Transport of non-associated electrolytes in acrylamide hydrogels

Diffusion of non-associated electrolytes (LiCl and KCI) in different hydrogels has been studied to identify the mechanism of electrolyte interaction with the structure of hydrogels and its dependence on electrolyte concentration and thermodynamic features of the electrolyte. Hydrogel membranes have been prepared from acrylamide (AAm) using N,N'-methylene-bisacrylamide (MBAAm) as the cross-linker. Properties of membranes have been altered varying the content of cross-linker. Integral diffusion coefficients of potassium chloride and lithium chloride in the hydrogel membranes have been compared with mutual diffusion coefficients of those electrolytes in aqueous solutions. The study of electrolyte diffusion was supported by data on water solubility in hydrogels (degree of swelling, and sorption and desorption isotherms) showing dependence of electrolyte diffusion coefficient on water content inside polymer matrix. Thermodynamic study showed irreversible character of the sorption of solutes, probably due to acidic hydrolysis of amide groups of gels. The main features, which characterise properties of aqueous solution of strong electrolytes, remain in polymer matrix thus defining diffusion coefficients and other parameters representative of electrolyte transport in polyacrylamide hydrogels. (C) 2001 Elsevier Science B.V. All rights reserved.