Order To Disorder Transition at The Polymer-Air Interface for Hydrophobic Octadecyl Side Chain Copolymers

Abstract

ABSTRACTMolecular orientation of octadecyl alkyl side chains at the poly (vinyl octadecyl carbamates-co-vinyl acetate) polymer-air interface has been studied using surface sensitive sum frequency generation (SFG) spectroscopy. At 280C, below the side chain crystalline transition temperature, the SFG spectra show strong methyl vibrations indicating ordered alkyl side chains at the polymer-air interface. In the liquid state (980C), the SFG spectra show higher contributions from the methylene vibrations indicating higher gauche defects at the interface. This surface order to disorder transition is gradual and spans over a broad temperature range (50-900C), where the bulk is in the smectic liquid crystalline state.