TY - JOUR
T1 - Relaxation time and excess entropy in viscous liquids
T2 - Electric field versus temperature as control parameter
AU - Richert, Ranko
N1 - Funding Information:
This work was supported by the National Science Foundation under Grant No. CHE-1564663. Helpful comments from V. Lubchenko, D. Matyushov, and P. Wolynes are gratefully acknowledged.
Publisher Copyright:
© 2017 Author(s).
PY - 2017/2/14
Y1 - 2017/2/14
N2 - On the basis of adiabatic calorimetry data and results obtained from dielectric relaxation studies in the presence of a high static electric field, the effects of temperature and electric field induced changes of the excess entropy are compared for the same sample: supercooled cresolphthalein dimethylether. A field induced reduction of the excess entropy by 45 mJ K−1 mol−1 at constant temperature increases the structural relaxation time by 0.75%, while the same entropy change originating from lowering the temperature at constant field increases the time constant by 3.5%. Therefore, there is no simple link connecting excess entropy and relaxation time that is independent of the control parameter that is used to modify the entropy. A consequence is that the Adam-Gibbs approach does not provide a quantitative prediction for how the dynamics of liquids depend on the electric field, and, more generally, on excess entropy. This work compares the dynamics for temperature versus field induced changes of isobaric excess entropy, thereby eliminating previous uncertainties arising from isochoric versus isobaric conditions and from unknown relations between thermodynamic, excess, and configurational entropies.
AB - On the basis of adiabatic calorimetry data and results obtained from dielectric relaxation studies in the presence of a high static electric field, the effects of temperature and electric field induced changes of the excess entropy are compared for the same sample: supercooled cresolphthalein dimethylether. A field induced reduction of the excess entropy by 45 mJ K−1 mol−1 at constant temperature increases the structural relaxation time by 0.75%, while the same entropy change originating from lowering the temperature at constant field increases the time constant by 3.5%. Therefore, there is no simple link connecting excess entropy and relaxation time that is independent of the control parameter that is used to modify the entropy. A consequence is that the Adam-Gibbs approach does not provide a quantitative prediction for how the dynamics of liquids depend on the electric field, and, more generally, on excess entropy. This work compares the dynamics for temperature versus field induced changes of isobaric excess entropy, thereby eliminating previous uncertainties arising from isochoric versus isobaric conditions and from unknown relations between thermodynamic, excess, and configurational entropies.
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U2 - 10.1063/1.4975389
DO - 10.1063/1.4975389
M3 - Article
C2 - 28201904
AN - SCOPUS:85012131939
SN - 0021-9606
VL - 146
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
IS - 6
M1 - 064501
ER -