Interaction of LC with a substrate in a system LC-porous glass studied by IR spectroscopy

IR spectra of porous glasses (PG) with a pore diameter of 20, 40 and 100 An gstrom, and those filled with 4-pentyl-4'-cyanobiphenyl (5CB) nematic liqui d crystal (LC) were studied at room temperature in 400-13 000 cm(-1) spectr al range. Incorporation of the LC into the porous glass results in the chan ges of some fundamental bands, overtones and combination tones in the IR ab sorption spectra of the porous glass and the liquid crystal. The most essen tial changes in the spectrum of PG were observed for the bands correspondin g to the absorption of the surface OH groups, whereas in the spectra of the LC, for the bands associated with the C=N group of the 5CB molecules. Chan ges observed in the spectral parameters of the 5CB are more pronounced in t he case of microporous glasses as compared to that of macroporous ones. The se results indicate the existence of strong interaction between the LC mole cules and porous glass matrix. In the case of the 5CB, such interactions ar e realized through the hydrogen bonds formation between the polar C=N group s of the 5CB molecules and the surface OH groups of PG. Using the IR spectr a of LC-PG system, one can also estimate the degree of the LC molecules pen etration into the pores. (C) 2000 Elsevier Science B.V. All rights reserved .