta-material to be fabricated can be controlled by adjusting the offtake at the separator tank 3. A number of distinct layers of vertically or horizontally aligned nano-platelets may be formed at the top of the separator tank 3 and collected at the nano-platelet outlet 8; in some examples each layer could feature a clear line separating it from another layer. As flakes move upward in the separator tank 3, they self-assemble into a layer; once a first layer achieves a terminal density of flakes, a further distinct layer may start to form beneath it.

The volume of nano-platelets separated into vertical and horizontal layers is determined by the size of the tank, for example a cross-sectional area of the separator tank 3 parallel to the surface of the dense fluid 13.

By way of example, offtake at the nano-platelet outlet 8 of 1 , 2, 3,... n nano-platelet layers can be achieved with purity of up to 90-95% by selecting the ratio of nano-platelet to laminar material mixture feed rate from the generator 2 to the separator tank 3, the rate of nano-platelet offtake from the separator tank 3, the height of the dense fluid 15 in the separator tank 3, the volume of feed gas 14, and the bubble size of the gas fed to bubble aerator 4. A meta-material is a material artificially produced having a pre-determined spatial alignment and structure of nano-platelets, representing a man-made and spatially structured form of interactions among nano-platelets, e.g. orientated horizontally or vertically. Capability to freely configure nano-platelets orientated in any direction in pre set numerical, volumetric, and spatial ratios, makes for an indefinite number of meta- material configuration alternatives. Mother of pearl is an example of a naturally occurring meta-material; in mother of pearl nano-platelets of calcium carbonate are arranged in parallel layers and bound with an elastic biopolymer. The properties of mother of pearl are affected by the specific arrangement of the nano-platelets. To make sure aligned nano-platelets are fixed in their alignments, and connect to one another to form a meta-material, a film-forming agent may be applied to the nano platelets to form a meta-material with the nano-platelets fixed relative to one another. For example a plastic film may be applied or formed to fix the vertical or horizontal spatial orientation of nano-platelets. Use of a film-forming agent can further help to prevent creation and growth of fissures and therefore, respectively, dust formation which can lead to subsequent destruction of the nano-platelets. Generally a film-forming agent can increase stability of the film incorporating the structured graphene flakes. The film forming agent can provide a wide range of characteristic to the film, depending on the characteristics of the film-forming agent.

In an example the top layer of immiscible liquid can include a film-forming substance such that nano-platelets are fixed as they enter the immiscible liquid. In another example the product offloaded from the nano-platelet outlet 8 may be treated as it leaves the separator tank 3 using a solution. In another example a film-forming substance is applied to the nano-platelets at a filtering surface of filter element 7.

An example film-forming agent suitable for graphene comprises 1-aminopyrene disuccinimidyl suberate (a conjugated molecule from 1-aminopyrene and disuccinimidyl suberate) whose molecules contain two planar interlinked aromatic pyrene rings resembling a graphene structure cell. Treatment with a 1-aminopyrene disuccinimidyl suberate solution leaves graphene flakes fixed in a spatially oriented state. For example the immiscible fluid may include a solution of 1-aminopyrene disuccinimidyl suberate at a concentration 01-02% by weight or by volume.

In another example the film-forming agent is a monomer that can be polymerised by ultraviolet irradiation, and an ultraviolet lamp is mounted at the nano-platelet outlet 8. On irradiation the monomer would polymerise and embed the graphene flakes, producing a polymer with graphene flakes bound therein in the requisite configuration.

The film-forming agent may be selected depending on the application-based requirements, such as: translucent, electrically conductive, high strength, or high elasticity (e.g. polysaccharides). The film forming agent may be such that it can be removed again. Such a removable film can be used as packaging to transport the structured graphene, and e.g. be washed off with a solvent prior to use. Such a film for packaging purposes could help avoid oxidation or damage of the structured graphene flakes. Packing of nano-platelets in a meta-material is affected by the take-off rate from the separator tank 3. The number of nano-platelet layers, n, in the offtake from the nano platelet outlet 8 depends on the ratio between the flow velocity of the surface carrying oriented flakes and the slot height. For example, n layers of oriented nano-platelets can be extracted simultaneously where the slot height is large enough. The number of layers of nano-platelets in the meta-material is adjusted by defining by the liquid phase depletion rate and the phase’s volumetric ratio.

Packing of nano-platelets in a meta-material is affected by the film-forming agent introduced, e.g. structure of the film forming agent, concentration of the film forming agent in e.g. a water solution, and amount of film-forming agent applied.

A resulting meta-material obtained from the resulting method, for example as arranged in a meta-material, can be output through an output 17.

