James Richard Hahn

Synthesis and use of colloidal silica for reinforcement in silicone elastomers

Abstract Aqueous suspensions of colloidal silicas are readily silylated with either chlorosilanes or disiloxanes in the presence of acid and isopropyl alcohol without aggregation of the silica particle. By using a mixture of chlorosilanes or disiloxanes, spherical nanoparticles with controlled functionality can be made and transferred to an organic phase to provide stable, water free suspensions. The hydrophobic silica particles readily disperse into silicone polymers. At sufficient loading levels, they provide mechanical reinforcement comparable to traditional fillers but with improved clarity and lower viscosities. Modulus and durometer control in the cured elastomer is possible by varying the ratio of the vinyl concentration on the filler particle to the vinyl concentration in the polymer phase.

Reinforcement of Silicone Elastomers with Treated Silica Xerogels: Silica—Silicone IPNs

Abstract The use of silylated xerogels as reinforcing fillers in silicone elastomers was investigated. The silylated xerogels used in this study were mesoporous solids with a high degree of surface treatment and an open, interconnected high porosity. Some macropores were also present in the original xerogel particle. During compounding the original size of the xerogel particles is reduced substantially by fracture through the macroporous regions. The mesoporous regions of the xerogel are retained and exist as a uniform dispersion of filler particles in the siloxane polymer phase. The absence of a bound rubber phase, and the presence of an open porosity in the xerogel suggests reinforcement occurs via a silica—silicone interpenetrating network. This creates additional chain restrictions which lead to increases in modulus and other mechanical properties.