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Entropy Basis for the Thermodynamic Scaling of the Dynamics of OTP

CM Roland·R Casalini
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Abstract

Structural relaxation times and viscosities for non-associated liquids and polymers are a unique function of the product of temperature, T, times specific volume, V, with the latter raised to a constant, g_tau. Similarly, for both neat o-terphenyl (OTP) and a mixture the entropy for different T and pressures, P, collapse to a single curve when expressed versus TV^g_s, with the scaling exponent for the entropy, g_s, essentially equal to the thermodynamic Gruneisen parameter. Since the entropy includes contributions from motions, such as vibrations and secondary relaxations, which do not affect structural relaxation, g_s < g_tau. We show herein that removal of these contributions gives a satisfactory accounting for the magnitude of g_tau. Moreover, the relaxation times of OTP are found to be uniquely defined by the entropy, after subtraction from the latter of a V-independent component.

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CM Roland, R Casalini. 2006-10-16. Entropy Basis for the Thermodynamic Scaling of the Dynamics of OTP. https://doi.org/10.1088/0953-8984%2F19%2F20%2F205118

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