Boundary Effect on Diffusiophoresis: Spherical Particle in a Spherical Cavity

Abstract

The boundary effect on the diffusiophoretic behavior of a particle is analyzed theoretically by considering the diffusiophoresis of a charged sphere under arbitrary surface potential and double-layer thickness at an arbitrary position in an uncharged spherical cavity. We show that the phenomenon under consideration is governed by double-layer relaxation, chemiosmotic/diffusioosmotic flow, and two types of competing double-layer polarization. The presence of the cavity has a profound influence on the diffusiophoretic behavior of the particle, especially when the surface potential is high. For instance, the scaled diffusiophoretic velocity of the particle has a local maximum as the position of the particle varies; it may have a local maximum and local minimum as the thickness of the double-layer varies. The significance of the effect of double-layer relaxation depends upon the level of surface potential and magnitude of the electric Peclet number.

Diffusiophoresis of an Elongated Cylindrical Nanoparticle along the Axis of a Nanopore

“…thick EDL and small gap between the particle surface and nanopore wall), the EDL surrounding the charged nanoparticle is compressed by the nanopore wall, and the type I DLP mainly arises from the EDL compression by the boundary. [34,37,38,48] If the EDL compression by the nanopore wall is insignificant, as the ratio a/a p increases, the degree of DLP decreases, leading to the decrease in the induced electrophoresis arising from the DLP-induced electric fields.…”

“…Compared to the conventional electrophoresis, driven by an externally imposed electric field, diffusiophoresis is driven by an imposed salt-concentration gradient, and thus avoids the Joule heating effect arising from the electric field present in a typical electrophoresis system. [38] Recently, diffusiophoresis has been successfully demonstrated to be an efficient means to manipulate particles in such processes as separation, sorting or focusing of colloidal particles for various microfluidic applications. [35,41,47] The possible control of the electrophoretic motion of a spherical nanoparticle in a nanopore by the diffusiophoretic control has been theoretically demonstrated.…”

Diffusiophoresis of a soft spherical particle along the axis of a cylindrical microchannel

“…If we let f, v, and n j be the electrical potential, the velocity of the liquid phase relative to the particle, and the number concentration of ionic species j, respectively, then the present problem can be described by the set of equations below (Hsu et al, 2007a(Hsu et al, , 2009b(Hsu et al, , 2010aKeh and Jan, 1996;Lou and Lee, 2008;Prieve et al, 1984;Zhang et al, 2009):…”

“…Dukhin and Deryagin (1974) initiated the analysis of diffusiophoresis and proposed that it plays a significant role in the deposition of rubber latex films on a salt-coated surface. If the liquid phase is an electrolyte solution, then the mechanisms involved in diffusiophoresis include double-layer polarization (DLP) (Hsu et al, 2009b), electrophoresis (Hsu et al, 2007b;Pawar et al, 1993), solvent flows (Chen and Keh, 2005;Hsu et al, 2010c;Keh and Ma, 2005), and the interaction between the coins outside the double layer and the particle (Hsu et al, 2010a). Because these mechanisms are not independent of each other, the phenomenon under consideration is complicated.…”

“…In fact, depending upon the geometry considered, the presence of a boundary is capable of accelerating, decelerating, and even reversing the direction of diffusiophoresis. The geometries considered in previous studies include, for example, a charged particle moving normal to a plane (Keh and Jan, 1996;Lou and Lee, 2008), parallel to two parallel planes (Chen and Keh, 2005), perpendicular to two parallel planes (Hsu et al, 2010c), in a spherical cavity (Hsu et al, 2009b;Zhang et al, 2009), and along the axis of a cylindrical pore (Hsu et al, 2010a). Hsu et al (2010a) found that the diffusiophoretic behavior of a sphere in the cylindrical pore can be quite different from that in other types of boundary.…”