WO2021130292A1

WO2021130292A1 - Ink composition for the production of micropatterns

Info

Publication number: WO2021130292A1
Application number: PCT/EP2020/087736
Authority: WO
Inventors: Mateusz ODZIOMEK; Marco FAUSTINI; Cédric BOISSIERE; Clément Sanchez
Original assignee: Sorbonne Universite; Centre National De La Recherche Scientifique (Cnrs); College De France
Priority date: 2019-12-23
Filing date: 2020-12-23
Publication date: 2021-07-01

Abstract

The invention relates to a method for forming at least one periodic array of cracks of an inorganic micropatterned coating, wherein each crack of said at least one periodic array of cracks extends over the substrate along an axis following a linear direction, each axis of each crack being parallel to the axis of the other cracks. The invention also relates to an inorganic micropatterned coating as defined, said coating being obtainable by the method of the invention. The invention also related to a device comprising an inorganic micropatterned coating of the invention, an ink composition for the production of an inorganic micropatterned coating of the invention and the use of said ink composition for obtaining an inorganic micropatterned coating of the invention.

Description

INK COMPOSITION FOR THE PRODUCTION OF MICROPATTERNS

FIELD OF THE INVENTION

The invention relates to a method for forming at least one periodic array of cracks of an inorganic micropatterned coating. The invention also relates to an inorganic micropatterned coating comprising at least one periodic array of cracks, a device comprising an inorganic micropatterned coating of the invention, an ink composition for the production of an inorganic micropatterned coating of the invention and the use of said ink composition for obtaining an inorganic micropatterned coating of the invention.

BACKGROUND OF THE INVENTION

Multi-scale structuration of functional materials in nano- and micro- levels is an active scientific field driven by the tremendous potential of miniaturized devices in microelectronics, optics (light harvesting, photonics), sensing (selective sensors) or microfluidics (lab-on-a-chip). Diverse micro-nanofabrication techniques are exploited for device fabrication.

Most of the devices used in said described fields are made with inorganic or ceramic materials having particular physico-chemical properties.

On one hand, top-down techniques are developed to fabricate complex micro- and nano- structures from bulk materials; this approach relies on lithography which offers a wide flexibility on the final object architecture but suffers from low-throughput and high costs that hinder its use for large-scale production.

On the other hand, bottom-up techniques based on the assembly of molecular or particulate building blocks are suited for the large-scale fabrication of nanostructured materials but are limited to simple architectures.

Both deposition and patterning techniques often suffer from the presence of cracks considered as a material failure mode. Cracks cause critical problems in various micro/nanofabrication processes such as colloidal assembly, thin film deposition, and even standard photolithography because they are hard to avoid or control. Cracks seems to be a real problem because the products obtained are not useable or operable.

There is therefore a need to find cheap and easy to implement solutions to create inorganic functionalized and structured devices, which are also comprising complex architectures allowing the corresponding devices to provide specific and useful optical or physical properties SUMMARY OF THE INVENTION

It has been found that crack propagation and patterning creating technique, using an ink composition comprising inorganic precursor and nanoparticles, is useful to create inorganic regular patterns with a controlled periodicity and provide devices with searched properties.

Further, the inventors have found a method for forming at least one oriented periodic array of cracks of an inorganic coating that allows to obtain patterns that range from simple unidirectional groove type patterns to multidirectional patterns prepared by multi-layer deposition.

The inventors have also found a method for controlling the periodicity and the orientation of the fabricated patterns, allowing the formation of an inorganic micropatterned coating with oriented cracks.

A first object of the invention is a method for forming at least one periodic array of cracks of an inorganic micropatterned coating, wherein said method comprises the following steps: a. Providing an ink composition comprising nanoparticles having a size obtained by dynamic light scattering (DLS) of between 10 and 500 nm, at least one inorganic precursor, and at least one solvent, the ratio of metal in the precursor to the mass of nanoparticles being between 0,05 and 3 mmol/g; b. Coating a substrate with the ink composition; c. Evaporating the solvent; d. Optionally calcinating the coated substrate obtained in step c); e. Optionally repeating at least once the steps a) to d) in order to obtain a multilayered inorganic micropatterned coating comprising a plurality of periodic arrays of cracks. wherein each crack of said at least one periodic array of cracks extends over the substrate along an axis following a linear direction, each axis of each crack being parallel to the axis of the other cracks.

Another object of the invention is an inorganic micropatterned coating comprising at least one periodic array of cracks, wherein each crack of said at least one periodic array of cracks extends over the substrate along an axis following a linear direction, each axis of each crack being parallel to the axis of the other cracks, said coating being obtainable by the method a of the invention. Another object of the invention relates to a device comprising an inorganic micropatterned coating comprising at least one periodic array of cracks of the invention.

Another object of the invention relates to an ink composition for the production of an inorganic micropatterned coating comprising at least one periodic array of cracks of the invention, wherein said ink composition comprises nanoparticles having a size obtained by dynamic light scattering (DLS) of between 10 and 500 nm, at least one inorganic precursor, and at least one solvent, the ratio of metal in the precursor to the mass of nanoparticles being between 0,05 and 3 mmol/g.

Another object of the invention relates to the use of an ink composition of the invention, for obtaining an inorganic micropatterned coating comprising at least one periodic array of cracks of the invention.

DETAILED DESCRIPTION OF THE INVENTION Definitions

For the purpose of the invention, the term “coating based on” is intended to mean a coating comprising the mixture and/or the in situ reaction product of the different basic components used, some of these components being able to react and/or being intended to react with each other, at least partially, during the different manufacturing phases of the ink composition and of the coating itself, for example during the evaporation step or the calcination step, modifying the composition as it is initially prepared.

For the purpose of the invention, the "coating" is therefore obtained by applying the ink composition to a substrate, the coating layer being then subjected to a calcination process.

For the purpose of the invention, the terms “with oriented cracks” in the expression “inorganic micropatterned coating with oriented cracks” mean one periodic array of cracks of an inorganic micropatterned coating wherein each crack of said at least one periodic array of cracks extends over the substrate along an axis following a linear direction, each axis of each crack being parallel to the axis of the other cracks. Said periodic array has a determined pitch and the cracks present a determined width.

