Fumed silica, also known as white carbon black, is an extremely fine amorphous silica produced by the high-temperature hydrolysis of halosilanes in an oxyhydrogen flame. Its surface is rich in a large number of silanol groups, giving it strong polarity and high hydrophilicity. Untreated hydrophilic fumed silica has a strong tendency to agglomerate, which can lead to excessive stress concentration in organic phases, causing various defects and severely affecting the performance of polymers. To expand the application fields of fumed silica, it is necessary to reduce the number of silanol groups on its surface, transforming it from strongly hydrophilic to hydrophobic, thereby improving its compatibility and bonding strength with organic phases.
Characteristics of Hydrophobic Fumed Silica
Hydrophobically modified silica exhibits distinct characteristics: it can be well dispersed in organic phases through its hydrophobic groups, while also forming strong interactions with organic phases via its silanol groups. This establishes a stable connection between the otherwise incompatible inorganic silica and the organic phase, achieving purposes such as reinforcement, anti-settling, anti-sagging, and scratch resistance.
Commonly Used Hydrophobic Modifiers
Commonly used hydrophobic modifiers for fumed silica include silicone oils, silane coupling agents, silicone resins, etc. The -R groups in silicone oil-based hydrophobic modifiers can be the same or different organic groups, or -H, -OH, etc. Depending on the different -R groups, the available silicone oil-based hydrophobic modifiers include: methyl silicone oil, ethyl silicone oil, methylphenyl silicone oil, methyl hydrogen-containing silicone oil, ethyl hydrogen-containing silicone oil, hydroxyl-containing silicone oil, diol copolymer silicone oil, higher alcohol-modified silicone oil, fatty acid-modified silicone oil, methylalkyl silicone oil, chloromethyl silicone oil, chlorophenyl silicone oil, carboxyalkyl silicone oil, aminoalkyl silicone oil, silazane silicone oil, and so on.