Diffusiophoresis of a colloidal cylinder in an electrolyte solution near a plane wall

The diffusiophoretic motion of a circular cylindrical particle in an electrolyte solution prescribed with a transverse concentration gradient, which is arbitrarily oriented with respect to a plane wall parallel to its axis, is analyzed at the quasi-steady state. The thickness of the electric double layers adjacent to the particle and wall surfaces is taken to be small but finite, and the relaxation effect of their diffuse ions is allowed. Through the use of cylindrical bipolar coordinates, the equations of conservation governing this problem are solved, and the translational and angular velocities of the confined cylinder are computed for various cases. The influences of the confining wall and double-layer polarization on the diffusiophoretic mobility of the particle are found to be significant and complicated. The proximity of the plane wall can enhance or reduce the diffusiophoretic velocity and even reverse its direction, because the wall effect of hydrodynamic resistance on the particle is in the competition with that of electrochemical enhancement or retardation, and the wall effect on the chemiphoresis of the particle is in the competition with that on the induced electrophoresis. The direction of the diffusiophoretic motion of a particle near a plane wall is different from that of the prescribed concentration gradient, except when it is oriented parallel or perpendicular to the wall. The effects of the plane wall on the diffusiophoresis of a cylindrical particle are more significant than those of a spherical one at the same separation because of more effective particle-wall interaction surfaces.