Enhancement of membrane transport of ions by spatially nonuniform electric fields

Abstract

The influence of spatially nonuniform electric fields on the transport of ions through ion-selective membranes is investigated both experimentally and theoretically. The flux of ions is determined indirectly by following the change of pH with time. The uniformity of the field is varied with a Pt wire electrode configuration by changing the relative positions of the anode and cathode. Higher fluxes are found for the nonuniform configuration than for the uniform configuration. These results were previously predicted in a theoretical investigation which revealed the importance of nonlinearity in the transport laws. The experimental observations are found to be consistent with theoretical calculations based on the Goldman flux equation.

Understanding Complexity in Biophysical Chemistry

“…In the case of a linear flux equation, this analysis showed that spatial nonuniformities should have no effect on the average rate of transport; in the case of nonlinear flux laws, the transport rate can be either enhanced or reduced, depending on the specific pattern of nonuniformity. This theoretical analysis was followed by an experimental investigation 78 designed to test the predictions of the model. This project was my first foray into the world of experimental science, a humbling but very important step for any theoretician or computational scientist to takesand I would suggest that eVery theoretician should, at least, collaborate closely with experimentalists.…”

“…The flux can, thus, be measured by following the change of pH with time in one of the compartments. Our experiments showed 78 that the flux did, in fact, increase in the presence of a nonuniform applied electric field as compared to that measured in the presence of a uniform applied field; the increase was on the order of 8-10% depending on the magnitude of the applied potential (here about 2 V). To ensure that our analysis was valid, we imposed nonuniform fields the spatial average of which was equal to that of the uniform field with which we made the direct comparison.…”

“…This theoretical analysis was followed by an experimental investigation designed to test the predictions of the model. This project was my first foray into the world of experimental science, a humbling but very important step for any theoretician or computational scientist to takeand I would suggest that every theoretician should, at least, collaborate closely with experimentalists.…”

Characterizing Flux through Micro- and Nanostructured Composites

“…Larter , has shown that when J l ( x 0 , x ) varies in space, flux through the system will be higher than when local flux is spatially invariant and equal to the spatial average of J l ( x 0 , x ). That is, local nonuniform gradients enhance flux.…”

Control of the Fixed Charge Distribution in an Ion-Exchange Membrane via Diffusion and the Reaction Rate of the Monomer

“…The properties of an ion-exchange membrane are determined by its chemical or physical characteristics, such as the type of fixed charge (cationic or anionic), ion-exchange capacity, the fixed charge distribution, and the hydrophobic or hydrophilic nature of the base polymer. , Despite extensive studies on the effect of the characteristics on the properties of an ion-exchange membrane, the studies on the effect of the fixed charge distribution (uniform or nonuniform) over the cross section of an ion-exchange membrane on its properties have involved only a theoretical approach because of the difficulties associated with the preparation of an ion-exchange membrane having controlled fixed charge distributions using currently available techniques. − Therefore, the control of the fixed charge distribution during the preparation of an ion-exchange membrane makes it possible to study the effect of the fixed charge distribution from an experimental point of view, which can provide useful information for applications.…”