Electrolytic solutions in ethylene glycol: ultrasonic and positron annihilation studies

Electrolytic solutions (KCl, KBr, tetra-n-butylammonium bromide--TBABr and hydrated cerium(III) chloride--CeCl3·6H2O) in ethane-1,2-diol (ethylene glycol) were studied using sound velocity, density and positron annihilation technique. For simple electrolytes (KCl, KBr, TBABr), effects similar to those known for respective aqueous solutions were observed: the slope of the dependence of sound velocity on salt concentration decreases with increasing size of solvated ion; for TBABr this dependence is even negative. It was also observed that in the latter system the adiabatic compressibility coefficient (calculated from density and sound velocity) is not linear with concentration, suggesting either structural transformations of the bulk solvent or easy formation of contact ionic pairs. Cerium chloride solutions were found to behave different. An anomaly occurs at CeCl3·6H2O mole fraction between 0.001 and 0.002, again interpreted either in terms of formation of ionic pairs of cations bonded by glycol molecules or cooperative interactions between glycol molecules in the close environment of the cerium ion (in inner solvation sphere) and those in the bulk. Positron annihilation measurements confirm well the conclusions arising from the ultrasonic ones