The terms “periodic array of cracks”, as used in the present invention, refer to an ordered arrangement of cracks appearing at regular intervals.

The term “pitch”, as used in the present invention, refers to the center-to-center distance between two successive cracks. The terms “withdrawal speed”, as used in the present invention, refer to a speed at which any point of the substrate moves relative to the meniscus of the ink formed with that substrate.

The terms “flash calcination”, as used in the present invention, refer to a calcination in which the calcined material is introduced from the ambient temperature into the pre heated oven to a set temperature.

The terms “dip coating”, as used in the present invention, refer to the immersion of a substrate into a reservoir filled with coating material, subsequent withdrawal and drying of the coated substrate.

The terms “roll to roll method”, as used in the present invention, refer to a continuous process of deposition on a substrate which is moved between two or more rolls,

The terms “knife coating method”, as used in the present invention, refer to a process in which excess of the liquid applied on the substrate is removed by mattering blade moving relative to the substrate.

The terms “screen-printing method”, as used in the present invention, refer to a process in which an ink is deposit on the substrate through a mesh. The ink pushed by the blade or squeegee passes through the holes and is stopped by a blocking stencil.

The terms “slot-die coating”, as used in the present invention, refer to a coating process in which an ink is dosed through a pump into slot-die head which is positioned over substrate (and it moves relative to it) and uniformly deposit the ink.

Ink composition

In the field of the invention, the appearance of cracks is strongly dependent on the properties of the ink composition that is used for forming an inorganic micropatterned coating. Each ink composition would have different cracking behaviour.

To make use of crack patterning for microfabrication purposes, it is mandatory to control the ink composition and as well the periodicity of the fabricated patterns and to be able to tune its value. The periodicity is a function of the film thickness h which is directly correlated to crack spacing by a nearly linear trend: λ_c-c = k^*h^α where a coefficient lies between 0,66 and 0,8 according to different reports. If the film thickness is too low, meaning that it is below critical cracking thickness, the cracks do not appear and patterning is not possible.

Up to know there are no reports exploiting crack patterning for functional inorganic structures. The inventors have surprisingly found that the ink composition of the invention, comprising nanoparticles and at least one inorganic precursor, allow to obtain an inorganic micropatterned coating with oriented cracks, when at least the following parameters are controlled: the particles size of the nanoparticles, the ratio of metal in the precursor to the mass of nanoparticles, and advantageously the content of nanoparticles.

Therefore, an object of the invention relates to an ink composition for the production of an inorganic micropatterned coating comprising at least one periodic array of cracks of the invention, wherein said ink composition comprises nanoparticles having a size obtained by dynamic light scattering (DLS) of between 10 and 500 nm, at least one inorganic precursor, and at least one solvent, the ratio of metal in the precursor to the mass of nanoparticles being between 0,05 and 3 mmol/g.

Advantageously, the nanoparticles are selected from the group consisting of polymeric nanoparticles, silica nanoparticles, titania nanoparticles, aluminates nanoparticles, fluoride nanoparticles, and optionally mixtures thereof. More advantageously, the nanoparticles are selected from the group consisting of polymeric nanoparticles and silica nanoparticles.

In particular, the nanoparticles are polymeric nanoparticles, advantageously latex nanoparticles. In the meaning of the invention, latex means a stable dispersion of polymer particles in an aqueous medium.

In the context of the invention, by stable it is understood a dispersion where there is no precipitation or gelation of dispersion over the time of deposition.

Advantageously, the polymeric nanoparticles or latex nanoparticles are based on monomers selected from the groups consisting of styrene, (meth)acrylate derivatives such as methyl methacrylate, and mixtures thereof. More advantageously, the polymeric nanoparticles or latex nanoparticles are polystyrene nanoparticles.

Advantageously, the nanoparticles that are used in the present invention have a size obtained by dynamic light scattering (DLS) of between 20 and 300 nm, advantageously between 30 and 250 nm, more advantageously between 50 and 200 nm. Advantageously, the particle sizes as defined above have a polydispersity index (PDI) of between 0.001 and 0.5. Advantageously, in the ink composition of the invention, the content of nanoparticles is controlled in order to obtain a stable composition, i.e. a composition that does not diphase, gel or precipitate under conditions of film deposition. Further, too low nanoparticles content could result in not well defined or lack of cracks due to the dependence of crack quality and spacing on the thickness of the film, and too high nanoparticles content might result in too viscous solution yielding films of poor quality with lot of inhomogeneity (very thick films often delaminate). These effects could however be counterbalanced to some degree by higher temperature of deposition or lower withdrawal speed for example.

Advantageously, in the ink composition of the invention, the content of nanoparticles is advantageously between 0.1 and 25 %wt, more advantageously between 0,5 and 20 %wt, more advantageously between 2 and 15 %wt.

When polystyrene nanoparticles are used, the content of nanoparticles is advantageously between 0.1 and 25 %wt, more advantageously between 0,5 and 20 %wt, more advantageously between 2 and 15 %wt.

The terms “inorganic precursor”, as used in the present invention, refers to a molecular compound acting as precursor and containing at least one metal atom. Such a compound is completely dissolved in the ink composition of the invention. A compound that acts as a precursor is a compound from which another compound is formed. For example, in the context of the invention, the inorganic precursor can be converted by thermal treatment to give a compound selected from the group consisting of TiO₂, ZrO₂, WO₃, IrO₂, Ir, Ga₂O₃, MoO2, MoO3, NiO, Ni₂O₃, FeO, FeO₂, Fe₃O₄, Fe₄O₅, Fe₅O₆, Fe₅O₇, Fe₂₅O₃₂, Fe₁₃O₁₉, Fe₂O₃, MnO, Mn₃O₄, Mn₂O₃, MnO₂, MnO₃, Mn₂O₇, CoO, CO₂O₃, CO₃O₄, SnO, SnO₂, VO, V₂O₃, VO₂, V₂O₅, HfO₂, Rh ₂O₃, RhO₂, RuO2, Rh, SiO₂, In₂O₃, Sb₂O₃ and mixtures thereof.