In a variant a number of meta-material films of graphene flakes are produced and then layered or sandwiched one on top of another. This can enable a complex layered structure in the resulting meta-material.

In a variant the meta-material is formed by coating an object with the orientated nano platelets and/or moulding a cast formed of the orientated nano-platelets. For example a film-forming agent may be applied to a mould and then a structured graphene flake layer may be applied and linked by the film-forming agent. In another example a specially prepared film may be glued on top of a structured graphene flake layer applied on an object.

Achieving horizontally and vertically aligned layers of graphene

Mechanisms for achieving vertical and horizontal alignment of graphene flakes are described below in relation to Figures 23 and 23. Figure 23 illustrates a schematic diagram for achieving horizontally aligned graphene flakes 20-2 on a surface of a dense fluid 15 in a separator tank 3. It will be appreciated that this diagram is for illustrative purposes only and is not intended to represent a true physical representation; no dimensional accuracy should be assumed. In this first example, horizontally aligned graphene flakes 20-2 can be achieved. One or more layers of graphene comprising horizontally aligned graphene flakes 20-2 can be obtained.

The mechanism for achieving horizontal alignment is described as follows: Vertically aligned graphene flakes 20-1 rise through the dense fluid 15 under the influence of gas bubbles. The graphene flakes 20-1 align with the vertical ascent of gas bubbles 22, for example columns of highly dispersed nitrogen bubbles. The gas bubbles 22 escape from the surface 13 of the dense fluid and are released to atmosphere causing the graphene flakes, released from the bubbles, to align horizontally on the dense fluid surface 13. One or more layers of horizontally aligned layers of graphene are positioned on or at the surface 13 of the dense fluid. The number of layers on the surface can be controlled by adjusting the rate of liquid through the nano-platelet outlet 8. Gas in the tank atmosphere, such as nitrogen, above the surface 13 of the dense fluid can be used to prevent oxidation of the horizontally aligned graphene flakes 20-2. In an example, the gas bubbles 22 may provide gas to fill the tank atmosphere.

The nano-platelet outlet 8 is positioned close to the surface, for example just below or just above the surface of the dense fluid 13 such that the surface 13 of the dense fluid comprising the horizontally aligned graphene 20-2 is bled off through the nano-platelet outlet 8. The positioning of the nano-platelet outlet 8 enables collection of the horizontally aligned graphene flakes 20-2. The direction of fluid and graphene flakes through the outlet is illustrated by an arrow leaving the separator tank 3.

In this first example, the filter element 7 in the filter tank 5 filters the graphene and dense fluid 15 from the separator tank 3. The resultant graphene film can be rolled up on a drum; in this case the end product comes in the form of an endless film reel. A film forming agent can help to protect and stabilise the film. The nano-platelet structure protected in such film and oxidation, spatial configuration change, accidental wear and tear, as well as defects can be reduced or avoided. Some arrangements of the nano platelets, e.g. in a fish scale pattern as described in more detail below, may be particularly well suited to rolling of the film without damage.

After the dense fluid 15 has been filtered it can be reused. A pump 6, for example a booster micro-pump, pumps the filtered dense fluid 15 back to the separator tank 3 to be reused.

In this first example, a meta-material comprising graphene flakes oriented horizontally parallel to the phase separation line can be obtained.

Optionally, a layer of a further liquid that is immiscible with the dense fluid 15 and forms a separate phase may be provided. Such a further liquid is described in more detail above and below with reference to the immiscible liquid 16. In this case, at the surface 13 of the dense fluid 15 a phase interface is formed where the graphene flakes move at least partially into the immiscible liquid. The immiscible liquid can help maintain flakes in a particular orientation. Gas bubbles 22 rising vertically can promote self-assembly of the graphene flakes at the phase interface.

By selecting the flow of gas through the suspension and the flow velocity at the nano platelet outlet 8 conditions for self-alignment of the nano-platelets can be created that can result in a range of patterns of one or more layers of horizontal nano-platelets. Figures 25a, 25b, 25c, 25d, 25e, 25f, 25g and 25h show different arrangements of horizontally aligned nano-platelets. In these figures examples are shown of nano platelets arranged in one or more layers in different regular patterns. Figure 25a shows a single layer arranged in a pattern with a hexagonal packing arrangement (also referred to as triangular packing), where the nano-platelets are permitted to assume a dense packing such that no overlapping occurs between the nano-platelets forming the layer. In this arrangement the nano-platelets do not overlap one another, but only contact each other at their edges. Figure 25b shows a single layer arranged in a fish scale pattern with partial overlapping of the nano-platelets forming the layer. Each nano-platelet is partially on top of one neighbour, and partially beneath another neighbour. Figure 25c shows a single layer arranged in a chainmail pattern with three flakes touching at their edges (as in a triangular packing) and a fourth flake arranged to partially overlap each of the three touching flakes. The nano-platelets are partially on top of one another.

