Reversible pore gating in aqueous mixtures via external potential

Abstract

We examine theoretically porous membranes in aqueous mixtures. We show that large membrane pores can be reversibly gated from 'off' (co-solvent-rich, poor conductor of ions and other solutes) to 'on' (water-rich, good conductor) states by an external potential. The transition voltage or charge for switching depends on the membrane hydrophilicity/hydrophobicity, the salt content, the preferential solvation of the salt ions, and the temperature. These parameters also determine whether the filling transition is abrupt or gradual.

Controlled Chemical Kinetics in Porous Membranes

“…We give here a concise description of this state based on our previous work. 20 When an initially homogeneous polar mixture is found near charged walls, the polar solvent (water) is enriched near the surfaces (cosolvent is depleted) . If the surface potential ψ s is too small, the composition ϕ varies slowly in space and the system is close to mixing.…”

“…The shift of the filling temperature T(ϕ 0 ) away from the binodal curve is stronger when Δu ± or n 0 are large. 20 Figure 1a shows the change in composition profiles as the pore potential increases from zero. Profiles were obtained by a simultaneous numerical solution to the Euler−Lagrange and Poisson's nonlinear equations.…”

“…17−19 In the grandcanonical ensemble, the system is coupled to a reservoir at composition ϕ 0 where the potential vanishes and n 0 ± are the bulk ion densities, which define the chemical potentials. 20…”

Solvo-osmotic flow in electrolytic mixtures

“…figure 2 shows a good agreement between the full numerical solutions and the linear theory. The numerical profiles of ϕ and n ± decay to values that slightly differ from their bulk values due to a weak nonlinear effect induced by solvation (Samin & Tsori 2016). The thickness of the charged layer at the surface ρ(r) = 2en 0 (g D ϕ−Ψ ) could be estimated in experiments from the characteristic lengths q −1 i .…”

“…The differences between the electrostatics of neat solvents compared to solvent mixtures has also been an area of intense research in recent years, with the growing use of miscible and non-miscible oil-water mixtures in colloidal science and microfluidics. A crucial role is played by the partitioning of ions between solvents, due to their preferential solvation in one of the liquids (Onuki & Kitamura 2004;Tsori & Leibler 2007;Zwanikken & van Roij 2007;Ben-Yaakov et al 2009;Araki & Onuki 2009;Samin & Tsori 2011Okamoto & Onuki 2011;Bier et al 2011;Pousaneh & Ciach 2011;Samin & Tsori 2012;Bier et al 2012;Pousaneh & Ciach 2014;Michler et al 2015;Samin & Tsori 2016) . The preferential wetting of one liquid at a solid surface or the presence of a liquid-liquid interface therefore also affects the electrostatics of the mixture.…”