The permeation of lipid substances through porous membranes

In aqueous systems, fatty acid salts below their critical micelle concentration (CMC) diffuse through collodion membranes of graded porosity at a rate which varies indirectly as the chain length of the fatty acids and directly as the porosity of the membranes. For a given salt the rate is somewhat less than for a nonelectrolyte of the same molecular weight.

When the concentration of the fatty acid salt is above the CMC, the rate is dependent on the size of the micelles relative to the pore size. Phospholipids, which exist in solution as very large micelles, are virtually impermeable even in very porous membranes. Cholesterol or benzene solubilized in lipid micelles can be transported through porous membranes, but the pores must be large enough to accommodate the micelles.