POLARIZABILITY SPECTRA AND THE STRUCTURE OF BOUNDARY-LAYERS OF POLYETHYLENE ON GERMANIUM

Spectra of the imaginary part of mean complex polarizability alpha'(v) in the range of stretching vibrations of methylene groups (2740-3040 cm(-1)) in the boundary layers of PE coatings obtained from polymer so lutions and melts on the surface of germanium monocrystals were invest igated. The n(v) and k(v) spectra of optical constants were obtained f rom ATR spectra using Fresnel and Kramers-Cronig procedures. The alpha '(v) spectra were calculated from the spectra of isotropic values of n (v) and k(v), whereas the spectra of anisotropic values alpha'(p)(v) a nd alpha'(s)(v) were obtained from the n(p)(v) and n(s)(v) spectra tin p- and s-polarizations of incident Light) in the Lorentz-Lorenz appro ximation. Plots of dichroic ratios and parameter of macromolecular ori entation Sigma versus temperature and polymer concentration c were cal culated from the alpha'(s) and alpha'(p) spectra for the v(s) (2848 cm (-1)) and v(as) (2912 cm(-1)) bands. Values of alpha'(s), alpha'(p), a nd dimensions s of the chain fragments contacting the crystal surface were compared with those of alpha(parallel to) and alpha(perpendicular to) for n-paraffins and PE in solutions (calculated from streaming bi refringence data) and with the size of Kuhn (statistical) segment. In polymer coatings at [eta] c < 1, s approximate to 8, which corresponds to the length of Kuhn segment; s approximate to 4 for [eta] c = 3-5. The transformation of planar orientation of macromolecules at the PE m elt-coated germanium surface to homeotropic orientation is accompanied by the changes in the values of alpha'(s), alpha'(p), dichroic ratio alpha'(s)/alpha'(p) and s, at 340-360 K.