Silica microcapsules and formulations thereof

Abstract

The present disclosure concerns a formulation, comprising latex particles and silica microcapsules; wherein each silica microcapsule comprises a shell of silica nanoparticles and an oil encapsulated within its cavity thereof; wherein the oil is characterised by a refractive index which is lower than that of the shell of the silica microcapsule; wherein the silica microcapsules are characterised by an average shell thickness of about 100 nm to about 700 nm; and wherein the formulation is characterised by a mass ratio of latex particles to silica microcapsules of about 0.2 to about 2. The present disclosure also concerns a method of forming the formulation. The present disclosure also concerns a method of reflecting visible light, ultraviolet and / or near infrared rays or whitening a surface, comprising contacting the formulation as disclosed herein on the surface.

Description

[0001] Silica Microcapsules and Formulations Thereof

[0002] Technical Field

[0003] The present invention relates, in general terms, to silica microcapsules and their formulations thereof.

[0004] Background

[0005] TiOz has been used heavily as pigments in many products, including paints, coatings, medicine and consumer care products owing to its high visible light-reflectivity (strong whiteness). One big challenge for TiO? is that it is non-sustainable and could be toxic to biological systems in long-term exposure. For example, TIO? nanoparticles used in skin- care / sunscreen products will leak into environment during human activities and subsequently cause toxicological effects to the marine lives. Therefore, there is strong interest to develop TiO2-free and more sustainable formulation that gives similar whiteness compared with TiO2-containing formulation. Hence, it may be valuable to obtain formulations that may reflect full UV / vis / NIR wavelength range for many important industrial applications such as sunscreen products.

[0006] In addition, there is a need for sustainable and non-toxic ingredients possibly generated by food grade ingredients like edible oil and silica in formulations with food colloids to provide whitening and opacifying benefits in foods confections, and sauces and soups.

[0007] Also, in personal care industry, TIC>2 nanoparticles, commonly used in sunscreen and cosmetics for their whitening effect, have raised concerns about potential health risks. While larger TiC particles are generally considered safe, there are worries about the impact of nanoparticles on human health when absorbed through the skin or inhaled.

[0008] It would be desirable to overcome or ameliorate at least one of the above-described problems.

[0009] Summary

[0010] The present disclosure concerns a formulation, comprising latex particles and silica microcapsules; wherein each silica microcapsule comprises a shell formed from silica nanoparticles and an oil encapsulated within its cavity thereof; wherein the oil is characterised by a refractive index which is lower than that of the shell of the silica microcapsule; wherein the silica microcapsules are characterised by an average shell thickness of about 100 nm to about 700 nm; and wherein the formulation is characterised by a mass ratio of latex particles to silica microcapsules of about 0.2 to about 2.

[0011] In some embodiments, the shell comprises siloxane bonds between the silica nanoparticles.

[0012] In some embodiments, the oil is characterised by a refractive index of about 1.4 to about 1.47.

[0013] In some embodiments, the oil is selected from natural oil, silicone oil, or a combination thereof.

[0014] In some embodiments, the natural oil is an oil derived from coconut, jojoba, rice bran, olive, argan, rosehip, almond, olive, grapeseed, avocado, soybean, corn, peanut, sesame, hazelnut, walnut, palm, Lavender, Rose, Jasmine, Orange, Lemon, Bergamot, Frankincense, Geranium, Neroli or a combination thereof.

[0015] In some embodiments, the silica nanoparticles are characterised by a particle size of about 100 nm to about 500 nm. In some embodiments, the particle size is about 300 nm to about 500 nm.

[0016] In some embodiments, the silica microcapsules are characterised by a particle size of about 1 pm to about 100 pm. In some embodiments, the particle size is about 10 pm to about 80 pm.

[0017] In some embodiments, the silica microcapsule is microporous and / or mesoporous.

[0018] In some embodiments, the silica microcapsule is characterised by a pore size of less than about 100 nm. In some embodiments, the silica microcapsule is characterised by a mass ratio of silica to oil in the silica microcapsule of about 5: 1 to about 8: 1.

[0019] In some embodiments, the oil is leachable from the silica microcapsule at a rate of about 20% to about 50% of oil in the silica microcapsule over about 12 hours.

[0020] In some embodiments, the silica microcapsules are of about 10 wt% to about 25 wt% relative to the formulation.

[0021] In some embodiments, the latex particles are selected from silicone particles, PDMS particles, PMMA particles, PBA particles, polyacrylate particles, PS particles, and a composite or combination thereof.

[0022] In some embodiments, the latex particles are characterised by a particle size of about 50 nm to about 500 nm. In some embodiments, the latex particles are characterised by a particle size of about 80 nm to about 120 nm.

[0023] In some embodiments, the latex particles are of about 5 wt% to about 30 wt% relative to the formulation. In some embodiments, the latex particles are of about 5 wt% to about 25 wt% relative to the formulation.

[0024] In some embodiments, the formulation is characterised by a mass ratio of latex particles to silica microcapsules of about 0.34 to about 0.84.

[0025] In some embodiments, the formulation further comprises at least one additive.

[0026] In some embodiments, the at least one additive is selected from a dispersing additive and an anti-sagging and anti-settling additive.

[0027] The present disclosure also concerns a method of forming a formulation as disclosed herein, the method comprising : a) homogenising an oil in an aqueous medium with a non-ionic surfactant to form an oil-in-water (O / W) emulsion, the aqueous medium comprising an alcohol; b) mixing the emulsion with a silica precursor to form silica nanocapsules, the silica nanocapsules forming a shell encapsulating the oil to form silica microcapsules; and c) mixing the silica microcapsules with latex particles to form the formulation. In some embodiments, the alcohol is selected from methanol, ethanol, isopropanol, butanol, and a combination thereof. In some embodiments, the alcohol is ethanol.

[0028] In some embodiments, the aqueous medium is characterised by a mole ratio of alcohol to water of about 1 :5 to about 1 : 15. In some embodiments, the mole ratio is about 1:9.

[0029] In some embodiments, the non-ionic surfactant is selected from polyethylene glycol alkyl ethers, polyethylene glycol alkyl phenyl ethers, sorbitan esters, polyoxyethylene sorbitan esters, decyl glucoside, lauryl glucoside, coco glucoside, PEG-7 glyceryl cocoate, PEG-40 hydrogenated castor oil, ceteareth-20, PEG-100 stearate, poloxamer 188 and a combination thereof.

[0030] In some embodiments, the method is characterised by a mole ratio of non-ionic surfactant to oil of about 1:3 to about 3: 1. In some embodiments, the mole ratio is about 1 :2 to about 3:2.

[0031] In some embodiments, step a) further comprises mixing a salt in the aqueous medium.

[0032] In some embodiments, the salt is selected from be NaCI, KCI, NH4CI, or a combination thereof. In some embodiments, the salt is NaCI.

[0033] In some embodiments, step a) is performed at a pressure of about 300 bar to about 1500 bar for about 1 cycle to about 10 cycles. In some embodiments, the pressure is about 500 bar to about 1000 bar for about 3 cycles to about 5 cycles.

[0034] In some embodiments, the silica precursor is selected from tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), tetrapropyl orthosilicate (TPOS), or a combination thereof. In some embodiments, the silica precursor is TEOS.

[0035] In some embodiments, the method is characterised by a mole ratio of silica precursor to oil of about 1 : 1 to about 30: 1. In some embodiments, the mole ratio is about 11 : 1 to about 25: 1. In some embodiments, the mole ratio is about 3:2 to about 2: 1.

[0036] In some embodiments, step b) is performed at a mixing rate of about 200 rpm to about 1000 rpm for a duration of about 1 day to about 8 days. In some embodiments, step b) is performed at a mixing rate of about 600 rpm for a duration of about 4 days.

[0037] The present disclosure also concerns a silica microcapsule comprising a shell of silica nanoparticles and an oil encapsulated within its cavity thereof; wherein the oil is characterised by a refractive index which is lower than that of the shell of the silica microcapsule; and wherein the silica microcapsules are characterised by an average shell thickness of about 100 nm to about 700 nm.

[0038] The present disclosure also concerns a method of forming a silica microcapsule as disclosed herein, the method comprising: a) homogenising an oil in an aqueous medium with a non-ionic surfactant to form an oil-in-water (O / W) emulsion, the aqueous medium comprising an alcohol; and b) mixing the emulsion with a silica precursor to form silica nanocapsules, the silica nanocapsules forming a shell encapsulating the oil to form silica microcapsules.

[0039] The present disclosure also concerns a method of reflecting visible light, ultraviolet and / or near infrared rays, or whitening a surface, comprising contacting the formulation as disclosed herein on the surface.

[0040] In some embodiments, the surface is biological or non-biological surface.

[0041] In some embodiments, the formulation is applied to form at least one layer of coating on a surface.

[0042] Brief description of the drawings

[0043] Embodiments of the present invention will now be described, by way of non-limiting example, with reference to the drawings in which:

[0044] Figure 1. Particle size distribution (top) and SEM image of the silicone oil loaded silica microcapsules Si-MC (bottom).

[0045] Figure 2. Thermogravimetric curves of silicone oil-loaded silica microcapsules Si-MC.

[0046] Figure 3. Particle size distribution (top) and SEM image of the coconut oil loaded silica microcapsules Co-MC-1 (bottom).

[0047] Figure 4. Thermogravimetric curves of coconut oil-loaded silica microcapsules Co-MC- 1.

[0048] Figure 5. Particle size distribution (top) and SEM image of the coconut oil loaded silica microcapsules Co-MC-2 (bottom).

