Hydrophilic and Hydrophobic Gaseous Silica: An In-depth Analysis of Characteristics and Disparities

Hydrophilic and Hydrophobic Fumed Silica: Characteristics, Applications, and Variances - Enhancing Industrial Innovations and Product Quality

1. Hydrophilic Gas-phase Silica

Hydrophilic gas-phase silica is a nanoscale amorphous silica powder that is produced through the high-temperature hydrolysis of silicon halides within a hydrogen-oxygen flame. Owing to the existence of hydroxyl groups on the surface of its particles, it inherently exhibits hydrophilic properties and can be moistened by water, attaining favorable dispersion in aqueous solutions.

In terms of physical structural attributes, its primary particle size falls within the range of 7 - 20nm, with the aggregate particle size (on average) approximately 150 - 300nm, and the agglomerate particle size (averagely) ranging from 1 - 50um. The specific surface area spans from 90 - 400 m²/g, and the pH (of a 4% aqueous solution) lies between 3.7 - 4.5.

From the vantage point of application performance, hydrophilic fumed silica showcases prominent hydrophilic and oleophobic characteristics. It demonstrates remarkable efficacy in numerous industrial application scenarios. For instance, in the realm of coatings and paints, it can proficiently modulate the rheological properties during processing; it can substantially augment the reinforcement effect in organic silicone elastomers; it can induce a thickening effect in non-polar liquids; and in relation to food and industrial powders, it contributes to the enhancement of flowability. Its application purview extends across a wide spectrum of industries, including coatings and paints, adhesives and sealants, unsaturated polyester and films, inks, silicone rubber, cosmetics, pharmaceuticals, elastomers, food, powders, and so forth.

1. Hydrophobic Gas-phase Silica

Hydrophobic fumed silica is fabricated by subjecting hydrophilic fumed silica to a chemical reaction with specific modifiers. Typical modifiers comprise hexamethyldisilazane (HMDS), dimethyldichlorosilane (DDS), polydimethylsiloxane (PMDS), and special silanes. After the modification process, the hydroxyl groups on the silica surface are either reacted or masked, thereby conferring hydrophobicity.

In comparison to hydrophilic silica, hydrophobic fumed silica presents distinctive property variances. It cannot be wetted by water, and even if its density exceeds that of water, it can still remain afloat on the water surface. It exhibits feeble moisture absorption and is less prone to moisture regain. In terms of particle size, it is larger than that of the hydrophilic type, while the specific surface area corresponding to the hydrophilic type is diminished. The pH (of a 4% 1:1 volume ratio isopropanol aqueous solution) ranges from 3 - 10.

Hydrophobic gas-phase silica possesses excellent properties such as oleophilicity, non-polarity, and low moisture absorption, and assumes a pivotal role in diverse industrial applications. It excels in facilitating dispersion and rheological control and can effect a thickening impact on polar liquids. It has significant implications in reinforcement, corrosion prevention, the endowment of hydrophobic characteristics, and the improvement of scratch resistance. For example, in the production of room temperature vulcanized (RTV) silicone rubber, hydrophobic fumed silica can be evenly dispersed within the silicone rubber system, effectively bolstering the mechanical properties like tensile strength and tear strength of the rubber, while imparting favorable hydrophobic attributes to the silicone rubber, enabling it to sustain stable performance in humid settings; in the coatings industry, it can enhance the rheological properties of coatings, avert pigment sedimentation, and augment the water resistance, weather resistance, and scratch resistance of coatings. For instance, in certain high-end automotive coatings, the addition of hydrophobic fumed silica markedly elevates the glossiness and durability of coatings; among organosilicon defoamers, hydrophobic fumed silica, as a crucial active constituent, can promptly reduce the surface tension of foam and cause the foam to rupture. Due to its hydrophobic nature, it is not readily wetted by liquid anew, thereby maintaining the long-term efficacy of the defoamer. It is principally applicable to RTV silicone rubber, adhesives and sealants, coatings, inks, powder coatings, liquid silicone rubber, silicone defoamer, printing toner, toner, vinyl ester resin, lubricating oil, cable gel, and other industries.

In conclusion, hydrophilic and hydrophobic fumed silica possess targeted applications in distinct industrial arenas on account of their unique properties. The two mutually complement each other and jointly propel the technological progress and product quality enhancement of related industries.