Selective ion transport and complexation in layer-by-layer assemblies of p-sulfonato-calix[n]arenes and cationic polyelectrolytes

ne first study of ion transport across self-assembled multilayered films of p-sulfonato-calix[n]arenes and poly(vinyl amine) (PVA) is presented. The films,are prepared by the alternate electrostatic layer-by-layer assembly of the anionic calixarenes and cationic PVA on porous polyacrylonitrile (PAN) supports. We use tetra-p-sulfonato-calix[4]arene (calix4), hexa-p-sulfonato-calix[6]arene (calix6), and octa-p-sulfonato-calix[8]arene (calix8) as the calixarenes. Ultraviolet (UV) studies indicate that dipping solutions of pH 6.8, without a supporting electrolyte, are most suited for film preparation. Calix8 is adsorbed in higher concentrations per layer than calix6 or calix4, probably because desorption is less pronounced. The permeation rates, P(R)s, of monovalent alkali-metal chlorides (Li, Na, K, Cs), magnesium chloride, divalent transition-metal chlorides (Ni, Cu, Zn), trivalent lanthanide chlorides (La, Ce, Pr, Sm), and sodium sulfate across the calix4/PVA, calix6/PVA, and calix8/PVA membranes are studied and compared with the corresponding P-R values across a poly(styrene sulfonate) (PSS)/PVA multilayer membrane prepared under the same conditions. The P-R values of the alkali-metal salts are between 4 and 17 X 10(-6) cm s(-1), those of magnesium chloride and the transition-metal salts are 0.2-1.3 x 10(-6) cm s(-1), and those of the lanthanide salts are about 0.1 X 10(-6) cm s(-1). Possible origins for the large differences are discussed. Ion transport is first of all controlled by electrostatic effects such as Donnan rejection of di- and trivalent ions in the membrane, but metal-ion complexation with the calixarene derivatives also plays a role. Complexation occurs especially between Li+ or Na+ and calix4, Mg2+, or Cu2+ and calix6, Cu2+, Zn2+, or the lanthanide ions and calix8. Divalent sulfate ions are found to replace the calixarene polyanions in the membrane. UV studies of the permeate solutions indicate that calix4especially is displaced during sulfate permeation.