Therefore, advantageously, in the ink of the invention, the at least one inorganic precursor is selected from the group consisting of inorganic precursors of TiO₂, ZrO₂, WO₃, IrO₂, Ir, Ga₂O₃, MoO2, MoO3, NiO, Ni₂O₃, FeO, FeO₂, Fe₃O₄, Fe₄O₅, Fe₅O₆, Fe₅O₇, Fe₂₅O₃₂, Fe₁₃O₁₉, Fe₂O₃, MnO, Mn₃ O₄, Mn₂O₃, MnO₂, MnO₃, Mn₂O₇, CoO, CO₂O₃, CO₃O₄, SnO, SnO₂, VO, V₂O₃, VO₂, V₂O₅, HfO₂, Rh₂O₃, RhO₂, RuO₂, Rh, SiO₂, In₂O₃, Sb₂O₃ and mixtures thereof. In particular, the at least one inorganic precursor is a metal salt of one or more compounds herein listed, such a metal salt being soluble in the ink composition according to the invention.

In the case of inorganic precursor of TiO₂, titania butoxide (TiBu) or titanium propoxide (TiPr) complexed with acetyloacetonate and titanium bis(ammonium lactato)dihydroxide (TBALDH) are advantageously selected.

In the case of inorganic precursor of ZrO₂, Zirconium(IV) oxynitrate (ZrO(NO₃)₂) is advantageously selected.

In the case of inorganic precursor of WO₃, ammonium metatungstate hydrate ((NH₄)₆H₂W₁₂O₄₀ xH₂O (AMT)) is advantageously selected. In the case of inorganic precursor of Ir or IrO₂, Iridium(lll) chloride (IrCl₃ ^*xH₂O) is advantageously selected.

In the case of inorganic precursor of Ga₂O₃, Gallium(lll) nitrate hydrate (Ga(NO₃)₃*xH₂O) is advantageously selected.

Advantageously, in the ink composition of the invention, the ratio of metal in the precursor to the mass of nanoparticles is controlled in order to obtain a stable composition, i.e. a composition that does not diphase, gel or precipitate under conditions of film deposition. Such a ratio can vary according to the nanoparticles and/or the inorganic precursors that are used. In the context of the invention, in the ink composition of the invention, the ratio of metal in the precursor to the mass of nanoparticles is between 0,05 and 3 mmol/g, advantageously between 0,08 and 2,5 mmol/g, more advantageously between 0,08 and 2,0 mmol/g.

In the context of the invention, the ratio between inorganic precursor and nanoparticles is expressed as number of moles of metal in the inorganic precursor to the mass of nanoparticles.

Advantageously, when polystyrene nanoparticles (PS) are used with inorganic precursor of TiO₂, the ratio of Ti/PS is between 0,21 and 3 mmol/g, more advantageously between 0,5 and 2 mmol/g.

Advantageously, when polystyrene nanoparticles (PS) are used with inorganic precursor of ZrO₂, the ratio of Zr/PS is between 0,12 and 2,95 mmol/g, more advantageously between 0,2 and 1,5 mmol/g.

Advantageously, when polystyrene nanoparticles (PS) are used with inorganic precursor of WO₃, the ratio is between 0,1 and 3 mmol/g, more advantageously between 1,8 and 3 mmol/g.

Advantageously, when polystyrene nanoparticles (PS) are used with inorganic precursor of Ir or IrO₂, the ratio is between 0,187 and 1,8 mmol/g, advantageously between 0,25 and 1,8 mmol/g, more advantageously between 0,4 and 1,8 mmol/g.

According to the invention, the ink composition also comprises at least one solvent, which is advantageously selected from the group consisting of water, alcohol solvents, and mixtures thereof. Advantageously, said solvent is selected from the group consisting of water, methanol, ethanol, propanol, isopropanol, butanol and mixtures thereof. Advantageously the ink composition comprises the solvent in a content of 1 to 2 % by weight, in relation to the total weight of the ink. Advantageously, the solvent is butanol, in particular butan-1 -ol. In the context of the invention, the addition of the solvent allows improving the quality of the film and reducing the wrinkling effect.

According to the invention, the ink composition may also comprise amphiphilic molecules such as poloxamer 407 (commercialised as Pluronic^® F127), Cetrimonium bromide; fluorescent molecules such as rhodamine; polymers such as polyvinylpyrrolidone; and/or plasmonic nanoparticles such as gold nanoparticles.

The ink composition according to the invention can be obtained by a method comprising the following steps: i. Providing nanoparticles solution wherein the nanoparticles have a size obtained by dynamic light scattering (DLS) of between 10 and 500 nm; ii. Providing at least one inorganic precursor in the form of a solution or in a solid form; iii. Mixing the nanoparticles solution of step i) and at least one inorganic precursor of step ii) for providing the ink composition comprising the nanoparticles, the at least one inorganic precursor, and at least one solvent, the ratio of metal in the precursor to the mass of nanoparticles being between 0,05 and 3 mmol/g.

Advantageously, step i) is carried out by synthetic protocols known by the one skilled in the art, or purchasing the selected redispersible nanoparticles in the solvent.

Advantageously, in the case of polystyrene nanoparticles, step i) is carried out by means known by the one skilled in the art. For example, the polystyrene nanoparticles can be obtained by dissolving a surfactant such as a poloxamer and styrene in water. After stirring, the solution may be flushed with N₂ in order to remove oxygen. Then, a polymerization initiator such as K₂S₂O₈, Na₂S₂O₈, (NH₄)₂S₂O₈, Na₂ S₂O₈ or azoisobutylnitrile (AIBN), is added and the solution is heated in order to allow the polymerisation. The particles size is then controlled.

Advantageously, step ii) is carried out by preparation of inorganic precursor by means known by the one skilled in the art. Most of them are commercially available. In some cases, like titania, the precursor is formed in additional steps including chelation, complexation or hydrolysis. For example, in the case of titania, acetyloacetonate is mixed with titania alkoxide, advantageously butoxide or propoxide and ethanol.

Advantageously, step iii) is carried out by dropping the nanoparticles solution into the inorganic precursor solution under stirring or by adding the inorganic precursor in the form of solution or powder into the nanoparticles solution. The solution can then be mixed and centrifuged in order to remove bigger aggregates of nanoparticles.

