PARTICLE INTERACTIONS IN DIFFUSIOPHORESIS - AXISYMMETRICAL MOTION OF MULTIPLE SPHERES IN NONELECTROLYTE GRADIENTS

A combined analytical-numerical study is presented for the diffusiopho retic motion of a finite chain of colloidal spheres in a gradient of a n uncharged solute prescribed along their line of centers. The spheres may be made up from different materials and have arbitrary radii, and they are allowed to be unequally spaced. Also, the spheres can be eit her freely suspended in the fluid or connected by infinitesimally thin rods. The range of the interaction between the solute and the particl e surfaces is assumed to be small compared to the radius of each parti cle and to the gap thickness between any two neighboring particles, bu t the polarization effect of the diffuse solute in the thin particle-s olute interaction layers caused by the strong adsorption of the solute is incorporated. A slip velocity of the fluid and a normal flux of th e solute at the outer edge of the diffuse layer are used as the bounda ry conditions for the fluid domain outside the thin diffuse layers. Th rough the use of a collocation technique along with these boundary con ditions, a set of transport equations governing this problem is solved in the quasisteady limit and the particle interaction effects are com puted for various cases. It is found that diffusiophoretic particles w ith the same surface properties will interact with one another, unlike the no-interaction results obtained in previous studies assuming that the diffuse layer is infinitesimally thin. The larger the polarizatio n effect in the diffuse layer is, the stronger the particle interactio ns in diffusiophoresis are. Generally speaking, the particle interacti on effects can be quite significant under appropriate conditions.