Electric Field Mediated Transport in Nanometer Diameter Channels

Abstract

Nanoporous polycarbonate (PCTE) nuclear-track-etched membranes were used to effect electric field modulation of the mass transport of cationic, anionic, and neutral species in aqueous buffer. The permeability response to electric fields depended on the molecular charge and electrolyte concentration. Solute and solvent fluxes through nanopores under an electrical potential result from a balance of diffusion, electroosmosis, and ion migration. The Debye length, κ -1 , associated with the electrical double layer within the pores relative to the pore diameter, 2a, plays a critical role in determining electrokinetic transport behavior. The channel walls adsorb anions preferentially to produce a largely immobile negative charge density, leaving a large and mobile cation population to mediate transport in the channel. By adjusting the supporting electrolyte concentration, κa can be tuned such that the electrical double layer is either small in relation to the pore (κa g 1) or more diffuse and spanning the pore (κa < 1). Electroosmotic transport, mediated primarily by buffer cations, dominates when κa < 1. In this case the pores are essentially permselective, and anion electromigration is virtually eliminated. When κa g 1, the sign of the applied potential can be used to select for anion vs cation/neutral molecule transport.

Electrokinetic transport and separations in fluidic nanochannels

“…The permeability of a nanoporous nuclear-track-etched polycarbonate membrane (PCTE), in a study by Kemery, Steehler, and Bohn, is shown to be dependent on the charge of molecules being electrokinetically driven through the negatively charged membrane as well as the ionic strength of the buffer used [109]. Adjusting the ionic strength of the buffer is an effective way to modify the length of the Debye layer.…”

Electroosmotic flow in nanoporous membranes in the region of electric double layer overlap

“…It is likely that the EDLs were overlapped in this study as the concentrations of buffer would produce Debye lengths of ~ 5-10 nm. Measurements in track-etched polymer membranes with pores of approximately 15 nm showed the persistence of EOF close to, but not beyond, the electric double layer overlap region (Kemery et al 1998). An experimental estimation of the magnitude of electroosmotic flow in the EDL overlap region is further complicated by practical limitations and by the presence of physical effects which prevent stable EOFs such as electrolysis and concentration polarisation (CP) (Erlandsson and Robinson 2011;Strickland et al 2010).…”

Tailoring of pore structure in mesoporous carbon for favourable flavin mediated interfacial electron transfer in microbial fuel cells

“…31 For the low ionic strength solution like 5 mM phosphate buffer, the double-layer thickness could reach 2-4 nm. 32 Hence, the MC-I shows reasonable avin redox behavior when the electrode was put into 0.1 M phosphate buffer. When the MC-I was applied in MFC anode with M9 medium (with similar ionic strength as 30 mM phosphate buffer), the relative low ion strength resulted in the increase of double-layer thickness, which would narrowed down the pore width and block the avin redox reaction.…”