HIFULL® Hydrophobic Fumed Silica (PDMS-Treated): Mechanism, Performance, and Prospects
To expand the application of fumed silica in highly polar systems, organic silicon-based modifiers are often used to impart hydrophobicity to its surface. Polydimethylsiloxane (PDMS), commonly known as silicone oil, is a linear organosilicon polymer characterized by excellent thermal stability, low surface energy, and good compatibility, making it an ideal hydrophobic modifier.
During the modification process, PDMS interacts with the silanol groups on the surface of hydrophilic fumed silica through physical coating or chemical reactions. The primary reaction pathways include:
Condensation reaction: The terminal silanol groups of PDMS undergo dehydration condensation with the hydroxyl groups on the SiO₂ surface, forming Si–O–Si bonds;
Physical adsorption and coating: The long-chain molecules of PDMS form a hydrophobic layer on the surface of the nanoparticles, shielding the original hydrophilic groups. After being treated with PDMS, the original HL-200 is transformed into the hydrophobic product HB-139 with significant changes observed in its key performance parameters.
Specific surface area: It decreases from 200±20 m²/g to 110±30 m²/g, indicating that the surface is covered by an organic layer, resulting in weakened nitrogen adsorption capacity;
Surface properties: The contact angle increases significantly, rendering it unwettable by water and exhibiting typical hydrophobic characteristics; pH value: In a 4% suspension (anhydrous ethanol:water = 1:1), the pH ranges from 4.0 to 7.0, which is higher than that of the hydrophilic product (pH range 3.9–4.5).
This is related to the weakly alkaline or neutral nature of PDMS; Particle size: The effective particle size of primary particles increases slightly due to the presence of the surface coating layer.
Performance Advantages of HIFULL® HB-139
With its unique performance advantages, hydrophobic fumed silica HB-139 demonstrates broad application prospects across multiple industries.
Firstly, its excellent thickening, thixotropic, and anti-sagging properties make HB-139 an ideal additive for silicone rubber, coatings, and inks. In these applications, HB-139 can effectively improve the rheological properties of products, prevent coatings from flowing on vertical surfaces, and enhance construction efficiency and finished product quality.
Secondly, the high filler loading capacity of HB-139 provides strong support for its reinforcing effect in silicone rubber. Compared with unmodified hydrophilic fumed silica, HB-139 does not induce the “structure effect”—that is, it does not cause material performance degradation due to excessive aggregation between particles—even at high filler loadings. This characteristic enables silicone rubber to achieve excellent mechanical properties while maintaining good processability and long-term stability.
Thirdly, the transparency of HB-139 is another highlight. In transparent systems, such as transparent silicone rubber and transparent coatings, the addition of HB-139 does not negatively affect the transparency of the products. Meanwhile, it provides high hydrophobicity, enhancing the water resistance and anti-fouling capabilities of the products.
Furthermore, HB-139 performs exceptionally well in the field of powder materials. Its excellent anti-caking and flow-aid properties prevent powder coatings from caking during storage and transportation, thereby improving production efficiency and product quality.
Additionally, HB-139 can be used as a functional additive in lubricants, cable gels, vinyl ester resins, and other fields to improve the overall performance of products.
Learn More: HB-139 Properties and Functional Applications
Application
Silicone rubber field: As a reinforcing filler, HB-139 can significantly enhance mechanical strength at high filler loadings (>30 wt%) while avoiding the “structure effect” induced by traditional hydrophilic silica. Its hydrophobic surface shows better compatibility with the silicone rubber matrix, helping to maintain processing fluidity and long-term stability.
Coatings and inks: HB-139 imparts excellent thixotropy and anti-sagging properties to systems, making it particularly suitable for high-polarity resin systems. In transparent varnishes, due to its nano-scale particle size and refractive index comparable to that of the resin, it does not affect the transparency of the coating when fully dispersed, while improving water resistance and anti-fouling properties.
Adhesives and sealants: In curable polyurethane or silicone sealants, HB-139 can effectively control rheological behavior, prevent sagging during construction, and enhance cohesive strength.
Lubricants and cable gels: As a thickening and thixotropic agent, HB-139 disperses stably in polar media, preventing oil separation or additive settling, and improving the reliability of lubrication systems.
Powder coatings: As an anti-caking agent and flow aid, HB-139 significantly improves the storage stability and spraying fluidity of powders, especially in ultra-fine powder systems.
Vinyl ester resins and composite materials: In resin systems, HB-139 can regulate viscosity, inhibit settling, and enhance the weather resistance and hydrophobicity of the final products.
From hydrophilic HL-200 to hydrophobic HB-139, PDMS modification technology perfectly illustrates the core role of surface engineering in the functionalization of nanomaterials. This is not merely a simple change in physical properties, but a profound transformation of chemical identity.
It has evolved fumed silica from a versatile inorganic filler into a specialized high-performance additive capable of precisely meeting the demands of specific high-end fields.
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.
