Diffusiophoretic Velocity Research Articles

Diffusiophoresis and electrophoresis of elliptic cylindrical particles

An exact analysis is presented for the diffusiophoresis and electrophoresis of a rigid elliptic cylindrical particle in a uniform applied field oriented arbitrarily with respect to its axis. The range of the interaction between the solute species and the particle surface is assumed 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 equations governing the system, a slip velocity of fluid and normal fluxes of solute species at the outer edge of the thin diffuse layer which balance convection and diffusion of the solute species along the particle 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 diffusiophoresis in a nonionic solute concentration gradient, diffusiophoresis in a concentration gradient of symmetric electrolyte, and electrophoresis in an external electric field. An interesting feature is found that the diffusiophoretic or electrophoretic velocity of the particle decreases with the reduction of the maximum length of the particle in the direction of migration. Also, the average migration velocity for an ensemble of identical, noninteracting elliptic cylinders with random orientation distribution is obtained for each case considered.

Diffusiophoresis and Electrophoresis of Colloidal Spheroids

An analytical study is presented for the diffusiophoresis and electrophoresis of a rigid nonconducting spheroid in a uniform applied field that is oriented arbitrarily with respect to its axis of revolution. The range of the interaction between the solute species and the particle surface is assumed to be small relative to the dimension of the particle, but the effect of polarization of the diffuse species in the thin solute-particle interaction layer is incorporated. To solve the conservative equations governing the system, a slip velocity of fluid and normal fluxes of solute species at the outer edge of the thin diffuse layer which balance convection and diffusion of the solute species along the particle surface are used as the boundary conditions for the fluid domain outside the diffuse layer. Explicit expressions for the migration velocity of the spheroidal particle are obtained for the cases of diffusiophoresis in a nonionic solute concentration gradient, diffusiophoresis in a concentration gradient of symmetric electrolyte, and electrophoresis in an external electric field. An interesting feature is found that the diffusiophoretic or electrophoretic velocity of the particle decreases with the reduction of the maximum length of the particle in the direction of migration. Also, the average migration velocity for an ensemble of identical, non-interacting spheroids with random orientation distribution is obtained for each case considered.

Diffusiophoresis and electrophoresis of colloidal cylinders

This paper deals with the theories of diffusiophoresis and electrophoresis of a rigid insulating cylinder of infinite length in a uniform applied field oriented arbitrarily with respect to its axis. The range of the interaction between the solute species and the particle's surface is assumed small relative to the particle's radius, but the polarization of the diffuse species in the solute-particle interaction layer is allowed. To solve the conservative equations governing the system, a slip velocity of fluid and normal fluxes of solute species at the outer edge of the thin diffuse layer can be used as the boundary conditions for the fluid domain outside the diffuse layer. Expressions for the migration velocity of the particle are obtained in simple closed forms for the cases of diffusiophoresis in a nonelectrolyte gradient, diffusiophoresis in a gradient of symmetric electrolyte, and electrophoresis in an external electric field. A remarkable feature is found that the diffusiophoretic or electrophoretic velocity of the cylinder in a transverse imposed field, neglecting the end effects, is exactly the same as the corresponding velocity of a rigid sphere with an equal radius.

Measurement of diffusiophoresis in liquids

By formulating diffusiophoresis as a multicomponent diffusion phenomenon, diffusiophoretic velocities may be measured directly. A diaphragm cell has been used to measure diffusiophoresis of 0.198-μm polystyrene latex particles in various electrolyte solutions. The experiments have shown that both the diffusion potential and chemiphoretic contributions to the total diffusiophoretic velocity can be identified individually. Agreement between measurements and existing theories of diffusiophoresis in electrolyte solutions is excellent, demonstrating both the validity of the theories and of the experimental method.

The separation of micron‐size particles from air by diffusiophoresis

AbstractThe continuous separation of micron‐size particles from air by diffusiophoresis in a parallel plate collector was studied theoretically. Two models for the particle behavior were considered. Model I was based on the assumption that the particles adopt the local fluid velocity whereas the Schmitt‐Waldmann equation was used to determine the diffusiophoretic velocity in Model II. The latter also included thermophoretic and gravitational effects.The two models yielded similar results when diffusiophoresis was predominant. The theoretical results were also used in the sizing of an experimental particle collector. The collector, which operated under laminar flow conditions, was capable of removing the particles effectively and its performance conformed with the theoretical work.