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

Abstract

The translation of a charged, elongated cylindrical nanoparticle along the axis of a nanopore driven by an imposed axial salt concentration gradient is investigated using a continuum theory, which consists of the ionic mass conservation equations for the ionic concentrations, the Poisson equation for the electric potential in the solution, and the modified Stokes equations for the hydrodynamic field. The diffusiophoretic motion is driven by the induced electrophoresis and chemiphoresis. The former is driven by the generated overall electric field arising from the difference in the ionic diffusivities and the double layer polarization, while the latter is generated by the induced osmotic pressure gradient around the charged particle. The induced diffusiophoretic motion is investigated as functions of the imposed salt concentration gradient, the ratio of the particle's radius to the double layer thickness, the cylinder's aspect ratio (length/radius), the ratio of the nanopore size to the particle size, the surface charge densities of the nanoparticle and the nanopore, and the type of the salt used. The induced diffusiophoretic motion of a nanorod in an uncharged nanopore is mainly governed by the induced electrophoresis, driven by the induced electric field arising from the double layer polarization. The induced particle motion is driven by the induced electroosmotic flow, if the charges of the nanorod and nanopore wall have the same sign.

Diffusiophoresis of a polyelectrolyte in a salt concentration gradient

“…The spontaneous movement of charged colloids in an electrolyte solution subject to an applied salt gradient, known as diffusiophoresis , has been studied recently by many investigators both theoretically and experimentally . Compared to conventional electrophoresis operations, diffusiophoresis has the advantages such as no Joules heat effect and metals in electrical contact .…”

Electrophoretic motion of a nanorod along the axis of a nanopore under a salt gradient

“…In the present study we extend this work [55] further, and combine the conventional electrophoresis, driven by the imposed electric field, with the diffusiophoresis, driven by the imposed salt concentration gradient, to analyze the regulation of electrophoresis of an elongated nanoparticle with the diffusiophoresis, providing further insights into this complicated but important problem. In the continuum model used the polarization of the EDL is fully accounted for with no assumption made concerning the thickness of the EDL, the magnitude of the zeta potential or surface-charge density, and that of the electric field or concentration gradient imposed.…”

“…More rigorous studies on the diffusiophoresis are performed by the authors for a spherical nanoparticle [50][51][52]. In order to mimic stretched DNAs translocating in a nanopore [61], our theoretical study was extended to an elongated cylindrical nanoparticle [55].…”

Diffusiophoretic mobility of charge‐regulating porous particles

“…This migration is known as diffusiophoresis [1][2][3][4][5][6] and provides a mechanism in various practical applications such as particle characterization, transport, manipulation, separation, and deposition in microfluidic and other devices [7][8][9][10]; DNA translocation and sequencing [11][12][13]; pattern formation [14,15]; and autonomous motions of micro/nano-motors [16][17][18]. For a charged particle in an ionic fluid, the particle-ion interaction is in the range of the reciprocal of the Debye screening parameter .…”