WO2021087207A1 - Synthesis of hollow silica particles and use in sun care compositions - Google Patents

Abstract

Described herein are hollow silica particles, processes for making hollow silica particles, and uses of hollow silica particles in sun care compositions. To form the hollow silica particles, swellable latex seeds are used to template the deposition of continuous silica shell, and voids are created by collapsing the swollen latex upon drying. Preferably, the process for making hollow silica particles comprises forming latex seeds for use as a template, depositing silica shells on the latex seeds, and collapsing the latex seeds to afford hollow silica particles.

Description

SYNTHESIS OF HOLLOW SILICA PARTICLES AND USE IN SUN CARE COMPOSITIONS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of Provisional U.S. Patent Application No. 62/928,184, filed October 30, 2019, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] Hollow silica particles refers to nano-sized spherical silicon oxide particles comprising a shell defining a hollow interior portion. Sometimes, a plurality of pores (e.g., channels) pass through the shell, extending from the hollow portion to the exterior surface of the shell. Hollow silica particles are useful in a number of applications, including waste treatment and drug delivery.

[0003] Hollow silica particles can prepared by growing silicon oxide crystals (e.g., using silicate precursors, such as, for example, alkoxy silanes, alkyl silicates, etc.) in the presence of one or more surfactants (e.g., ionic, nonionic, polymeric, organic, etc.) and, optionally, a spherical template compound, and subsequently removing the surfactant (e.g., and if present, the spherical template compound), for example, with acid (e.g., hydrochloric acid) or base, to afford the hollow silica particles. Spherical template compounds provide size and shape control, however, removal steps, including calcination, requires additional processing and can be disadvantageous.

[0004] Accordingly, what is needed are new processes for forming hollow silica particles, and new uses for the same.

SUMMARY

[0005] Described herein are hollow silica particles, processes for making hollow silica particles, and uses of hollow silica particles in sun care compositions. To form the hollow silica particles, swellable latex seeds are used to template the deposition of continuous silica shell, and voids are created by collapsing the swollen latex upon drying. Preferably, the process for making hollow silica particles comprises forming latex seeds for use as a template, depositing silica shells on the latex seeds, and collapsing the latex seeds to afford hollow silica particles.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a pair of Transmission Electron Microscope (TEM) images of a first hollow silica particle agglomerate and a substantially similar second hollow silica particle agglomerate. [0007] FIG. 2 is a TEM image of non-agglomerated hollow silica particles.

[0008] FIG. 3 is a diagram of sun protection factor (SPF) measurements for heat aged comparative sun care formulations (e.g., no SPF booster or a conventional SPF booster) and a sun care formulation that includes a first set of hollow silica particles (e.g., as an SPF booster).

[0009] FIG. 4 is a diagram of sun protection factor (SPF) measurements for heat aged comparative sun care formulations (e.g., no SPF booster or a conventional SPF booster) and a sun care formulation that includes a second set of hollow silica particles (e.g., as an SPF booster).

[0010] FIG. 5 is a pair of Scanning Electron Microscope (SEM) images of a heat aged sun care formulation that includes the first set of hollow silica particles.

DETAILED DESCRIPTION

[0011] Described herein are hollow silica particles, processes for making hollow silica particles, and uses of hollow silica particles in sun care compositions. Preferably, the hollow silica particles are generally spherical, having an outer diameter (e.g., particle size) defining a hollow inner cavity. The hollow silica particle wall is interchangeably described herein as a shell. Accordingly, the particle size minus two shell thicknesses (e.g., to account for each wall) approximates the hollow cavity diameter.

[0012] To form the hollow silica particles, swellable latex seeds are used to template the deposition of continuous silica shell, and voids are created by collapsing the swollen latex upon drying. This method has the advantage of size and shape control in common with other templating methods, but does not require an additional template removal step, such as, for example, calcination, to afford hollow silica particles.

[0013] Preferably, the process for making hollow silica particles comprises forming latex seeds for use as a template, depositing silica shells on the latex seeds, and collapsing the latex seeds to afford hollow silica particles.

