Thermodynamic properties of thin films of some dipolar liquids adjacent to fused silica surfaces

The disjoining pressure of some dipolar organic liquids (PhNO2, PhCN, PhCH2CN, PhCF3, MeCN) forming thin layers between two fused silica surfaces shows maximum values in temperature ranges which refer to thermodynamic transitions of higher order. Here the molecules in the bulk liquid seem to gain an additional rotational degree of freedom about one axis, whereas the molecules in the oriented surface zone still show a rotational restriction about this axis. Thermodynamic quantities for the liquid boundary layers are introduced and discussed.