Mechanism of Osmotic Flow in Porous Membranes

Abstract

A model for osmotic flow in porous membranes is developed from classical transport and thermodynamic relations. Mathematical expressions for the reflection coefficient as a function of solute dimension and shape, and more generally pore/bulk distribution coefficient, are derived for long cylindrical pores of circular cross section. For a rigid, spherical macromolecule the osmotic reflection coefficient equals (1 - Phi)(2), where Phi is the solute distribution coefficient; this result differs significantly from expressions found in the literature. The effect of weak solute adsorption to (or repulsion from) the pore wall can also be accounted for in the derivation. The driving force for osmotic flow arises from solute-pore wall interactions which cause radial variations in concentration and concomitant gradients in pressure normal to the wall. Implications of this three-dimensionality of osmotic phenomena are discussed with particular reference to the adequacy of one-dimensional treatments in relating reflection coefficient to membrane and solute properties.

Effects of electric charge on osmotic flow across periodically arranged circular cylinders

“…The predicted values of ω and σ s exhibited reasonable agreement with experimental observations (Sugihara-Seki 2006). Zhang, Curry & Weinbaum (2006) studied osmotic flow through the EGL model using a method developed by Anderson & Malone (1974) for osmotic flow in porous membranes. From considerations of classical transport and thermodynamics, Anderson & Malone (1974) showed that the presence of an exclusion region of solute near the pore walls produces a radial discontinuity in hydrostatic pressure and solute concentration, which generates the driving force for the osmotic flow.…”

“…Zhang, Curry & Weinbaum (2006) studied osmotic flow through the EGL model using a method developed by Anderson & Malone (1974) for osmotic flow in porous membranes. From considerations of classical transport and thermodynamics, Anderson & Malone (1974) showed that the presence of an exclusion region of solute near the pore walls produces a radial discontinuity in hydrostatic pressure and solute concentration, which generates the driving force for the osmotic flow. Zhang et al (2006) applied this formulation to the osmotic flow across the EGL model consisting of hexagonally arranged cylinders.…”

“…In a previous study , we examined the charge effect on the osmotic flow for membranes with circular cylindrical pores by extending the formulation of osmotic flow developed by Anderson & Malone (1974). We considered the case in which the surfaces of the solute and the pore walls are negatively charged, and the solvent is an electrolyte containing small ions.…”

Osmotic reflextion coefficients of capillary walls to low molecular weight hydrophilic solutes measured in single perfused capillaries of the frog mesentery.

“…The results of capillary E from Table 2 are compared, in Fig. 5, with theoretical curves consistent with the equations of Curry (1974) and Anderson & Malone (1974). A curve drawn for a pore radius of 1-1 or 1P2 nm fits the data for sodium chloride and urea but is inconsistent with the data for sucrose which is fitted by a theoretical curve for a pore radius of 2-4 nm.…”

“…to= PC (1-P)+a-P. Bean, 1972;Curry, 1974;Anderson & Malone, 1974 The data in Tables 1 and 2 Tables 1 and 2 These calculations suggest that about 10 % of the average filtration coefficient is represented by the exclusive water pathway (the cells), the remainder being accounted for by the shared pathway (the pore system). They also offer evidence for the hypothesis that variations in permeability properties between different capillaries arise from variations in the number rather than the dimensions of the 'pores'.…”