Thickness dependence of microphase-separated structure of polyurethane ultrathin films

Polyurethane ultrathin films with two hard segment contents (20 and 45 wt%) were prepared onto a silicon wafer by a spin coating method. The change in microphase separation of polyurethane ultrathin films was investigated by fourier transform infrared (FT-IR) spectroscopy x-ray photoelectron spectroscopy (XPS) and atomic forced microscopy (AFM) as a function of film thickness and hard segment content. FT-IR measurement revealed that hydrogen bonded hard segment chains orient perpendicular to the film surface for the ultrathin film (∼6 nm). The size of hard segment domains for the ultrathin film decreased with decrease in film thickness. This is due to confinement effect because the film thickness itself (∼6 nm) is much smaller than the domain size (20 nm) formed in the bulk PUEs.