ION-EXCHANGE USING A SCINTILLATING POLYMER WITH A CHARGED SURFACE

The surface of a polystyrene-based plastic scintillator was sulfonated to yield an ultrathin cation-exchanging layer of well-defined geometry. The thickness of the layer (0.2-10 000 nm) is a strong function of the concentration of SO3 in the sulfonating reagent. Radioisotopes absorbed into this layer cause efficient scintillation, permitting in situ measurement of ion content, selectivity coefficients, and exchange kinetics. Self-exchange was performed using radiolabeled calcium (beta-emitter) as a probe ion, which could be displaced, with differing efficacy, by the addition of other cations. An electrochemistry-based analysis of the hydrodynamics of the system revealed that the rate-limiting process is diffusion through a thin film of solution at the surface of the exchanger rather than mass transport through the polymer.