Figure 25d shows multiple layers arranged in a stacked pattern, where no overlapping occurs between the nano-platelets forming a layer (triangular packing as in Figure 25a), and the nano-platelets of different layers are vertically stacked such that nano-platelets of different layers overlie one another to a maximum extent. Figures 25e and 25f show variants of the chainmail pattern with multiple layers, where no overlapping occurs between the nano-platelets forming a layer (triangular packing as in Figure 25a), and the nano-platelets of different layers are offset from one another such that nano-platelets of different layers partially overlie one another. Figure 25e shows an example where neighbouring layers are offset by offset vectors that always have the same orientations, whereas Figure 25f shows an example where the offset vectors between different neighbouring layers have different orientations. Figures 25g and 25h show variants of the fish scale pattern with multiple layers, where the nano-platelets forming a layer partially overlap one another, and the nano-platelets of different layers are arranged such that an overlaying flake contacts the edge of an underlying flake. Figure 25g shows an example where neighbouring layers are offset by offset vectors that always have the same orientations, whereas Figure 25h shows an example where the offset vectors between different neighbouring layers have different orientations.

Self-alignment the horizontal nano-platelets of different layers into a particular pattern is promoted as follows. As nano-platelets move to the surface 13 of the dense fluid 15 (with or without an overlying layer of immiscible liquid) gas bubbles 22 rising vertically promote self-assembly of the graphene flakes at the surface 13. When a continuous layer of flakes is formed at the surface 13, a second layer begins to form beneath it. The second layer, while slightly submerged, can lift the overlaying layer above the surface 13 (optionally into the immiscible liquid). Both fluid flow at the surface 13 (whether of the dense fluid 15 or the immiscible fluid) and gas flow rate affect flake self-orientation. For a given tank configuration and set of materials a ratio between gas medium flow velocity and liquid flow velocity can be selected in order to provide nano-platelet layers arranged in a particular pattern. The specific ratio for a desired pattern depends on the tank configuration and set of materials used.

By suitable selection and control of the process parameters films of nano-platelets of various spatial orientations overlying one another in various arrangements can be provided. Figure 24 illustrates a schematic diagram for achieving vertically aligned graphene flakes 20-3. It will be appreciated that this diagram is for illustrative purposes only and is not intended to represent a true physical representation; no dimensional accuracy should be assumed. In this second example, a liquid 16 immiscible in water is present in the system.

Vertically aligned graphene flakes 20-1 rise through the dense fluid 15 as described above in relation to Figure 23. At the phase interface 13 the graphene flakes 20-1 move at least partially into the immiscible liquid 16. The immiscible liquid 16 can help stabilise the flakes in their vertical orientation. As vertical orientated flakes accumulate at the phase interface they self-assemble into vertical alignment as illustrated in Figure 24. Dynamic shaking of the liquid flow by small gas bubbles as they move vertically through the immiscible liquid can assist compaction and vertical alignment of flakes. Gas bubbles 22 rising vertically maintain the graphene flakes in vertical positioning. The graphene flakes 20-1 may be prevented from floating upward in the immiscible liquid 16 and collecting at the surface 12 by selecting a fluid with a lower density than graphene. One or more densely packed layers of vertically aligned graphene flakes 20-3 can be obtained, dependent on factors such as: bleed-off rate, rate of arrival of the graphene 20-1 at the dense fluid surface 13, immiscible liquid 16 volume, etc. The height of the outlet slot 8 can be increased or decreased thus determining the offtake rate and, correspondingly, the number of aligned layers to be removed from the separator tank 3 at a time. In some examples, densely packed graphene may not be required.

The immiscible liquid 16 containing vertically aligned graphene flakes 20-3 therein is bled off through nano-platelet outlet 8 above the dense liquid surface 13 (also referred to as the phase interface between the immiscible liquid and the dense liquid). The nano platelet outlet 8 is positioned between the dense liquid surface 13 and the immiscible liquid surface 12. The positioning of the nano-platelet outlet 8 provides the means for collecting vertically aligned graphene flakes 20-3. The direction of fluid and graphene flakes through the outlet is illustrated by an arrow leaving the separator tank 5.

In this example, a filter element 7 in the filter tank 5 filters the graphene and immiscible liquid 16. After the immiscible liquid 16 has been filtered it can be reused. A pump 6, for example a booster micro-pump, pumps the filtered immiscible liquid 16 back to the separator tank 3 to be reused. Fragments and defective raw material may, to a small extent, collect in a layer between liquid interfaces. If so, such a layer could be removed back into water 9 using a bottom shaft of a vacuum filter drum (filter element 7); once water is recirculated, such fragments and defective raw material could be removed.