[0014] Preferably, the latex seeds are a swellable latex particle. Preferably, the swellable latex particle is a core shell polymer. Preferably, the latex seeds comprise polymerized styrene, methyl methacrylate, and methacrylic acid monomers. Preferably the latex seeds comprise at least one of 3-(tri meth oxy si ly I) propyl methacrylate and/or 3-(triethoxysilyl) propyl methacrylate (e.g., to create a better linkage between the latex template and silica shell). The latex seeds may include 1 part tie coat (TC) to about 4 parts TC. The TC may improve the compatibility of the initial seed latex chemistry with the chemistry of the silica materials that will become the shell of the particles. The TC may (e.g., may also) help maintain particle integrity (e.g., during swelling). The TC may (e.g., may also) help maintain particle integrity (e.g., in bases). The latex seeds may be greater than about 10 % solids, greater than about 12 % solids, greater than about 15 % solids, and less than about 25 % solids, less than about 17 % solids, and less than or equal to about 12.5 % solids.

[0015] The latex seeds may be spherical, with a particle size greater than about 170 nm, greater than about 195 nm, greater than about 230 nm, and less than about 400 nm, less than about 350 nm, less than about 300 nm, and less than about 250 nm. Transmission Electron Microscope (TEM) images may be used to determine particle size measuring manually using a scale bar.

[0016] The silica shells may be deposited on the latex seeds. Preferably, alkyl silicates are used. More preferably, tetraethyl orthosilicate is used to form the silica shells.

[0017] The latex seeds with silica shells may be collapsed by drying. Preferably, the latex seeds with silica shells are freeze dried, affording the hollow silica particles. Preferably, the hollow silica particles may be de-agglomerated, such as by ultrasonication.

[0018] Transmission Electron Microscopy may be used to observe the presence of a hollow void (e.g., cavity) and to determine particle size, shell thickness, and cavity diameter, measuring manually using a scale bar.

[0019] Preferably, the hollow silica particles have a particle size (e.g., an outer diameter) of about 100 nm to about 600 nm, more preferably, about 200 nm to about 400 nm. The particle size of the hollow silica particles may be greater than about 130 nm, greater than about 190 nm, greater than about 205 nm, greater than about 240 nm, and less than about 550 nm, less than about 400 nm, less than about 370 nm, less than about 340 nm, and less than about 260 nm. More preferably, the particle size of the hollow silica particles may be about 310 nm to about 370 nm, most preferably around 338 nm.

[0020] Preferably, the hollow silica particles have a shell thickness of about 35 nm to about 70 nm. The shell thickness may be greater than about 30 nm, greater than about 35 nm, greater than about 40 nm, and less than about 80 nm, less than about 70 nm, and less than about 67 nm. More preferably, the shell thickness of the hollow silica particles may be about 56 nm to about 76 nm, most preferably around 66 nm. [0021] Preferably, the hollow silica particles have a hollow cavity of about 150 nm to about 250 nm. The hollow cavity may be greater than about 150 nm, greater than about 155 nm, greater than about 160 nm, and less than about 250 nm, less than about 220 nm, and less than about 200 nm. More preferably, the hollow cavity of the hollow silica particles may be about 160 nm to about 220 nm, most preferably around 190 nm.

[0022] Hollow silica particles described herein may be used in sun care compositions. A sun care composition is a personal care composition for protecting a user from UV radiation. Examples of sun care compositions include compositions having an SPF rating (for example, sunscreen compositions) and/or personal care compositions where a UV blocker would be beneficial, such as, for example, moisturizers, lip balms, etc.

