Silica, especially Fumed Silica , is a good reinforcing agent for silicone rubber, but there is a problem of making the mixed rubber hard base, commonly known as the "structural effect". Its structural type improves with the prolongation of rubber material storage time, even to the extent that it cannot be returned for refining or scrapping. There are two explanations, one is that the end groups of silicone rubber are condensed with hydroxyl groups on the surface of silica; At the same time, it is felt that the silicon oxygen chain of silicone rubber forms hydrogen bonds with the surface hydroxyl groups of silica. There are two ways to prevent structural types. One is to add certain substances that can react with the hydroxyl groups on the surface of silica during mixing, such as hydroxysilicone oil, diphenylsilanediol, silazane, etc. When using diphenylsilanediol, it should be treated at 160-200 ℃ for 0.5-1h after mixing. This can prevent the structural type of silica filled silicone rubber from forming. Another approach is to pre modify the surface of white carbon black by removing some surface hydroxyl groups, fundamentally eliminating the structural type.


When Fumed Silica is dispersed in a non-polar liquid, it bridges the silanol groups on the surface of different particles through hydrogen bonding interactions, and thickens by forming a three-dimensional structure. When this structural system is subjected to mechanical external forces, such as stirring or shaking, the structure is damaged, and the type and duration of the mechanical external forces determine the degree of damage, resulting in the thickened system becoming a liquid again. If left stationary, the gas-phase white carbon black particles will be connected again to restore their original viscosity. This phenomenon is called pseudoplasticity.



A system thickened by gas-phase silica requires a small amount of energy to initiate its flow, in other words, there is a so-called "yield point". The thickening effect of hydrophilic Fumed silica on polar or semi polar liquids is not significant. In these systems, especially in liquid mixtures or solutions, surface modified gas-phase silica is displayed.