Diffusiophoresis of charged colloidal particles in the limit of very high salinity

Abstract

Diffusiophoresis is the migration of a colloidal particle through a viscous fluid, caused by a gradient in concentration of some molecular solute; a long-range physical interaction between the particle and solute molecules is required. In the case of a charged particle and an ionic solute (e.g., table salt, NaCl), previous studies have predicted and experimentally verified the speed for very low salt concentrations at which the salt solution behaves ideally. The current study presents a study of diffusiophoresis at much higher salt concentrations (approaching the solubility limit). At such large salt concentrations, electrostatic interactions are almost completely screened, thus eliminating the long-range interaction required for diffusiophoresis; moreover, the high volume fraction occupied by ions makes the solution highly nonideal. Diffusiophoretic speeds were found to be measurable, albeit much smaller than for the same gradient at low salt concentrations.

Interfaces and mixing: Nonequilibrium transport across the scales

“…This issue reports significant successes that have been achieved recently in understanding interfaces, mixing, and nonequilibrium dynamics based on theoretical analysis, large-scale numerical simulations, laboratory experiments, and technology development (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34). These include theoretical approaches for handling complex multiscale, nonlocal, and statistically unsteady dynamics and boundary value problems; developments of efficient Eulerian and Lagrangian methods of large-scale numerical modeling; advancements in laboratory experiments in low-and high-energy density regimes; and possibilities for dramatic improvements in precision, accuracy, dynamic range, reproducibility, and data acquisition rate with the use of modern technologies (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34).…”

“…These works represent frontier research in interaction of molecules and chemical reactions, interfacial dynamics and nonequilibrium processes, fluid turbulence and turbulent mixing, supernovas and nuclear synthesis, formation of fluid phases at molecular scales, first-principlesbased reaction kinetics, ion transport of nanoscales, electric and magnetic fields structures, dynamics of high-energy density plasmas, subdiffusive and superdiffusive transport, formation of vortices in geophysical flows, diffusiophoresis of charged particles, and electron transport in macromolecules. They motivate the discussions of rigorous mathematical problems, theoretical approaches, and state-of-the-art numerical simulations along with advanced experimental methods and technological applications (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32).…”

“…The contributions in this issue include 6 perspective papers and 7 research papers (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32). They are ordered from perspective to research papers, from macroscopic to microscopic scales, and from fundamentals to applications.…”

The lift force on a charged sphere that translates and rotates in an electrolyte

“…For a silica colloid in water and at , which gives for a particle of radius . The ion diffusion coefficient is found from the Stokes–Einstein relation ; taking yields . Therefore, .…”

“…For instance, consider a particle settling under gravity, for which Stokes' drag law gives the sedimentation speed U = 2a 2 ⌬ g /9, where ⌬ is the difference in density between the particle and fluid and g = 9.81 m/s 2 is the gravitational acceleration. For a silica colloid in water ⌬ = 1.65 × 10 3 kg/m 3 and = 0.89×10 −3 Pa.s at T = 298 K, which gives U = 4.04 m/s for a particle of radius a = 1 m. The ion diffusion coefficient is found from the Stokes-Einstein relation D = k B T/6a ion ; taking a ion = 0.25 nm [13] yields D = 9.8×10 −10 m 2 /s. Therefore, Pe t = 0.004.…”