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Poly(ethylene terephthalate) (PET) track-etched membranes with average pore diameters of 692 and 1629 nm were functionalized using the monomer N-isopropylacrylamide (NIPAAm) and a photoinitiated "grafting-from" approach in which a surface-selective reaction has been most efficiently achieved by combinations of the unmodified PET surface with benzophenone and, alternatively, of an aminated PET surface with benzophenone carboxylic acid. Consistent estimations of the pore diameters of the base PET membranes and of the effective grafted polyNIPAAm layer thicknesses on the PET pore walls were possible only on the basis of the permeabilities measured with aqueous solutions of higher ionic strength (e.g., 0.1 M NaCl). However, the permeabilities measured with ultrapure water indicated that the "electroviscous effect" was significant for both base membranes. The influences of membrane pore diameter, surface charge, and solution ionic strength could be interpreted in the framework of the space-charge model. Functionalized membranes with collapsed grafted polymer hydrogel layer thicknesses of a few nanometers exhibited almost zero values of the zeta potential estimated from the trans-membrane streaming potential measurements. This was caused by a "hydrodynamic screening" of surface charge by the neutral hydrogel. Very pronounced changes in permeability as a function of temperature were measured for PET membranes with grafted polyNIPAAm layers, and the effective layer thickness in the swollen state--here up to approximately 300 nm--correlated well with the degree of functionalization. The subtle additional effects of solution ionic strength on the hydrodynamic layer thickness at 25 degrees C were different from the effects for the base PET membranes and could be explained by a variation in the degree of swelling, resembling a "salting-out" effect. Overall, it had been demonstrated that the functionalized capillary pore membranes are well suited for a detailed and quantitative evaluation of the relationships between the synthesis, the structure, and the function of grafted stimuli-responsive polymer layers.

A mechanistic understanding of transport phenomena in compacted clays is essential for the use of such materials as engineered barrier systems for the safe geological disposal of radioactive wastes. The present contribution is a first step in the development of an integrative treatment of the properties of tracer cations in compacted bentonites with respect to diffusion and sorption. The diffusion of 22Na and 85Sr in highly compacted montmorillonite and kaolinite is investigated as a function of the "external salt concentration" (NaClO4), i.e., of the solution in equilibrium with the clay. Consistent results were obtained from through-diffusion experiments and tracer profile analysis. Knowledge of genuine diffusion coefficients of the filter plates turned out to be crucial in cases where the diffusive resistance of the filter plates was similar to that of the clay. Diffusion coefficients formally calculated on the basis of the tracer concentration gradient in the external aqueous phase, and the sorption distribution ratios were found to decrease with increasing external salt concentration in the case of montmorillonite. In a logarithmic representation of these data, a slope of -1 was obtained for the monovalent 22Na, whereas the slope was -2 for the divalent 85Sr. In the case of kaolinite, diffusion coefficients were independent of the external salt concentration. It is postulated that the diffusion of the tracer cation through the interlayer water is the dominant pathway in compacted swelling clays under the experimental conditions tested. Effective diffusion coefficients, based on a tracer concentration gradient in the interlayer water of the clay, were found to be independent of the composition of the external aqueous phase. The latter gradient is assumed to be a function of the external salt concentration, according to a calculated distribution of the tracer cation between free pore water and the interlayer water via cation exchange.

Electrodialysis (ED) membranes typically exhibit modest selectivities between monovalent and divalent ions. This paper reports a dramatic enhancement of the monovalent/divalent cation selectivities of Nafion 115 membranes through coating with multilayer poly(4-styrenesulfonate) (PSS)/protonated poly(allylamine) (PAH) films. Remarkably, K(+)/Mg(2+) ED selectivities reach values >1000, and similar monovalent/divalent cation selectivities occur with feed solutions containing K(+) and Ca(2+). For comparison, the corresponding K(+)/Mg(2+) selectivity of bare Nafion 115 is only 1.8 ± 0.1. However, with 0.01 M KNO3 and 0.01 M Mg(NO3)2 in the source phase, as the applied current density increases from 1.27 to 2.54 mA cm(-2), the K(+)/Mg(2+) selectivities of coated membranes decrease from >1000 to 22. Water-splitting at strongly overlimiting current densities may lead to a local pH increase close to the membrane surface and alter film permeability or allow passage of Mg(OH)x species to decrease selectivity. When the source phase contains 0.1 M KNO3 and 0.1 M Mg(NO3)2, the K(+) transference number approaches unity and the K(+)/Mg(2+) selectivity is >20,000, presumably because the applied current is below the limiting value for K(+) and H(+) transport is negligible at this high K(+) concentration. The high selectivities of these membranes may enable electrodialysis applications such as purification of salts that contain divalent or trivalent ions.