CHROMOIONOPHORE-MEDIATED IMAGING OF WATER TRANSPORT IN ION-SELECTIVE MEMBRANES

The K+ complex of 2-(4-dipropylaminophenylazo)benzoic acid octadecyl e ster (ETH 2418), a new lipophilic chromoionophore, is used to monitor the water uptake of dry solvent polymeric membranes based on 2-nitroph enyl octyl ether/poly(vinyl chloride) (2:1). Upon contact with an alka line solution, its lambda(max) changes from 535 to 435 nm. This proces s can be reversed by drying the membranes. From the time-dependent rec ordings of absorbance changes, an apparent water diffusion coefficient , D-H2O, of 2x10(-8) cm(2) s(-1) is determined. In contrast to results obtained with hydrophilic water indicators, no light scattering due t o water droplets is observed in the bulk of the membrane.