IONICALLY CONDUCTING POLYETHER COMPOSITES

Ionic conductivity in polymer-salt electrolytes occurs in the amorphou s regions of the complex. Poly(ethylene oxide) (PEO) is the best polye ther for complexing salts. Unfortunately, it is partially crystalline at ambient temperatures. With inorganic (i.e., alumina) or organic (i. e., poly(acrylamide) (PAAM)) fillers the crystallization of PEO is inh ibited and the room temperature conductivity is enhanced in these mixe d phase systems by over two orders of magnitude (ro similar to 10(-4) S/cm) above the base PEO-salt system (<10(-6) S/cm). Even adding PAAM to an initially amorphous system (oxymethylene-linked PEO-LiClO4) incr eases the room temperature conductivity by 2 to 3 times. Various alkal i metal salts (Li, Na) and NH4SCN are used with alpha-Al2O3, theta-Al2 O3, PAAM' and poly(N,N'-dimethyl acrylamide) as filters. The aluminas stiffen the complex and increase T-g. The addition of the organic fill ers lowers T-g, as is to be preferred. It is suggested that changes in thr conductivity with changes in salt and filler concentration ari du e to changes in the ultrastructure and morphology and are the result o f an equilibrium between various Lewis acid - Lewis base reactions. Qu alified success has been achieved in modelling ionic conductivity in t hese composite electrolyte systems using an effective medium approach. In this approach it has been assumed that the main conductivity enhan cement takes place in thin amorphous levers of the polyether that coat the dispersed polyacrylamide particles separated in a microphase. In the best complexes this layer Is identified by a second T-g.