POSITRONIUM-SALT INTERACTIONS AND IONIC-CONDUCTIVITY IN POLY(2-HYDROXYETHYL METHACRYLATE) GEL ELECTROLYTES

The effects of copolymerization of poly(2-hydroxyethyl methacrylate) w ith oligo-(ethylene glycol) dimethacrylates (OEDs) on the ionic conduc tivity of the gel electrolyte copolymers was investigated. A series of HEMA-OED cross-linked copolymers were produced with the number of eth ylene glycol units varying between zero (uncross-linked) and nine. The conductivity of samples containing distilled and deionized water (DDI W) and 1 M KBr electrolytes was characterized by AC impedance measurem ents. The relationship between the amount of water/salt solution conta ined within the gel electrolytes and resultant conductivity is investi gated and discussed with reference to the free volume in the system. T he free-volume characteristics were probed by positron annihilation li fetime spectroscopy (PALS), and the influence of free volume and the a mount of water/solution in the gels on conductivity discussed. The res ults indicate a positive correlation between the amount of mobile cond ucting phase and the available free volume in the system, with the amo unt of conducting phase present matched by a proportionate amount of f ree volume in the gel. The system showed evidence of orthopositronium (oPs) inhibition in the ion containing samples when compared with the DDIW samples. Slight differences in the oPs pickoff rate recorded in D DIW and KBr solution are attributed to microviscosity differences betw een the two fluids, rather than oPs quenching. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.