Study of the Adsorption Layer of Nematic Mesogen with Branched End Fragments at the Carbon Adsorbent Surface

Abstract
apor adsorption of organic compounds of different polarity on graphite-like adsorbent Carbopack Y modified by a monomolecular layer of a "double swallowtail type" liquid crystal was studied using gas chromatography. Adsorption thermodynamic characteristics (differential molar heats of adsorption and the entropy change during adsorption) were determined through the temperature dependencies of the Henry constant. Adsorption thermodynamic characteristics of the original carbon adsorbent and the adsorbent covered with the liquid crystal monomolecular layer were compared. The theoretical model of delocalized adsorption (model of an ideal two-dimensional gas) is used to analyze the change in entropy values. It is shown that the modification as a whole leads to the increase of the adsorption localization. Analysis of values of the thermodynamic characteristics revealed that they are influenced by possible monomolecular layer structure of liquid crystal. Possible structure of a monolayer of the "double swallowtail type" liquid crystal on a flat uniform carbon surface of Carbopack Y is proposed. The nature of the adsorption entropy change leads to the conclusion that the liquid crystal molecules are self-organized in the monolayer as a regular structure with little linear size intervals not permitting the interaction of the substrate with the adsorbate molecules.

Keywords: adsorption, gas-adsorption chromatography, modified carbon adsorbents, monolayers, liquid crystals, adsorbate-adsorbent interactions