[0023] Presently described sun care compositions comprise hollow silica particles and at least one sunscreen active (one or more (e.g., mixtures) sunscreen actives). Sunscreen actives is intended to include physical UV blockers (e.g., titanium dioxide, zinc oxide) and chemical UV absorbers (e.g., para- aminobenzoic acid, octyl methoxycinnamate). Examples of suitable sunscreen actives include titanium dioxide, zinc oxide, para-aminobenzoic acid, octyl methoxycinnamate, ethylhexyl methoxycinnamate, ethylhexyl salicylate, Octocrylene (2-ethylhexyl-2-cyano-3,3 diphenylacrylate), butyl methoxydibenzoylmethane, Avobenzone (4-t-butyl-4'-methoxydibenzoyl-methane), oxybenzone, dioxybenzone, cinoxate (2-ethoxyethyl-p-methoxy-cinnamate), diethanolamine-p-methoxycinnamate, ethylhexyl-p-methoxy-cinnamate, isopentenyl-4-methoxycinnamate, 2-ethylhexyl salicylate, digalloyl trioleate ethyl 4-bis(hydroxypropyl)aminobenzoate, glyceryl aminobenzoate, methyl anthranilate, homosalate (3, 3, 5-tri methy lcyclohexy I salicylate), triethanolamine salicylate, 2-phenyl-benzimidazole-5- sulfonic acid, sulisobenzone (2-hydroxy-4-methoxy-benzophenone-5-sulfonic acid), Padimate A (amyl p- dimethylaminobenzoate), Padimate 0 (octyl dimethyl para aminobenzoate), 4-Methylbenzylidene camphor, sunscreen actives sold under the tradenames ECAMSULE™, TINOSORB™, NEO HELIOPAN™, MEXORYL™, BENZOPHENONE™, UVINUL™, UVASORB™, and/or PARSOL™, and/or mixtures thereof. Preferably, the sunscreen active is a mixture of avobenzone, octocrylene, and homosalate. More preferably, the sunscreen active is a mixture of avobenzone, octocrylene, homosalate, and octisalate. [0024] Preferably, the present sun care compositions contain greater than about 5 parts by weight (pbw) of the composition, greater than about 7 pbw, greater than or equal to about 10 pbw, and less than about 15 pbw, less than about 13 pbw, and less than or equal to about 11 pbw, total sunscreen active(s).

[0025] Preferably, the present sun care compositions contain greater than about 2 pbw of the composition, greater than about 2.5 pbw, greater than or equal to about 3 pbw, and less than about 5 pbw, less than about 4 pbw, and less than or equal to about 3.5 pbw, hollow silica particles. More preferably, the present sun care compositions contain about 3% hollow silica particles by weight of the composition.

[0026] Preferably, the present sun care compositions may comprise at least one of a cosmetically acceptable emollient, humectant, pigment, optical modifier, vitamin, moisturizer, conditioner, oil, silicone, suspending agent, opacifier/pearlizer, surfactant, emulsifier, preservative, rheology modifier, colorant, pH adjustor, propellant, reducing agent, anti-oxidant, fragrance, foaming or de-foaming agent, tanning agent, insect repellant, and/or biocide. Preferably, the present sun care compositions may comprise at least one of a cosmetically acceptable emollient, humectant, vitamin, moisturizer, conditioner, oil, silicone, suspending agent, surfactant, emulsifier, preservative, rheology modifier, pH adjustor, reducing agent, antioxidant, and/or foaming or de-foaming agent. Preferably, a sun care composition may contain at least one of a humectant, a surfactant, and/or an emollient.

[0027] Hollow silica particles described herein may be used in sun care compositions as SPF boosters. Too high a concentration of sunscreen active results in impairment of the composition’s aesthetics (such as tackiness, greasiness, grittiness, whiteness, etc.) and/or undesirable toxicological effects. Consequently, SPF boosters (e.g., compounds which are not recognized sunscreen actives, but work to increase the SPF) are added to sun care compositions to increase the SPF without adding more sunscreen actives.

Preferably, the presently described hollow silica particles act as an SPF booster for sun care compositions. Preferably, the SPF of the sun care composition is more than 40% higher than a comparative composition without the hollow silica particles.

[0028] In use, sun care compositions including the presently described hollow silica particles may be used to protect a mammal from damage caused by UV radiation (e.g., UVA radiation and/or DVB radiation). For example, a method of protecting a mammal (e.g., the skin of a mammal) from damage caused by UV radiation comprises applying sun care compositions including the presently described hollow silica particles to the skin of the mammal.

[0029] The following examples are for illustrative purposes only and are not intended to limit the scope of the appended claims.

EXAMPLES

Example 1

[0030] An acrylic emulsion core (Acrylic Emulsion 1) was prepared as follows. A 5-liter, four necked round bottom flask was equipped with a paddle stirrer, thermometer, nitrogen inlet, and reflux condenser. 1700 g deionized water and 6.50 grams (g) of DISPONIL™ FES-993 was added to the kettle and heated to 85°C under a nitrogen atmosphere. A monomer emulsion was prepared by mixing 770 g of deionized water, 5.20 g of DISPONIL™ FES-993, 10.0 g of methacrylic acid, and 858.0 g of methyl methacrylate. From this monomer emulsion, 164.0 g were removed and set aside. To the remaining monomer emulsion was added 54.60 g of DISPONIL™ FES-993 and 432.0 g of methacrylic acid. With the kettle water at 85°C, the monomer emulsion removed from the initial monomer emulsion was added to the kettle, followed by the addition of a mixture of 5.50 g of sodium persulfate in 40.0 g of deionized water. The contents of the kettle were stirred for 15 minutes. The remaining monomer emulsion was then fed to the kettle over a two hour period at 85°C. After the completion of the monomer feed the dispersion was held at 85°C for 15 minutes, cooled to 25°C and filtered to remove any coagulum. The filtered dispersion had a pH of 2.8, 32.0% solids content and an average particle size of 135 nm.

