Fumed silica aggregate has a three-dimensional branch structure, can form an interactive network in the dispersion system, using this characteristic, fumed silica in the field of sealant, as a thickener and thixotropic agent, can increase viscosity, ensure the free flow of the rubber, with the prevention of caking, flow hanging, collapse and other effects. The thickening and thixotropic mechanism of fumed silica is mainly realized through the interaction of hydrogen bonds of the silicon hydroxyl group on the surface. When the silica is dispersed in polysiloxane, hydrogen bonds are generated between different particles through the silicon hydroxyl group on the surface, forming a silica network, which limits the fluidity of the system, increases the viscosity and plays a role of thickening. When subjected to shear force, the silica network is damaged, resulting in a decrease in system viscosity and thixotropic effect, which is conducive to construction. Once the shear force disappears, the hydrogen bond is formed again, the silica network is restored, and the viscosity of RTV silicone rubber compound system also gradually rises, effectively preventing the phenomenon of fluid hanging in the vulcanization process of the compound [17]. The anti-hanging properties of the system are closely related to the yield value and the network reduction rate after the material is subjected to shear during use. In practical application, the higher the yield value, the better the anti-flow performance of the compound. The ideal compound should have high yield value, high shear dilution index and fast reduction rate.

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