LIQUID ION-EXCHANGE MEMBRANES WITH WEAKLY IONIZED GROUPS .2. RESISTANCE ELECTROMOTIVE FORCE OF A THIN MEMBRANE

Previously developed theories for liquid ion-exchange membranes, in particular the conclusions of part I, are tested on a thin (0.65-mm) membrane formed by dissolving the acid cation exchanger bis(2-ethylhexyl)-phosphoric acid in amyl alcohol. This system is shown to conform reasonably well with the assumptions on which the theories are based, notably completely trapped sites with weakly ionized groups and a convection-free membrane. The transients of the emf and the membrane resistance are measured simultaneously following step changes in external-solution conditions containing mixtures of HCl and NaCl, from which it is concluded that the emf is established instantaneously long before the profiles have reached their steady states. Measurements are also made of the steady-state resistance for various external solutions and applied electric fields which confirm the theoretical predictions that the resistance is practically independent of the electric field but strongly dependent on the external-solution compositions. The ranges of concentrations in these experiments are chosen such that the co-ions are excluded from the membrane. However, experiments are also performed with HCl in different concentrations on the two sides of the membrane, and a strong rectification tendency is observed when the co-ions are not excluded which is also predicted by the theory.