Theories of Liquid Viscosity.

Brush, Stephen G.

doi:10.1021/cr60220a002

Cited by 99 publications

(37 citation statements)

References 164 publications

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“…21 In contrast we adopt Eq. ͑9͒ as a temperature-dependent relation between the viscosity and an effective activation barrier to be extracted from appropriate TSP trajectory data.…”

Section: B Single Path Approximationmentioning

confidence: 99%

Computing the viscosity of supercooled liquids

Kushima

Lin

et al. 2009

The Journal of Chemical Physics

139

184

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We describe an atomistic method for computing the viscosity of highly viscous liquids based on activated state kinetics. A basin-filling algorithm allowing the system to climb out of deep energy minima through a series of activation and relaxation is proposed and first benchmarked on the problem of adatom diffusion on a metal surface. It is then used to generate transition state pathway trajectories in the potential energy landscape of a binary Lennard-Jones system. Analysis of a sampled trajectory shows the system moves from one deep minimum to another by a process that involves high activation energy and the crossing of many local minima and saddle points. To use the trajectory data to compute the viscosity we derive a Markov Network model within the Green-Kubo formalism and show that it is capable of producing the temperature dependence in the low-viscosity regime described by molecular dynamics simulation, and in the high-viscosity regime (10(2)-10(12) Pa s) shown by experiments on fragile glass-forming liquids. We also derive a mean-field-like description involving a coarse-grained temperature-dependent activation barrier, and show it can account qualitatively for the fragile behavior. From the standpoint of molecular studies of transport phenomena this work provides access to long relaxation time processes beyond the reach of current molecular dynamics capabilities. In a companion paper we report a similar study of silica, a representative strong liquid. A comparison of the two systems gives insight into the fundamental difference between strong and fragile temperature variations. We describe an atomistic method for computing the viscosity of highly viscous liquids based on activated state kinetics. A basin-filling algorithm allowing the system to climb out of deep energy minima through a series of activation and relaxation is proposed and first benchmarked on the problem of adatom diffusion on a metal surface. It is then used to generate transition state pathway trajectories in the potential energy landscape of a binary Lennard-Jones system. Analysis of a sampled trajectory shows the system moves from one deep minimum to another by a process that involves high activation energy and the crossing of many local minima and saddle points. To use the trajectory data to compute the viscosity we derive a Markov Network model within the Green-Kubo formalism and show that it is capable of producing the temperature dependence in the low-viscosity regime described by molecular dynamics simulation, and in the high-viscosity regime ͑10 2 -10 12 Pa s͒ shown by experiments on fragile glass-forming liquids. We also derive a mean-field-like description involving a coarse-grained temperature-dependent activation barrier, and show it can account qualitatively for the fragile behavior. From the standpoint of molecular studies of transport phenomena this work provides access to long relaxation time processes beyond the reach of current molecular dynamics capabilities. In a companion paper we report a similar study of ...

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“…21 In contrast we adopt Eq. ͑9͒ as a temperature-dependent relation between the viscosity and an effective activation barrier to be extracted from appropriate TSP trajectory data.…”

Section: B Single Path Approximationmentioning

confidence: 99%

Computing the viscosity of supercooled liquids

Kushima

Lin

et al. 2009

The Journal of Chemical Physics

139

184

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“…Hence, the frictional force is related to Stokes coefficient (c), which is system-and temperature-dependent. When a solute particle exhibits Brownian motion in a solvent fluid, c tends to fall by increasing temperature [18]. In gaseous state, however, it increases with increasing the absolute temperature (T) and is found to be proportional to T 1/2 [18,19].…”

Section: Introductionmentioning

confidence: 99%

“…When a solute particle exhibits Brownian motion in a solvent fluid, c tends to fall by increasing temperature [18]. In gaseous state, however, it increases with increasing the absolute temperature (T) and is found to be proportional to T 1/2 [18,19]. In liquids, a variety of empirical models have been proposed to predict the temperature dependency of liquid viscosity.…”

Section: Introductionmentioning

confidence: 99%

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Effect of temperature on kinetic nanofriction of a Brownian adparticle

Jafary-Zadeh

Reddy

Zhang

2013

Chemical Physics Letters

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“…3 The equations concerning the macroscopic behavior of liquids are usually derived from considerations on microscopic models, and the theories more widely applied are based on the concept of a liquid structure which is assumed to be actually full of cavities or hole^.^-^ T h y constitute 211 extra volumc or "frec volund' v, which has been defined :is the cxccss of the specifi(* volumc of the liquid v ovcr that of thc corrcsporrding glass at :hsolutc zcro uU: Of = 1 -UIJ (1) Assuming that the molecular motions are permitted only if a free volume is available, the liquid fluidity should increase with vf, as suggested by Batschinki. ' The equation relating the viscosity tc the free volume, first given by Doolittle,* has been derived theoretically by Buecheg and Cohen and Turnbulllo on the basis of a liquid model of hard spheres within which there is a statistical redistribution of the free volume:…”

Section: Free Volume Representationmentioning

confidence: 99%

Viscosity of concentrated polymer solutions. II. Application of a free‐volume treatment to solutions of poly(vinyl chloride) in cyclohexanone and to other polymer solutions

Pezzin¹

1966

J of Applied Polymer Sci

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SynopsisThe Kelley-Bueche free-volume treatment of the viscosity of polymeric solutions has been applied to the previously reported data on poly(viny1 chloride)--cyclohexanone solutions and to several other polymer-diluent systems. It has been shown that the theoretical equations, based on the assumption of the additivity of free volumes of the components, are capable of predicting with remarkable accuracy the concentration, temperature, and molecular weight dependence of the viscosity of the investigated solutions over very large ranges of the variables.

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Theories of Liquid Viscosity.

Cited by 99 publications

References 164 publications

Computing the viscosity of supercooled liquids

Computing the viscosity of supercooled liquids

Effect of temperature on kinetic nanofriction of a Brownian adparticle

Viscosity of concentrated polymer solutions. II. Application of a free‐volume treatment to solutions of poly(vinyl chloride) in cyclohexanone and to other polymer solutions

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