Two-dimensional (2D) correlation analysis based on time-resolved FT-IR/attenuated total reflection (ATR)spectroscopy has been used to study the diffusion behavior of water and mono- or divalent anions in thepositively charged membranes of different charge density. In 2D FT-IR/ATR spectra, the splitting of thewater
(OH) bending band in the spectral range
1700-
1500 cm
-1 indicates that there are three differentstates of water in the positively charged membrane, that is, the water molecules forming strong or weakhydrogen bonds with hydrophilic groups of the membrane and water molecularly dispersed with weakerhydrogen bonds. The wavenumber difference of the
(OH) band in the low- and high-charge-density membraneindicates that water molecules form much stronger hydrogen bonds with hydrophilic groups in the high-charge-density membrane. The sequential order of the three water bands intensity changes shows that, in theprocess of water diffusion into the high-charge-density membrane, the hydrogen-bonding interaction betweenhydrophilic groups of the membrane and water molecules takes place gradually due to the highly cross-linked network structure of the membrane; in the process of water diffusion into the low-charge-densitymembrane, the strong hydrogen-bonding interaction between hydrophilic groups of the membrane and watermolecules takes place instantaneously and this type of water easily diffuses due to the weak interactionsbetween the water molecules and the membrane polymer. Furthermore, the diffusion processes of the electrolytesolution such as NaAc and Na
2SO
4 aqueous solutions in the positively charged membrane have also beenexamined.