[0049] Figure 6. Thermogravimetric curves of coconut oil-loaded silica microcapsules Co-MC- 2.

[0050] Figure 7. Images of coatings based on different formulations, (a) Commercial binder and Ti-Pure™ R-706 TiCh; (b) P-125 hydrophobic latex and MC-silicone oil Si-MC; (c) P- 125 hydrophobic latex and MC-coconut oil Co-MC-2; and (d) P-125 hydrophobic latex and MC-coconut oil Co-MC-1. Si-MC is microcapsule containing silicone oil as core material, and both Co-MC-2 and Co-MC-1 are silica microcapsules containing coconut oil as core material.

[0051] Figure 8. Reflectance spectrum (%R versus wavelength) of formulated coatings based on TiO2, MC-silicone oil Si-MC, MC-coconut oil Co-MC-1, and MC-coconut oil Co-MC-2 silica microcapsules at 15 wt% and 20 wt% solid content.

[0052] Figure 9. Bar diagrams for comparing total solar reflectance (TSR) of formulated coatings. TSR values were measured in three wavelength regions accordingly to ASTM E903 - UV region (250 nm - 399 nm), visible light region (400 nm - 720 nm) and NIR region (721- 2500 nm). Top diagram indicates that both MC-silicone oil Si-MC and MC- coconut oil Co-MC-2 showed high UV- (up to 3.5x) and NIR (up to 1.3x) reflectivity as compared to the TiC -containing coatings with similar solid content and film thickness. Bottom diagram indicates that the increase in reflectivity (up to 1.7x) of MC-silicone oil Si-MC and MC-coconut oil Co-MC-2 at higher solid content (20 wt%) across all wavelengths.

[0053] Figure 10. Bar diagram for comparing sunscreen protection factor (SPF) for formulation containing coconut oil-microcapsule (Co-MC-2) and silicone oil-microcapsule. It was found that the SPF factors of Co-MC-2 and silicone oil-based formulation are 58% and 78% higher as compared to control formulation.

[0054] Figure 11. Applications of TiO? and possible issues associated with TIOz.

[0055] Figure 12. Schematic diagram on the synthesis of the formulation comprising silica microcapsules and latex particles.

[0056] Figure 13. SEM image of silica microcapsule showing hierarchical architecture of the capsules shell consisting of silica nanoparticles.

[0057] Figure 14. Size distribution by intensity of latex particles.

[0058] Detailed description The cosmetic industry is constantly evolving, with consumers seeking products that not only perform well but also align with their values. The consumers may demand for safer, more sustainable, and effective ingredients for safer, more sustainable, and effective ingredients. Silica microcapsules have emerged as versatile tools across numerous industries due to their unique properties. These microscopic capsules, composed of silica shells, find extensive use in fields such as pharmaceuticals, cosmetics, food, and materials science. However, silica microcapsules are normally engineered for targeted and controlled release, and not for brightening effects and protection against harmful ultraviolet (UV) rays.

[0059] The present disclosure concerns a formulation, comprising latex particles and silica microcapsules. Each silica microcapsule comprises a shell formed from silica nanoparticles and an oil encapsulated within its cavity thereof. The silica nanoparticles are formed via the Stober process. The Stober process is a chemical process used to prepare silica particles of controllable and uniform size. It is a sol-gel process wherein a molecular precursor, such as tetraethyl orthosilicate (TEOS), is reacted with water in an alcoholic solution. The TEOS precursor undergoes hydrolysis and condensation reactions to form siloxane bonds (Si-O-Si) and producing silica nanoparticles. The Stober process may produce silica nanoparticles with diameters ranging from 50 nm to about 2000 nm. During the Stober process, silica nanoparticles may be grown around a core, such as an oil core, to form a core-shell structure. This may be done by carrying out the Stober process in the presence of the core materials. For example, silicone oil may be dispersed in an ethanol / water mixture, forming an emulsion with emulsifiers. TEOS precursor may be added to the emulsion to trigger the Stober process to form silica nanoparticles. The silica nanoparticles may begin to aggregate and deposit onto emulsion droplets of silicone oil, forming a shell of silica nanoparticles. The aggregation may be driven by the formation of additional siloxane bonds between the silica nanoparticles via the silanol (Si-OH) groups on the surface of the silica nanoparticles. The shell formed may be a solid shell. The shell formed may also be a microporous and / or mesoporous shell.

[0060] Without being bound by theory, it is hypothesised that having an oil with lower refractive index than the silica nanoparticle in the silica microcapsule may result in higher reflectivity of electromagnetic waves such as visible light, ultraviolet and / or near infrared rays. This may allow the formulation to be used in personal care products such as sunscreen, coatings to reflect heat, opacifying agent in food technology and tableting technology, and skincare products for skin lightening.

[0061] The higher reflectivity of electromagnetic waves may be explained by Mie Scattering theory. Mie Scattering describes the scattering patterns and interference effects that arise from the interaction of electromagnetic waves with spherical particles of similar particle size to the wavelength of the electromagnetic wave incident on the particle. For example, the electromagnetic wave or light irradiating the silica microcapsule may undergo enhanced reflection or enhanced scattering. The core-shell structure of the microcapsule may form a hierarchical architecture of repeating features of higher refractive index materials (i.e. the silica nanoparticles) and lower refractive index materials (i.e. the oil, such as silicone oil or coconut oil). When light, particularly in the UV and near infrared (NIR) regions, interacts with this hierarchical architecture of higher and lower refractive index materials, Mie scattering occurs. The Mie scattering effects, due to the refractive index contrast and the hierarchical architecture, may lead to enhanced reflection of the light, particularly of the UV and NIR rays. The shell thickness may affect the reflectivity of the silica microcapsule. The average shell thickness may be about 100 nm to about 700 nm. A shell thickness of about 200 nm to about 400 nm may lead to high reflectivity.

[0062] The shell may also act as a barrier between the core oil and the external environment. The oil molecules may diffuse through the microporous and / or mesoporous shell to be released or leached out. A thicker shell may provide a longer diffusion path for the oil molecules, slowing down the leaching rate. A slower leaching rate may enable the silica microcapsule to retain its reflective property for a longer duration as the reflectivity of light by the silica microcapsule is dependent on both the shell formed from silica nanocapsules and the core oil.

[0063] Latex particles may act as a binder and a stabiliser that support and enhance the performance of the silica microcapsules in the final product, for example as a coating. Latex particles may form a continuous film that binds the silica microcapsules into the formulation when the formulation dries or cures as a coating. This may improve the adhesion and cohesion of the coating. Latex particles may also provide a matrix that holds the silica microcapsules in place, preventing them from easily falling off or being washed away. Latex particles may also help encapsulate and protect the silica microcapsules from premature rupture or leakage due to environmental factors. Accordingly, the present disclosure concerns a formulation, comprising latex particles and silica microcapsules; wherein each silica microcapsule comprises a shell formed from silica nanoparticles and an oil encapsulated within its cavity thereof; wherein the oil is characterised by a refractive index which is lower than that of the shell of the silica microcapsule; wherein the silica microcapsules are characterised by an average shell thickness of about 100 nm to about 700 nm; and wherein the formulation is characterised by a mass ratio of latex particles to silica microcapsules of about 0.2 to about 2.

[0064] In some embodiments, the oil is characterised by a refractive index which is lower than that of the shell of the silica microcapsule. For example, the oil may have a refractive index of about 1.4 to about 1.47 while the shell may have a refractive index of about 1.475.

[0065] In some embodiments, the oil is characterised by a refractive index of about 1.4 to about 1.47. In other embodiments, the refractive index is about 1.4 to about 1.46, about 1.4 to about 1.45, about 1.4 to about 1.44, about 1.4 to about 1.43, about 1.4 to about 1.42, about 1.4 to about 1.41, about 1.41 to about 1.47, about 1.41 to about 1.46, about 1.41 to about 1.45, about 1.41 to about 1.44, about 1.41 to about 1.43, about 1.41 to about 1.42, about 1.42 to about 1.47, about 1.42 to about 1.46, about 1.42 to about 1.45, about 1.42 to about 1.44, about 1.42 to about 1.43, about 1.43 to about 1.47, about 1.43 to about 1.46, about 1.43 to about 1.45, about 1.43 to about 1.44, about 1.44 to about 1.47, about 1.44 to about 1.46, about 1.44 to about 1.45, about 1.45 to about 1.47, about 1.45 to about 1.46, or about 1.46 to about 1.47. In some embodiments, the refractive index is about 1.405 to about 1.45.

[0066] In some embodiments, the silica microcapsules are characterised by an average shell thickness of about 100 nm to about 700 nm. In other embodiments, the average shell thickness is about 100 nm to about 600 nm, about 100 nm to about 500 nm, about 100 nm to about 400 nm, about 100 nm to about 300 nm, about 100 nm to about 200 nm, about 200 nm to about 700 nm, about 200 nm to about 600 nm, about 200 nm to about 500 nm, about 200 nm to about 400 nm, about 200 nm to about 300 nm, about 300 nm to about 700 nm, about 300 nm to about 600 nm, about 300 nm to about 500 nm, about 300 nm to about 400 nm, about 400 nm to about 700 nm, about 400 nm to about 600 nm, about 400 nm to about 500 nm, about 500 nm to about 700 nm, about 500 nm to about 600 nm, or about 600 nm to about 700 nm. In some embodiments, the average shell thickness is about 200 nm to about 400 nm.