The immiscible liquid 16 can both protect graphene from undesired exposure to air, and so can prevent contamination of separated graphene; and it can also assist with spatial orientation of the graphene flakes on the surface of the dense aquatic solution 15, as described above. Spatially orientated graphene can be used to form a meta-material having determined properties.

The size of the graphene flakes has no major bearing on the formation, spatial orientation, or the creation of graphene layers at the dense fluid surface. One determinant of the size of graphene flakes is graphite purity. A value of around 99.5% graphite purity is preferred, however, other purities can also be used.

In this second example, a meta-material comprising graphene flakes oriented vertically, perpendicular to the phase separation line, can be obtained. The volume ratio of the aquatic phase to the immiscible liquid is maintained between 100:2 and 100:4. In a variant the alignment of graphene flakes is tuned to an arbitrary orientation other than vertical or horizontal, e.g. 45 degrees incline, by applying a shear force to the aligned graphene flakes and/or to a film formed of aligned flakes. This may be achieved before or after offtake of the film from the liquid interface as described above. In an example an extra shaft is provided at the vacuum drum filter (filter element 7) so as to apply a shear force to the film at the with the vacuum drum filter. The extra shaft may sandwich the film with the vacuum drum filter but move at a different speed at the film surface than the vacuum drum filter in order to create shear stress; the shear, and hence the angle of flake incline, is controlled by selecting a ratio of speeds at the film top and bottom surfaces. The flakes could be fixed following such a shear treatment.

In addition, or alternatively, a film of vertically arranged flakes may be rolled onto a spool. Shear force occurs along the centre of the roll, which can be used to control alignment of the flakes in a desired orientation. If a film forming agent is applied such that the film layers are bound to one another as well as fixing the flakes within the film, then a stable meta-surface in the shape of a pipe can be formed.

Generally, various spatial and geometric ratios of flake incline angles are possible by applying a suitable shear force. Such a force may be applied before or after a film forming agent is applied, and before or after flakes are fixed relative to one another, depending on the nature of the film forming agent. The shear force can be applied in an arcuate arrangement for fanning of the flakes relative to a centrepoint. The shear force, whether arcuate or linear, can be applied along a more complex three dimensional path and direction, e.g. in a spiral or helical or coiled helical shaped path and direction.

In a variant the alignment of graphene flakes is controlled over time such that the alignment is varied in a particular sequence (e.g. initially a horizontally aligned portion of graphene flakes is produced, then the conditions are changed such that a vertically aligned portion of graphene flakes is produces. Due to the continuous nature of the meta-material formed this can provide a meta-surface with neighbouring areas having different properties (e.g. different flake orientations).

It will be appreciated that whilst the above example relates to horizontal and vertical alignment of graphite and graphene, other laminar and nano-platelet structures can be achieved using a similar process. In an example, the meta-materials described above are used in an optical material such as a heat mirror. Heat mirrors typically include coatings on a substate such as glass, with the coatings designed to reflect light in the infrared and ultraviolet spectral bands while allowing visible light to pass. Windows that are designed in this way can improve thermal insulation in buildings. Optical materials generally are designed to achieve selective transmittance, absorbance, and reflectance of specific spectral ranges. The meta-materials described above can be designed to provide a desired arrangement of nano-platelets (e.g. graphene) such that specific optical properties are provided. Another application of optical material involves high absorption of radiation across the solar spectrum and conversion to heat for solar energy harvesting, e.g. by conversion of heat into electric energy, or by evaporation of seawater for desalination, or by space heating. Other applications of optical material relate to optical components such as modulators and interconnects for communication devices, and photodetectors.

In another example, the meta-materials described above are used in an electrical material such as in superconductive cables and in supercapacitors. The arrangement of nano-platelets (e.g. graphene) in the meta-material can be engineered in order to provide specific electrical properties, including in superconductivity and supercapacitance.

In another example, the meta-materials described above are used in a material designed to provide specific thermal properties - for example extremely high thermal insulation, to the extent that it provides heat mirror functionality instead of any heat transfer. A high thermal insulation material can prevent heat losses in many applications. For example thermal insulation of a furnace could increase the efficiency from typically 35-40% up to 70%. A thermal focus could be created inside a furnace on heating elements of the heat transfer agent without heat losses. A high thermal insulation material can reduce or prevent heat emissions into the environment from any type of industrial or civilian structures, modes of transportation, high voltage trunk power transmission lines; seafaring fleets could stop heating up the seas.

