On the Relationship Between Plateau Modulus and Shear Relaxation Time in Transient Networks

2015 ◽  
Vol 24 (3) ◽  
pp. 208-217 ◽  
Author(s):  
Ana West ◽  
James T. Kindt
Keyword(s):  
Relaxation Time ◽  
Plateau Modulus ◽  
Shear Relaxation ◽  
Transient Networks ◽  
The Relationship ◽  
Shear Relaxation Time

Coordination numbers and physical properties in molten salts and their mixtures

2016 ◽  
Vol 190 ◽  
pp. 471-486 ◽  
Author(s):  
Dario Corradini ◽  
Paul A. Madden ◽  
Mathieu Salanne
Keyword(s):  
Relaxation Time ◽  
Physical Properties ◽  
Metal Cations ◽  
Alkali Halides ◽  
Coordination Shell ◽  
Atomic Scale ◽  
Trivalent Metal ◽  
Shear Relaxation ◽  
Glass Forming Materials ◽  
The Relationship

Mixtures of trivalent metal halides with alkali halides are involved in many technologies but, from a more fundamental and general perspective, are worthy of study as interesting systems in which to examine the relationship between atomic-scale structure and physical properties. Here we examine the relationship between the viscosity and local and longer range structural measures in such mixtures where the trivalent metal cations span a significant size range and exhibit different behaviours in the dependence of their viscosity on the mixture composition. We characterise the structure and dynamics of the first coordination shell and the relationship between its structural relaxation time and the shear relaxation time of the mixture (the Maxwell relaxation time). We are then led to an examination of the structure of the networks which progressively form between the trivalent metal cations as their concentration increases in the mixtures. Here we find significant differences between small and larger cations, sufficient to explain the different behaviour of their viscosities. We draw attention to the similarities and differences of these networks with those which form in highly viscous, glass-forming materials like BeF2:LiF.

Investigation of the density dependence of the shear relaxation time of dense fluids

2005 ◽  
Vol 83 (3) ◽  
pp. 236-243 ◽  
Author(s):  
Mehrdad Bamdad ◽  
Saman Alavi ◽  
Bijan Najafi ◽  
Ezat Keshavarzi
Keyword(s):  
Relaxation Time ◽  
Shear Modulus ◽  
Density Dependence ◽  
Radial Distribution ◽  
Shear Viscosity ◽  
Viscosity Coefficient ◽  
Dense Fluids ◽  
Lennard Jones ◽  
Shear Relaxation ◽  
Shear Relaxation Time

The shear relaxation time, a key quantity in the theory of viscosity, is calculated for the Lennard–Jones fluid and fluid krypton. The shear relaxation time is initially calculated by the Zwanzig–Mountain method, which defines this quantity as the ratio of the shear viscosity coefficient to the infinite shear modulus. The shear modulus is calculated from highly accurate radial distribution functions obtained from molecular dynamics simulations of the Lennard–Jones potential and a realistic potential for krypton. This calculation shows that the density dependence of the shear relaxation time isotherms of the Lennard–Jones fluid and Kr pass through a minimum. The minimum in the shear relaxation times is also obtained from calculations using the different approach originally proposed by van der Gulik. In this approach, the relaxation time is determined as the ratio of shear viscosity coefficient to the thermal pressure. The density of the minimum of the shear relaxation time is about twice the critical density and is equal to the common density, which was previously reported for supercritical gases where the viscosity of the gas becomes independent of temperature. It is shown that this common point occurs in both gas and liquid phases. At densities lower than this common density, even in the liquid state, the viscosity increases with increasing temperature.Key words: dense fluids, radial distribution function, shear modulus, shear relaxation time, shear viscosity.

Sign in / Sign up

Export Citation Format

Share Document