Effect of Surface Molecular Aggregation State and Surface Molecular Motion on Wetting Behavior of Water on Poly(fluoroalkyl methacrylate) Thin Films

The effect of surface molecular motion on the wetting behavior of water on the thin film surfaces of poly(fluoroalkyl methacrylate)s with various fluoroalkyl (R-f) groups [PFMA-C-y; y: fluoromethylene number in R-f groups, y = 1, 2, 4, 6, and 8] was characterized, The receding contact angle of PFMA-C-y with short R-f groups (y = 1, 2,4, and 6) was larger than that of poly(fluoroalkyl acrylate) with short R-f group, [PFA-C-y, y <= 6]. This stable hydrophobicity observed for PFMA-C-y is due to tile restriction of thermal molecular motion by tile alpha-methyl group. Wide-angle X-ray diffraction (WAXD) and grazing incidence WAXD measurements revealed that tile R-f groups [PFMA-C-y, y <= 6] were not crystallized. PFMA-C-8 showed high advancing and receding contact angles due to the crystallization Of fluoroalkyl groups at the surface region. The hydrophobicity of PFMA-C-8 was improved after annealing due to the ordering of fluoroalkyl groups.