Axisymmetric diffusiophoresis of a colloidal particle of revolution in nonelectrolyte gradients normal to one or two plane walls

A theoretical study of the quasisteady axisymmetric diffusiophoresis of a colloidal particle of revolution situated at an arbitrary position in a nonelectrolyte solution between two parallel plane walls is presented. The solute concentration gradient is uniformly imposed along the particle's axis of revolution and normal to the plane walls. The particle-solute interaction layer is assumed to be thin relative to the particle size and particle-wall gaps, but the polarization effect of the diffuse solute in the thin interfacial layer caused by the strong adsorption of the solute is incorporated. A method of distribution of spherical singularities within the particle is used to find the general solutions for the solute concentration and fluid velocity distributions. The solute polarization and fluid slip conditions at the particle surface are satisfied by applying a boundary collocation technique to these general solutions. Numerical results for the diffusiophoretic velocity of a prolate or oblate spheroid along its axis of revolution and perpendicular to one or two plane walls are obtained with good convergence behavior for various cases, and the boundary effect on the particle migration is found to be significant and interesting. The diffusiophoretic velocity of the confined spheroid for a given separation parameter normalized by that for the corresponding motion of an identical particle in an infinite fluid in general increases with an increase in its polarization parameter or axial-to-radial aspect ratio. The presence of the confining walls can reduce or enhance the particle velocity, depending upon the polarization parameter and aspect ratio of the particle as well as the relative particle-wall separation distances.