THERMODYNAMICS OF SOLUTIONS WITH LIQUID CRYSTAL SOLVENTS .2. SURFACE EFFECTS WITH NEMATOGENIC COMPOUNDS

Differential scanning calorimetry and gas-liquid chromatography are used in a thermodynamic investigation of surface effects with two nematogenic liquid crystals (p-azoxyanisole and 4,4′-dihexyloxyazoxybenzene). Studied are bulk samples (film thickness of about 4 × 10-2 cm) and samples where the compound is spread on various common chromatographic support materials (film thicknesses ranging from 40 to 2200 Å). It is found that surface effects are absent at the solid-liquid crystal interface. However, at the gas-liquid crystal interface small surface effects are sometimes present with two-component systems (i.e., when nonmesomorphic solute is added), but may be neglected provided that the film thickness is at least 1000 Å.