GB2615807A

GB2615807A - A material comprising a polymer

Info

Publication number: GB2615807A
Application number: GB2202286.7A
Authority: GB
Inventors: Charles McLaughlin Pearce Robert; Leland Rees Thomas Adrian; Wilhelm Ludwig Paul Vollrath Friedrich
Original assignee: Xo Mat Ltd
Current assignee: Xo Mat Ltd
Priority date: 2022-02-21
Filing date: 2022-02-21
Publication date: 2023-08-23
Also published as: WO2023156798A1; GB202202286D0

Abstract

A passive radiative cooling material comprising a polymer, which surrounds a void lined with a hydrophobic particle. Also provided is a composition comprising a polymer, which surrounds a polar solvent surrounded by hydrophobic particles. The hydrophobic particles may be fumed silica; may have a surface treatment to alter hydrophobicity; may have been modified with a surfactant. The polymer may be poly(dimethyl siloxane), poly(vinylidene fluoride), poly(acrylic acid), poly)methyl methacrylate), acrylic, silicone, polyvinyl alcohol (PVA), cellulosic polymer, chlorinated elastomer, vinyl, acrylic, polyurethane, polyester, epoxy, silicone-based polymer. It may be formed by using high shear mixing, sonication. Wherein the hydrophobic particles are surrounding a polar solvent, may be generated by combining a mist or spray of a polar solvent with the hydrophobic particles in a mixer; may be generated by condensing an aerosol or vapor of a polar solvent onto the hydrophobic particles; the hydrophobic particles may be reduced in size by grinding; may have a diameter of 5-10 micrometres. The composition may comprise hollow or solid microspheres; may comprise a broadband or solar spectrum specific reflector; may have a paint-like consistency, may reflect light in the solar spectrum and emit infrared electromagnetic radiation. The polar solvent may be water.

Description

A material comprising a polymer

Field

The present disclosure relates to a passive radiative cooling composition and a method of making a passive radiative cooling composition. The present disclosure also related to a method of applying the composition to a substrate to form a passive radiative cooling layer.

Background

The sun radiates heat energy to the earth in the form of electromagnetic radiation.

io Because of this mode of heat transfer, objects in direct sunlight that absorb electromagnetic radiation in the same bandwidth as the sun's radiation will heat up more than objects that are reflective in this bandwidth. Such objects may also be hotter than the ambient air.

/5 Simultaneously, warm objects spontaneously emit heat in the form of electromagnetic radiation. For objects that are within the temperature range of standard outdoor temperatures, this emitted radiation tends to occur in the infrared spectrum, outside of the spectrum of any incoming solar radiation. That the emitted and reflected radiation occurs in distinct, non-overlapping bandwidths is important to note, because generally objects that are emissive in a given spectrum are also absorptive in the same spectrum.

Given this information, an object will be maximally cool in direct sunlight if it is highly reflective in the solar spectrum, and highly emissive outside of that spectrum. However, there are additional factors to consider. One such factor is the role of the atmosphere. The atmosphere also absorbs and emits energy in the form of electromagnetic radiation. Therefore, in order to maximize the cooling potential of an object, it should be emissive (and therefore absorptive) in spectra that the atmosphere does not emit and absorb. Such spectra are called 'Atmospheric Windows' and are known to exist at 0.3 pm to 1.1 pm, 1.4 pm to 2.5 pm, 3.5 pm to 5 pm, 8 ttm to 13 pm, etc.. By emitting electromagnetic radiation within atmospheric windows, objects are able to directly radiate their heat energy into space.

Devices that use these principles to cool objects are often referred to as Passive Radiative Coolers (PRCs). PRCs most common theoretical application is the cooling of structures and vehicles. Due to climate change, there exists a high demand for cooling solutions that reduce the need for carbon-intensive air conditioning, which is typically based on vapour-compression.

Standard white paints and coatings are commonly used to cool objects in direct sunlight, especially buildings. Though PACs can sometimes look like white paint, they provide significant cooling power compared to standard white paints and coatings.

There are other important factors to consider in the design of a PRC coating. The coating should be UV resistant, easy to apply, simple to manufacture, and resistant to weathering. A PRC coating should also be insulative in order to limit the amount of heat energy the PRC absorbs through conduction and convection from the surrounding air.

One further important consideration is the cost of the material. Some PRCs have failed to gain commercial traction because they are extremely expensive to produce in commercial quantities, but even inexpensive designs must be cost competitive with standard coatings to maximize their value to the end-user. In commercial coatings, great care is taken to limit the thickness of a given coating to bring down the bulk costs of the material's ingredients.