A multi-layer meta-material, with a thermal conductor layer between thermal insulator layers can provide a heat conductor with negligible heat losses during transfer. Boron is a widely occurring natural substance. A boron monolayer one molecule thick (also referred to as borophene) can exceed the tensile strength of steel by a factor of 100. In an example the thermal conductivity of borophene has been calculated to be about 14.34 W/mK, which is much smaller than that of graphene (about 3500 W/mK, making graphene highly thermally conductive); hexagonal boron nitride (BN) on the other hand also provides high thermal conductivity (about 751 W/mK). It is thought that borophene can provide extremely high thermal insulation. A method of aligning boron monolayer nano-platelets is provided as described above to form a meta-material of oriented boron monolayer nano-platelets, to provide a high thermal insulation material. The space between boron nano-platelets is filled with a composite or polymer, while maintaining the boron nano-platelets’ spatial configuration. The boron monolayers are not necessarily formed by flaking as described above, but may be formed otherwise and suspended in a liquid for alignment as described above.

In another example the immiscible liquid described above is a flat flow of a liquid polymer, or pre-polymer, that is in the process of hardening or can be hardened e.g. by irradiation or heating. The spatially oriented nanoflakes (graphene or other material) described above move at least partially into the liquid polymer which is then permitted to harden or polymerise. In this manner an endless flat surface of monomolecular layers, arranged in a particular orientation, is formed on a polymer film as a substrate, to produce a meta-material film. The polymer substrate can cover the monomolecular layers, while exposing and fixing the monomolecular layers. Such a polymer substrate can provide support for handling the monomolecular layers.

The size, in particular the thickness and length, of a meta-material film would only be limited by the amount of liquid polymer and transportation capabilities. However, given the multicore and backup requirements, manufacture directly at the consumption location is possible. Twisting a meta-material film can help achieve any angles between the flakes.

A meta-material film can be used to form electrically superconducting cable, for transfer of signals for example. Meta-material film can be used to form a cable with other superconducting properties for transferring other types of signal, for instance optical and laser signals. Alternatives

In the process described above, no simultaneous extraction of horizontally and vertically oriented nano-platelet layers along the offtake surface takes place. However, either layer could be produced separately (e.g. sequentially) using a single apparatus without interrupting the manufacturing process.

In some examples a mixture of graphene and graphite is obtained by a conventional technique such as ultrasonication, and component parts of the mixture are separated as described above in a liquid with a suitably selected density.

In some examples a suspension of graphene is obtained by a conventional technique such as intercalation, and the graphene is aligned to form a layer or film as described above.

Summary

A summary of the process described above is illustrated in Figure 26, which illustrates stages of a method to produce meta-materials according to the present disclosure. The steps of the method are independent processes as described above, and are not required to be performed together; each step can be performed individually or by an alternative method.

A worked example is described above in relation to source graphite and resulting graphene as a product. However, it will be appreciated that other 3D materials can be treated using a similar process to create 2D layered materials including nano-platelets.

According to a first step 200, monomolecular 2D layers, or nano-platelets, are flaked from a 3D product or laminar material by generating high frequency alternating flow velocities and pressure oscillations of a first fluid solution comprising a suspension of the 3D product. A 3D product, such as graphite, to be separated into monomolecular 2D layers, such as graphene, is added to a first fluid solution in a first tank 1. A generator 2 as described above creates conditions for flaking nano-platelets from the source laminar material at defect sites and stress concentration sites inherent in the source material.

In a second step 210, the 2D flakes are separated from the 3D product using a second fluid solution 15 in a second tank, for example a separator tank 5, the second fluid solution 15 having a density lower than the 3D product. In a third step 220, 2D flakes are aligned in a desired orientation. A meta-material comprising aligned 2D flakes can be fabricated.

It will be appreciated from the above description that many features of the different examples are interchangeable and combinable. The disclosure extends to further examples comprising features from different examples combined together in ways not specifically mentioned. Indeed, there are many features presented in the above examples and it will be apparent to the skilled person that these may be advantageously combined with one another.

Claims

1. A method of flaking nano-platelets from particles of a laminar material, comprising steps of: providing a suspension of the particles of the laminar material in a liquid; and forming a flow with toroidal vortices in the suspension of the particles such that the particles are exposed to alternating flow velocities and alternating pressures.

2. A method according to claim 1 , wherein the flow comprises local pressures of at least 10 MPa, preferably at least 25 MPa, further preferably at least 50 MPa.

3. A method according to claim 1 or 2, wherein the flow comprises local pressures of up to 1 mPa, preferably up to 0.1 mPa, further preferably up to 0.01 mPa

4. A method according to any preceding claim, wherein the flow comprises local velocities of at least 100 meters per second, preferably at least 150 meters per second, further preferably at least 200 meters per second.

