DIFFUSION THROUGH NARROW PORES - MOVEMENT OF IONS, WATER AND NONELECTROLYTES THROUGH TRACK-ETCHED PETP MEMBRANES

The rates at which ions (Rb-86(+), [H-3]-choline, Cl-36), (H2O)-H-3 an d nonelectrolytes ([C-14]-urea, [C-14]glycerol, and [C-14]-sugars) equ ilibrate across track-etched polyethyleneterephthalate (PETP) membrane s (isotopic diffusion) have been measured by a 'static' and a 'dynamic ' technique under conditions where no net flow takes place; the two te chniques give essentially the same results. All tracers diffuse faster the longer the membranes are etched, consistent with an increase in p ore size, Water and neutral solutes diffuse at rates that are relative ly independent of ionic strength, pH or the presence of divalent catio ns. Diffusion of cations is decreased by high ionic strength, by reduc ing pH or by addition of divalent catons; diffusion of chloride is inc reased by these procedures. Treatment of the membrane with diazomethan e to reduce the negative fixed charge decreases diffusion of cations a nd increases that of anions; diffusion of water and neutral solutes is unaffected by methylation except in the membranes with the narrowest pores (i.e., those etched for the shortest time), in which case diffus ion is reduced. We conclude (1) that the special features of flow near a charged surface apply to ions but not to water or nonelectrolytes a nd (2) that calculation of absolute rates of diffusion leads to values for the radii of pores through track-etched PETP membranes that are i n remarkably good agreement with measured values.