There exists a market demand to create a PRC that meets all of the above criteria. There is also an opportunity to create a PRC that can fulfil three of those criteria (high reflectance, high thermal insulation, lower material use) with one structural feature -voids. Small voids within a material are great at backscattering light and provide excellent thermal insulation, all while reducing the amount of bulk material required to coat an object. The most reflective commercially available material is sintered polytetrafluoroethylene (PTFE). These sintered blocks of PTEE use air voids to or backscatter about 99% of all light in the visible spectrum. This backscattering occurs due to light reflecting and refracting as it interacts with the voids. Thermally insulative foam also uses voids in order maximize its thermal insulative properties. Voids filled with air are excellent insulators because gasses are generally poor thermal conductors and the walls of the void immobilize the air effectively eliminating any convective heat transfer.

An effective PRC material has been demonstrated that uses voids within a polymer matrix. The polymer acts as an emitter in the atmospheric window between 8 pm and 13 pm and the voids serve to increase the reflectivity of the material by backscattering light. Though highly effective as a PRC, this material comes with a few key drawbacks. The voids in the material are created by mixing water and large quantities of acetone -3 -into a polymer, and allowing the acetone and water to evaporate out. Acetone comprises the bulk of the wet material. This high quantity of acetone make the wet material highly flammable and greatly increases the cost of the material. The process produces a high amount of acetone vapours, which are an irritant and can cause damage to the nervous system when inhaled. The vapours are flammable and present an explosion risk in enclosed areas. Another aspect of this PRC design, is that the microstructure may change with the temperature of the surface it is being applied to. Resulting in a more or less effective end product that depends on the surface it is being applied to and the weather on the day it is applied.

Clearly, there is a need for a porous PRC material with similar properties to the aforementioned material that uses a different approach to creating reflective voids. -4 -

Summary

According to a first aspect of the present invention, there is provided a material comprising a polymer surrounding a void lined with hydrophobic particles.

That is, the void may be surrounded or encapsulated by the hydrophobic particles, which in turn may be surrounded (or encapsulated) by the polymer.

The fluid in the void may be a gas, for example, air.

jo The polymer may be a single type polymer or may be a polymer mixture, e.g. a mixtures of polymers with different properties. The mixture may further comprise a polymer derivative. Alternatively the polymer may be substituted by a polymer derivative.

Thus, the material forms a passive radiative cooling material which reflects electromagnetic radiation in the solar spectrum and emits infrared electromagnetic radiation. Such a material can help with cooling a surface or substrate.

According to a second aspect of the present invention, there is provided a composition comprising a polymer and a polar solvent surrounded by hydrophobic particles.

That is, the polar solvent may be surrounded or encapsulated by the hydrophobic particles. The surrounded or encapsulated polar solvent maybe, in turn, surrounded (or encapsulated) by the polymer. The polymer may only partially surround the polar solvent surrounded by the hydrophobic particles.

Thus, the composition can be applied to a substrate and allowed to cure and evaporate forming the material of the first aspect.

The hydrophobic particles surrounding a polar solvent may also be referred to as a "globule".

The hydrophobic particles of the material or composition may comprise, consist or be formed from fumed silica.

The hydrophobic particles of the material or composition may have a surface treatment to alter their hydrophobicity. -5 -

The polymer of the material or composition maybe selected from the group consisting of poly(dimethyl siloxane), poly(vinylidene fluoride), poly(acrylic acid), poly(methyl methacrylate), acrylic, silicone, polyvinyl alcohol, or polydimethylsiloxane. The polymer (or polymeric binding matrix) may be selected from a wide range of polymers ranging from cellulosic, chlorinated elastomer, vinyl, acrylic, polyester, polyurethane, epoxy, and silicone-based materials, for example, silicone-based polymers. A combination of these or other suitable polymers may be used. Additional materials may be added to the polymer, for example, silicone-based materials.

The surface energy of the hydrophobic particles surrounding a polar solvent of the material or composition may be modified with the addition of a surfactant.

The hydrophobic particles surrounding a polar solvent of the composition or a void of the material may be formed using high shear mixing or sonication.

The hydrophobic particles surrounding a polar solvent of the material or composition may be generated by combining a mist or spray of a polar solvent with the hydrophobic particles in a mixer.

The mixer maybe an agitating chamber.

