A most interesting result of a recently completed study of aqueous and methanolic solutions was the observation of solute/solvent clustering in solutions undergoing reverse osmosis. Previously, many believed that there was some sort of surface interactions between the membrane and the solutes that would prevent the solutes from permeating the membrane. In our study, the membrane was composed of simple Lennard-Jones particles with no additional coulombic forces. The figures given below are from the results of this study.

For further information, one should consult our article "Molecular simulation of osmosis, reverse osmosis, and electro-osmosis in aqueous and methanolic electrolyte solutions" (Molecular Physics, 1998, Vol. 95, No. 3, 401-408).

 This schematic diagram shows the relative sizes of the solutes and solvent relative to the size of the pores in the membrane. Note that the sodium and lithium ions should easily fit through the pore if they are not clustered with solvent molecules.

 This picture shows an ion-solvent cluster. Note how the sodium ion is completely surrounded by water molecules. The electrostatic forces that bind the ion to the water molecules is strong enough to prevent the ion from penetrating the membrane.

 This figure shows that the ion-solvent clusters form larger clusters.