[0067] In some embodiments, the formulation is characterised by a mass ratio of latex particles to silica microcapsules of about 0.2 to about 2. The mass ratio of latex particles to silica microcapsules may affect the properties of the formulation. A higher mass ratio of latex particles to silica microcapsules may improve the film-forming ability of the formulation when dried or cured and the flexibility of the film. However, it may reduce the relative contribution of the silica microcapsules. The silica microcapsules may contribute to the reflectivity of visible light, ultraviolet and / or near infrared rays. Reducing the relative amount of silica microcapsules may reduce the reflectivity of the formulation. A lower mass ratio of latex particles to silica microcapsules may result in the formulation having higher UV and NIR reflectivity. Increasing the relative amount of silica microcapsules may increase the reflectivity of the formulation. Accordingly, the mass ratio of latex particles to silica microcapsules may be adjusted depending on the specific application of the formulation. Preferably, the mass ratio of latex particles to silica microcapsules is about 0.34 to about 0.84.

[0068] In other embodiments, the mass ratio is about 0.2 to about 1.8, about 0.2 to about 1.5, about 0.2 to about 1.2, about 0.2 to about 1, about 0.2 to about 0.8, about 0.2 to about 0.5, about 0.5 to about 2, about 0.5 to about 1.8, about 0.5 to about 1.5, about 0.5 to about 1.2, about 0.5 to about 1, about 0.5 to about 0.8, about 0.8 to about 2, about 0.8 to about 1.8, about 0.8 to about 1.5, about 0.8 to about 1.2, about 0.8 to about 1, about 1 to about 2, about 1 to about 1.8, about 1 to about 1.5, about 1 to about 1.2, about 1.2 to about 2, about 1.2 to about 1.8, about 1.2 to about 1.5, about 1.5 to about 2, about 1.5 to about 1.8, or about 1.8 to about 2. In some embodiments, the mass ratio is about 0.3 to about 1.7. In some embodiments, the mass ratio is about 0.34 to about 1.67. In some embodiments, the mass ratio is about 0.34 to about 0.84.

[0069] In some embodiments, the shell comprises siloxane bonds between the silica nanoparticles.

[0070] In some embodiments, the oil is selected from natural oil, silicone oil, or a combination thereof. "Natural oil" refers to an oil derived from a natural source. The source may be a plant source or an animal source. A variety of natural oils such oils used in personal care (Jojoba Oil, Argan Oil, Rosehip Oil, Almond Oil, Olive Oil, Grapeseed Oil, Avocado Oil etc.), oils used in natural perfumes which contains essence / extracts / or steam distilled products of Lavender, Rose, Jasmine, Orange, Lemon, Bergamot, Frankincense, Geranium Oil, Neroli Oil etc. and edible oils including the one used in personal care such as Soybean Oil, Corn Oil, Peanut Oil, Sesame Oil, Grapeseed Oil, Avocado Oil, Hazelnut Oil, Walnut Oil, Palm Oil, Rice Bran Oil etc. In addition to these individual oils, a combination of different types of natural oils also could be used.

[0071] In some embodiments, the natural oil is an oil derived from coconut, jojoba, rice bran, olive, argan, rosehip, almond, olive, grapeseed, avocado, soybean, corn, peanut, sesame, hazelnut, walnut, palm, Lavender, Rose, Jasmine, Orange, Lemon, Bergamot, Frankincense, Geranium, Neroli or a combination thereof.

[0072] Microcapsules and nanocapsules are types of encapsulation systems that may be used to contain and / or deliver various substances, such as fragrances, oils or other active ingredients. Microcapsules are small particles with diameters of about 1 pm to about 1000 pm. The microcapsules may comprise a core, for example oil, surrounded by a shell, for example silica nanoparticles. The shell may protect the core material from the external environment, control the release of the core material, or provide targeted delivery. Microcapsules may be used in the food industry, cosmetics and agriculture. Nanocapsules are small particles with diameters of about 10 nm to about 1000 nm. The small size and spherical shape of the nanocapsules may result in a high surface area to volume ratio, which may enhance reactivity and functionality. The small size may also enhance the reflectivity of light when the nanocapsules form the shell of a microcapsule comprising an oil core.

[0073] In some embodiments, the silica nanocapsules are characterised by a particle size of about 100 nm to about 500 nm. In other embodiments, the particle size is about 100 nm to about 400 nm, about 100 nm to about 300 nm, about 100 nm to about 200 nm, about 200 nm to about 500 nm, about 200 nm to about 400 nm, about 200 nm to about 300 nm, about 300 nm to about 500 nm, about 300 nm to about 400 nm, or about 400 nm to about 500 nm. In some embodiments, the particle size is about 300 nm to about 500 nm. In some embodiments, the silica microcapsules are characterised by a particle size of about 1 pm to about 100 pm. In other embodiments, the particle size is about 1 pm to about 80 pm, about 1 pm to about 50 pm, about 1 pm to about 20 pm, about 1 pm to about 5 pm, about 5 pm to about 100 pm, about 5 pm to about 80 pm, about 5 pm to about 20 pm, about 20 pm to about 100 pm, about 20 pm to about 80 pm, about 20 pm to about 50 pm, about 50 pm to about 100 pm, about 50 pm to about 80 pm, or about 80 pm to about 100 pm. In some embodiments, the particle size is about 5 pm to about 12 pm. In some embodiments, the particle size is about 10 pm to about 80 pm.

[0074] In some embodiments, the silica microcapsules are microporous and / or mesoporous. Microporous and mesoporous materials have pores in different size ranges, which may affect how the materials interact with other substances. Microporous materials have pores with sizes typically less than 2 nm in diameter. The small pore size may give the microporous material a high surface area. Mesoporous materials have pores with sizes typically ranging from about 2 nm to about 50 nm. Mesoporous materials have larger pore sizes compared to microporous materials. The silica microcapsules may have pores of about 2 nm to about 50 nm in diameter and pores of less than about 2 nm in diameter. The silica microcapsules may have pores of less than about 100 nm in diameter. The presence of the pores may result in a gradual leaking of oil from the silica microcapsules over time. A smaller pore size may reduce the rate of oil leaking from the silica microcapsule.

[0075] In some embodiments, the silica microcapsule is characterised by a pore size of less than about 100 nm. In other embodiments, the pore size is less than about 90 nm, less than about 80 nm, less than about 70 nm, less than about 60 nm, less than about 50 nm, less than about 40 nm, less than about 30 nm, less than about 20 nm, less than about 10 nm, less than about 5 nm, or less than about 2 nm.

[0076] In some embodiments, the silica microcapsule is characterised by a mass ratio of silica to oil in the silica microcapsule of about 5: 1 to about 8: 1. In other embodiments, the mass ratio is about 5: 1 to about 7: 1, about 5: 1 to about 6: 1, about 6: 1 to about 8: 1, about 6: 1 to about 7: 1, or about 7: 1 to about 8: 1.

[0077] In some embodiments, the oil is leachable from the silica microcapsule. The oil molecules may diffuse through the microporous and / or mesoporous shell to be released or leached out. In some embodiments, the oil is leachable from the silica microcapsule at a rate of about 20% to about 50% of oil in the silica microcapsule over about 12 hours. In other embodiments, the oil is leachable from the silica microcapsule at a rate of about 20% to about 45%, about 20% to about 40%, about 20% to about 35%, about 20% to about 30%, about 20% to about 25%, about 25% to about 50%, about 25% to about 45%, about 25% to about 40%, about 25% to about 40%, about 25% to about 35%, about 25% to about 30%, about 30% to about 50%, about 30% to about 45%, about 30% to about 40%, about 30% to about 35%, about 35% to about 50%, about 35% to about 45%, about 35% to about 40%, about 40% to about 50%, about 40% to about 45%, or about 45% to about 50% of oil in the silica microcapsule over about 12 hours.

[0078] In some embodiments, the silica microcapsules are of about 10 wt% to about 25 wt% relative to the formulation. In other embodiments, the silica microcapsules are of about 10 wt% to about 20 wt%, about 10 wt% to about 15 wt%, about 15 wt% to about 25 wt%, about 15 wt% to about 20 wt%, or about 20 wt% to about 25 wt% relative to the formulation. In some embodiments, the silica microcapsules are about 15 wt% to about 20 wt% relative to the formulation. In some embodiments, the silica microcapsules are about 15 wt%, about 17 wt%, about 18 wt%, or about 20 wt% relative to the formulation.

[0079] In some embodiments, the latex particles are amorphous polymer particles. Amorphous polymer particles are small, solid particles made from amorphous (non-crystalline) polymers, where the polymer chains are randomly arranged, unlike in an ordered structure in crystalline polymers. Latex particles may be made from amorphous polymers such as silicone, poly(styrene-butadiene), polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), polybutyl acrylate (PBA), polyacrylate, polystyrene (PS), or a composite thereof.

[0080] In some embodiments, the latex particles are selected from silicone particles, PDMS particles, PMMA particles, PBA particles, polyacrylate particles, PS particles, and a composite particles or combination thereof.

[0081] In some embodiments, the latex particles comprise silicone and polyacrylate. In some embodiments, the latex particles are core-shell silicone-acrylic particles. In some embodiments, the latex particles are characterised by a particle size of about 50 nm to about 500 nm. In other embodiments, the particle size is about 50 nm to about 400 nm, about 50 nm to about 300 nm, about 50 nm to about 200 nm, about 50 nm to about 100 nm, about 100 nm to about 500 nm, about 100 nm to about 400 nm, about 100 nm to about 300 nm, about 100 nm to about 200 nm, about 200 nm to about 500 nm, about 200 nm to about 400 nm, about 200 nm to about 300 nm, about 300 nm to about 500 nm, about 300 nm to about 400 nm, or about 400 nm to about 500 nm. In some embodiments, the latex particles are characterised by a particle size of about 60 nm to about 150 nm. In some embodiments, the latex particles are characterised by a particle size of about 80 nm to about 120 nm.

