Shear-induced softening in fumed silica-reinforced silicone

Fumed silica is widely used as a reinforcing filler and rheology modifier for polymer composites. Untreated, hydrophilic fumed silica formulated into silicone polymer typically leads to a stiff, brittle material due to strong association between the silica surface silanol and the siloxane backbone. However, this hydrophilic silica/silicone mixture can be sheared into a flowable material, with comparable rheological behaviour to a mixture of silicone polymer and a hydrophobically modified silica. In this work, we utilize various characterization techniques such as rheology, bound polymer test, and differential scanning calorimetry (DSC) to understand the mechanism by which agitation softens the hydrophilic silica/silicone mixture. The combined observations indicated the role of shear induced rearrangement of bound polymer bridging the silica particles to drive the rheological behaviour of this kinetically arrested system.