Characterization of the Organic-inorganic Hybrid Coating Surfaces Using Sum Frequency Generation Vibrational Spectroscopy

Surface structures of organic-in organic hybrid coatings of polyvinylalcohol (PVA) /polyacrylicacid (PAA)-silica, which have high gas barrier properties, have been investigated using X-ray photoelectron spectroscopy (XPS) and sum frequency generation spectroscopy (SFG). The cross-linked PVA/PAA surfaces show that these polymers are well mixed homogeneously even at the surface regions. In contrast, the backbones of the PAA preferentially appear at the surfaces of the PVA/PAA-silica hybrid films. The SFG spectral changes suggest that the topmost surfaces of the PVA/PAA-silica hybrid films are almost covered with the PAA. This observation is due to the polymers and silica being mixed homogeneously even at the surface region. No significant changes of the SFG spectra are observed under highly humid conditions, which suggests that the surface structures of the polymer-silica hybrid coatings do not affect the gas permeability.