Liquid-porous sorbent equilibrium

If the membrane happens to be porous (or microporous) and uncharged, the nature of the liquid-membrane equilibrium will be determined by the relative size of the solute molecules with respect to the pore dimensions in the absence of any specific solute-pore wall interaction. Similar considerations are also valid for liquid-porous sorbent equilibria. If the solute dimensions are at least two orders of magnitude smaller, then the solute concentration in the solution in the pore should be essentially equal to that in the external solution. However, the solute concentration in the porous membrane/porous sorbent/gel will be less than that in the external solution due to the porosity effect. Assuming that the solute exists only in the pores of the memhrane/porous sorbent with a porosity e , the value of kirn should be equal to the membrane or sorbent porosity e if the solute characteristic dimensions are at least two orders of magnitude smaller than the radius of the pore. 

The radius, r, cm, of the solute molecule (which is assumed spherical) needs to be known in liquid-porous membrane/porous sorbent equilibrium. For relatively small molecular species, the specific molar volume of the solute will lead to... 

There are two aspects to liquid-membrane equilibrium. The first one is concerned with the osmotic equilibrium between two solutions on two sides of a semipermeable membrane permeable to the solvent and impermeable to the solute the second one covers partitioning of the solute between the solution and the membrane. Both porous and nonporous membranes are of interest. The second aspect is also useful for porous sorbent/gel particles. 

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