[0082] In some embodiments, the latex particles are of about 5 wt% to about 30 wt% relative to the formulation. In other embodiments, the latex particles are of about 5 wt% to about 25 wt%, about 5 wt% to about 20 wt%, about 5 wt% to about 15 wt%, about 5 wt% to about 10 wt%, about 10 wt% to about 30 wt%, about 10 wt% to about 25 wt%, about 10 wt% to about 20 wt%, about 10 wt% to about 15 wt%, about 15 wt% to about 30 wt%, about 15 wt% to about 25 wt%, about 15 wt% to about 20 wt%, about 20 wt% to about 30 wt%, about 20 wt% to about 25 wt%, or about 25 wt% to about 30 wt% relative to the formulation. In some embodiments, the latex particles are of about 5 wt% to about 25 wt% relative to the formulation.

[0083] In some embodiments, the formulation further comprises at least one additive. Additives may enhance performance, stability, appearance or processability of the formulation. The additive may help stabilise the silica microcapsules and latex particles and prevent agglomeration and sedimentation. The additive may also modify the rheology of the formulation by adjusting the viscosity and flow properties. In other embodiments, the formulation further comprises at least two additives, at least three additives or at least four additives.

[0084] The additive may be a dispersing additive which may break up and stabilise the silica microcapsules and / or latex particles, improving the dispersion of the particles within the formulation. This may aid in preventing agglomeration and ensuring uniform distribution of the silica microcapsules and latex particles. The additive may also be a preservative, a defoamer, a wetting agent, a corrosion inhibitor, an antioxidant, a colorant or pigment, a surfactant or a lubricant. The dispersing additive may be ammonium polyacrylate based. The additive may be an anti-sagging additive which may prevent the sagging of the formulation in vertical or inclined surfaces before the formulation dries or cures. The anti-sagging additive may increase the viscosity of the formulation to counter the gravitational forces that may cause the silica microcapsules and latex particles to sag. The anti-sagging additive may be fumed silica, organoclays, or modified urea. The additive may be an anti-settling additive. The anti-settling additive may prevent the silica microcapsules and latex particles from settling at the bottom of a container during storage. The anti-settling additive may modify the rheology of the formulation to keep the silica microcapsules and latex particles suspended. The anti-settling additive may also be an anti-sagging additive, for example a modified urea-based additive.

[0085] In some embodiments, the at least one additive is selected from a dispersing additive and an anti-sagging and anti-settling additive.

[0086] The formulation may comprise an aqueous medium. The latex particles and silica microcapsules are thus dispersed in the aqueous medium. The term 'aqueous medium' used herein refers to a water based solvent or solvent system, and which comprises of mainly water. Such solvents can be either polar or non-polar, and / or either protic or aprotic. Solvent systems refer to combinations of solvents which resulting in a final single phase. Both 'solvents' and 'solvent systems' can include, and is not limited to, pentane, cyclopentane, hexane, cyclohexane, benzene, toluene, dioxane, chloroform, diethylether, dichloromethane, tetrahydrofuran, ethyl acetate, acetone, dimethylformamide, acetonitrile, dimethyl sulfoxide, nitromethane, propylene carbonate, formic acid, butanol, isopropanol, propanol, ethanol, methanol, acetic acid, ethylene glycol, diethylene glycol or water. Water based solvent or solvent systems can also include dissolved ions, salts and molecules such as amino acids, proteins, sugars and phospholipids. Such salts may be, but not limited to, sodium chloride, potassium chloride, ammonium acetate, magnesium acetate, magnesium chloride, magnesium sulfate, potassium acetate, potassium chloride, sodium acetate, sodium citrate, zinc chloride, HEPES sodium, calcium chloride, ferric nitrate, sodium bicarbonate, potassium phosphate and sodium phosphate.

[0087] The present disclosure also concerns a method of forming a formulation as disclosed herein, the method comprising : a) homogenising an oil in an aqueous medium with a non-ionic surfactant to form an oil-in-water (O / W) emulsion, the aqueous medium comprising an alcohol; b) mixing the emulsion with a silica precursor to form silica nanocapsules, the silica nanocapsules forming a shell encapsulating the oil to form silica microcapsules; and c) mixing the silica microcapsules with latex particles to form the formulation.

[0088] An oil-in-water (O / W) emulsion is a type of emulsion where tiny droplets of oil are dispersed within a continuous water phase, and emulsifiers are used to stabilise the mixture, preventing the oil and eater from separating. The oil droplet in the O / W emulsion may be dispersed in an aqueous medium. An aqueous medium refers to a water based solvent or solvent system, and which comprises of mainly water. Water based solvent or solvent systems may also include dissolved ions, salts and molecules such as amino acids, proteins, sugars and phospholipids. Such salts may be sodium chloride, potassium chloride, ammonium chloride, ammonium acetate.

[0089] In some embodiments, the aqueous medium comprises alcohol. The aqueous medium comprising alcohol aids the hydrolysis of the silica precursor in the Stober process to form the silica nanoparticles.

[0090] In some embodiments, the alcohol is selected from methanol, ethanol, isopropanol, butanol, and a combination thereof. In some embodiments, the alcohol is ethanol.

[0091] In some embodiments, the aqueous medium is characterised by a mole ratio of alcohol to water of about 1 : 5 to about 1 : 15. In other embodiments, the mole ratio is about 1:5 to about 1 : 12, about 1 :5 to about 1 : 10, about 1 : 5 to about 1 :8, about 1:8 to about 1 : 15, about 1 :8 to about 1 : 12, about 1:8 to about 1 : 10, about 1 : 10 to about 1 : 15, or about 1 : 10 to about 1 : 12. In some embodiments, the mole ratio is about 1 :9.

[0092] Non-ionic surfactants are a type of surfactant that do not carry an electrical charge in solution. They are characterised by having both hydrophilic and hydrophobic groups within the same molecule, allowing them to reduce surface tension and facilitate the mixing of oil and water. The non-ionic surfactant may be selected from synthetic surfactant, bioderived neutral surfactant, neutral polymeric surfactant and a combination thereof. Synthetic non-ionic surfactants may be polyethylene glycol alkyl ethers (e.g. ceteth-20, steareth-20, laureth-4), polyethylene glycol alkyl phenyl ethers, sorbitan esters (e.g. sorbitan monolaurate (Span 20), sorbitan monooleate (Span 80)), and polyoxyethylene sorbitan esters (e.g. polysorbate 20, polysorbate 80), ceteareth- 20, and poloxamer 188. Bioderived neutral surfactants may be decyl glucoside, lauryl glucoside and coco glucoside. Neutral polymeric surfactants may be PEG-7 glyceryl cocoate, PEG-40 hydrogenated castor oil and PEG-100 stearate.

[0093] In some embodiments, the non-ionic surfactant is selected from polyethylene glycol alkyl ethers, polyethylene glycol alkyl phenyl ethers, sorbitan esters, polyoxyethylene sorbitan esters, decyl glucoside, lauryl glucoside, coco glucoside, PEG-7 glyceryl cocoate, PEG-40 hydrogenated castor oil, ceteareth-20, PEG-100 stearate, poloxamer 188, and a combination thereof.

[0094] In some embodiments, the non-ionic surfactant is selected from polyethylene glycol alkyl ethers, polyethylene glycol alkyl phenyl ethers, sorbitan esters, polyoxyethylene sorbitan esters, polysorbate 20, polysorbate 80, ceteth-20, steareth-20, laureth-4, sorbitan monolaurate (Span 20), sorbitan monooleate (Span 80), decyl glucoside, lauryl glucoside, coco glucoside, PEG-7 glyceryl cocoate, PEG-40 hydrogenated castor oil, ceteareth-20, PEG-100 stearate, poloxamer 188, and a combination thereof.

[0095] In some embodiments, the method is characterised by a mole ratio of non-ionic surfactant to oil of about 1 :3 to about 3: 1. In other embodiments, the mole ratio is about 1 :3 to about 3:2, about 1:3 to about 1: 1, about 1:3 to about 1:2, about 1 :2 to about 3: 1, about 1 :2 to about 3:2, about 1 :2 to about 1 : 1, about 1: 1 to about 3: 1, about 1: 1 to about 3:2, or about 3:2 to about 3: 1. In some embodiments, the mole ratio is about 1 :2 to about 3:2.

[0096] In some embodiments, step a) further comprises mixing a salt in the aqueous medium. The salt may prevent droplet aggregation of the oil and may affect surfactant adsorption at the oil-water interface. This may lead to smaller and / or more uniform oil droplet sizes and hence lead to more uniform silica microcapsules.

[0097] In some embodiments, the salt may be NaCI, KCI, NH4CI, or a combination thereof. In some embodiments, the salt may be NaCI.

[0098] In some embodiments, the method further comprises a step before step a) of mixing an oil in an aqueous medium with a non-ionic surfactant at a mixing rate of about 2000 rpm to about 8000 rpm for a duration of about 30 seconds to about 5 minutes to obtain a pre-emulsion. A pre-emulsion is an intermediate step in the formation of an emulsion, where a mixture of two immiscible liquids (oil and an aqueous solution) is formed and stabilised with a surfactant. The pre-emulsion is not yet fully emulsified into a stable O / W emulsion. This may help to obtain a pre-emulsion with oil droplets of size ranging from about 50 pm to about 200 pm.

