DIFFUSIOPHORESIS AND ELECTROPHORESIS OF ELLIPTIC CYLINDRICAL PARTICLES

An exact analysis is presented for the diffusiophoresis and electropho resis of a rigid elliptic cylindrical particle in a uniform applied fi eld oriented arbitrarily with respect to its axis. The range of the in teraction between the solute species and the particle surface is assum ed to be small relative to the minimum dimension of the particle, but the effect of polarization of the diffuse species in the thin particle -solute interaction layer is incorporated. To solve the conservative e quations governing the system, a slip velocity of fluid and normal flu xes of solute species at the outer edge of the thin diffuse layer whic h balance convection and diffusion of the solute species along the par ticle surface are used as the boundary conditions for the fluid domain outside the diffuse layer. Expressions for the migration velocity of the particle are obtained in closed forms for the cases of diffusiopho resis in a nonionic solute concentration gradient, diffusiophoresis in a concentration gradient of symmetric electrolyte, and electrophoresi s in an external electric field. An interesting feature is found that the diffusiophoretic or electrophoretic velocity of the particle decre ases with the reduction of the maximum length of the particle in the d irection of migration. Also, the average migration velocity for an ens emble of identical, noninteracting elliptic cylinders with random orie ntation distribution is obtained for each case considered.