Molecular Structure of Hydrophobic Alkyl Side Chains at Comb Polymer-Air Interface

Surface sensitive sum-frequency generation (SFG) spectroscopic technique has been used to study the orientation of alkyl side chains for comb polymers at polymer-air interface. The SFG spectra at 24oC for thick spin-coated polymer films and adsorbed layer (on mica substrate) show strong signals associated with methyl asymmetric and symmetric vibrations indicating ordered methyl terminal groups. However, the ratio of methylene to methyl stretch vibrations is higher for the adsorbed layer than that observed for spin-coated films. This spectroscopic evidence of poor packing of alkyl chains with enhanced gauche defects correlates well with low water contact angles measured for the adsorbed films. In this talk, the surface structure as a function of chain length and temperature will be discussed