Quasi-macroscopic boundary structures in “nonsimple” fluids: experiment and model

Experiments have shown that near the boundary of a “nonsimple” fluid (such as nitrobenzene) on a solid substrate, there may exist an extended, so-called epitropic, phase with evidence of ordered arrangement of molecules (akin to that in a nematic liquid crystal). New data on the temperature dependence of the thickness of this phase in nitrobenzene on a metallic substrate are reported. These data (as well as earlier data for a nitrobenzene/quartz system) are interpreted in terms of a modified theoretical model of the epitropic phase as a pile of oligomers adhering to the substrate by means of adsorption forces. Ordering is essentially governed by lateral interactions in an ensemble of adsorbed oligomers. The possibility of boundary phase existence as a superheated crystal (in particular, nitrobenzene) stabilized by adsorption forces from the side of the substrate is discussed.