5. A method according to any preceding claim wherein the peripheral flow velocity in a toroidal vortex is greater than the flow velocity in the fluid outside the toroidal vortex by a factor of at least 10, preferably by a factor of 16, further preferably by a factor of 20.

6. A method according to any preceding claim, wherein the flow comprises high- frequency alternating flow velocities.

7. A method according to any preceding claim, wherein the flow comprises high- frequency alternating pressures.

8. A method according to any preceding claim, wherein the flow comprises alternating flow velocities produced at a frequency of at least 500 Hz, preferably 1000 Hz, further preferably 3000 Hz

9. A method according to any preceding claim, wherein the flow comprises alternating pressures produced at a frequency of at least 500 Hz, preferably at least 1000 Hz, further preferably at least 2000 Hz.

10. A method according to any preceding claim, wherein the toroidal vortices have a typical diameter of at least 10 pm, preferably at least 20 pm, further preferably at least 40 pm.

11. A method according to any preceding claim, wherein the flow includes at least 150, preferably at least 200, further preferably at least 500 toroidal vortices per litre of suspension.

12. A method according to any preceding claim, wherein the suspension of the particles comprises at least 1, preferably at least 2, further preferably at least 3 parts fluid per 1 part particles by mass.

13. A method according to any preceding claim, wherein the suspension of the particles comprises up to 50, preferably up to 10, further preferably up to 5 parts fluid per 1 part particles by mass.

14. A method according to any preceding claim, wherein the suspension is a suspension in water, de-ionised water, de-mineralised water, surfactant-free water, ultrapure water, ethanol, tetrahydrofurane, chloroform, acetone or toluene.

15. A method according to any preceding claim, wherein the particles are graphite, and the nano-platelets include graphene.

16. A method according to any preceding claim, further comprising a step of dispersing particles of a laminar material in a liquid to form a suspension.

17. A method according to any preceding claim, wherein the flow is formed by a notched rotor rotating in cooperation with a notched stator to block and open cyclically a plurality of passages for a fluid.

18. A method according to any preceding claim, further comprising a step of separating a mixture of graphite and nano-platelets including graphene, comprising suspending the mixture of graphite and nano-platelets including graphene in a liquid with 1.5-2.5 g/cm³ density for selective movement of a component part of the mixture toward a specific portion of the liquid under the influence of gravity.

19. Apparatus for flaking nano-platelets from particles of a laminar material, comprising a flow generator adapted to form a flow with toroidal vortices in a suspension of the particles of the laminar material such that the particles are exposed to alternating flow velocities and alternating pressures.

20. Apparatus according to claim 19, further comprising a separator for separating a mixture of graphite and nano-platelets including graphene, comprising a liquid with a density of 1.5-2.5 g/cm³ for selective movement of at least one of the graphite and the nano-platelets toward a specific portion of the liquid under the influence of gravity.

21. Apparatus according to claim 19 or 20, further comprising an aligner for aligning nano-platelets in a suspension, the aligner comprising an arrangement for bubbling a gas through the suspension for vertical orientation of the nano-platelets; and a layer of a further liquid that is immiscible with the liquid of the suspension, such that the nano platelets move at least partially into the further liquid under the influence of gas bubbles.

22. A method of separating a mixture of graphite and nano-platelets including graphene, comprising a step of: suspending the mixture of graphite and nano-platelets including graphene in a liquid with a density of 1.5-2.5 g/cm³ for selective movement of at least one of the graphite and the nano-platelets toward a specific portion of the liquid under the influence of gravity.

23. A method according to claim 18 or 22, wherein the movement is settling of the graphite toward a bottom portion of the liquid.

24. A method according to claim 18 or 22 or 23, wherein the movement is flotation of the nano-platelets toward a top portion of the liquid.

25. A method according to any of claims 18 or 22 to 24, wherein the liquid has a density in the range of 1.7-2.4 g/cm³.

26. A method according to any of claims 18 or 22 to 25, wherein the liquid has a density selected based on the density of the graphite.

27. A method according to any of claims 18 or 22 to 26, wherein the liquid has a density of up to 99.9% the density of the graphite, preferably up to 99.5% the density of the graphite, further preferably up to 99% or 98.5% the density of the graphite.

28. A method according to any of claims 18 or 22 to 27, wherein the liquid has a density of at least 90% the density of the graphite, preferably at least 95% the density of the graphite, further preferably at least 98% or 98.5% the density of the graphite.

29. A method according to any of claims 18 or 22 to 28, wherein the liquid has a density in the range of 98-99% the density of the graphite, preferably approximately 98.5% the density of the graphite.

