Elastically Cooperative Activated Barrier Hopping Theory of Relaxation in Viscous Fluids. II. Thermal Liquids

Journal Article · Thu May 01 00:00:00 EDT 2014 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4874843· OSTI ID:1136835

Mirigian, Stephen ^[1]; Schweizer, Kenneth ^[2]

---

1. University of Illinois at Urbana-Champaign
2. University of Illinois

Building on the elastically collective nonlinear Langevin equation theory developed for hard spheresin Paper I, we propose and implement a quasi-universal theory for the alpha relaxation of thermalliquids based on mapping them to an effective hard sphere fluid via the dimensionless compressibility.The result is a zero adjustable parameter theory that can quantitatively address in a unifiedmanner the alpha relaxation time over 14 or more decades. The theory has no singularities abovezero Kelvin, and relaxation in the equilibrium low temperature limit is predicted to be of a roughlyArrhenius form. The two-barrier (local cage and long range collective elastic) description results ina rich dynamic behavior including apparent Arrhenius, narrow crossover, and deeply supercooledregimes, and multiple characteristic or crossover times and temperatures of clear physical meaning.Application of the theory to nonpolar molecules, alcohols, rare gases, and liquids metals is carriedout. Overall, the agreement with experiment is quite good for the temperature dependence of thealpha time, plateau shear modulus, and Boson-like peak frequency for van der Waals liquids, thoughless so for hydrogen-bonding molecules. The theory predicts multiple growing length scales uponcooling, which reflect distinct aspects of the coupled local hopping and cooperative elastic physics.Calculations of the growth with cooling of an activation volume, which is strongly correlated with ameasure of dynamic cooperativity, agree quantitatively with experiment. Comparisons with elastic,entropy crisis, dynamic facilitation, and other approaches are performed, and a fundamental basisfor empirically extracted crossover temperatures is established. The present work sets the stage foraddressing distinctive glassy phenomena in polymer melts, and diverse liquids under strong confinement.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1136835
• Journal Information: Journal of Chemical Physics, Vol. 140, Issue n/a; ISSN 0021-9606
• Country of Publication: United States
• Language: English