Viscous flow and self-diffusion in densely and loosely packed metallic melts

Pure substances can often be cooled below their melting points and still remain in the liquid state. For some supercooled liquids, a further cooling slows down viscous flow greatly, but does not slow down self-diffusion as much. We formulate a continuum theory that regards viscous flow and self-diffusion as concurrent, but distinct, processes. We generalize Newton's law of viscosity to relate stress, rate of deformation, and chemical potential. The self-diffusion flux is taken to be proportional to the gradient of chemical potential. The relative rate of viscous flow and self-diffusion defines a length, which, for some supercooled liquids, is much larger than the molecular dimension. A thermodynamic consideration leads to boundary conditions for a surface of liquid under the influence of applied traction and surface energy. We apply the theory to a cavity in a supercooled liquid and identify a transition. A large cavity shrinks by viscous flow, and a small cavity shrinks by self-diffusion.

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First-principles study of self-diffusion and viscous flow in diopside (CaMgSi2O6) liquid

American Mineralogist ◽

10.2138/am.2012.4123 ◽

2012 ◽

Vol 97 (11-12) ◽

pp. 2049-2055 ◽

Cited By ~ 14

Author(s):

A. K. Verma ◽

B. B. Karki

Keyword(s):

Viscous Flow ◽

First Principles ◽

Self Diffusion ◽

First Principles Study

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Viscosity and self-diffusion in benzene-cyclohexane mixtures

Australian Journal of Chemistry ◽

10.1071/ch9640516 ◽

1964 ◽

Vol 17 (5) ◽

pp. 516 ◽

Cited By ~ 7

Author(s):

DA Collins ◽

H Watts

Keyword(s):

Activation Energy ◽

Diffusion Coefficient ◽

Viscous Flow ◽

Mole Fraction ◽

Excess Volume ◽

The Self ◽

Excess Viscosity ◽

Self Diffusion ◽

Mole Fraction Range ◽

Self Diffusion Coefficient

The self-diffusion coefficient of benzene in benzene-cyclohexane mixtures was measured at 15�, 25�, and 35�. Viscosities of the mixtures were measured at the same temperatures. The diffusion coefficient is a maximum, while the viscosity is a minimum at a mole fraction of benzene between 0.6 and 0.8. The activation energy for viscous flow is a minimum in the mole fraction range 0.6-0.8 of benzene. The excess viscosity and the excess activation energy of viscous flow are minimal at a mole fraction 0.5, the same composition at which the maxima occur in excess volume and heat mixing. The product Dn is a linear function of mole fraction.

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Permeability in Relation to Viscosity and Structure of Rubber

Rubber Chemistry and Technology ◽

10.5254/1.3543138 ◽

1942 ◽

Vol 15 (3) ◽

pp. 537-544 ◽

Cited By ~ 3

Author(s):

Richard M. Barrer

Keyword(s):

Viscous Flow ◽

Thermal Energy ◽

Diffusion Constant ◽

The Self ◽

Self Diffusion ◽

Functional Relations ◽

Diffusion Media ◽

Entropy Of Activation ◽

Arrhenius Energy ◽

And Diffusion

Abstract Some properties of flow of solutes in and through rubbers are outlined. These properties indicate that, due to fluctuations of thermal energy, activated zones exist in certain polymers, of which viscous flow and diffusion are a consequence. A simple statistics of activated zones has been given, and from it equations are obtained for ΣN, D, Ds, and η, denoting respectively the total number of activated zones in rubber, the diffusion constant of simple solutes in the polymer, the self-diffusion constant of rubber, and its viscosity. Functional relations are predicted between log Do, log ηo, or ΔS* (the entropy of activation) and the Arrhenius energy of activation for diffusion or viscous flow. The available data clearly demonstrate this relationship. They also indicate no discontinuity between rubbers and liquids as diffusion media.

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