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

Abstract

IR spectra of porous glasses (PG) with a pore diameter of 20, 40 and 100Å, and those filled with 4-pentyl-4′-cyanobiphenyl (5CB) nematic liquid crystal (LC) were studied at room temperature in 400–13 000cm−1 spectral range. Incorporation of the LC into the porous glass results in the changes of some fundamental bands, overtones and combination tones in the IR absorption spectra of the porous glass and the liquid crystal. The most essential changes in the spectrum of PG were observed for the bands corresponding 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. Changes observed in the spectral parameters of the 5CB are more pronounced in the case of microporous glasses as compared to that of macroporous ones. These results indicate the existence of strong interaction between the LC molecules and porous glass matrix. In the case of the 5CB, such interactions are realized through the hydrogen bonds formation between the polar CN groups of the 5CB molecules and the surface OH groups of PG. Using the IR spectra of LC–PG system, one can also estimate the degree of the LC molecules penetration into the pores.