[0031] A second acrylic emulsion core (Acrylic Emulsion 2) was prepared as follows: A 5-liter, four necked round bottom flask was equipped with a paddle stirrer, thermometer, nitrogen inlet, and reflux condenser. 1700 g deionized water and 3.25 g of DISPONIL™ FES-993 was added to the kettle and heated to 85°C under a nitrogen atmosphere. A monomer emulsion was prepared by mixing 780 g of deionized water, 5.0 g of DISPONIL™ FES-993, 10.0 g of methacrylic acid, and 780.0 g of methyl methacrylate. From this monomer emulsion, 165.0 g were removed and set aside. To the remaining monomer emulsion was added 29.75 g of DISPONIL™ FES-993 and 510.0 g of methacrylic acid. With the kettle water at 85°C, the monomer emulsion removed from the initial monomer emulsion was added to the kettle, followed by the addition of a mixture of 5.50 g of sodium persulfate in 40.0 g of deionized water. The contents of the kettle were stirred for 15 minutes. The remaining monomer emulsion was then fed to the kettle over a two hour period at 85°C. After the completion of the monomer feed the dispersion was held at 85°C for 15 minutes, cooled to 25°C and filtered to remove any coagulum. The filtered dispersion had a pH of 2.4, 31.9% solids content and an average particle size of 184 nm.

Example 2

[0032] Swellable latex seeds were prepared as follows.

[0033] Latex Seeds 1, 3, and 4 (TABLE 1) were prepared using Acrylic Emulsion 1 from Example 1 as follows. For example, for Latex Seed 1 , 893 g of deionized water with 0.34 g of acetic acid followed by a 2 g deionized water rinse was charged to a 4L round bottom flask (kettle). The kettle was heated to 89 °C with a N2 sweep. When the temperature was reached, 4.14 g of sodium persulfate in 30 g deionized water was shot-added to the kettle. 267.19 g of Acrylic Emulsion 1 with a 30 g deionized water rinse was added to the kettle. The temperature controller setpoint was adjusted to 78° C.

[0034] A monomer emulsion, comprising 85 g deionized water, 6.77 g POLYSTEP™ A-16-22 anionic surfactant, 85.5 g styrene, 66.68 g methyl methacrylate, and 10.26 g glacial methacrylic acid was fed to the kettle at a feed rate of 4.4 g/min. Thirty minutes after start of the monomer emulsion feed, 8.55 g of 3- (trimethoxysilyl) propyl methacrylate was shot-added to the monomer emulsion with mixing (for example, to create a better linkage between the latex template and silica shell). This affords core shell swellable latex particles. When the monomer emulsion feed was complete, a 40 g deionized water rinse was added. [0035] The latex was then held at 78 °C for 30 minutes before cooling to room temperature. The resulting latex seed (Latex Seed 1) had a particle size of 196 nm, 16.6% solids, pH of 2.7, and 2 parts tie coat.

[0036] Latex Seeds 2, 5, and 6 (TABLE 1), having a larger particle size, were prepared by a method similar to that described above, but replacing the Acrylic Emulsion 1 with Acrylic Emulsion 2 from Example 1, an acrylic emulsion which has approximately half as much surfactant/emulsifier (DISPONIL™ FES-993 emulsifier, commercially available from BASF).

[0037] Varying the levels of a tie-coat material polymerized on an initial seed latex will affect particle size.

[0038] Latex seeds of varying characteristics are shown in TABLE 1.