The hydrophobic particles surrounding a polar solvent of the material or composition may be generated by condensing an aerosol or vapour of a polar solvent onto the or hydrophobic particles or into a plurality of the hydrophobic particles.

The hydrophobic particles surrounding a polar solvent of the material or composition may be further reduced in size through a grinding process.

The hydrophobic particles surrounding a polar solvent of the material or composition may have a diameter of between 5 and to micrometres.

The emitted infrared of the material is mostly or exclusively within the bandwidth of 813 micrometres. -6 -

The material or composition may further comprise hollow or solid microspheres. The microspheres may comprise or consist of glass or silica.

The material or composition may further comprise a broadband or solar spectrum specific reflector.

The broadband or solar spectrum specific reflector may be one of barium sulphate, titanium dioxide, calcium carbonate, Polytetrafluoroethylene, alumina or a combination of these.

The composition may have a paint-like consistency.

The material may be configured to reflect light in the solar spectrum and emit infrared electromagnetic radiation.

The void in the material may be formed by evaporating a fluid from a globule of the fluid coated in the hydrophobic particles that have been mixed with the polymer. The evaporated fluid may be water.

The material or composition may further comprise a hydrophobicity modifying coating such as dimethyl-dichloro-silane, trimethoxy-octyl-silane, hexamethyl-di-silazane, carboxylic acids, or poly-dimethyl-siloxane.

The material or composition may further comprise surface energy or surface tension modifiers or wetting modifiers.

According to a third aspect of the invention, there is provided a method of making a composition comprising: receiving hydrophobic particles and a polar solvent; performing high-shear mixing on the hydrophobic particles and polar solvent; adding a polymer; and performing low-shear mixing to a point of homogeneity.

The method may further comprise combining a mist or spray of a polar solvent with the hydrophobic particles.

The method may further comprise: condensing an aerosol or vapour of a polar solvent onto the hydrophobic particles or into a plurality of the hydrophobic particles. -7 -

According to a fourth aspect of the invention, there is provided a method of generating a passive radiative coating, the method comprising: applying the composition of the second aspect to a substrate; and allowing the polar solvent to evaporate.

According to a fifth aspect of the invention there is provided a method of generating a passive radiative coating, the method comprising: applying the composition of the second aspect to a substrate; and allowing the polymer to cure.

lo The evaporation and curing may take place, for example, in air. -8 -

Brief Description of the Drawings

Certain embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an illustration of one application of the present invention as a coating for 5 reducing the temperature of a building; Figure 2 is an illustration of a cross section of a first cured and dried PRC material; Figure 3 is a micrograph of a representative version of the material comprising a polymer matrix with fumed-silica lined pores; Figure 4 is a graph of the reflectance of an idealized passive radiative cooling material over a range of wavelengths; Figures is block diagram identifying the initial ingredients necessary for creating the present invention Figure 6 is a process flow diagram demonstrating a process for creating a passive radiative cooling material; Figure 7 is an illustration that demonstrates the application of the paintable precursor of the present invention to a substrate to be cooled; Figure 8 is process flow diagram demonstrating a process for applying the precursor to a substrate to be cooled; Figure 9 is a cross section of a passive radiative cooling material; and Figure 10 is a schematic of a precursor composition for the passive radiative material of Figure 9. -9 -

Detailed Description of Certain Embodiments

A Passive Radiative Cooling (PRC) material and a composition for making the PRC are described in this document along with a method for making PRC materials and the composition.

A PRC coating keeps objects cool in direct sunlight with a combination of high reflectance in the solar spectrum and high emittance a bandwidth known as an 'atmospheric window'. Atmospheric windows are bandwidths of electromagnetic radiation in which most of the radiation can transmit through the atmosphere without /.0 being reflected, absorbed, or dispersed. These combined properties allow PRC coatings to cool objects below ambient temperatures even in direct sunlight.

The present disclosure provides a passive radiative cooling coating material that uses a porous structure created by mixing globules of a polar solvent (e.g. water) surrounded by hydrophobic material, for example, a hydrophobic particle or powder (e.g. fumed silica, microfibrillated cellulose, diamide-based organic thixotrope) into a polymer matrix. A globule may be a spheroid or spheroid-like shape, for example, a sphere or an extended sphere. The disclosure further describes the material following a curing and evaporation phase, that occurs after application, in which the polymer matrix cures and the polar solvent evaporates out of the system, leaving the aforementioned pores. The porous structure created using this technique can effectively backscatter light, and the hydrophobic particle lining the voids of the structure may be emissive within the atmospheric window between 8 gm and 13 pm.

