Methyl Side Groups: The Mechanisms Behind Water Repellence & Adhesion
Like all silicones, Liquid Silicone Rubber (LSR) is characterized by a flexible, fully saturated backbone of alternating silicon and oxygen atoms. The siloxane bonds have a partial ionic nature and give the material its high strength. The backbone is shielded by closely packed hydrophobic methyl side groups, which have low intermolecular forces between them. This allows the surface energy or surface tension to be low, while also being hydrophobic. This characteristic enables liquid silicone rubber to be water repellent, while allowing it to adhere only to materials with higher surface energy such as polyamide 66 or polycarbonates.
For other material combinations, self-adhesive grades can be used which are modified with silane-based products for this purpose. The siloxane-based products act as internal adhesion promoters. The promoters diffuse to the surface during curing since the groups are not compatible with the cross-linked structure of silicone. The addition of promoters on the surface allows a chemical bond to form with the substrate.
 M. J. Owen, “Siloxane Surface Activity” in Silicon-Based Polymer Science, A Comprehensive Resource, Eds. J, Ziegler and F. W Gordon Fearon, Advances in Chemistry Series 223, American Chemical Society, Washington DC, 1990
 N. N., Solid and Liquid Silicone Rubber, Wacker Chemie AG, München, brochure no. 6706e/06.11, 2011
At SIMTEC Silicone Parts, a leading company in manufacturing high precision parts and components, we are exclusively focused and specialized in the production of Liquid Silicone Rubber (LSR) and LSR/Thermoplastic (Two-Shot) components.
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