Advantageously in the case of titania and polystyrene nanoparticles (PS), the solution of PS is dropped into the precursor solution of titania precursor under continuous magnetic stirring. The mixture is then centrifuged in order to remove potentially present larger aggregates.

In the context of the invention, the ink composition as defined above, is used for obtaining an inorganic micropatterned coating comprising at least one periodic array of cracks, wherein each crack of said at least one periodic array of cracks extends over the substrate along an axis following a linear direction, each axis of each crack being parallel to the axis of the other cracks.

Method for forming at least one periodic array of cracks of an inorganic micropatterned coating

In the field of the invention, the appearance of cracks is also strongly dependent on the method used for forming the inorganic micropatterned coating. Indeed, the appearance of cracks is strongly dependent on the coating thickness. If the coating thickness is too low, meaning that it is below critical cracking thickness, the cracks do not appear and patterning is not possible.

The inventors have found that the method of the invention allow to obtain an inorganic micropatterned coating with oriented cracks. The inventors have therefore found a method allowing the control of the coating thickness and therefore allowing the control of the periodicity of the cracks.

In the context of the invention, the control of the coating thickness and thus the control of the periodicity of the cracks is obtained by controlling the ink composition and the different conditions of the method for forming the coating.

An object of the invention of the invention is thus a method for forming at least one periodic array of cracks of an inorganic micropatterned coating, wherein said method comprises the following steps: a. Providing an ink composition comprising nanoparticles having a size obtained by dynamic light scattering (DLS) of between 10 and 500 nm, at least one inorganic precursor, and at least one solvent, the ratio of metal in the precursor to the mass of nanoparticles being between 0,05 and 3 mmol/g; b. Coating a substrate with the ink composition; c. Evaporating the solvent; d. Optionally repeating at least once the steps a) to c) in order to obtain a multilayered inorganic micropatterned coating comprising a plurality of layers comprising periodic arrays of cracks, e. Optionally, calcinating the coated substrate obtained in step c) or d); and wherein each crack of said at least one periodic array of cracks extends over the substrate along an axis following a linear direction, each axis of each crack being parallel to the axis of the other cracks.

Advantageously, the ink composition of step a) is as defined above, in particular in the part named “Ink composition”. The method for providing such an ink composition is also disclosed in the part “Ink composition”.

One of the particular advantages of the invention is that the coating can be applied on any kind of substrate, whatever its shape (with simple or complex architecture), in particular any kind of inorganic substrate.

Advantageously, the substrate that can be coated according to the invention, in particular in step b) of the method of the invention, is a solid support with any shape, with surface accessible to liquid solution and allowing the evaporation of the solvent.

Advantageously, the substrate can be an inorganic substrate such as silicon, glass, alumina, titania, steal or plastic with the requirement of film adhesion to the substrate.

Advantageously, the step b) of coating is carried out by dip coating method, roll to roll method, knife coating method, screen-printing method or slot-die method. More advantageously, the step b) of coating is carried out by dip coating, advantageously with a withdrawal speed of between 1 and 100 μm/s. Alternatively, when the substrate is flat, the step b) of coating may be carried out by blade coating, advantageously with deposition rate between 0,05 and 1 mm/s and advantageously with heated substrate up to 100°C, the gap between blade and covered surface is advantageously between 0,1 to 2 mm.

Advantageously, step b) of coating and c) of evaporating the solvent are carried out simultaneously, for example by heating the chamber where the coating takes place, and/or reducing the relative humidity in the chamber.

Advantageously, the steps b) and c) are carried out so that the thickness of the coating can be controlled. For example, when water is used as the solvent of the ink composition, the temperature in the chamber may be increased, typically up to 90° C, in order to enhance the evaporation rate which increases the thickness of film.

Advantageously, the step e) of calcinating is a thermal treatment, typically in air, inert or reducing atmosphere. Advantageously, the step e) of calcinating is carried out at temperature of between 20°C and 2000° C, advantageously of between 400-800° C.

In one aspect of the invention, step e) is advantageously carried out by flash calcination, advantageously at temperature between 20 and 1000 °C during 0.05 and 10000 minutes, more advantageously at temperature between 400 and 800° C during 1 and 100 minutes.

In another aspect of the invention, step e) is advantageously carried out by calcination with a heating ramp of up to 1500°C/min to a temperature of between 20 and 1000 °C, more advantageously, with a heating ramp of between 100 and 1500°C/min to a temperature of between 400 and 800° C.

Advantageously, the coating thickness that can be obtained thanks to the method of the invention is between 100 nm and 100 μm, more advantageously between 100 nm and 50 μm, more advantageously between 200 nm and 5 μm, after step e) of calcination.

The method of the invention allows to form an inorganic coating not only with unidirectional grove-like patterns but also for multidirectional patterns by simply adding further layers according to step d) of the process described above, corresponding to a multilayer deposition. For example, a second layer can be deposited on the first layer in the way that cracks propagate at certain angle to the cracks of the layer below. The multilayer deposition allows also for mixing two or more different inorganic precursor and preparation of composite or sandwich type films.

Therefore, in one aspect of the present invention, a step d) is optionally carried out for repeating at least once the steps a) to c) or a) to c) and e), in order to obtain a multilayered inorganic micropatterned coating comprising a plurality of periodic arrays of cracks, wherein each crack of each periodic array of cracks extends over the substrate along an axis following a linear direction, each axis of each crack being parallel to the axis of the other cracks of said array.

Advantageously, when multilayered inorganic micropatterned coating is contemplated, the step a) may be repeated with a different ink composition for each layer so that different properties can be obtained. Advantageously, when multilayered inorganic micropatterned coating is contemplated, the step b) may be repeated with another angle than the first step b), or for each layer, in order to obtain a multidirectional inorganic micropatterned coating. In such a case, the cracks of each periodic array extend over the substrate at an angle greater than 0° to the cracks of the other periodic arrays.

Advantageously, the micropatterned coating obtained by the method according to the invention and with its corresponding ink, is not subject to additional or further cracking on each micropatterns generated and have a sufficient uniformity to provide clear and efficient contemplated physical effect.

