The diffusiophoretic motion of a colloidal sphere suspended in a nonelectrolyte solution possessing a uniform solute concentration gradient is analytically studied for a small but finite Péclet number Pe. The interfacial layer of interaction between the solute molecules and the particle surface is assumed to be thin, but the polarization of its mobile molecules is allowed. Through the use of a method of matched asymptotic expansions, the continuity and momentum equations governing the problem are solved and an expansion formula for the diffusiophoretic velocity of the particle good to O(Pe3) is obtained in closed form. This singular perturbation analysis shows that the perturbed solute concentration and fluid velocity fields are of O(Pe), but the first correction to the particle velocity is of O(Pe2). This correction can be either negative or positive depending on the relaxation parameter of the thin interfacial layer, indicating that the effect of solute convection is complex and can retard or enhance the diffusiophoresis of the particle. The solute convection effect is generally negligible as Pe ≤ 0.1 but significant as Pe equals about unity.
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