Communal entropy of bulky molecules. Pressure–volume–temperature relations of triphenylchloromethane

Abstract

Pressure–volume–temperature relations of the liquid, the supercooled liquid, and the crystal of triphenylchloromethane (TPCM) are presented. The excess entropy of the liquid and glass over the crystal at constant volume has been determined and compared with the previous result for o-terphenyl (o-TP). While the excess entropy of TPCM in the liquid is larger than that of o-TP by about 2R, where R is the gas constant, the communal entropy (defined as the increment of the excess entropy in the liquid over that in the glass) of these molecules is almost the same. This is evidence that the difference of the entropy in the liquid is mainly due to the structural contributions, which depend on individual molecules and are frozen-in by the vitrification. The communal entropy of these asymmetrical, bulky molecules depends on volume and temperature and seems to approach 3R at the zero-density extreme.