Water structure and selective permeation of cellulose-based membranes

The techniques used in the study of water in pores are extensively reviewed. Particular importance is given to ATR-FTIR, which allows the study of the active layer in the wet state. Taking further advantage of this technique, mathematical simulation studies on the ATR-FTIR spectra of water in cellulose acetate and cellulose acetate butyrate asymmetric membranes are performed. The OH-stretching band in the spectra of cellulose acetate membranes is deconvoluted into four components, which are ascribed to water clusters of different sizes. Results support the idea that the apparent rejection to salts may be associated to the size and number of water clusters whereas the flux depends on other factors, e.g. the thickness of the active layer. The effect of salts, such as MgCl2 and KCl, on the structure of water in the pores is also studied. The ATR-FTIR spectra of membranes previously equilibrated with solutions of such salts are deconvoluted. (C) 1999 Elsevier Science B.V. All rights reserved.