Properties of Fumed Silica and Its Application in Cosmetics

1. Preface

Fumed silica (commonly known as fumed silica) is an artificially synthesized amorphous white free-flowing powder, featuring non-toxicity, odorlessness, and non-pollution. It has a primary particle size of 7-80 nm and a specific surface area usually greater than 100 m²/g. Relying on nanoscale effects, it possesses excellent properties such as reinforcement, thickening, thixotropy, insulation, matting, and anti-sagging, and is widely used in rubber, plastics, coatings, cosmetics, sealants, and other fields. This article focuses on its properties and applications in cosmetics.

2. Properties of Fumed Silica

2.1 Basic Characteristics

It is produced by high-temperature hydrolysis of halosilanes in an oxyhydrogen flame, with small particle size, uniform particle size distribution, large specific surface area, and high surface activity.

2.2 Classification and Surface Characteristics

1. Hydrophilic fumed silica: The surface silanol group (SiOH) density is approximately 2 OH/nm², which can be wetted by water and uniformly dispersed in water.
2. Hydrophobic fumed silica: Part of the surface SiOH groups are replaced by SiO(CH₃)₃, reducing the silanol group density to approximately 10 H/nm², making it unable to disperse in water.

2.3 Core Mechanism of Action

Both types of fumed silica have silanol groups (active centers) on their surfaces. When added to a liquid system, the silanol groups of adjacent particles form hydrogen bonds and develop into a three-dimensional network structure, which restricts the movement of liquid particles, improves liquid viscosity and stability. When shear force is applied, the hydrogen bond network is destroyed, and the system viscosity decreases. Therefore, fumed silica can thicken, stabilize, and improve thixotropic properties and skin feel.

2. Properties of Fumed Silica and Its Application in Cosmetics

1. Preface

Fumed silica (commonly known as fumed silica) is an artificially synthesized amorphous white free-flowing powder, featuring non-toxicity, odorlessness, and non-pollution. It has a primary particle size of 7-80 nm and a specific surface area usually greater than 100 m²/g. Relying on nanoscale effects, it possesses excellent properties such as reinforcement, thickening, thixotropy, insulation, matting, and anti-sagging, and is widely used in rubber, plastics, coatings, cosmetics, sealants, and other fields. This article focuses on its properties and applications in cosmetics.

2. Properties of Fumed Silica

2.1 Basic Characteristics

It is produced by high-temperature hydrolysis of halosilanes in an oxyhydrogen flame, with small particle size, uniform particle size distribution, large specific surface area, and high surface activity.

2.2 Classification and Surface Characteristics

1. Hydrophilic fumed silica: The surface silanol group (SiOH) density is approximately 2 OH/nm², which can be wetted by water and uniformly dispersed in water.
2. Hydrophobic fumed silica: Part of the surface SiOH groups are replaced by SiO(CH₃)₃, reducing the silanol group density to approximately 10 H/nm², making it unable to disperse in water.

2.3 Core Mechanism of Action

Both types of fumed silica have silanol groups (active centers) on their surfaces. When added to a liquid system, the silanol groups of adjacent particles form hydrogen bonds and develop into a three-dimensional network structure, which restricts the movement of liquid particles, improves liquid viscosity and stability. When shear force is applied, the hydrogen bond network is destroyed, and the system viscosity decreases. Therefore, fumed silica can thicken, stabilize, and improve thixotropic properties and skin feel.

3. Applications in Cosmetics (Personal Care Products)

3.1 Skincare Products

• Ointments, gels, and creams: Adding hydrophilic fumed silica can significantly thicken the products, improve their stability and thixotropy, and ensure smooth application without astringency.
• W/O emulsion products: Using hydrophobic fumed silica can increase product viscosity, reduce greasiness, and enhance freshness.
• Transparent gels: It can increase viscosity and improve the pseudoplasticity of products.
• Water-in-oil (W/O) emulsions: Hydrophobic fumed silica is suitable for increasing the viscosity of W/O emulsions, enhancing the water resistance of creams and emulsions, and reducing the dosage of surfactants.

3.2 Sunscreen Products

• Solving Industry Pain Points: Physical sunscreens (e.g., titanium dioxide, zinc oxide) are prone to agglomeration and sedimentation, resulting in poor skin feel and difficulty in uniform spreading. Chemical sunscreens (e.g., octyl methoxycinnamate) are prone to photodegradation, requiring increased dosage, which in turn increases skin irritation and allergy risks.
• Specific Functions: Adding a small amount of fumed silica can form a protective layer on the surface of physical sunscreen particles, fill surface irregularities, reduce particle attraction, and lower the possibility of agglomeration, making the system more uniform and stable. At the same time, it endows the system with thixotropic properties, helping the product spread uniformly on the skin surface, improving skin feel and hand feel. It can also enhance the water resistance of the formula and make the distribution of physical and chemical UV filters more uniform, increasing the sun protection factor (SPF).

3.3 Color Cosmetics

3.4 Hair Care Products

• Hair bleaching agents: Prevents bleaching powder from absorbing moisture and caking; used as a thickener and stabilizer in bleaching creams, with a recommended addition amount of 2.0%-4.0%.
• Hair dyes: Prevents premature reaction and caking of powdered color-matching components; hydrophilic fumed silica with a concentration higher than 4.0% is a high-efficiency desiccant, and hydrophobic fumed silica is a high-efficiency flow regulator (specific amount not specified).
• Hair conditioners: Hydrophilic fumed silica compounded with quaternary ammonium compounds can improve hair combability and fullness, with a usual addition amount of 1.0%-2.0%.
• Hair sprays: Hydrophilic fumed silica helps improve hair fullness (specific amount not specified).

3.5 Antiperspirant Products

It can increase the adsorption, viscosity, suspension stability, and overall stability of products (specific addition amount not specified).

4. Characteristics of Fumed Silica Series Products

1. It can thicken and improve the thixotropic properties of liquids.
2. It can enhance suspension and redispersibility in liquid phases.
3. In powdered products such as pressed powders, it can improve fluidity and storage stability, and play an anti-caking role.
4. Due to its high specific surface area, it can also be used as an adsorbent and carrier to adsorb gases, liquids, and solids.

5. Major Domestic and Foreign Manufacturers and Models of Fumed Silica

5.1 Foreign Brands

5.2 Domestic Brands