Positronium-salt interactions and ionic conductivity in poly(2-hydroxyethyl methacrylate) gel electrolytes

The effects of copolymerization of poly(2-hydroxyethyl methacrylate) with oligo-(ethylene glycol) dimethacrylates (OEDs) on the ionic conductivity of the gel electrolyte copolymers was investigated. A series of HEMA-OED cross-linked copolymers were produced with the number of ethylene glycol units varying between zero (uncross-linked) and nine. The conductivity of samples containing distilled and deionized water (DDIW) and 1 M KBr electrolytes was characterized by AC impedance measurements. The relationship between the amount of water/salt solution contained within the gel electrolytes and resultant conductivity is investigated and discussed with reference to the free volume in the system. The free-volume characteristics were probed by positron annihilation lifetime spectroscopy (PALS), and the influence of free volume and the amount of water/solution in the gels on conductivity discussed. The results indicate a positive correlation between the amount of mobile conducting phase and the available free volume in the system, with the amount of conducting phase present matched by a proportionate amount of free 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 DDIW and KBr solution are attributed to microviscosity differences between the two fluids, rather than oPs quenching. (C) 1998 Elsevier Science Ltd. All rights reserved.