Diffusiophoresis in Multivalent Electrolytes

Abstract

Diffusiophoresis is the spontaneous movement of colloidal particles in a concentration gradient of solutes. As a small-scale phenomenon that harnesses energy from concentration gradients, diffusiophoresis may prove useful for passively manipulating particles in lab-on-a-chip applications as well as configurations involving interfaces. Though naturally occurring ions are often multivalent, experimental studies of diffusiophoresis have been mostly limited to monovalent electrolytes. In this work, we investigate the motion of negatively charged polystyrene particles in one-dimensional salt gradients for a variety of multivalent electrolytes. We develop a one-dimensional model and obtain good agreement between our experimental and modeling results with no fitting parameters. Our results indicate that the ambipolar diffusivity, which is dependent on the valence combination of cations and anions, dictates the speed of the diffusiophoretic motion of the particles by controlling the time scale at which the electrolyte concentration evolves. In addition, the ion valences also modify the electrophoretic and chemiphoretic contributions to the diffusiophoretic mobility of the particles. Our results are applicable to systems where the chemical concentration gradient is comprised of multivalent ions, and motivate future research to manipulate particles by exploiting ion valence.

Diffusioosmosis-driven dispersion of colloids: a Taylor dispersion analysis with experimental validation

“…2020; Wilson et al. 2020; Alessio et al. 2021), a dead-end pore configuration is used to set up a transient one-dimensional (1-D) diffusion of solutes; significant colloidal dispersion is observed, which the typical models are unable to capture.…”

Non-Faradaic Electric Currents in the Nernst-Planck Equations and Nonlocal Diffusiophoresis of Suspended Colloids in Crossed Salt Gradients

“…To my knowledge, the existing phenomena that have been discussed in the above context pertain to binary electrolytes or assume one-dimensional gradients [6,[19][20][21][22][23]. In this Letter, I argue that a still further enriched phenomenology arises in multicomponent electrolytes when concentration gradients are superimposed in different directions ("crossed" salt gradients).…”

CO2-driven diffusiophoresis and water cleaning: Similarity solutions for predicting the exclusion zone in a channel flow

“…Diffusiophoresis is the spontaneous motion of colloidal particles under a solute concentration gradient. Since the first recognition 1,2 , the phenomenon has been widely studied theoretically and experimentally [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] . When the solute is an electrolyte, the net motion of particles has electrophoretic and chemiphoretic contributions, induced by, respectively, the diffusivity difference(s) among the ions and the osmotic pressure gradient near the particle surface 5 .…”

“…Various experimental investigations have been reported for the diffusiophoresis of micron-sized particles, either in the presence or absence of liquid flow [12][13][14][18][19][20][21][22] . Recently, it has been demonstrated that dissolution of gas can drive diffusiophoresis of charged particles [22][23][24][25][26][27] .…”