Entropy basis for the thermodynamic scaling of the dynamics ofo-terphenyl

Abstract

Structural relaxation times and viscosities for non-associated liquidsand polymers are a unique function of the product of temperature,T, times specific volume,V, with the latterraised to a constant, γτ.Similarly, for both neat o-terphenyl (OTP) and a mixture, the entropy for differentT andpressure, P, collapses to a single curve when expressed versusTVγS, with the scaling exponent for the entropy essentially equal to the thermodynamicGrüneisen parameter. Since the entropy includes contributions from motions such asvibrations and secondary relaxations, which do not affect structural relaxation,γS<γτ.We show herein that removal of these contributions gives a satisfactory account of the magnitude ofγτ. Moreover, the relaxation times of OTP are found to be uniquelydefined by the entropy, after subtraction from the latter of aV-independent component.