SEMISIL R620 Fumed Silica (Hydrophobic, PDMS Treated)

SEMISIL R620 is a uniquely hydrophobic fumed silica produced by Shanghai Semitech New Material Co., Ltd. through the surface treatment of fumed silica with polydimethylsiloxane (PDMS). Unlike DDS or HMDS treatments which create small, defined surface groups, PDMS treatment grafts polymer chains onto the silica surface, creating a flexible, thick hydrophobic coating that provides distinctive performance advantages in specific applications.

The PDMS coating on SEMISIL R620 imparts outstanding compatibility with silicone-based systems, including silicone elastomers, silicone gels, silicone sealants, and PDMS fluids of all viscosities. Because the surface groups are chemically identical to the silicone matrix, SEMISIL R620 disperses readily in silicone systems with minimal energy input and forms a stable, uniform structure. This makes it the standard choice for reinforcing HTV (high temperature vulcanizing) and RTV (room temperature vulcanizing) silicone rubber compounds, where it provides both thixotropy and mechanical reinforcement.

Beyond silicone systems, SEMISIL R620 also performs excellently as a free-flow aid for powder coatings, a defoamer carrier, and in non-polar coatings requiring silicone-like surface properties. Its PDMS coating renders it extraordinarily hydrophobic (methanol wettability >65%), with moisture uptake below 0.2%. SEMISIL R620 is the direct equivalent of Evonik Aerosil R202 silicone-coated grades.