Selective Ion Transport and Complexation in Layer-by-Layer Assemblies of p-Sulfonato- calix[n]arenes and Cationic Polyelectrolytes

The 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, PRs, 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 PR values across a poly(styrene sulfonate) (PSS)/PVA multilayer membrane prepared under the same conditions. The PR values of the alkali‐metal salts are between 4 and 17 × 10–6 cm s–1, those of magnesium chloride and the transition‐metal salts are 0.2–1.3 × 10–6 cm s–1, and those of the lanthanide salts are about 0.1 × 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 calix4 especially is displaced during sulfate permeation. Self‐assembled films of p‐sulfonato‐calix[n]arenes with n = 4, 6, and 8 and poly(vinylamine) are prepared via alternating electrostatic layer‐by‐layer adsorption. First measurements of ion permeation indicate a highly selective transport with separation factor α(NaCl/LaCl3) as large as 143 or α(NaCl/MgCl2) as large as 72, for example. The selectivity originates from complex formation of distinct metal ions with the calix[n]arene units and from Donnan rejection of the permeating di‐ and trivalent ions fr