Water structures in ion-exchange resin particles: Solvation dynamics of Nile Blue A

The structures of water, partitioned in cation-exchange resin particles, were studied on the basis of fluorescence dynamics of Nile Blue A (NB). The fluorescence lifetime of NB in the resin was longer than that in water and increased with increasing cross-linking density of the resin (ρ). The results demonstrated that the water structures in the resin were significantly different from those in water and dependent on ρ. A study on solvation dynamics of NB in the resin, reflecting structured water around the ion-exchange group, revealed the roles of "bound water" molecules in the water structures, since the solvent relaxation time (τs) in the resin was much longer than that in water and depended on ρ; τ_S increased from 34 to 55 ps with increasing p from 2 to 8%. The origin of the ρ dependence of τ_S was discussed in terms of the separation distance between the ion-exchange groups, and the effects of the counterion of the ion-exchange group on the solvation processes were also discussed.