ISSN:
1572-8927
Keywords:
NMR-relaxation
;
hydration
;
ion-exchange resin
;
enthalpy
;
entropy
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Measurements of NMR spin-lattice relaxation times T 1 were performed for sorbed H2O and D2O in a sulfonated ion-exchange resin at varying degrees of hydration with alkaline cations as counter ions. From the sorption isotherms at three different temperatures the partial molar enthalpiesΔ $$\bar H$$ and entropiesΔ $$\bar S$$ of sorption show a minimum for all alkaline cations at water concentrations of n ≈0.8, i.e., there are 0.8 water molecules per −SO 3 − group. The first water molecules sorbed in the ion-exchange resin matrix are characterized by anisotrtopic rotational diffusion processes with correlation times of the order of τ1 ≈ 50 ns and τ2 ≈ 30 ps, respectively. This indicates that they are located in the electrostatic field between the corresponding ion pair. Although these two correlation times are very similar at a given temperature for all alkaline cations studied in the present investigation, the existence of a second spin-lattice relaxation time for sorbed H2O at n=0.8 indicates that for Cs about 50% of the sorbed water diffuses between locations in the resin. This fraction decreases with ionic radii and with falling temperatures. For Li the amount is less than 20%.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00650518
Permalink