30. A method according to any of claims 18 or 22 to 29, wherein the liquid is an aqueous solution.

31. A method according to any of claims 18 or 22 to 30, wherein the liquid is a solution of a chlorine salt, optionally NaCI, CaC or KCI.

32. A method according to any of claims 18 or 22 to 31 , further comprising bubbling a gas through the liquid, optionally wherein the gas is introduced at or near a bottom portion of the liquid.

33. A method according to claim 32, wherein the gas is highly dispersed in the liquid.

34. A method according to claim 32 or 33, wherein the gas is introduced from an outlet having a size of at least 0.05 mm, preferably at least 0.1 mm, further preferably at least 0.2 mm.

35. A method according to any of claims 32 to 34, wherein the gas is introduced from an outlet having a size of up to 1 mm, preferably up to 0.7 mm, further preferably up to

0.5 mm.

36. A method according to any of claims 32 to 35, wherein the gas is nitrogen.

37. A method according to any of claims 32 to 36, wherein a flow rate of the gas into the liquid is up to 0.004 m³/sec per 1 m² of a top surface of the liquid, or up to 0.002 m³/sec per 1 m² of a top surface of the liquid.

38. A method according to any of claims 32 to 37, wherein the gas is bubbled into the liquid at a pressure of up to 10 kPa in excess of the liquid column pressure, preferably up to 5 kPa in excess of the liquid column pressure, further preferably up to 4 kPa in excess of the liquid column pressure.

39. A method according to any of claims 18 or 22 to 38, further comprising providing a layer of a further liquid that is immiscible with the liquid of the mixture, such that one of graphite and the nano-platelets move toward and into the further liquid, optionally wherein the further liquid is less dense than the liquid of the mixture.

40. A method according to claim 39, wherein the further liquid is hydrophobic.

41. A method according to claim 39 or 40, further comprising flowing the further liquid relative to the liquid of the mixture for entrainment of a component part of the mixture by the further liquid.

42. A method according to any of claims 39 to 41 , further comprising continuously flowing the further liquid over a surface of the liquid of the mixture.

43. A method according to any of claims 39 to 42, further comprising recovering the further liquid for collection of the nano-platelets.

44. A method according to any of claims 18 or 22 to 43, further comprising bubbling a gas through the suspension of graphite and nano-platelets including graphene for orientation of the nano-platelets; and providing a layer of a further liquid that is immiscible with the liquid of the suspension, such that the nano-platelets including graphene move at least partially into the further liquid under the influence of gas bubbles.

45. Apparatus for separating a mixture of graphite and nano-platelets including graphene, comprising a liquid with a density of 1.5-2.5 g/cm³ for selective movement of at least one of the graphite and the nano-platelets toward a specific portion of the liquid under the influence of gravity.

46. Apparatus according to claim 45, further comprising an aligner for aligning nano platelets in a suspension, the aligner comprising an arrangement for bubbling a gas through the suspension for vertical orientation of the nano-platelets; and a layer of a further liquid that is immiscible with the liquid of the suspension, such that the nano platelets move at least partially into the further liquid under the influence of gas bubbles.

47. A method of aligning nano-platelets in a suspension, comprising steps of: providing a suspension of the nano-platelets in a liquid; bubbling a gas through the suspension for orientation of the nano-platelets; and providing a layer of a further liquid that is immiscible with the liquid of the suspension, such that the nano-platelets move at least partially into the further liquid under the influence of gas bubbles.

48. A method according to claim 44 or 47, wherein the orientated nano-platelets self- assemble in an ordered structure at an interface of the liquid of the suspension under the influence of gas bubbles.

49. A method according to claim 44 or 47 or 48, wherein the orientation of the nano platelets is a vertical orientation or a horizontal orientation.

50. A method according to any of claims 44 or 47 to 49, wherein the liquid of the suspension is water or an aqueous solution.

51. A method according to any of claims 44 or 47 to 50, wherein the further liquid is a water-insoluble liquid, preferably wherein the further liquid is or includes at least one of: kerosene, petroleum oils, mineral oils, tetrachloroethylene, trichloroethylene, white spirit, organosilicon compounds, dibutoxymethane and food oils.

52. A method according to any of claims 44 or 47 to 51, further comprising flowing the further liquid relative to the liquid of the suspension for entrainment of nano-platelets by the further liquid.

53. A method according to claim 52, further comprising continuously flowing the further liquid over a surface of the liquid of the suspension.

54. A method according to any of claims 44 or 47 to 53, further comprising recovering the further liquid for collection of the nano-platelets.

