Measurement of Diffusiophoresis in Liquids via a Ternary Diffusion Formulation
Lechnick, William Jay
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https://hdl.handle.net/2142/69746
Description
Title
Measurement of Diffusiophoresis in Liquids via a Ternary Diffusion Formulation
Author(s)
Lechnick, William Jay
Issue Date
1984
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Abstract
The phenomenon of diffusiophoresis causes a flux of micron and sub-micron sized particles as the result of the movement of some solute in solution. This phenomenon is quantified for a system of charged polystyrene latex-electrolyte-water.
Diffusiophoresis is modeled as a ternary diffusion effect with the polystyrene cross-term diffusion coefficient (D(,12)) being related to this effect. The ternary diffusion formulation is derived from irreversible thermodynamics. Ternary diffusion coefficients are obtained by means of a modified, high cell constant diaphragm cell.
A pattern search method based on the minimization of residuals is developed for determining ternary diffusion coefficients from diaphragm cell raw data when the cross term diffusivities are large relative to the main term diffusivities. The need for a pattern search method which directly calculates residuals arises because previous methods, which approximate the residuals, are unable to adequately handle systems with dominant cross-term diffusivities.
Studies of various concentrations of polystyrene latex in the presence of 1.25 x 10('-3) M 1:1, 2:1, and 2:2 electrolytes demonstrated that the diffusiophoretic velocity is independent of particle concentration. These studies also demonstrated, via experiment, the existence of two distinct diffusiophoretic effects, diffusion potential and chemiphoresis, as previously predicted by theory. Chemiphoresis is shown to always cause the particle to move toward areas of higher electrolyte concentration and to be the same magnitude for all electrolytes of a particular type while the direction and magnitude of diffusion potential depends upon the charge of the particle and the diffusion characteristics of the ions making up the electrolyte. Simple analytical theories accurately predict the magnitude of the diffusion potential for electrolyte concentrations above 1 x 10('-3) M but overestimate the actual values for electrolyte concentrations below 1 x 10('-3) M. These studies also demonstrated that the chemiphoretic effect is accurately predicted by a previous numerical solution of the Navier-Stokes equation.
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