Example 3

[0039] Latex Seed 1 from Example 2 was diluted to a solid content of 0.4 wt% using deionized water before use. 600 g dilute latex solution was charged to a 1 -liter beaker equipped with an overhead stirrer and a pH probe. The solution pH was raised to 10 by adding NaOH solution (1.5 M) dropwise. 5.3 mL cetyltrimethylammonia chloride (CTAC) solution (25 wt.%) was added and the solution was stirred for 30 min. The solution pH was raised back to 10 by adding NaOH solution (1.5 M). Addition of 37.2 mL tetraethyl orthosilicate (TEOS) into the stirring solution was performed using a syringe pump at a fixed speed of 210 μL/min. The solution pH was maintained around 10 by adding NaOH solution (1.5 M) using a separate syringe pump.

[0040] After addition of the TEOS was complete, the solution was transferred into a closed container to stir overnight. The next day, the solution was centrifuged to concentrate the product, which was later washed with water three times. The product was further freeze-dried to obtain powder comprising hollow silica particles (Batch 1).

[0041] Hollow silica particles (Batch 2) were prepared substantially according to the process for making Batch 1, but resulting in a slightly thicker shell. The difference in shell thickness is within the standard deviation for the samples (see TABLE 2).

[0042] Latex Seed 2 from Example 2 was diluted to a solid content of 0.4 wt% using deionized water before use. 1000 g dilute latex solution was charged to a 2-liter three-neck round bottom flask equipped with an overhead stirrer and a pH probe. The solution pH was raised to 10.9 by addition of 35 mL NH4OH solution (7.5 M).

[0043] After stirring overnight, 4 g of TERGITOL™ 15-S-40 surfactant was dissolved in the latex solution for 1 h. 10 mL CTAC solution (25 wt.%) was added and the solution was stirred for 1 h. Addition of 126 mL TEOS into the solution was performed using a syringe pump at a fixed speed 350 μL/min. Meanwhile NH4OH solution (7.5 M) was added using a separate syringe pump to maintain the solution pH between 10.2-10.4.

[0044] After addition of the TEOS was complete, the solution was transferred into a closed container to stir overnight. The next day, the solution was centrifuged to concentrate the product, which was later washed with water three times. The product was further freeze-dried to obtain powder comprising hollow silica particles (Batch 3).

[0045] To characterize the hollow silica particles, Transmission Electron Microscope (TEM) images were used to observe the presence of a hollow void (e.g., cavity) and to determine particle size, shell thickness, and cavity diameter, measuring manually using a scale bar. TEM experiments were performed using a FEI Titan probe-corrected field emission gun (FEG) transmission electron microscope. This TEM was operated at an accelerating voltage 200 keV for imaging. All size measurements were performed manually with Imaged software. Results are shown in TABLE 2.

[0046] As synthesized, the hollow silica samples comprised of 5 μm agglomerates (see FIG. 1 , showing TEM images of Batch 1 as a hollow silica particle agglomerate and Batch 2 as a hollow silica particle agglomerate). The agglomerates may be broken down by ultrasonication. FIG. 2 shows a TEM image of Batch 3 as non-agglomerated hollow silica particles. Addition of TERGITOL™ 15-S-40 surfactant was used to achieve highly dispersed hollow silica particles for Batch 3.

Example 4 (Comparative)

[0047] To ascertain the SPF of comparative sun care compositions, sunscreen formulations Comparative Batch A and Comparative Batch B were prepared having the ingredients as listed in Table 3.

[0048] Amounts are listed as parts by weight (pbw). Water is added so that the total equals 100 pbw (e.g., there is 3.5 pbw less water in Comparative Batch B).

[0049] Phase A components were mixed together and heated to 75° C. In a separate vessel, Phase B components were mixed together and heated to 75° C. With agitation, Phase B was gradually mixed into Phase A. After complete mixing, Phase C was added to the A/B mixture and the mixture was then cooled to 40° C, while maintaining agitation. When the mixture was 40° C or lower, Phase D was added. The formulation was allowed to sit for a day prior to SPF test to verify that no visible phase separation occurred. [0050] Comparative Batch A has no SPF boosters. Comparative Batch B has SUNSPHERES™ hollow polystyrene spheres, an SPF booster.

Example 5

[0051] To ascertain the SPF of inventive sun care compositions, sunscreen formulations Batch C and Batch D were prepared having the ingredients as listed in Table 4.

[0052] Amounts are listed as parts by weight (pbw). Water is added so that the total equals 100 pbw. [0053] Agglomerates in Batch 1 were broken down to ~ 1.2 um by ultrasonication before formulation. [0054] Phase A components were mixed together and heated to 75° C. In a separate vessel, Phase B components were mixed together and heated to 75° C. With agitation, Phase B was gradually mixed into Phase A. After complete mixing, Phase C was added to the A/B mixture and the mixture was then cooled to 40° C, while maintaining agitation. When the mixture was 40° C or lower, Phase D was added. The formulation was allowed to sit for a day prior to SPF test to verify that no visible phase separation occurred.