Inorganic micropatterned coating with oriented cracks

The method as disclosed above allows to obtain an inorganic micropatterned coating with oriented cracks that have a controlled periodicity.

One object of the invention is also an inorganic micropatterned coating comprising at least one periodic array of cracks, wherein each crack of said at least one periodic array of cracks extends over the substrate along an axis following a linear direction, each axis of each crack being parallel to the axis of the other cracks, said coating being obtainable by the method as defined in above.

In the context of the invention, the inorganic micropatterned coating with oriented cracks of the invention is a mono- or multilayered coating.

In the context of multilayered coating, the inorganic micropatterned coating of the invention comprises a plurality of layers comprising periodic arrays of cracks, advantageously between 2 and 200 μm periodic arrays of cracks. Advantageously, the cracks of each periodic array extend over the substrate at an angle greater than 0° to the cracks of the other periodic arrays in order to obtain a multidirectional inorganic micropatterned coating.

Advantageously, each periodic array of cracks of the coating of the invention is based on an ink composition as disclosed above, in particular in part “ink composition”. In the case of multilayered coating, said ink composition may be identical or different for each periodic array of cracks. For example, one periodic array of cracks may be obtained using a titania precursor and one other may be obtained using a zirconia precursor. This allows to obtain a multilayered inorganic micropatterned coating with different properties such as optical properties. These multilayered inorganic micropatterned coating could for example act as diffraction gratings. Advantageously, the at least one periodic array of the inorganic micropatterned coating of the invention has a pitch comprised between 2 and 200 μm, more advantageously between 7 and 80 μm.

In the context of multilayered inorganic micropatterned coating, each periodic array of the inorganic micropatterned coating of the invention has advantageously a pitch comprised between 2 and 200 μm, more advantageously between 7 and 80 μm.

Advantageously, the width of each cracks of the at least one or of each periodic array is between 500 nm and 20 μm, more advantageously between 1 and 10 μm.

Advantageously, the height/depth of each cracks of the at least one or of each periodic array is between 100 nm and 50 μm, more advantageously between 200 nm and 5 μm.

In the context of the invention, the inorganic micropatterned coating with oriented cracks of the invention has advantageously a thickness of between 100 nm and 50 μm, more advantageously between 200 nm and 5 μm.

As disclosed above, the periodicity is a function of the as deposit film thickness h which is directly correlated to crack spacing by a nearly linear trend: λ_c-c = k^*h^α where a coefficient lies between 0,66 and 0,8 according to different reports.

Advantageously, the at least one periodic array or each periodic array of cracks of the inorganic micropatterned coating of the invention has a periodicity λ_c-c of between 2 and 200 μm. In the context of multilayered inorganic micropatterned coating, each periodic array of the inorganic micropatterned coating of the invention has a periodicity λ_c-c of between 2 and 200 μm, said periodicity could be identical or different for each periodic array.

Advantageously, the inorganic micropatterned coating with oriented cracks of the invention is porous. The porosity of the film is obtained when nanoparticles, such as polymeric nanoparticles, decompose during thermal treatment (calcination).

A device comprising an inorganic micropatterned coating with oriented cracks

The present invention also relates to a device comprising an inorganic micropatterned coating comprising at least one periodic array of cracks as defined above.

Advantageously, the thickness of said coating is between 100 nm and 50 μm.

In the context of the invention, the inorganic micropatterned coating can be deposited on any kind of substrate, whatever its shape (with simple or complex architecture), in particular any kind of inorganic or plastic substrate. Therefore, the device of the invention can be of any kind.

Advantageously, said device is a microelectronic device, optical device, sensing device such as sensors, fluidic device, opto-electronic device, water harvesting device, battery, catalysis, photocatalysis, electrocatalysis, smart windows, decorative surfaces, superhydrophobic/superoleophobic and superhydrophilic, antifogging, antifrosting, antifouling, antistatic, adhesive coating.

Uses

The present invention also relates to the use of an ink composition as defined above, in particular in part “ink composition”, for obtaining an inorganic micropatterned coating comprising at least one periodic array of cracks as defined above.

The present invention also relates to the use of the ink composition as defined above, in particular in part “ink composition”, for obtaining a device as defined above.

The present invention also relates to the use of an inorganic micropatterned coating as defined above, comprising at least one periodic array of cracks, wherein each crack of said at least one periodic array of cracks extends over the substrate along an axis following a linear direction, each axis of each crack being parallel to the axis of the other cracks, for obtaining a device as defined above.

Advantageously, the inorganic micropatterned coating of the invention can be used in the fields of microfluidic, microelectronic, optic, sensing device, opto-electronic, water harvesting, battery, catalysis such as photocatalysis, electrocatalysis, smart windows, or decorative surfaces, superhydrophobic/superoleophobic and superhydrophilic, antifogging, antifrosting, antifouling, antistatic, adhesive coating.

The invention is further illustrated by the following non-limitative examples.

FIGURES DESCRIPTION

Figure 1 represents examples of titania patterned films: (a) Ti-1, u=12 μm/s; (b) Ti-5, u=12 μm/s (Example 2.3).

Figure 2 represents titania patterned film with 35 days old ink (Example 2.4).

Figure 3 represents Titania patterned films with ramp calcination of 10 °C/min (Example 2.5).

Figure 4 represents examples of ZrO₂ patterned films, (a) Zr-02: u=12 μm/s; (b) Zr-05: u=12 μm/s (Example 3).

Figure 5 represents example of IrO2 patterned film lr-07 u=12 μm/s (Example 4). Figure 6 represents Ga₂O₃ crack-patterned film after calcination, u=15 μm/s (Example

6).

Figure 7 represents example of metallic Ir patterned films u=15 μm/s (Example 7). Figure 8 represents example of multicomponent and multidirectional crack pattern made of bottom layer of Zirconia and upper layer of Titania (Example 8).

Figure 9 represents example of SiO₂ crack-patterned film after calcination, u=10 μm/s (Example 9).

Figure 10 represents diffraction and splitting of the red diode laser light upon reflection from micropatterned titania. Right picture shows 6 diffraction orders (Example 10).

Figure 11 represents example of Sb doped In₂O₃ (ITO) patterned films u=0,009 (Example

11 ).

