Driving an electrolyte through a corrugated nanopore

Abstract

We characterize the dynamics of a z − z electrolyte embedded in a varying-section channel. In the linear response regime, by means of suitable approximations, we derive the Onsager matrix associated to externally enforced gradients in electrostatic potential, chemical potential, and pressure, for both dielectric and conducting channel walls. We show here that the linear transport coefficients are particularly sensitive to the geometry and the conductive properties of the channel walls when the Debye length is comparable to the channel width.In this regime, we found that one pair of off-diagonal Onsager matrix elements increases with the corrugation of the channel transport, in contrast to all other elements which are either unaffected by or decrease with increasing corrugation. Our results have a possible impact on the design of blue-energy devices as well as on the understanding of biological ion channels through membranes

Diffusive escape through a narrow opening: new insights into a classic problem

“…Clearly, a similar argument holds for the case of the EW with an energy barrier; in this case f can be interpreted as the rate of successful passages through the EW and is dependent on the energy barrier via the standard Arrhenius equation. Last but not least, even when the confining boundary is a structureless hard wall so that an energy barrier is absent, a particle, penetrating from a bigger volume (microdomain) to a narrower region of space, will encounter an entropy barrier ∆S at the entrance to the EW; in this case β∆S ∼ ln(a/R) [42,43], a being the lateral size of the escape window. This suggests, in turn, that κ, associated with an entropy barrier, depends linearly on a and hence, linearly on ε.…”

“…The particle may then adsorb onto the boundary in a non-localised way, perform surface diffusion and desorb back to the bulk, re-appear in the vicinity of the boundary again, and etc. This is precisely the physical picture underlying the idea of the so-called intermittent, surface-mediated search for the EW. or an entropy barrier, the latter being dominated by the window size [2,42,43]. Similarly, chemical reactions with a specific site on the boundary of the micro-domain are also never perfect but happen with a finite probability defining some rate constant κ [44].…”

Active microrheology in corrugated channels

“…For example, the transport across synthetic [1][2][3] and biological [4,5] channels and pores is controlled by their shape, as well as by the effective interactions between channel walls and the transported objects. Similarly, in micro-and nano-fluidic circuitry the shape of the channel has been exploited to realize fluidic transistors [6] or diodes [7][8][9] and to control ionic [10,11] and electro-osmotic [12] fluxes.…”

Local pressure for confined systems

“…Indeed, electrolytes confined in varying section pores have been observed to undergo novel regimes [7][8][9][10][11] absent in the corresponding unbound scenarios. Similarly both passive [12][13][14][15][16][17] and active [18][19][20][21][22] colloidal particles as well as polymers [23][24][25][26][27] display confinement-induced dynamical regimes when embedded within varying section channels. In order to unravel the the general mechanisms responsible of these diverse phenomena, it is of primary importance to understand the physical origin of the effective coupling between the fluid medium and the confining walls.…”