[0099] In other embodiments, the method further comprises a step before step a) of mixing an oil in an aqueous medium with a non-ionic surfactant at a mixing rate of about 2000 rpm to about 6000 rpm, about 2000 rpm to about 4000 rpm, about 4000 rpm to about 8000 rpm, about 4000 rpm to about 6000 rpm, or about 6000 rpm to about 8000 rpm for a duration of about 30 seconds to about 3 minutes, about 30 seconds to about 1 minute, about 1 minute to about 5 minutes, about 1 minute to about 3 minutes, or about 3 minutes to about 5 minutes. In some embodiments, the mixing is performed at a mixing rate of about 4000 rpm for about 2 minutes. In some embodiments, the mixing is performed at a mixing rate of about 6500 rpm for about 2 minutes.

[0100] The homogenisation may be a high pressure homogenisation. High pressure homogenisation is a mechanical process where a fluid mixture is forced through a narrow gap or valve at high pressure, usually about 100 bar to about 2000 bar, causing intense shear, turbulence and cavitation forces that break down the oil droplets into smaller sizes. The high pressure homogenisation may be performed for one or more cycles. Each cycle may progressively break down the oil droplets into smaller and more uniformly sized oil droplets. Smaller and more uniform oil droplets may lead to more stable emulsions.

[0101] In some embodiments, step a) is performed at a pressure of about 300 bar to about 1500 bar for about 1 cycle to about 10 cycles. In other embodiments, the pressure is about 300 bar to about 1200 bar, about 300 bar to about 1000 bar, about 300 bar to about 800 bar, about 300 bar to about 500 bar, about 500 bar to about 1500 bar, about 500 bar to about 1200 bar, about 500 bar to about 1000 bar, about 500 bar to about 800 bar, about 800 bar to about 1500 bar, about 800 bar to about 1200 bar, about 800 bar to about 1000 bar, about 1000 bar to about 1500 bar, about 1000 bar to about 1200 bar, or about 1200 bar to about 1500 bar for about 1 cycle to about 8 cycles, for about 1 cycle to about 5 cycles, for about 1 cycle to about 3 cycles, for about 3 cycles to about 10 cycles, for about 3 cycles to about 8 cycles, for about 3 cycles to about 5 cycles, for about 5 cycles to about 10 cycles, or for about 5 cycles to about 8 cycles. In some embodiments, the pressure is about 500 bar to about 1000 bar for about 3 cycles to about 5 cycles. In some embodiments, the pressure is about 500 bar for about 3 cycles. In some embodiments, the pressure is about 1000 bar for about 5 cycles.

[0102] In some embodiments, step b) comprises mixing the emulsion with a silica precursor to form silica nanocapsules, the silica nanocapsules forming a shell encapsulating the oil to form silica microcapsules. The silica precursor is a molecule comprising silicon bonded to alkoxy groups, which may be transformed into Si-O-Si bonds to form a solid silica under Stober process.

[0103] In some embodiments, the silica precursor is selected from tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), tetrapropyl orthosilicate (TPOS), or a combination thereof. In some embodiments, the silica precursor is TEOS.

[0104] In some embodiments, the method is characterised by a mole ratio of silica precursor to oil of about 1:1 to about 30:1. In other embodiments, the mole ratio is about 1:1 to about 25:1, about 1:1 to about 20:1, about 1:1 to about 15:1, about 1:1 to about 10:1, about 1:1 to about 5:1, about 5:1 to about 30:1, about 5:1 to about 25:1, about 5:1 to about 20:1, about 5:1 to about 15:1, about 5:1 to about 10:1, about 10:1 to about 30:1, about 10:1 to about 25:1, about 10:1 to about 20:1, about 10:1 to about 15:1, about 15:1 to about 30:1, about 15:1 to about 25:1, about 15:1 to about 20:1, about 20:1 to about 30:1, about 20:1 to about 25:1, or about 25:1 to about 30:1. In some embodiments, the mole ratio is about 3:2 to about 25:1. In some embodiments, the mole ratio is about 11:1 to about 25:1. In some embodiments, the mole ratio is about 3:2 to about 2:1.

[0105] In some embodiments, step b) is performed at a mixing rate of about 200 rpm to about 1000 rpm for a duration of about 1 day to about 8 days. In other embodiments, the step b) is performed at a mixing rate of about 200 rpm to about 800 rpm, about 200 rpm to about 600 rpm, about 200 rpm to about 400 rpm, about 400 rpm to about 1000 rpm, about 400 rpm to about 800 rpm, about 400 rpm to about 600 rpm, about 600 rpm to about 1000 rpm, about 600 rpm to about 800 rpm, or about 800 rpm to about 1000 rpm for a duration of about 1 day to about 5 days, about 1 day to about 3 days, about 3 days to about 8 days, about 3 days to about 5 days, or about 5 days to about 8 days. In some embodiments, step b) is performed at a mixing rate of about 600 rpm for a duration of about 4 days. In some embodiments, step c) comprises mixing the silica microcapsules with latex particles to form the formulation.

[0106] The present disclosure also concerns a silica microcapsule comprising a shell of silica nanoparticles and an oil encapsulated within its cavity thereof; wherein the oil is characterised by a refractive index which is lower than that of the shell of the silica microcapsule; and wherein the silica microcapsules are characterised by an average shell thickness of about 100 nm to about 700 nm.

[0107] In some embodiments, the silica microcapsule reflects visible light, ultraviolet and / or near infrared rays. For example, a sunscreen formulation comprising the silica microcapsules may have a higher sun protection factor (SPF) than a sunscreen formulation without the silica microcapsules. SPF is a measure of how effective a sunscreen product protects the skin from UV radiation. UV radiation may result in sunburns on skin. A higher SPF may have a better level of protection against UV radiation. As shown in Table 5 and Figure 10, the inclusion of the silica microcapsules led to an increase in SPF compared to control formulations without the silica microcapsules. This suggests that the silica microcapsules contribute to UV protection and may be a potential alternative to TiCh and may be a more sustainable alternative.

[0108] The present disclosure also concerns a method of forming a silica microcapsule as disclosed herein, the method comprising: a) homogenising an oil in an aqueous medium with a non-ionic surfactant to form an oil-in-water (O / W) emulsion, the aqueous medium comprising an alcohol; and b) mixing the emulsion with a silica precursor to form silica nanocapsules, the silica nanocapsules forming a shell encapsulating the oil to form silica microcapsules.

[0109] In some embodiments, the alcohol is selected from methanol, ethanol, isopropanol, butanol, and a combination thereof. In some embodiments, the alcohol is ethanol.

[0110] In some embodiments, the aqueous medium is characterised by a mole ratio of alcohol to water of about 1 : 5 to about 1 : 15. In other embodiments, the mole ratio is about 1:5 to about 1 : 12, about 1 :5 to about 1 : 10, about 1 : 5 to about 1 :8, about 1:8 to about 1 : 15, about 1 :8 to about 1 : 12, about 1:8 to about 1 : 10, about 1 : 10 to about 1 : 15, or about 1 : 10 to about 1 : 12. In some embodiments, the mole ratio is about 1 :9. In some embodiments, the non-ionic surfactant is selected from polyethylene glycol alkyl ethers, polyethylene glycol alkyl phenyl ethers, sorbitan esters, polyoxyethylene sorbitan esters, decyl glucoside, lauryl glucoside, coco glucoside, PEG-7 glyceryl cocoate, PEG-40 hydrogenated castor oil, ceteareth-20, PEG-100 stearate, poloxamer 188, and a combination thereof.

[0111] In some embodiments, the method is characterised by a mole ratio of non-ionic surfactant to oil of about 1:3 to about 3: 1. In other embodiments, the mole ratio is about 1:3 to about 3:2, about 1:3 to about 1: 1, about 1:3 to about 1:2, about 1:2 to about 3: 1, about 1 :2 to about 3:2, about 1 :2 to about 1 : 1, about 1: 1 to about 3: 1, about 1: 1 to about 3:2, or about 3:2 to about 3: 1. In some embodiments, the mole ratio is about 1 :2 to about 3:2.

[0112] In some embodiments, the method further comprises a step before step a) of mixing an oil in an aqueous medium with a non-ionic surfactant at a mixing rate of about 2000 rpm to about 8000 rpm for a duration of about 30 seconds to about 5 minutes to obtain a pre-emulsion. In other embodiments, the mixing is performed at a mixing rate of about 2000 rpm to about 6000 rpm, about 2000 rpm to about 4000 rpm, about 4000 rpm to about 8000 rpm, about 4000 rpm to about 6000 rpm, or about 6000 rpm to about 8000 rpm for a duration of about 30 seconds to about 3 minutes, about 30 seconds to about 1 minute, about 1 minute to about 5 minutes, about 1 minute to about 3 minutes, or about 3 minutes to about 5 minutes. In some embodiments, the mixing is performed at a mixing rate of about 4000 rpm for about 2 minutes. In some embodiments, the mixing is performed at a mixing rate of about 6500 rpm for about 2 minutes.

