Diffusiophoresis of a Charge-Regulated Spherical Particle Normal to Two Parallel Disks

Abstract

The diffusiophoresis of a charge-regulated spherical particle normal to two parallel disks as a response to an applied uniform electrolyte concentration gradient is modeled theoretically. The fixed charge on the particle surface comes from the dissociation/association reactions of the functional groups, yielding a charge-regulated surface, which simulates biological cells. Numerical simulations are conducted to examine the behavior of a particle under various conditions: the parameters considered in the simulation include the thickness of the double layer, the charged conditions on the particle surface, the relative size of the particle, and the particle-disk distance. Because the diffusiophoretic mobility of a particle can be dominated by chemiphoresis, electrophoresis, or osmotic flow, the diffusiophoretic behavior of the particle is complicated. For instance, the diffusiophoretic mobility may have two local maximums and a local minimum as the thickness of the double layer varies. This behavior is of practical significance if diffusiophoresis is adopted as a separation operation or as a tool to characterize the surface properties of a particle.

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

“…As ka p increases, the type I (II) DLP increases (decreases), leading to the increase (decrease) in the induced electrophoresis driven by E IÀDLP (E IIÀDLP ). [48] The two competing opposite electrophoretic effects by E IÀDLP and E IIÀDLP lead to the decrease in the particle velocity as ka p increases. When ka p > (ka p ) c , the induced electrophoresis driven by E IÀDLP becomes dominant, leading to the particle migrating toward higher salt concentration, and the particle velocity increases as ka p further increases.…”

“…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.…”

Influence of double-layer polarization and chemiosmosis on the diffusiophoresis of a non-spherical polyelectrolyte

“…The first one comes from a deformed EDL, known as chemiphoresis or double-layer polarization (DLP). Two types of DLP need be considered: type I (II) DLP occurs inside (outside) the EDL, yielding a local electric field driving the particle toward the high-(low-) concentration side [17][18][19][20]. The second one arises from the difference in the ionic diffusivities, known as electrophoresis effect [21][22][23].…”

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

“…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.…”