Electrokinetic phenomena in microporous membranes with a fixed transverse charge distribution

Pressure-driven ionic transport through nanochannels with inhomogenous charge distributions

The effect of spatially inhomogeneous fixed charge distributions on the pressure-driven transport of ions through cylindrical nanopores have been investigated theoretically by means of an approximate version of the Poisson-Nernst-Planck model that can be used with confidence for moderately charged nanopores with radius smaller than the Debye screening length of the system. Salt rejection rate has been computed as a function of the applied pressure difference for various one-dimensional (1D) unipolar charge distributions and has been compared with that obtained for a homogeneously charged nanochannel with an identical average volume charge density. The ion rejection capabilities of charged nanopores can be optimized by an appropriate distribution of the fixed charge concentration. When ions are forced to enter the nanopores by the end with the lowest fixed charged concentration, the salt rejection rate exhibits a nonmonotonous variation with the applied pressure. This phenomenon has been attributed to the influence of the inhomogeneous charge distribution on the electric field that arises spontaneously so as to maintain the electroneutrality within the nanopore.

Low frequency changes in skin surface potentials by skin compression: experimental results and theories

Human living skin generates an increase in the skin potential when compressed. This was measured on eight subjects with a matrix of nine Ag/AgCl electrodes. The potential increased with the pressure until it reached a maximum. When the pressure was increased stepwise, the response showed an overshoot at each step. Human cadaver skin did not show these potential increments. Neither did pads of collagen, paper tissue soaked in a KCl solution, nor layers of cultured keratinocytes. Three theories are described that may explain the origin of the measured skin potentials. The first is based on the piezoelectric characteristics of proteins in the skin. The second theory assumes that the skin is a charged membrane which generates a streaming potential when deformed. A third theory is proposed in which deformation of absorbed charged protein layers on structures in the skin change the alignment of Donnan potentials in the surrounding tissue.