[0113] In some embodiments, step a) is performed at a pressure of about 300 bar to about 1500 bar for about 1 cycle to about 10 cycles. In other embodiments, the pressure is about 300 bar to about 1200 bar, about 300 bar to about 1000 bar, about 300 bar to about 800 bar, about 300 bar to about 500 bar, about 500 bar to about 1500 bar, about 500 bar to about 1200 bar, about 500 bar to about 1000 bar, about 500 bar to about 800 bar, about 800 bar to about 1500 bar, about 800 bar to about 1200 bar, about 800 bar to about 1000 bar, about 1000 bar to about 1500 bar, about 1000 bar to about 1200 bar, or about 1200 bar to about 1500 bar for about 1 cycle to about 8 cycles, for about 1 cycle to about 5 cycles, for about 1 cycle to about 3 cycles, for about 3 cycles to about 10 cycles, for about 3 cycles to about 8 cycles, for about 3 cycles to about 5 cycles, for about 5 cycles to about 10 cycles, or for about 5 cycles to about 8 cycles. In some embodiments, the pressure is about 500 bar to about 1000 bar for about 3 cycles to about 5 cycles. In some embodiments, the pressure is about 500 bar for about 3 cycles. In some embodiments, the pressure is about 1000 bar for about 5 cycles.

[0114] In some embodiments, step b) comprises mixing the emulsion with a silica precursor to form silica nanocapsules, the silica nanocapsules forming a shell encapsulating the oil to form silica microcapsules.

[0115] In some embodiments, the silica precursor is selected from tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), tetrapropyl orthosilicate (TPOS), or a combination thereof. In some embodiments, the silica precursor is TEOS.

[0116] In some embodiments, the method is characterised by a mole ratio of silica precursor to oil of about 1:1 to about 30:1. In other embodiments, the mole ratio is about 1:1 to about 25:1, about 1:1 to about 20:1, about 1:1 to about 15:1, about 1:1 to about 10:1, about 1:1 to about 5:1, about 5:1 to about 30:1, about 5:1 to about 25:1, about 5:1 to about 20:1, about 5:1 to about 15:1, about 5:1 to about 10:1, about 10:1 to about 30:1, about 10:1 to about 25:1, about 10:1 to about 20:1, about 10:1 to about 15:1, about 15:1 to about 30:1, about 15:1 to about 25:1, about 15:1 to about 20:1, about 20:1 to about 30:1, about 20:1 to about 25:1, or about 25:1 to about 30:1. In some embodiments, the mole ratio is about 3:2 to about 25:1. In some embodiments, the mole ratio is about 11:1 to about 25:1. In some embodiments, the mole ratio is about 3:2 to about 2:1.

[0117] In some embodiments, step b) is performed at a mixing rate of about 200 rpm to about 1000 rpm for a duration of about 1 day to about 8 days. In other embodiments, the step b) is performed at a mixing rate of about 200 rpm to about 800 rpm, about 200 rpm to about 600 rpm, about 200 rpm to about 400 rpm, about 400 rpm to about 1000 rpm, about 400 rpm to about 800 rpm, about 400 rpm to about 600 rpm, about 600 rpm to about 1000 rpm, about 600 rpm to about 800 rpm, or about 800 rpm to about 1000 rpm for a duration of about 1 day to about 5 days, about 1 day to about 3 days, about 3 days to about 8 days, about 3 days to about 5 days, or about 5 days to about 8 days. In some embodiments, step b) is performed at a mixing rate of about 600 rpm for a duration of about 4 days. The present disclosure also concerns a coating and / or film formed from the formulation as disclosed herein.

[0118] The formulation may be applied as a layer on a surface and then dried and / or cured to form the coating and / or film in solid state.

[0119] In some embodiments, the coating and / or film reflects visible light, ultraviolet and / or near infrared rays.

[0120] The reflectance of a material is its effectiveness in reflecting light or other electromagnetic rays. A coating and / or film with high reflectance may reflect sunlight, resulting in a cooler surface. A lower reflectance may result in an absorption of sunlight, leading to a hotter surface.

[0121] In some embodiments, the coating and / or film is characterised by a reflectance of about 10% to about 70% for wavelengths between 250 nm to about 2500 nm. In other embodiments, the reflectance is about 10% to about 50%, about 10% to about 50%, about 10% to about 30%, about 30% to about 70%, about 30% to about 50%, or about 50% to about 70%. In some embodiments, the reflectance is about 30% to about 65%.

[0122] The coating may be used for exterior paints, fagade coatings and other architectural applications where the reflection of heat is required.

[0123] The coating and / or film formed from the formulation as disclosed herein may reflect wavelengths more uniformly across the visible light, ultraviolet rays and near infrared rays as compared to a formulation comprising TiC as a UV reflector (Figure 8). This uniformed reflection may be preferred in applications where the reflection of heat from sunlight is required. The sun emits electromagnetic radiation across the electromagnetic spectrum from ultraviolet to infrared. The visible and infrared regions of the electromagnetic spectrum may account for majority of the sun's total energy output. Thus, the visible and infrared regions of the electromagnetic spectrum are the primary carriers of heat from the sun. By reflecting visible light and near infrared rays, the coating and / or film may reduce the amount of heat absorbed from sunlight and help to lower the amount of heat that needs to be removed from a building interior through air conditioning or other cooling methods. This may lead to more energy savings and reduced greenhouse gas emissions.

[0124] Total Solar Reflectance (TSR) is a measure of the amount of sunlight or solar energy that is reflected by a surface or a material, such as the coating and / or film. A material with a lower TSR may absorb more sunlight compared to a material with a higher TSR. For example, a coating and / or film formed from the formulation as disclosed herein may have higher TSR value compared to a coating and / or film formed from a formulation comprising TiOz (Figure 9), especially in the UV region and NIR region. This may lead to more sunlight being reflect at the UV region and NIR region, resulting in more heat being reflected by the coating. This may lead to a reduction of the amount of heat absorbed by the surface on which the coating and / or film is applied, leading to a cooler surface.

[0125] In some embodiments, the coating and / or film is characterised by a TSR value of about 10% to about 70%. In other embodiments, the TSR value is about 10% to about 50%, about 10% to about 50%, about 10% to about 30%, about 30% to about 70%, about 30% to about 50%, or about 50% to about 70%. In some embodiments, the TSR value is about 30% to about 65%.

[0126] The present disclosure also concerns a method of reflecting visible light, ultraviolet and / or near infrared rays, or whitening a surface, comprising contacting the formulation as disclosed herein on the surface. The surface may be a biological or a non-biological surface. A biological surface may be any surface that is part of or associated with a living organism. This may include human skin, animal skin, plant surfaces such as leaf and bark, and biological implants. For example, the formulation may be applied onto human skin as a UV blocking coating (e.g. as sunblock) or a skin-whitening film that reflects visible light for optical brightening (e.g. as whitening cream). A non-biological surface may be any surface of an inanimate or synthetic material, not derived from or part of a living organism. This may include exterior building walls, plastic, glass, ceramics, vehicles, solar panels, and textiles. For example, the formulation may be applied to an exterior building wall as a reflective coating to reduce the amount of heat absorbed by the building wall. The formulation may also be applied onto satellites or electronics as thermal control coatings to reduce the heat absorption. The formulation may also be applied onto textiles such as medical bandages for the reflection of NIR rays to reduce heat absorption. In some embodiments, the surface is biological or non-biological surface.

[0127] In some embodiments, the formulation is applied to form at least one layer of coating on a surface.

[0128] The formulation may contribute to the whitening or brightening of a surface through the reflection and scattering of light by the silica microcapsules and latex particles. The contrast in the refractive index between the silica microcapsules and latex particles may lead to enhance light scattering, resulting in a whiter or brighter appearance. The silica microcapsules may also scatter and reflect light due to the hierarchical architecture of the core oil and silica nanoparticles shell, contributing to the overall whitening and / or brightening effect. The presence of silica microcapsules and latex particles dispersed in the formulation may increase the opacity of the formulation, masking the underlying surface and resulting in a more uniform and whiter appearance. The formulation may be used in various applications such as paints, coatings, cosmetic products and sunscreen products.

[0129] The present disclosure also concerns a formulation comprising the silica microcapsules as disclosed herein. The formulation may contribute to the whitening or brightening of a surface through the reflection and scattering of light by the silica microcapsules. The silica microcapsules may also scatter and reflect light due to the hierarchical architecture of the core oil and silica nanoparticles shell, contributing to the overall whitening and / or brightening effect.

[0130] The formulation may be applied onto a biological surface and / or a non-biological surface. The formulation may be used in various applications such as cosmetic products and sunscreen products and thus may be applied onto a biological surface such as skin. The formulation may also be applied onto textiles such as medical bandages for the reflection of NIR rays to reduce heat absorption.

[0131] The formulation may further comprise a moisturising agent. The moisturising agent may be an emollient, a humectant, an occlusive or a combination thereof. The moisturising agent may be glycerin, hyaluronic acid, shea butter, squalene, ceramide, petrolatum, beeswax or a combination thereof. The moisturising agent may be Emolin.

[0132] The formulation may be a cream or a lotion. Creams and lotions may be used to moisturise skin and may create a protective barrier on the skin's surface to help seal in moisture or to help reflect sunlight. Creams may be thicker with a higher moisturising agent content for more intensive moisturisation. Creams may be suitable for more dry skin. Lotions may be thinner with a higher water content compared to creams. The formulation may be applied as a layer of coating on skin to reflect visible light, ultraviolet and / or near infrared rays, or for whitening skin. The formulation may be used in various applications such as cosmetic products and sunscreen products.

[0133] In some embodiments, the formulation is characterised by a mass ratio of silica microcapsules to moisturising agent of about 1 : 1 to about 1 : 10. In other embodiments, the mass ratio is about 1 : 1 to about 1 :8, about 1 : 1 to about 1 :5, about 1 : 1 to about 1 :3, about 1 :3 to about 1 : 10, about 1 :3 to about 1 :8, about 1 :3 to about 1 : 5, about 1 : 5 to about 1 : 10, about 1 :5 to about 1 :8, or about 1 :8 to about 1 : 10. In some embodiments, the mass ratio is about 1 : 5.

