Impact of the Network Density of Rough Poly(dimethylsiloxane)-Model Systems on the Hydrophobicity Assessment and Dynamic Wetting Behavior

Abstract

Silicone-based elastomers are widely in use as a housing material for composite insulators, e.g., for high-voltage outdoor applications. Especially, their outstanding hydrophobic properties make them suitable for high-voltage applications since conductive electrolytic paths on the surface that result in short circuits need to be avoided. While static hydrophobicity can be analyzed by contact-angle measurements, the analysis is more difficult for moving droplets. In this paper, we show that not only dynamic contact-angle measurements should be used to evaluate the hydrophobic properties of insulator materials, but also the occurrence of the so-called pearling effect must be considered. This effect describes the instability of accelerated drops resulting in small, pinned droplets on a material surface. We observed that occurrence of the pearling effect is dependent not only on external parameters (such as droplet volume) but also on the network density of the silicone elastomer. We have synthesized variable silicone elastomers with tunable network structures by reacting vinyl-terminated poly(dimethylsiloxane) and tetrakis(dimethylsiloxy)silane via hydrosilylation. The network properties are varied by controlling the stoichiometric balance between the monomers. The well-defined materials obtained that way allowed a careful examination of the impact of network densities (i.e., mechanical properties) and low-molecular-weight residues (sol) on the hydrophobic behavior in terms of dynamic wetting.