Quadrupolar and polar anisotropy in end-grafted alpha-helical poly(gamma-benzyl-L-glutamate) on solid substrates

Using grazing incidence reflectance Fourier transform infrared spectroscopy (GIR-FTIR) and electro-optic (EO) measurements, we have determined the deg ree of quadrupolar and polar anisotropy in end-grafted alpha-helical poly(g amma-benzyl-L-glutamate) (PBLG) chains. The results are compared to data ob tained on spin-cast and on Langmuir-Blodgett-Kuhn (LBK) films. End-grafted films were prepared by a vapor-deposition-polymerization (VDP) scheme and h ave thicknesses of up to 70 nm. The quadrupolar order of VDP films, as esti mated by the nematic order parameter S, is higher than in spin-cast and LBK films. This result indicates a preferentially perpendicular alignment of P BLG chains in VDP films. Furthermore, after the removal of the physisorbed chains from the grafted films by intensive washing with solvent, the quadru polar order is lowered while the polar order increases significantly, sugge sting that the physisorbed chains might form anti-parallel pairs with the s urface-grafted chains. (C) 1999 American Institute of Physics. [S0021-9606( 99)51536-5].