One possible combination of polar solvent and hydrophobic material or particles for this application is water and fumed silica. Hereinafter the composition and material forming the passive radiative cooler will be described using water and fumed silica, however, any suitable hydrophobic particles or polar solvent may be used.

Water and fumed silica can form a substance called 'dry-water' after being mixed together under high shear conditions. Dry-water is a solid powder made by combining water and hydrophobic fumed silica particles together such that the water is broken up into globules and surrounded by fumed silica. Dry water gets its name because although it can be as much as 98% water by weight, it is dry to the touch.

-10 -These particles may then be mixed into a polymer matrix. This polymer matrix comprises a polymer, or mixture of polymers, known to be normally transparent in the solar spectrum and which may additionally be emissive in mid-infrared, or especially within an atmospheric window. Such a polymer matrix may comprise poly(dimethyl siloxane), poly(vinylidene fluoride), poly(acrylic acid), and poly(methyl methacrylate), acrylic, silicone, polyvinyl alcohol, or polydimethylsiloxane or any other suitable polymer, polymer derivative, or polymer mixture. The polymer (or polymeric binding matrix) may be selected from a wide range of polymers ranging from cellulosic, chlorinated elastomer, vinyl, acrylic, polyester, polyurethane, epoxy, and silicone-based /0 materials, for example, silicone-based polymers. A combination of these or other suitable polymers may be used. Additional materials may be added to the polymer or polymer mixture or matrix, for example, silicone-based materials.

Once the water is allowed to evaporate out of the mixture or composition and the polymer sets or cures, the resulting structure comprises a polymer film or coating with fluid-filled voids (e.g. gas, or air-filled voids) corresponding to the size of the dry-water globules. These voids are lined or enclosed with emissive fumed silica enabling the material to be reflective in the solar spectrum and emissive in the atmospheric window between 8 Jim and 13 um. This combination of material properties enables the device to be an effective passive radiative cooler.

Referring to Figure 1, one application of the disclosed material is a coating for reducing the temperature of a building, the PRC mixture (before curing and evaporation) is applied as a coating ito a roof 2 of a building 3. That it, the PRC mixture 1 is been -0 or applied to a substrate where it then cures and dries, forming a layer of the coating 1 on the substrate. The coated roof enables incoming solar radiation 4 to be reflected 5 while simultaneously emitting infrared 6 within the atmospheric window between 8 pm and 13 um.

Referring to Figure 2, a cross section of a PRC 7 includes voids 8 and a polymer matrix 9. The PRC 7 has a first surface 10 and a second surface 11. The second surface ii may be in contact with a substrate 12. The substrate 12 may be a substrate 12 which may need to be cooled, for example, a structure such as a building, a car, a tent etc. Solar radiation 4 is directed towards the first surface 10 of the PRC 7 where it is backscattered 13 through interaction with the voids 8. The PRC i is thick enough that the incoming solar radiation 4 is reflected before reaching the second surface ii and being absorbed by the substrate 12. Simultaneously, the PRC material emits infrared radiation 6 that is substantially within the atmospheric window between 8 pm and 13 pm.

Referring to Figure 3, a micrograph of a representative version of a PRC material comprising a polymer matrix with fumed-silica lined voids 8 within a polymer matrix 9. The material in this micrograph contains voids larger than the size optimal for high reflectivity in order to improve photogeneity and show the structure of the material clearly under an optical microscope.

Referring to Figure 4, a graph is presented showing the reflectance of an idealized passive radiative cooling material over a range of wavelengths. The graph shows that an idealized passive radiative cooling material will be fully reflective across the solar spectrum and fully absorptive and emissive within an atmospheric window (in this case between 8 and 13 micrometres).

Referring to Figure 5, initial ingredients 15 for the PRC precursor (i.e., the mixture which is cured and dried to form the PRC coating) 25 includes a hydrophobic particle additive 18, for example a fumed silica additive, which includes hydrophobic particles 19 and, optionally, a hydrophobicity modifying coating 20, for example dimethyl-dichloro-silane, poly-dimethyl-siloxane or other suitable surface treatments, but any suitable hydrophobicity modifying coating may be used. The initial ingredients also include a polar solvent 21 for example, water, ethanol or acetone, and optionally, surface tension or wetting modifiers such as polysorbate, sodium dodecyl sulphate, or or any other suitable surfactant.