Figure 12 represents example of VO_x patterned films u=0,1 (Example 12).

Figure 13 represents example of metallic CoTiO₃ patterned films u=0,015 (Example 13). Figure 14 represents example of RuO₂ patterned films after flash calcination at 450 °C (u=0,006) (Example 14).

Figure 15 represents example of metallic Ru patterned films after N₂ calcination with the heating ramp of 10 °C/min up to 450 °C (u=0,006) (Example 14).

EXAMPLES

Example 1 : Preparation of polystyrene (PS) latex nanoparticles

• PS Latex 01

Pluronic F127 (3,35 g) was dissolved in MiliQ water (133 ml). Further, not purified commercial styrene (20 g) and NaHCO₃ (0,288 g) were added under magnetic stirring. Solution was flushed with N₂ for 1h in order to remove oxygen. Next, a second solution made of MiliQ water (15 ml) and K₂S₂O₈ (0,31 g) was added under magnetic stirring. Glass balloon, was then heated up to 90 °C in the oil bath for 4h. After that time, the balloon was cooled down at room temperature. The white suspension obtained was dialysed in water changed each 12 h, in total 5 times.

The final solution showed DLS size between 160 and 175 nm with PDI between 0,130 and 0,150.

• PS latex - 02

Pluronic F127 (5 g) was dissolved in MiliQ water (200 ml). Further, not purified commercial styrene (30,3 g) and NaHCO₃ (0,456 g) were added under magnetic stirring. Solution was flushed with N₂ for 1h in order to remove oxygen. After the heating solution up to 80 °C, the second solution (14 ml H ₂O + 0,450 g K ₂S₂O₈ ) was added. The solution was kept between 80 - 90°C for 5 h after which was cooled down at room temperature. The white suspension obtained was dialysed in water changed each 12 h, in total 5 times.

The final solution showed DLS size between 180 and 190 nm with PDI between 0,008 and 0,08.

Example 2: Preparation of inorganic micropatterned film according to the invention with titania precursor

2.1 Preparation of titania precursor

The precursor solution of titania was prepared by transferring a certain amount (see 2.2.) of titania butoxide (TBT) into a flask. Further, acetyloacetone (acac) was added dropwise under magnetic stirring (600 - 700 rpm) and the solution was left to mix for 10 min. Next, the ethanol (EtOH) was added dropwise under magnetic stirring (600 - 700 rpm) and the solution was again left for stirring for 15 min. The solution was put into the oven at 70 °C for 30 min, after which it was cooled down to room temperature. The clear yellowish-orange solution was obtained.

2.2 General protocol for ink preparation and film deposition

1 ) The aqueous solution of PS01 or PS02 latex beads was optionally mixed with additional MiliQ water. Further it was dropped into the precursor solution of titania under magnetic stirring (the proportions used are shown in the table 1). The solution was mixed for 15 min and centrifuged at 8500 rpm for 5 min. In each case a yellowish precipitate was obtain together with a yellow supernatant. The supernatant solution was used as a liquid for dip- coating.

2) Silicon substrates (2,5 x 1 cm) were cleaned with a tissue and acetone. Dip-coating was performed in a closed chamber with a temperature oscillating between 52-56°C. The solution volume was about 2 ml. The dip-coating was performed in a capillary regime.

3) The deposited films were subsequently calcined at 450°C for at least 2 min. Table 1. The compositions used for crack-patterning of titania films.

2.3 PS:Ti compositional range To determine the appropriate ratio range between PS latex and Ti precursors (TBT : acac : EtOH ratio 1 : 1 ,6 : 4), several mixtures of different compositions (showed in the Table 1 ) were prepared. The all prepared solutions were used within 30 min after their preparation. The silicon substrates were withdrawn with a programmed speed (3 mm with 6 μm/s; 8 mm with 12 μm/s; 8 mm with 25 μm/s). The films were then flash calcined at 450 °C for 2 min under the air.

Results: The films show patterns if the ratio of Ti and PS01 latex is below 3,42 mmol/g. Examples of tests Ti-1 and Ti-5 are shown in the Figure 1. In the case of Ti-6 the film did not present visible cracks under optical microscope. 2.4 Stability of the ink

To investigate the stability of prepared PS-Ti solutions, the solution denoted as test Ti-1 (in the previous experiment) was used again 7 and 35 days later in the same conditions with a single withdrawal speed 12 μm/s (table 2). In each case the patterns and the quality of the films were well-reproduced. Sample 1c is shown on Figure 2. Table 2 Description of solutions used for investigation the stability of PS/titania inks.

2.5 Ramp calcination

To investigate the influence of calcination (flash vs step), the ink 1 used in the previous experiments 2.1 and 2.2 was utilized again to deposit a film and calcine it stepwise (Table 3). Sample 1d was calcined with the heating ramp of 10 °C/min to 450 °C and kept for two minutes (in contrast to flash calcined sample previously).

The pattern and the quality of the film were well-reproduced. In fact, the solid lines made of titania were less cracked than in the case of flash calcination (Figure 3). Table 3 The composition of used ink

Example 3: Preparation of inorganic micropatterned film according to the invention with zirconia precursor

3.1 PS:Zr compositional range The aqueous solution of PS latex beads obtained in example 1 was first optionally diluted with certain amount of water (table 4) and added to a vial containing Zr salt: ZrO(NO₃)₂. The solution was stirred for 15 min, sonicated for 30 sec and centrifuged for 5 min at 8000 rpm. Small amount of white precipitate appeared in each case. The supernatant solution was used for dip coating. The compositions prepared are summarized in the Table 4. The preparation of silicon substrate, deposition and thermal treatment were the same as in the case of titania (see example 2.2).

Table 4 the compositions used for inks containing ZrO₂ precursors.

Results: The patterned films of sufficient quality were obtained with the Zr:PS ratio of these tests. Examples of micropatterned ZrO₂ obtained are shown in the Figure 4.