Example 6

[0055] The respective sun care compositions from Examples 4 and 5 were each coated on a 5cm x 5cm PMMA plate using a wire round rod. The drawdown film was allowed to dry for at least 30 mins before SPF measurements are taken to allow adequate water evaporation.

[0056] In vitro SPF was determined using a UV-2000S SPF Analyzer with an integrating sphere and SPF Operating Software supplied by Labsphere (North Sutton, NH, USA). The UV-2000S measured the UV absorbance spectrum of the drawdown sunscreen film over UV radiation wavelengths (290-400 nm) and calculated an SPF value based on the UV absorbance spectrum. Multiple data points were collected (e.g., from different locations on the film designated by the UV-2000S), with repeats for each formulation. [0057] The sunscreen formulations were heat aged at 45°C for 3 months to test the formulation stability. SPF tests were conducted at different time points to monitor the stability. Results are shown in FIG. 3 (Batch C) and FIG. 4 (Batch D).

[0058] Referring to FIG. 3, Batch C (formulation containing Batch 1 hollow silica particles) showed an SPF value that was much higher than the formulation without boosters (Comparative Batch A), indicating that hollow silica particles acted as a SPF booster. Batch C’s SPF was not as high as the SPF of Comparative Batch B (with SUNSPHERES™ hollow polystyrene spheres, a commercially available SPF booster).

[0059] Referring to FIG. 4, Batch D (formulation containing Batch 3 hollow silica particles) showed an SPF value that was much higher than the formulation without boosters (Comparative Batch A), indicating that hollow silica particles acted as a SPF booster. Batch D’s SPF was also higher than the SPF of Comparative Batch B. [0060] To compare Batch C to Batch D, an SPF boost ratio was calculated using Equation 1.

The results of the SPF boost ratio calculation are shown in TABLE 5.

Accordingly, Batch D is a better SPF booster than Batch C, both initially and after 2 weeks of heat aging at 45°C.

[0061] The void integrity of the hollow silica particles was analyzed by Scanning Electron Microscope (SEM) imaging over the course of heat aging (e.g., see FIG. 5, where the majority of the air voids in Batch C (formulation containing Batch 1 hollow silica particles) were retained, indicating good thermal stability in sunscreen formulation). Batch C also showed good visual formulation stability over the course of heat aging at 45°C.

[0062] It is understood that this disclosure is not limited to the embodiments specifically disclosed and exemplified herein. Various modifications of the invention will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the appended claims. Moreover, each recited range includes all combinations and sub-combinations of ranges, as well as specific numerals contained therein.

Claims

Claims

1. A process for making hollow silica particles, comprising: forming latex seeds for use as a template; depositing silica shells on the latex seeds; and collapsing the latex seeds to afford hollow silica particles.

2. The process of claim 1 , wherein the latex seeds comprise at least one of 3-(tri methoxysi ly I) propyl methacrylate and/or 3-(triethoxysilyl) propyl methacrylate.

3. The process of claim 1, wherein tetraethyl orthosilicate is used to form the silica shells.

4. The process of claim 1, wherein the latex seeds with silica shells are freeze dried.

5. The process of claim 1, further comprising ultrasonicating the hollow silica particles.

6. Hollow silica particles made according to the process of claim 1 , wherein the hollow silica particles have a particle size of about 200 nm to about 400 nm.

7. The hollow silica particles of claim 6, wherein the hollow silica particles have a shell thickness of about 35 nm to about 70 nm.

8. A sun care composition, comprising: hollow silica particles made according to the process of claim 1; and at least one sunscreen active.

9. The sun care composition of claim 8, further comprising at least one of a cosmetically acceptable emollient, humectant, pigment, optical modifier, vitamin, moisturizer, conditioner, oil, silicone, suspending agent, surfactant, emulsifier, preservative, rheology modifier, pH adjustor, reducing agent, anti-oxidant, and/or foaming or de-foaming agent.

10. The sun care composition of claim 8, wherein a sun protection factor (SPF) of the sun care composition is more than 40% higher than a comparative composition without the hollow silica particles.