Diffusiophoresis and Diffusio-osmosis into a Dead-End Channel: Role of the Concentration-Dependence of Zeta Potential

Abstract

Chemically induced transport methods open up new opportunities for colloidal transport in dead-end channel geometries. Diffusiophoresis, which describes particle movement under an electrolyte concentration gradient, has previously been demonstrated in dead-end channels. The presence of solute concentration gradients in such channels induces particle motion (phoresis) and fluid flow along solid walls (osmosis). The particle velocity inside a dead-end channel is thus influenced by particle diffusiophoresis and wall diffusio-osmosis. The magnitude of phoresis and osmosis depends on the solute’s relative concentration gradient, the electrokinetic parameters of the particle and the wall, and the diffusivity contrast of cations and anions. Although it is known that some of those parameters are affected by electrolyte concentration, e.g., zeta potential, research to date often interprets results using averaged and constant zeta potential values. In this work, we demonstrate that concentration-dependent zeta potentials are essential when the zeta potential strongly depends on electrolyte concentration for correctly describing the particle transport inside dead-end channels. Simulations including concentration-dependent zeta potentials for the particle and wall matched with experimental observations, whereas simulations using constant, averaged zeta potentials failed to capture particle dynamics. These results contribute to the fundamental understanding of diffusiophoresis and the diffusio-osmosis process.

Diffusiophoretic Behavior of Polyelectrolyte-Coated Particles

“…It was previously observed that the electrolyte concentration inside the dead-end channel can influence the zeta potential of the particles, which further affects the dynamics of the particles. 15,19 Here, we observed stable zeta potential values throughout the experimental range after coating with polyelectrolytes, allowing for experimental investigation with a constant zeta potential of particles. Diffusiophoresis experiments were performed with one bilayer of PDADMAC/PSS-coated particles that were coated at varying salt concentrations during coating.…”

“…For example, theoretical calculations (based on eq ) show that a change of zeta potential from −10 to −55 mV results in approximately an order of magnitude difference in diffusiophoretic velocity for the same NaCl gradient. Previously, we experimentally demonstrated that the change in salt concentrations influences the diffusiophoretic particle mobility, resulting in a deviation between numerical predictions based on constant zeta-potential and experimental results for the case when the particle zeta potential strongly depends on the salt concentration . We were able to achieve good agreement between experiments and simulations by adjusting the zeta potential according to the salt concentration at a given location and time.…”

“…53 To describe the zeta potential change with salt concentration for the PDMS surface, we used the following equation: ζ = a + b log 10 (c) with a = 6.27 mV and b = 29.75 mV where c is in M, as in our previous work. 15 UV−vis spectroscopy was used to analyze the poly-(styrenesulfonate) amount, 22 using a UV−vis spectrophotometer (Shimadzu UV-1800, Japan) at λ max = 225 nm, the maximum absorbance wavelength for PSS. See Supporting Information S2 for the details of the analysis and calibration curves.…”

Diffusioosmotic dispersion of solute in a long narrow channel

“…2017; Gupta, Shim & Stone 2020 b ; Alessio et al. 2022; Lee, Lee & Ault 2022; Migacz & Ault 2022; Akdeniz, Wood & Lammertink 2023). For typical solutes with modest zeta potentials, the diffusioosmotic mobility, , can range from approximately to .…”

Diffusiophoresis-enhanced Turing patterns

“…This regime might appear to be difficult to obtain in the absence of fluid flow. However, such a regime is commonly observed in microfluidic experiments with colloidal particles via the process of diffusiophoresis, i.e., transport of colloidal particles in response to solute concentration gradients (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30). The key feature observed in diffusiophoretic systems is the banding of colloidal particles that creates a region of sharp colloidal concentration gradients (18,21,25,26,(29)(30)(31).…”