Example 4: Preparation of inorganic micropatterned film according to the invention with Iridium oxide precursor

• Evaluation of PS:lr composition range lrCl₃*xH₂O was added into the aqueous PS latex solution (optionally diluted with water). Solution was put into the oven at 70 °C to facilitate dissolution of Ir salt. 20 min later solution was taken out from the oven and magnetically stirred for 10 min and centrifuged at 8000 rpm for 5 min. The compositions of solution are shown in the table 5. The preparation of the substrate, the deposition and the calcination was the same as in the case of titania and zirconia (see 2.2 and 3.1 ). Table 5 The compositions used for inks containing IrO₂ precursors.

Results: The patterned films of sufficient quality were obtained with the lr:PS ratio of these tests. The example lrCl₃-7 of IrO₂ crack patterned structures are shown in the Figure 5.

Example 5: Preparation of inorganic micropatterned film according to the invention with tungsten oxide precursor

• Evaluation of W:PS composition range

Tungsten oxide precursor salt: (NH₄)₆H₂W₁₂O₄₀ xH₂O (AMT) was dissolved in MiliQ water. Then PS latex solution was added and stirred with magnetic stirrer for 20 min. Such prepared solution was directly used for dip coating. The ratio between compounds are shown in the Table 6. The substrate preparation, the procedure of dip coating and calcination were the same as in previous case (see 2.2.) Table 6 The compositions used for inks containing WO₃ precursors.

Results: The patterned films of sufficient quality were obtained with the W:PS ratio of these tests.

Example 6: Preparation of inorganic micropatterned film according to the invention with Ga₂O₃ precursor

5,008 g of aqueous PS latex solution (PS-01 10,4 wt%) was mixed with 0,182 g of Ga(NO- ₃)₃*XH₂O for 15 min. The solution was centrifuged at 8000 rpm for 5 min. The deposition was performed at 50 °C with 3 different speeds (8 μm/s, 15 μm/s and 30 μm/s). Crack patterned structures were obtained at 8 and 15 pm/s withdrawal speed. Subsequently, the film was flash calcined in air at 450°C (Figure 6).

Parameters of the ink: Ga/PS ratio: 0,711 mmol/g; 10,0 wt% of PS

Example 7: Preparation of inorganic micropatterned film according to the invention with Ir precursor

5 g of PS-01 latex solution (10,4 wt%) was mixed with 0,186 of IrCl₃ ^*H₂O. The solution was put into the oven for 30 min to facilitate dissolution of the salt. Then, the solution was cooled down and used for dip - coating on silicon substrate with 3 different withdrawal speeds (8 μm/s, 15 μm/s and 30 μm/s). Then the substrate was calcined in tubular oven under the flow of N₂ with the heating ramp of 0,5 °C/min up to 550 °C and naturally cooled down (Figure 7).

Parameters of the ink: Ir/PS ratio: 0,99 mmol/g; 10,0 wt% of PS

Example 8 Preparation of inorganic micropatterned multicomponent multilayer films according to the invention with Ti and Zr precursors The two directional pattern made from zirconia and titania precursors was prepared. The zirconia precursor ink was prepared by the protocol described in the experiment 3 with following ink parameters: Zr/PS = 0,409 mmol/g; PS wt%=9,6% (zirconium salt (0,05 g), PS02- 20 wt% (2 g) and H₂O (2,1 g)). The titania ink was prepared according to protocol described in experiment 2 with the following composition of the ink: Ti/PS = 1 ,189 mmol/g and PS wt% = 11 ,1% (TiO₂ precursor (0,65 g), H₂O (2,5 g), P-02 20 wt% (4 g)).

First the zirconia film was deposited on silicon substrate with a withdrawal speed of 0,010 μm/s and temperature 56-58 °C. Then, the second deposition was made from titania precursor ink with the substrate rotated at certain angle close to 90°, at the same conditions as the first deposition (Figure 8 left). Then the film was flash calcined at 450°C for 5 min.

Example 9: Preparation of micropatterned silica.

1 ) Silica precursor was prepared by adding 0,01M HCl aqueous solution into the mixture of TEOS and ethanol (weight ratio between H20, TEOS and EtOH - 1 :1 :1 , 5). The solution was mixed for 1h at room temperature and filtered through nylon syringe filter of pore size 0,45 μm.

2) 2g of PS02 solution (10 wt%) was dropped into the 0,16 g precursor solution of SiO₂. Then the solution was used for dip-coating at the temperature of 52°C. The silicon substrate was withdrawn at the speed of 10 μm s^-1 and further flash calcined at 450°C. The micropatterned SiO₂ was obtained as shown in Figure 9. The parameters of the ink Si/PS = 1 ,097 mmol/g; PS wt% = 9,3 wt%

Example 10: Micropatterned titania as diffraction grating

Titania film prepared according to the protocol of the sample Ti-1 (see 2.2.) has been tested as diffraction grating by reflecting the red light from conventional diode laser pointer (wavelength = 650 nm, max output < 1mw). The light was angularly diffracted and split up into several diffraction orders (at least 6), see figure 10.

Example 11 : Preparation of inorganic micropatterned film according to the invention with antimony doped Indium oxide precursor

4 g of aqueous PS latex solution (PS-02 15 wt%) was mixed with 0,109 g of indium (III) acetate, 0,010 g of antimony (III) acetate and 0,060 g of butan-1 -ol for 15 min. The solution was centrifuged at 8000 rpm for 5 min. The deposition was performed by dip coating at 50 °C with withdrawal speeds of 9 μm/s. Subsequently, the film was flash calcined in air at 450°C (Figure 11 ).

Parameters of the ink: (ln+Sb)/PS ratio: 0,744 mmol/g; 15,0 wt% of PS

Example 12: Preparation of inorganic micropatterned film according to the invention with vanadium oxide precursor

5,120 g of aqueous PS latex solution (PS-02 14,7 wt%) was mixed with 0,114 g of VOSO₄and 0,100 g of butan-1 -ol for 15 min. The solution was centrifuged at 8000 rpm for 5 min. The deposition was performed by blade coating with preheated surface to 63°C with deposition speed of 0,1 mm/s and gap between blade and the covered surface of 0,6 mm. Subsequently, the film was flash calcined in air at 450°C (Figure 12).

