Hydrophobic vs. Hydrophilic Fumed Silica: A Complete Guide

What is Hydrophilic Fumed Silica?

Hydrophilic fumed silica refers to high-purity amorphous silica micro powder directly generated by the high-temperature hydrolysis of volatile chlorosilanes in a hydrogen-oxygen flame. It undergoes accumulation, purification, collection, compression, and packaging without any other chemical treatment. The particle surface retains a large number of silanol groups (Si–OH), which endow it with excellent hydrophilicity. This loose white powder can be wetted by water and disperses well in water.

From a chemical perspective, hydrophilic fumed silica possesses extremely high purity, large specific surface area, and very fine particle size, providing outstanding physical and chemical properties.

Characteristics of Hydrophilic Fumed Silica

• Hydrophilic, polar

  
  

• Oleophobic

  
  

• High chemical purity

  
  

• Good water dispersibility

  
  

• Excellent thermal insulation, even at high temperatures

  
  

Functions of Hydrophilic Fumed Silica

• Improve rheology, easy to process

  
  

• Reinforce silicone elastomers

  
  

• Thicken non-polar liquids

  
  

• Act as a flow aid for food and industrial powders

  
  

• Convert liquids into powder carriers (pharmaceutical, cosmetic applications)

  
  

Applicable Industries

• Coatings and Paints

  
  

• Adhesives and Sealants

  
  

• Unsaturated Polyester, Films

  
  

• Inks, Silicone Rubber

  
  

• Cosmetics, Pharmaceuticals, Elastomers

  
  

• Food Additives, Powder Handling

  
  

What is Hydrophobic Fumed Silica?

Hydrophobic fumed silica is based on hydrophilic fumed silica, which undergoes a surface chemical reaction with reactive silanes (such as trimethylchlorosilane and hexamethyldisilazane) to form a water-insoluble product covered with methyl groups on its surface, thereby exhibiting excellent hydrophobicity (water repellency).

Unlike hydrophilic type, hydrophobic fumed silica cannot be wetted by water; even if its density is greater than water, it can float on the water surface. At the same time, the surface moisture absorption is significantly reduced, making it suitable for many water-sensitive applications.

Characteristics of Hydrophobic Fumed Silica

• Hydrophobic, non-polar

  
  

• Low hygroscopicity

  
  

• Good dispersibility, can effectively adjust rheology even in polar systems

  
  

• High addition levels have little impact on system viscosity

  
  

Functions of Hydrophobic Fumed Silica

• Provide optimal processing rheology

  
  

• Thicken polar liquids (like epoxy resins)

  
  

• Reinforce silicone elastomers

  
  

• Achieve high loading in molded products

  
  

• Enhance corrosion resistance and hydrophobicity

  
  

• Improve dielectric properties (such as in cable compounds)

  
  

• Used as flame retardant agents and powder flow aids

  
  

• Increase scratch resistance in coatings and plastic systems

  
  

Applicable Industries

• Room-Temperature Vulcanizing (RTV) Silicone Rubber

  
  

• Adhesives and Sealants

  
  

• Coatings, Inks, Powder Coatings

  
  

• Liquid Silicone Rubber, Defoamers

  
  

• Printer Toner and Developers

  
  

• Vinyl Ester Resins, Lubricants, Cable Gels, etc.

  
  

Significance of Fumed Silica

Fumed silica is an extremely important ultrafine high-tech inorganic new material with a super large specific surface area, high adsorption, high dispersibility, and excellent thermal and electrical resistance. Owing to its excellent stability, reinforcing, thickening, and thixotropic properties, it plays an irreplaceable role in coatings, rubber, plastics, electronics, cosmetics, pharmaceuticals, food, and other fields.

SiSiB® Fumed Silica Product Overview

SiSiB SILICONES offers a complete range of fumed silica products, covering both hydrophilic and hydrophobic systems:

• Hydrophilic Fumed Silica: Precise particle size control, high purity, suitable for fields such as coatings, inks, and electronic materials.

  
  

• Hydrophobic Fumed Silica: Various surface treatment technologies (such as methyl, long-chain alkyl modifications) to meet high.

  
  

• requirements for water resistance, rheology, and reinforcing performance in different industries.

SiSiB® Fumed Silica, with its excellent consistency, high stability, and customization capability, is widely used in multiple high-end industries globally, helping customers optimize formulations and enhance product performance.