Diffusion polarization, solution velocity effect

An increase in feed concentration alters the viscosity, density, and diffusivity of the feed solution, causing a decrease in permeate flow rate [7]. An increase in tanperature results in a decrease in fluid viscosity and increase in molecular mobility, that is, in diffusivity. For its part, an increase in tangential velocity increases the permeate flow rate by provoking greater turbulence, causing a dispersion in the solute molecules concentrated on the monbrane surface, reducing the thickness of the gel layer. This is one of the simplest and most effective methods to control the effect of concentration polarization [6,14,15]. 

Equations 1 and 2 indicate that the diffusiophoretic velocities of a particle are independent of the particle size and shape (and there is no rotational motion of the particle). However, their validity is based on the assumptions that the local radii of curvature of the particle are much larger than the thickness of the particle-solute interaction layer (diffuse layer) at the particle surface and that the effect of polarization (relaxation effect) of the diffuse solute species in the interfacial layer due to nonuniform osmotic flow is negligible. Important advances have been made in the past in the evaluation of the diffusiophoretic velocities of colloidal particles relaxing these assumptions and will be discussed below. 

It could be found from Eqs. 5 and 11 that the effect of polarization of the diffuse layer is to decrease the particle velocity. The reason for this outcome is that the transport of the solute within... 

When the polarization effect of solute species in the diffuse layer surrounding the particle is considered, the particle-interaction and boundary effects on diffusiophoresis can be quite different from those on electrophoresis, due to the fact that the particle size and some other unique factors are involved in each transport mechanism. Through the use of a boundary collocation method, the quasisteady axis3mmetric diffusiophoresis of a chain of colloidal spheres with thin but polarized diffuse layers was examined and numerical results of the diffusiophoretic velocity of the particles were presented for various cases. The diffusiophoretic velocities of two spherical particles with thin polarized diffuse layers but with arbitrary surface properties, arbitrary sizes, and arbitrary orientation with respect to the imposed solute concentration gradi-... 

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