Referring to Figure 6, a process flow diagram is presented that demonstrates one process for creating a paintable wet precursor of a PRC material. The process starts with the reception of the initial ingredients Sr, which arc further described in Figure 5.

These initial ingredients are then mixed under high shear conditions 52. This step 52 is performed until droplets of the polar solvent in the initial ingredients are surrounded by hydrophobic particles forming globules. Additionally or alternatively, this step may include other processes to produce a similar globules by means of sonication, vapour deposition, or by mixing the polar solvent in the form of a mist or spray with the hydrophobic particles. This step S2 may further be accompanied by grinding of the globules to reduce their size. Following the high-shear mixing step S2, there is a step S3 -12 -in which polymer is added to the mixture. The polymer in this step 53 maybe selected from the group consisting of poly(dimethyl siloxane), poly(vinylidene fluoride), poly(acrylic acid), and poly(methyl methacrylate), cellulosic polymers, chlorinated elastomer, vinyl, acrylic, polyester, polyurethane, epoxy, and silicone-based materials, or a combination of these. In the next step 54, the polymer is mixed under conditions of low shear with the globules created in step 52. This step S4, low shear mixing is used so as to not disrupt the structural integrity of the globules. In this low-shear mixing step 54, mixing may be performed until homogeneity is reached and a wet precursor is formed 55 that has a consistency which may be suitable for application to a substrate or ro surface by painting, spraying, atomising or other suitable methods.

Referring to Figure 7, the PRC precursor 25 may be paint-like in consistency and may be applied using a paintbrush 26 or other suitable applicator to a substrate or surface 10.

Referring to Figure 8, a process flow diagram is presented that demonstrates how the paintable wet precursor 25 maybe applied to a surface as is illustrated in Figure 7 to form a PRC layer. The process flow diagram begins with step Sio, wherein the paintable wet precursor 25 is received. In the following step Sri, the paintable wet precursor 25 is applied to a surface 10 or substrate that may need to be cooled. Following application Sir, the precursor 25 undergoes an evaporation and curing process in the next step S12. In step 512, the polar solvent 21 present within the precursor evaporates into the environment, leaving voids lined with hydrophobic particles within the polymer matrix. In this step S12, the polymer matrix cures and hardens, preserving the structural or integrity of the void-laden structure. Then, following step 512 in step 513, a PRC coating is formed.

The PRC or the composition forming a precursor 25 for the PRC may include a polymer matrix that is itself also emissive within the atmospheric window.

The aforementioned globule mixture may also receive secondary grinding or high-shear mixing treatments to micronize the particles.

Several sizes of dry-water particles maybe combined into the polymer mixture to create 35 an end product with multiple, controlled sizes of globules which, when dried and cured, may better scatter light.

-13 -The dry-water may be further treated with agents to modify the surface interactions of the dry-water polymer mixture. Such agents may be used, for example, to modify the surface tension of the water to improve mixing or grinding outcomes. Such agents include polysorbate, sodium dodecyl sulfate, or any other surfactant or surface modifier known to a person of ordinary skill in the art.

Alternatively or in addition to high-shear mixing or grinding, the dry water may be created by combining fumed silica with a water mist or spray in an agitating chamber.

Jo The material may be embedded with thermochromic particles or finished with a thermochromic layer that reduces emissivity in the atmospheric window or reflectivity in the solar spectrum in cold conditions, while allowing such emissivity and reflectivity under warm conditions. This embodiment may further include ultraviolet protective layers or components to stop ultraviolet light from damaging the thermochromic particles or layer.

The material may include glass or silica microspheres or particles, for example, glass microbubbles, or any other atmospheric window infrared emitter known to one skilled in the art. These materials may be embedded into the material to improve the emissive 20 property of the PRC material.

The materials may include barium sulphate, titanium dioxide, calcium carbonate, VITE, alumina, or any other broadband or solar spectrum specific reflector known to one skilled in the art in order to enhance the reflective property of the material.

Though fumed silica is a possible source of hydrophobic particles for this application and water is a possible polar solvent, the description of the invention provided herein does not preclude the use of alternative hydrophobic particles and polar solvents that in combination may produces a similar structure to dry-water.

The material or composition may further comprise hollow or solid microspheres. The microspheres may comprise or consist of glass or silica. The material or composition may further comprise a broadband or solar spectrum specific reflector.

Referring to Figure 9, a cross section of a PRC material or layer has a cured polymer matrix 9, a void 8 which is surrounded or encapsulated by hydrophobic particles 27.

