Molecular structure of hydrophobic alkyl side chains at comb polymer-air interface

The spectroscopic measurement of the molecular structure of octadecyl alkyl side chains at poly(vinyl octadecyl carbamates-co-vinyl acetate)-air interface using the surface sensitive sum-frequency generation (SFG) technique was reported. The SFG signals in the 7 nm thick dip coated and 65 nm thick spin-coated surfaces showed strong methyl asymmetric and symmetric stretching vibrations indicating ordered methyl terminal groups. For the adsorbed octadecyl films, the SFG signal associated with methylene vibrations was higher indicating increased gauche defects in comparison with the spin-coated thicker films. The irregularity in packing of the alkyl chains for the 7 nm polymer films was also reflected in an unstable and rapidly changing contact angle.