A network microcapillary model for electrokinetic phenomena through microporous membranes

The streaming potential and the electro-osmotic pressure are calculated thr ough a simulation procedure, for a membrane consisting of a sample of equal ly charged pores, but are arranged differently to approach the real structu re of actual membranes. It is presumed that a microporous membrane consists in an ensemble of cylindrical microcapillaries with the same pore charge d ensity. The pores can have two sizes, which can be interconnected in three main ways: (1) parallel, (2) series, and (3) square network. On the other h and, it is assumed that these two pore sizes are, in fact, the central valu es of two Gaussian distributions, of equal relative standard deviations. In particular, here, mean diameters 0.2 or 0.1 and 0.02 or 0.01 mu m, with st andard deviations of 0%, 15% and 25%, in parallel, series and network struc tures, are considered. This is carried out for several charge densities and concentrations of LiCl aqueous solutions. In these conditions, both the st udied electro-kinetic parameters are determined by the widest pore in paral lel, and its narrowest section. Interconnections of pores are seen to play a significant role, only when narrow and wide pores are almost equally pres ent. Increasing standard deviations affect differently, but only slightly, the overall result for the electro-kinetic parameters, depending on the ass umed structure. All these results indicate that high concentration results of streaming potential should be preferred, to obtain the membrane charge v ersus the concentration profiles. (C) 1998 Elsevier Science B.V. All rights reserved.