HIFULL® Hydrophobic Fumed Silica (HMDS-Treated): Mechanism, Performance, and Prospects
Fumed silica, also known as white carbon black, is a nano-scale amorphous silicon dioxide powder generated through the high-temperature hydrolysis of silicon halides (such as silicon tetrachloride) in a hydrogen-oxygen flame.
However, the surface of untreated fumed silica is rich in hydrophilic hydroxyl groups, resulting in poor dispersibility in non-polar or weakly polar systems, which limits its application in hydrophobic systems. Therefore, the industry often employs organosilane modifiers for surface hydrophobic treatment, among which hexamethyldisilazane (HMDS) is one of the most commonly used modifiers.
The molecular formula of hexamethyldisilazane (HMDS) is [(CH₃)₃Si]₂NH. The modification reaction on the surface of fumed silica is essentially a condensation reaction between silanol groups and HMDS. This reaction converts the hydrophilic hydroxyl groups (–OH) on the surface of fumed silica into hydrophobic trimethylsiloxy groups (–OSi(CH₃)₃), while releasing ammonia gas.
By controlling the amount of HMDS, reaction temperature, time, and the specific surface area of the raw material, different degrees of surface coverage can be achieved, thereby regulating key indicators such as the hydrophobicity, carbon content, and specific surface area of the final product.
In industry, hydrophobic products with varying performances are typically obtained by treating hydrophilic fumed silica with different specific surface areas using HMDS. Based on actual production data, the results can be summarized as follows:
HB-612 & HB-615
Hydrophilic fumed silica with a specific surface area of 150 m²/g: After HMDS treatment, HB-612 and HB-615 are obtained.
Their physical and chemical indicators are basically consistent, but HB-615 has a higher carbon content, indicating a higher degree of surface treatment, superior hydrophobicity, and better thixotropy.
HB-612 is suitable for industries such as room temperature vulcanized (RTV) silicone rubber, adhesives and sealants, coatings, inks, and powder coatings.
It can serve as a thickening thixotropic agent and reinforcing agent for RTV silicone rubber. Its hydrophobicity endows RTV silicone rubber with a good shelf life. In coatings and inks, it plays roles in anti-settling, anti-sagging, and thixotropic control, and improves the free-flowing property of powder coatings, preventing caking.
On the basis of HB-612’s applications, HB-615, with its more outstanding and stable hydrophobicity and thixotropy, plays a significant role in elastomers, toners, high-temperature vulcanized (HTV) silicone rubber, and liquid silicone rubber (LSR).
It is an excellent reinforcing agent and rheology control agent for adhesives and sealants, and a superior reinforcing filler for elastomers, capable of preventing the structuralization of HTV silicone rubber and improving the uniformity and stability of pigments.
HB-620 & HB-132
Raw material with a specific surface area of 200 m²/g: HB-620 is obtained after treatment; if deep modification is carried out (i.e., with a higher HMDS dosage or more thorough reaction), HB-132 is obtained.
It is noteworthy that the nitrogen adsorption specific surface area of HB-132 is lower than that of HB-620, but its carbon content is higher. This indicates that while deep modification partially blocks pores and reduces the specific surface area, it significantly enhances hydrophobicity.
HB-620 is suitable for HTV silicone rubber, LSR, coatings and inks, adhesives and sealants, and powder coatings. It has excellent hydrophobicity and stable thixotropy. It can serve as a reinforcing agent for HTV silicone rubber, preventing structuralization. In coatings and inks, it provides anti-settling, anti-sagging, and thixotropic effects. It is a good hydrophobic and rheology control raw material for adhesives and sealants, and can improve the free-flowing property of powder coatings, preventing caking.
HB-132 is widely used in silicone rubber, adhesives and sealants, defoamers, and toners. Due to its extremely low thickening effect and excellent operability, it allows for a high filler loading in polymers. HB-132 is very suitable for systems requiring low thickening and high thixotropy. It exhibits excellent reinforcing performance when used as a filler in silicone rubber, and plays a significant role in self-leveling one-component RTV (RTV-1), two-component RTV (RTV-2K) silicone rubber, and LSR. It can also improve the free-flowing property of powder coatings
HB-630
Raw material with a high specific surface area of 400 m²/g: HB-630 is obtained after HMDS treatment. This product has the highest specific surface area and carbon content among all HMDS-modified products, combining excellent dispersibility, transparency, and hydrophobicity.
HB-630 is suitable for elastomers, especially HTV silicone rubber and LSR, coating and ink systems, defoamers, and printer toner fields. With its high specific surface area, small particle size, and good dispersion uniformity, it possesses higher transparency, ultra-high hydrophobicity, and stable thixotropy.
It can be applied as a reinforcing agent for HTV silicone rubber and LSR. In coatings and inks, it provides anti-settling, anti-sagging, and thixotropic effects. It endows defoamers with good defoaming and anti-foaming capabilities, and improves the free-flowing property, uniformity, and stability of toner.
Due to these differences in characteristics, the different models from Hubei Huifu Nanomaterial Co., Ltd. have distinct applications.
The HMDS modification technology provides an efficient path for the functionalization of fumed silica. By adjusting the specific surface area of the raw material and the modification depth, hydrophobic products that meet the needs of different application scenarios can be precisely designed. From HB-612 to HB-630, the series of products covers the full spectrum of applications from general-purpose to high-performance, fully reflecting the material science logic that “structure determines performance, and process determines function.”
Hello, Customers
My name is Van, I’m the business manager of HIFULL, I have been in Fumed Silica Industry for more than 10 years. Feel free to contact me. I’m happy to provide you the best service and products.
