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Rounded stretched exponential for time relaxation functions

delete2009-12-07
delete10
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J
J.G. Powles *
D
D. M. Heyes
G
G. Rickayzen
W
W.A. Evans
DOI:10.1063/1.3268702delete
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摘要

摘要

En 中文
A rounded stretched exponential function is introduced, C(t) = exp{(tau(0)/tau(E))(beta)[1-(1 + (t/tau(0))(2))(beta/2)]},where t is time, and tau(0) and tau(E) are two relaxation times. This expression can be used to represent the relaxation function of many real dynamical processes, as at long times, t >> tau(0), the function converges to a stretched exponential with normalizing relaxation time, tau(E), yet its expansion is even or symmetric in time, which is a statistical mechanical requirement. This expression fits well the shear stress relaxation function for model soft soft-sphere fluids near coexistence, with tau(E) << tau(0). The function gives the correct limits at low and high frequency in Cole-Cole plots for dielectric and shear stress relaxation (both the modulus and viscosity forms). It is shown that both the dielectric spectra and dynamic shear modulus imaginary parts approach the real axis with a slope equal to 0 at high frequency, whereas the dynamic viscosity has an infinite slope in the same limit. This indicates that inertial effects at high frequency are best discerned in the modulus rather than the viscosity Cole-Cole plot. As a consequence of the even expansion in time of the shear stress relaxation function, the value of the storage modulus derived from it at very high frequency exceeds that in the infinite frequency limit (i.e., G(infinity)) (C) 2009 American Institute of Physics. [doi: 10.1063/1.3268702]
Keyword:
ANOMALOUS DIELECTRIC-RELAXATION
STEEPLY REPULSIVE POTENTIALS
SPHERICAL-TOP MOLECULES
ROTATIONAL DIFFUSION
TRANSPORT-COEFFICIENTS
RHEOLOGICAL PROPERTIES
HIGH-FREQUENCIES
WILLIAMS-WATTS
LIQUIDS
FLUIDS
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期刊

Journal of Chemical Physics 封面图
Journal of Chemical Physics
IF:
3.1
论文数:
7.2W
被引数:
23.2W

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