Parameters of the ink: V/PS ratio: 0,930 mmol/g; 14,7 wt% of PS

Example 13: Preparation of inorganic micropatterned film according to the invention with cobalt titanate precursor

5,000 g of aqueous PS latex solution (PS-02 15,0 wt%) was mixed with 0,3 g of TBT₁(acac)1,6(EtOH)₄ precursor (as in the example 2.2) and 0,103 g of CoCl₂ ^*6H₂O for 15 min. The solution was centrifuged at 8000 rpm for 5 min. The deposition was performed by dip- coating at 50 °C with withdrawal speed of 15 μm/s. Subsequently, the film was flash calcined in air at 800°C for 30 min (Figure 13).

Parameters of the ink: Co-Ti/PS ratio: 1 ,16 mmol/g; 15,0 wt% of PS

Example 14: Preparation of inorganic micropatterned film according to the invention with metallic ruthenium or ruthenium oxide precursor

5,00 g of aqueous PS latex solution (PS-02 10,0 wt%) was mixed with 0,096 g of RuCl₃ ^*3,5H₂O for 15 min. The solution was centrifuged at 8000 rpm for 5 min. The deposition was performed by dip-coating at 50 °C with withdrawal speed of 6 μm/s. Subsequently, the film was flash calcined in air at 450°C (Figure 14) to obtain RuO₂ or in tubular oven under the flow of N₂ with the heating ramp of 10 °C/min up to 450 °C and naturally cooled down (Figure 15) to obtain metallic Ru pattern. Parameters of the ink: Ru/PS ratio: 0,711 mmol/g; 10,0 wt% of PS

Claims

1. A method for forming at least one periodic array of cracks of an inorganic micropatterned coating, wherein said method comprises the following steps: a. Providing an ink composition comprising nanoparticles having a size obtained by dynamic light scattering (DLS) of between 10 and 500 nm, at least one inorganic precursor, and at least one solvent, the ratio of metal in the precursor to the mass of nanoparticles being between 0,05 and 3 mmol/g; b. Coating a substrate with the ink composition; c. Evaporating the solvent; d. Optionally repeating at least once the steps a) to c) in order to obtain a multilayered inorganic micropatterned coating comprising a plurality of layers comprising a periodic array of cracks. e. Optionally calcinating the coated substrate obtained in step c) or d); wherein each crack of said at least one periodic array of cracks extends over the substrate along an axis following a linear direction, each axis of each crack being parallel to the axis of the other cracks.

2. The method according to claim 1 , wherein the step b) of coating is carried out by dip coating method, roll to roll method, knife coating method, screen -printing method, or slot-die coating.

3. The method according to claim 1 or 2, wherein the nanoparticles are selected from the group consisting of polymeric nanoparticles, silica nanoparticles, titania nanoparticles, aluminates nanoparticles, fluoride nanoparticles, and optionally mixtures thereof.

4. The method according to any one of claims 1 to 3, wherein the content of nanoparticles in the ink composition is between 0.1 and 25 %wt, advantageously between 0,5 and 20 %wt.

5. The method according to any one of claims 1 to 4 wherein the nanoparticles size obtained by dynamic light scattering (DLS) is of between 10 and 500 nm with a polydispersity index (PDI) of between 0.001 and 0.5.

6. The method according to any one of claims 1 to 5, wherein the ratio of metal in the precursor to the mass of nanoparticles is between 0,08 to 2,5 mmol/g.

7. The method according to any one of claims 1 to 6, wherein step e) is carried out by flash calcination, advantageously at a temperature between 50 and 1000 °C during 0.05 and 10000 minutes or the step e) is carried out by calcination with a heating ramp of between 0.1 and 1500°C/min to a temperature of between 50 and 1000 °C.

8. An inorganic micropatterned coating comprising at least one periodic array of cracks, wherein each crack of said at least one periodic array of cracks extends over the substrate along an axis following a linear direction, each axis of each crack being parallel to the axis of the other cracks, said coating being obtainable by the method as defined in any of claims 1 to 7.

9. The coating according to claim 8, wherein said periodic array has a pitch comprised between 2 and 200 μm.

10. The coating according to claim 8 or 9, wherein said coating is based on an ink composition comprising nanoparticles having a size obtained by dynamic light scattering (DLS) of between 10 and 500 nm, at least one inorganic precursor, and at least one solvent, the ratio of metal in the precursor to the mass of nanoparticles being between 0,05 and 3 mmol/g, advantageously between 0,08 to 2,5 mmol/g, and wherein the nanoparticles are advantageously as defined in any one of claims 3 to 6.

11. The coating according to claim 10, comprising a plurality of periodic arrays of cracks, wherein each periodic array of cracks is based on said ink composition that is identical or different from the other.

12. The coating according to claim 11 , wherein the cracks of each periodic array extend over the substrate at an angle greater than 0° to the cracks of the other periodic arrays in order to obtain a multidirectional inorganic micropatterned coating.

13. A device comprising an inorganic micropatterned coating comprising at least one periodic array of cracks as defined in any of claims 8 to 12, advantageously wherein said coating has a thickness between 100 nm and 50 μm.

14. Use of the device according to claim 13 in a microelectronic device, optical device, sensing device such as sensors, fluidic device, opto-electronic device, water harvesting device, battery, catalysis, photocatalysis, electrocatalysis, smart windows, decorative surfaces.

15. An ink composition for the production of an inorganic micropatterned coating comprising at least one periodic array of cracks as defined in any one of claims 8 to 12, wherein said ink composition comprises nanoparticles having a size obtained by dynamic light scattering (DLS) of between 10 and 500 nm, at least one inorganic precursor, and at least one solvent, the ratio of metal in the precursor to the mass of nanoparticles being between 0,05 and 3 mmol/g.

16. The ink composition according to claim 15, wherein the nanoparticles are selected from the group consisting of polymeric nanoparticles, silica nanoparticles, titania nanoparticles, aluminates nanoparticles, fluioride nanoparticles, and optionally mixtures thereof.

17. The ink composition according to claim 15 or 16, wherein the content of nanoparticles in the ink composition is between 0.1 and 25 %wt, advantageously between 0,5 and 20 %wt.

18. The ink composition according to any one of claims 15 to 17, wherein the nanoparticles size obtained by dynamic light scattering (DLS) is of between 30 and 250 nm with a polydispersity index (PDI) of between 0.05 and 0.25.