[0134] Examples

[0135] Silica microcapsules have emerged as versatile tools across numerous industries due to their unique properties. These microscopic capsules, composed of silica shells, find extensive use in fields such as pharmaceuticals, cosmetics, food, and materials science. In pharmaceuticals, they serve as carriers for controlled drug delivery, ensuring precise release and absorption. Cosmetics utilize silica microcapsules for encapsulating active ingredients, enhancing stability and efficacy in skincare products. Furthermore, in the food industry, these microcapsules are employed to encapsulate flavors, nutrients, or additives, safeguarding their integrity and controlled release in food products. Their application extends to materials science, where they reinforce coatings, paints, and adhesives, imparting durability and controlled release properties. The versatility and customizable nature of silica microcapsules make them invaluable in various applications, contributing significantly to advancements in multiple industries.

[0136] Silica microcapsules are normally engineered for targeted and controlled release, as these capsules have the potential to precisely deliver actives to required surfaces. On the contrary, our current invention deals with brightening effect and property of the capsules form protective barrier against harmful UV rays. Silica microcapsules with non-renewable materials such as silicon oil and renewable core materials such as coconut oil were synthesized in controlled sizes. We successfully prepared the formulation by studying the composition of hydrophobic latex and silica microcapsules. The results showed that the coatings showed higher UV- and NIR- reflectivity as compared to TiOz-containing formulations.

[0137] Some advantages of the silica microcapsules and formulations are:

[0138] • Scalable and reproducible synthesis of silica microcapsules with sustainable core materials (coconut oil)

[0139] • A core-shell microcapsule formulation providing protection from deep UV and NIR radiations

[0140] • A method to formulate protective films using latex particles and core-shell microcapsules for high UV- and NIR- reflective white coatings

[0141] • A potential alternative to TIOz in personal care formulations to achieve different textures, finishes, or appearances

[0142] • Potential TiOz and calcium carbonate substitute for whitening or creating opacity in food and beverage applications (for capsules made of edible oils)

[0143] Experimental:

[0144] Synthesis of silica microcapsules comprising silicone oil (Si-MC): NaCI (0.56g, 12mM) and Triton X (9.12ml, 15.12mmol) were dissolved in 640ml of ethanol / water solvent mixture (26 / 74 v / v). After which, Xiameter PMX-200 (polydimethylsiloxane, 91.2mL, 14.3 vol%) was added to the mixture and stirred with ultra-turrax (4000rpm) for approximately 2 minutes to obtain a coarse pre-emulsion with size ranging from 50- 200 microns. Subsequently, the pre-emulsion was subjected to high pressure homogenization (500bar, Scycles, EmulsiFlex-05) to obtain a uniform emulsion with mono-modal particle size distribution. The particle size was monitored by light microscopy. The mixture was then transferred to a IL reactor fitted with overhead stirrer and stirred at 600rpm under ambient conditions for 5 minutes. After that, TEOS (55.2ml, 8.62 vol%) was added via syringe pump over a period of 30mins. The reaction mixture was stirred for another 4 days under ambient conditions. Particle size distribution as determined by laser diffraction revealed the mean particle size of 7 ,um (Figure 1) and imaging by scanning electron microscopy confirmed the spherical morphology. The amount of silicone oil encapsuled in the capsules was found to be ~85% by TGA analysis (Figure 2). Synthesis of silica microcapsules comprising coconut oil (Co-MC-1): NaCI (0.14g) and Triton-X (10ml) were dissolved in EtOH / DI water (26 / 74 v / v %), equivalent to 36.4ml of EtOH and 103.6ml DI water. Coconut oil (22.8ml) was added to the mixture and stirred using ultra-turrax at 6500rpm for 2min to obtain a coarse pre-emulsion. The resulting mixture was then subjected to high pressure homogenization for 5 cycles at a pressure level of 1000 bar. Subsequently, TEOS (11.7ml) was added dropwise at a rate of 0.5ml / min. The reaction was then left to stir at 600rpm for 4 days at room temperature. Particle size distribution as determined by laser diffraction revealed the mean particle size of 20 pm (Figure 3). The amount of coconut oil encapsuled in the capsules was found to be ~85% by TGA analysis (Figure 4).

[0145] Synthesis of silica microcapsules comprising coconut oil (Co-MC-2): A similar procedure to that of Si-MC was followed for the synthesis of Co-MC-2, except that coconut oil was used instead of silicone oil. Particle size distribution as determined by laser diffraction revealed the mean particle size of 27 pm (Figure 5). Amount of coconut oil encapsuled in the capsules was found to be ~88% by TGA analysis (Figure 6).

[0146] Representative example on synthesis of silicone emulsion

[0147] Dodecylbenzene sulfonic acid (0.17 g) was dissolved in DI water (24 g) at room temperature under stirring. Octamethylcylcotetrasiloxane (5 g), methyltrimethoxysilane (0.52 g), and vinyltrimethoxysilane (0.35 g) were added into the reaction mixture under stirring to form stable emulsion. The reaction mixture was stirred at 70 °C for 24 h. After cooling to room temperature, the silicone emulsion was used without further purification. ic latex, P-125

[0148] Silicone emulsion (30 g) and DI water (80 g) were degassed in a reactor with argon for 30 minutes. A solution of ammonium persulfate (APS) (0.2 g) in DI water (5 g) was added into the reactor and the reaction mixture was heated to 70 °C. A mixture of butyl acrylate (10 g) and methyl methacrylate (10 g) was added slowly via syringe (5 mL / hr) to the reaction mixture under argon flow. The reaction mixture was stirred at 70 °C for 6h. After cooling to room temperature, the pH of the latex was adjusted to pH 7 - 8 by adding ammonia. The latex was concentrated to reach solid content of 20 wt%.

[0149] Formulation of coating containing silica microcapsules P-125 (0.5 g) was added into a beaker followed by addition of Si-MC (1 g) or Co-MC-2 (1 g). The mixture was stirred for 5 minutes at room temperature under air. The formulation was coated on BYK black and white chart by using a bar applicator with a wet thickness 200 pm. The coating was left to dry at room temperature for 6 h prior to reflectivity measurement.

[0150] Formulation of sunscreen containing silica microcapsules

[0151] Emolin (5 g) was added into a beaker followed by addition of Si-MC (1 g) or Co-MC-2 (1 g). The mixture was stirred for 30 minutes at room temperature at 60 °C follow by cooling down. The formulation was submitted for sunscreen protection factor (SPF) measurement.

[0152] Results and Discussion

[0153] In efforts to incorporate these microcapsules into coatings, commercial binder or latex were added into the microcapsule formulation. However, it was found that the commercial binder has a problem in miscibility with our hydrophobic silica microcapsules. The commercial binder is hydrophilic (water-like) and silica microcapsule is hydrophobic (oil-like), that resulted in the immiscibility between two phases. Therefore, we synthesized hydrophobic latex by incorporating silicone emulsion onto PMMA. Various compositions of hydrophobic latex were studied (Table 1). The latex was formed through emulsion polymerisation using APS as the initiator.

[0154] Table 1. Compositions of hydrophobic latex based on silicone emulsion. Next, we studied the miscibility of our synthesized hydrophobic latex with silica microcapsules in coating formulation (Table 2). It was found that the hydrophobic latex P-125 showed good miscibility with silica microcapsules and gave good film formation as shown in Figure 7. Silica microcapsules with silicone oil or coconut oil mixed well with

[0155] P-125 and give white coatings (Figure 7b and 7c). On the other hand, silica microcapsule Co-MC-1 showed poor film formation due to phase separation of microcapsules from latex. Due to the formulation of Co-MC-1, which has smaller surfactant (Triton-X)-to- silica ratio as compared to Co-MC-2, the smaller amount of surfactant may have resulted in phase separation between Co-MC-1 and hydrophobic latex.

[0156] Table 2. Formulation of UV- and NIR-reflective coatings by using hydrophilic / hydrophobic latex and silica microcapsules. The solid contents for hydrophobic latex and silica microcapsules are 20 wt% and 30 wt%, respectively.

[0157] Table 3. Formulation of UV-reflective coatings.

[0158] Following this, the light reflectivity of these microcapsule coatings was studied by using a UV-vis-NIR spectrophotometer (250 nm - 2500 nm) and compared with TiOz-based coatings. It was found that TiCh-based coatings showed higher visible light reflectivity (400 - 720 nm) and render them a whiter coating as compared to our silica microcapsule coatings. Interestingly, our silica microcapsule showed higher UV- (250 nm to 399 nm) and NIR-reflectivity (721 - 2500 nm) as compared to TiOz-based coatings (Figure 8 and Figure 9). On the other hand, the microcapsule (Co-MC-1) showed lower reflectivity in all wavelengths as compared to Co-MC-2. Coatings with higher solid contents from 15 wt% to 20 wt% showed increase in reflectivity in all wavelengths.

[0159] In addition to coating applications, we also explored the potential use of silica microcapsules in sunscreen applications. Sunscreens typically comprise a variety of ingredients that serve as UV filters to provide the desired level of sun protection. The effectiveness of a sunscreen is measured by its sun protection factor (SPF) which indicates the amount of solar energy required to cause sunburn on protected skin to unprotected skin. In other words, it measures how well a sunscreen protects the skin from UV radiation-the higher the SPF, the greater the level of protection it offers.