-14 -Referring to Figure 10, a composition made using the method described earlier has a polymer 28 and a polar solvent 29 which is surrounded or encapsulated by hydrophobic particles 27.

Modifications It will be appreciated that various modifications may be made to the embodiments hereinbefore described. Such modifications may involve equivalent and other features which are already known in the design, manufacture and use of passive radiative cooler io materials, precursors and coatings and component parts thereof and which may be used instead of or in addition to features already described herein. Features of one embodiment may be replaced or supplemented by features of another embodiment.

Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel features or any novel combination of features disclosed herein either explicitly or implicitly or any generalization thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention.

The applicants hereby give notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims

-15 -Claims 1. A material comprising a polymer surrounding a void lined with hydrophobic particles.
2. A composition comprising a polymer and a polar solvent surrounded by hydrophobic particles.
3. A material or composition according to claim 1 or 2, wherein the hydrophobic /o particles comprise fumed silica.
4. A material or composition according to claim ito 3, wherein the hydrophobic particles have a surface treatment to alter their hydrophobicity.
5. A material or composition according to any one of claims ito 4, wherein the polymer is selected from the group consisting of poly(dimethyl siloxane), poly(vinylidene fluoride), poly(acrylic acid), poly(methyl methacrylate), acrylic, silicone, polyvinyl alcohol, polydimethylsiloxane, a cellulosic polymer, chlorinated elastomer, vinyl, acrylic, polyester, polyurethane, epoxy, and a silicone-based polymer.
6. A material or composition according to any one of claims ito 5, wherein the surface energy of the hydrophobic particles surrounding a polar solvent has been modified with the addition of a surfactant.
7. A material or composition according to any one of claim ito 6, wherein the hydrophobic particles surrounding a polar solvent or a void is formed using high shear mixing or sonication.
8. A composition according to any one of claims 2 to 7, wherein the hydrophobic particles surrounding a polar solvent are generated by combining a mist or spray of a polar solvent with the hydrophobic particles in a mixer.
9- A composition according to any one of claims 2 to 8, wherein the hydrophobic particles surrounding a polar solvent is generated by condensing an aerosol or vapour 35 of a polar solvent onto the hydrophobic particles or into a plurality of the hydrophobic particles.
10. A composition according to any one of claims 1 to 9, wherein the hydrophobic particles surrounding a polar solvent is further reduced in size through a grinding process.
11. A material or composition according to any one of claims 1 to 10, wherein the hydrophobic particles surrounding a polar solvent has a diameter of between 5 and lo micrometres.
12. A material or composition according to any one of claims ito 11, wherein the material or composition further comprises hollow or solid microspheres.
13. A material or composition according to any one of claims ito 12, wherein the material or composition further comprises a broadband or solar spectrum specific reflector.
14. A composition of any one of claims ito 13 wherein the composition is a paint-like consistency.
15. A material according to claim 1, wherein the material reflects light in the solar spectrum and emits infrared electromagnetic radiation.
16. A material according to claim 1, wherein the void in the material is formed by evaporating a fluid from a globule of the fluid coated in the hydrophobic particles that have been mixed with the polymer.
17. A material according to claim 1, wherein the evaporated fluid is water.
18. A material or composition according to any one of claims ito 17 further comprising a hydrophobicity modifying coating.
19. A material or composition according to any one of claims ito 18 further comprising surface energy modifiers or wetting modifiers.
20. A method of making a composition comprising: receiving hydrophobic particles and a polar solvent; -17 -performing high-shear mixing on the hydrophobic particles and polar solvent; adding a polymer; and performing low-shear mixing to a point of homogeneity.
21. A method according to claim 21 further comprising: combining a mist or spray of a polar solvent with the hydrophobic particles.
22. A method according to claim 20 or 21 further comprising: condensing an aerosol or vapour of a polar solvent onto the hydrophobic particles or into a plurality of the hydrophobic particles.
23. A method of generating a material according to any one of claims i to 7, n to 13 or 15 to 19, the method comprising: applying the composition of any one of claims 2 to 14 to a substrate; and allowing the polar solvent to evaporate.
24. A method of generating a material according to any one of claims ito 7, n to 13 or 15 to 19, the method comprising: applying the composition of any one of claims 2 to 14 to a substrate; and allowing the polymer to cure.
25. A material or composition according to claim 12, wherein the hollow microspheres include glass microbubbles.