Wetting behavior of films of new fluorinated styrene - Siloxane block copolymers

Two new block copolymers containing dimethylsiloxane and semifluorinated styrene blocks (BSF6 and BSF8) were prepared using a polysiloxane azo-macroinitiator and corresponding semifluorinated styrene monomers StyF6 and StyF8. The thermal properties of the block copolymers were investigated by DSC, which showed the formation of a thermotropic mesophase in BSF8. This was attributed to the self-assembly of the semifluorinated side groups in microphase-separated domains of the incompatible polymer blocks. Coatings with 300 nm thicknesses had a root-mean-square roughness of 10 nm by atomic force microscopy. Using water and alcohols, wetting behavior was studied along with a model poly(dimethylsiloxane) (PDMS) network. High advancing (theta(adv) = 122degrees) and receding (theta(rev) = 82degrees) water contact angles were observed for BSF8. Using 2-propanol, BSF8 displayed oleophobicity (theta(adv) = 64degrees and theta(rec) = 45degrees) while a reference PDMS coating was completely wetted (theta(adv) = theta(rec) = 0degrees). Utilizing theta(adv) for a series of alcohols, a fit to a modified equation of state gave a low value for BSF8 surface tension (gamma(SV) = 10.5 mN/m). Both the wetting behavior of BSF8 and surface dynamics associated with wetting are consistent with the presence of a well-ordered, liquid crystalline fluorocarbon surface domain. In contrast, BSF6 surfaces are swollen by alcohols and display a cycle-dependent wetting behavior in water. BSF6 surfaces are thus labile to surface reorganization and/or solvent adsorption.