Molecular structure of polystyrene at air/polymer and solid/polymer interfaces

IR-visible sum-frequency generation(SFG) spectroscopy has been used in a to tal internal reflection geometry to study the molecular structure of polyst yrene (PS) at PS/sapphire and PS/air interfaces, simultaneously. The symmet ric vibrational modes of the phenyl rings dominate the SFG spectra at the P S/air interface as compared to the antisymmetric vibrational modes at the P S/sapphire interface. This indicates approximately parallel orientation of the phenyl rings at the PS/air interface while nearly perpendicular orienta tion at the PS/sapphire interface, with respect to the surface normal.