55. A method according to any of claims 44 or 47 to 54, further comprising drawing off the further liquid at an aperture arranged at or near a phase interface between the further liquid and the liquid of the suspension.

56. A method according to claim 55, wherein the aperture is a slot, preferably a horizontal slot.

57. A method according to claim 56, wherein the slot is formed by flaps arranged to adapt to fluid flowing through the slot.

58. A method according to any of claims 44 or 47 to 57, further comprising fixing the orientated nano-platelets relative to one another to form a meta-material of ordered nano-platelets.

59. A method according to claim 58, wherein fixing consists of linking nano-platelets to one another, embedding nano-platelets in a matrix, or linking nano-platelets to one another with a linking agent.

60. A method according to claim 59, wherein the nano-platelets are graphene and linking with a linking agent consists of linking with 1-aminopyrene disuccinimidyl suberate.

61. A method according to any one of claims 58 to 60, wherein the meta-material is a film, an arrangement of films, a mat, a filament or an arrangement of filaments.

62. A method according to any one of claims 58 to 61 , wherein the meta-material is formed continuously.

63. A method according to any one of claims 58 to 62, wherein the meta-material comprises nano-platelets arranged in one or more layers in a regular arrangement, preferably in a fish scale pattern, a stacked pattern, or a chainmail pattern.

64. A method according to any one of claims 58 to 63, wherein the meta-material is formed by coating an object with the orientated nano-platelets and/or moulding a cast formed of the orientated nano-platelets.

65. A method according to any of claims 44 or 47 to 64, wherein the gas is introduced at or near a bottom portion of the liquid of the suspension.

66. A method according to any of claims 44 or 47 to 65, wherein the gas is highly dispersed in the liquid of the suspension.

67. A method according to any of claims 44 or 47 to 66, wherein the gas is introduced from an outlet having a size of at least 0.05 mm, preferably at least 0.1 mm, further preferably at least 0.2 mm.

68. A method according to any of claims 44 or 47 to 67, wherein the gas is introduced from an outlet having a size of up to 1 mm, preferably up to 0.7 mm, further preferably up to 0.5 mm.

69. A method according to any of claims 44 or 47 to 68, wherein a flow rate of the gas into the liquid is up to 0.004 m³/sec per 1 m² of a top surface of the liquid, or up to 0.002 m³/sec per 1 m² of a top surface of the liquid.

70. A method according to any of claims 44 or 47 to 69, wherein the gas is bubbled into the liquid at a pressure of up to 10 kPa in excess of the liquid column pressure, preferably up to 5 kPa in excess of the liquid column pressure, further preferably up to 4 kPa in excess of the liquid column pressure.

71. Apparatus for aligning nano-platelets in a suspension, comprising an arrangement for bubbling a gas through the suspension for orientation of the nano platelets; and a layer of a further liquid that is immiscible with the liquid of the suspension, such that the nano-platelets move at least partially into the further liquid under the influence of gas bubbles.

72. A meta-material formed by aligning nano-platelets in an orientation in a suspension, and fixing the orientated nano-platelets relative to one another to form a meta-material of ordered nano-platelets.

73. The meta-material according to claim 72 wherein the nano-platelets are fixed relative to one another such that each nano-platelet lies within substantially the same plane.

74. The meta-material according to claim 72 wherein the nano-platelets are fixed relative to one another such that the nano-platelets are arranged in separate, parallel planes.

75. The meta-material according to any of claims 72 to 74 wherein fixing comprises applying a film forming agent to the oriented nano-platelets.

76. The meta-material according to any of claims 72 to 75 further formed by applying an arcuate or linear shear force to the aligned nano-platelets to arrange the nano platelets in an orientation.

77. The meta-material according to any of claims 72 to 76 wherein the meta-material is in the form of a substantially planar two-dimensional surface, a substantially one dimensional wire or a substantially cylindrical surface.

78. The meta-material according to any of claims 72 to 77 wherein the meta-material comprises a continuous one-dimensional structure of unconstrained length.

79. The meta-material according to any of claims 72 to 78 wherein the material comprises a plurality of regions comprising at least a first region having nano-platelets arranged in a first orientation and a second region having nano-platelets arranged in a second orientation.

80. A meta-material according to any of claims 72 to 79 formed according to the method of any of claims 44 or 47 to 70.

81. An optical material, preferably a heat mirror, comprising a meta-material according to any of claims 72 to 80, preferably including nano-platelets of graphene.

82. An electrical material, preferably a superconductor or a supercapacitor, comprising a meta-material according to any of claims 72 to 80, preferably including nano-platelets of graphene.

83. A thermal material, preferably a thermal insulator, comprising a meta-material according to any of claims 72 to 80, preferably including nano-platelets of boron.