[0160] We incorporated the silica microcapsules into sunscreen formulations and evaluated their impact on sun protection performance. The resulting formulations were assessed for their SPF values, and the data (Table 4 and Figure 10) clearly demonstrated that the inclusion of silica microcapsules led to a notable enhancement in SPF compared to control formulations without the microcapsules. This improvement suggests that the silica microcapsules not only contribute to UV protection but also hold promise as a potential alternative to TiOz. Given growing concerns over the environmental and health impacts of traditional inorganic UV filters like TiCh, the use of silica microcapsules could offer a more sustainable and safer approach to sunscreen formulation.

[0161] Table 4. SPF values of our sunscreen formulations incorporated with silica microcapsules.

[0162] The silica microcapsules and formulations may be used in UV-reflective sunscreen, giving a wider protection range, in NIR-reflective coatings to reflect heat, as an opacifying agent in food technology and tableting technology. They may also be used for skin lightening in skincare products to reduce the appearance of dark spots, hyperpigmentation, and uneven skin tones.

[0163] Without being bound by theory, it is hypothesised that having an oil with lower refractive index than the silica nanoparticle in the silica microcapsule may result in higher reflectivity in coatings. The improved UV / NIR reflectivity of silica microcapsule may be explained by Mie Scattering theory - where the light used to irradiate repeating structures (silica nanoparticle with hierarchical architecture) of high and low refractive index materials undergoes enhanced reflection. The microcapsule shell is made of silica nanoparticles of 300-500 nm (Figure 13). This hierarchical architecture with higher refractive index silica nanoparticles (1.475) and lower refractive index of oils (coconut oil (1.45) and silicone oil (1.405)) in the coating may lead to high reflectivity. Importantly, the shell thickness within 200-400 nm may lead to high reflectivity. The microcapsules are microporous and the encapsuled oils (silicone and coconut oil) are expected to gradually leak out over time. The leaching of oils from the silica shell depends on the shell thickness and hence may influence their reflective property.

[0164] Conclusion In conclusion, the silica microcapsules encapsulated with silicone oil and coconut oils were successfully synthesized and their solid contents, particle sizes, and amount of encapsulation were fully characterized. The silicone-based hydrophobic latexes were also synthesized by emulsion polymerization to better incorporate our hydrophobic silica microcapsules in the solution. The formulation test was studied to achieve a good film formation by using P-125 as binder for both Si-MC (silicone oil) and Co-MC-2 (coconut oil) silica microcapsules. These films showed higher UV- and NIR- light reflectivity when compared to TiOz-containing film at 15 wt% solid content. The results showed the potential for the replacement of TiOz pigment with more sustainable silica microcapsules encapsulated with coconut oil in the UV- and NIR- reflective coatings or paints. In addition, our latest results suggest potential applications of the capsules in skincare, in particular, for the development of TiOz-free sunscreen products. Employing microcapsule compositions for whitening, opacification, and radiation protection will be valuable for addressing issues across various sectors, including personal care and food technology (for example packaging).

[0165] It will be appreciated that many further modifications and permutations of various aspects of the described embodiments are possible. Accordingly, the described aspects are intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.

[0166] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0167] Throughout this specification and the claims which follow, unless the context requires otherwise, the phrase "consisting essentially of", and variations such as "consists essentially of" will be understood to indicate that the recited element(s) is / are essential i.e. necessary elements of the invention. The phrase allows for the presence of other non-recited elements which do not materially affect the characteristics of the invention but excludes additional unspecified elements which would affect the basic and novel characteristics of the method defined.

[0168] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

Claims1. A formulation, comprising latex particles and silica microcapsules; wherein each silica microcapsule comprises a shell of silica nanoparticles and an oil encapsulated within its cavity thereof wherein the oil is characterised by a refractive index which is lower than that of the shell of the silica microcapsule; wherein the silica microcapsules are characterised by an average shell thickness of about 100 nm to about 700 nm; and wherein the formulation is characterised by a mass ratio of latex particles to silica microcapsules of about 0.2 to about 2.

2. The formulation according to claim 1, wherein the shell comprises siloxane bonds between the silica nanoparticles.

3. The formulation according to claim 1 or 2, wherein the oil is characterised by a refractive index of about 1.4 to about 1.47.

4. The formulation according to any one of claims 1 to 3, wherein the oil is selected from natural oil, silicone oil, or a combination thereof.

5. The formulation according to claim 4, wherein the natural oil is an oil derived from coconut, jojoba, rice bran, olive, argan, rosehip, almond, olive, grapeseed, avocado, soybean, corn, peanut, sesame, hazelnut, walnut, palm, Lavender, Rose, Jasmine, Orange, Lemon, Bergamot, Frankincense, Geranium, Neroli or a combination thereof.

6. The formulation according to any one of claims 1 to 5, wherein the silica nanoparticles are characterised by a particle size of about 100 nm to about 500 nm.

7. The formulation according to any one of claims 1 to 6, wherein the silica microcapsules are characterised by a particle size of about 1 pm to about 100 pm.

8. The formulation according to any one of claims 1 to 7, wherein the silica microcapsule is microporous and / or mesoporous.

9. The formulation according to any one of claims 1 to 8, wherein the silicamicrocapsule is characterised by a pore size of less than about 100 nm.

10. The formulation according to any one of claims 1 to 9, wherein the silica microcapsule is characterised by a mass ratio of silica to oil in the silica microcapsule is about 5: 1 to about 8: 1.

11. The formulation according to any one of claims 1 to 10, wherein the oil is leachable from the silica microcapsule at a rate of about 20% to about 50% of oil in the silica microcapsule over about 12 hours.

12. The formulation according to any one of claims 1 to 11, wherein the silica microcapsules are of about 10 wt% to about 25 wt% relative to the formulation.

13. The formulation according to any one of claims 1 to 12, wherein the latex particles are selected from silicone particles, PDMS particles, PMMA particles, PBA particles, polyacrylate particles, PS particles, and a composite particles or combination thereof.

14. The formulation according to any one of claims 1 to 13, wherein the latex particles are characterised by a size of about 50 nm to about 500 nm.

15. The formulation according to any one of claims 1 to 14, wherein the latex particles are of about 5 wt% to about 30 wt% relative to the formulation.

16. The formulation according to any one of claims 1 to 15, wherein the formulation is characterised by a mass ratio of latex particles to silica microcapsules of about 0.34 to about 0.84.

17. The formulation according to any one of claims 1 to 16, wherein the formulation further comprises at least one additive.

18. The formulation according to claim 17, wherein the at least one additive is selected from a dispersing additive and an anti-sagging and anti-settling additive.

19. A method of forming a formulation according to any one of claims 1 to 18, the method comprising:a) homogenising an oil in an aqueous medium with a non-ionic surfactant to form an oil-in-water (O / W) emulsion, the aqueous medium comprising an alcohol; b) mixing the emulsion with a silica precursor to form silica nanocapsules, the silica nanocapsules forming a shell encapsulating the oil to form silica microcapsules; and c) mixing the silica microcapsules with latex particles to form the formulation.

20. The method according to claim 19, wherein the alcohol is selected from methanol, ethanol, isopropanol, butanol, and a combination thereof.

21. The method according to claim 19 or 20, wherein the aqueous medium is characterised by a mole ratio of alcohol to water of about 1:5 to about 1 : 15.

22. The method according to any one of claims 19 to 21, wherein the non-ionic surfactant is selected from polyethylene glycol alkyl ethers, polyethylene glycol alkyl phenyl ethers, sorbitan esters, polyoxyethylene sorbitan esters, decyl glucoside, lauryl glucoside, coco glucoside, PEG-7 glyceryl cocoate, PEG-40 hydrogenated castor oil, ceteareth-20, PEG-100 stearate, poloxamer 188, and a combination thereof.

23. The method according to any one of claims 19 to 22, wherein the method is characterised by a mole ratio of non-ionic surfactant to oil of about 1 :3 to about 3: 1.

24. The method according to any one of claims 19 to 23, wherein step a) further comprises mixing a salt in the aqueous medium.

25. The method according to claim 24, wherein the salt is selected from be NaCI, KCI, NH4CI, or a combination thereof.

26. The method according to any one of claims 19 to 25, wherein the silica precursor is selected from tetraethyl orthosilicate (TEOS), tetramethyl orthosilicate (TMOS), tetrapropyl orthosilicate (TPOS), or a combination thereof.

27. The method according to any one of claims 19 to 26, wherein the method is characterised by a mole ratio of silica precursor to oil of about 1 : 1 to about 30: 1.

28. The method according to any one of claims 19 to 27, wherein step a) is performed at a pressure of about 300 bar to about 1500 bar for about 1 cycle to about10 cycles.

29. The method according to any one of claims 19 to 28, wherein step b) is performed at a mixing rate of about 200 rpm to about 1000 rpm for a duration of about 1 day to about 8 days.

30. A silica microcapsule comprising a shell of silica nanoparticles and an oil encapsulated within its cavity thereof; wherein the oil is characterised by a refractive index which is lower than that of the shell of the silica microcapsule; and wherein the silica microcapsules are characterised by an average shell thickness of about 100 nm to about 700 nm.

31. A method of forming a silica microcapsule according to claim 30, the method comprising : a) homogenising an oil in an aqueous medium with a non-ionic surfactant to form an oil-in-water (O / W) emulsion, the aqueous medium comprising an alcohol; and b) mixing the emulsion with a silica precursor to form silica nanocapsules, the silica nanocapsules forming a shell encapsulating the oil to form silica microcapsules.

32. A method of reflecting visible light, ultraviolet and / or near infrared rays, or whitening a surface, comprising contacting the formulation according to any one of claims 1 to 18 on the surface.

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