Mechanical properties of PAN-based gel electrolytes: small-amplitude oscillatory shear study

Polymer electrolytes with ionic conductivities on the order of mS cm -1 at room temperature were prepared from the gelification of LiClO4/ethylene carbonate-propylene carbonate (EC-PC) solutions into a poly(acrylonitrile) (PAN) matrix. Oscillating rheological experiments were performed on gels prepared at different solvent/salt molar ratios in order to investigate their mechanical properties. Temperature sweep tests (25-120°C) showed changes in the rheological behaviour that was related to structural transitions. A strong-weak gel transition takes place at about 80°C, independent of salt concentration hence assignable only to the polymeric matrix, This transition is completely reversible during cooling ramps and represents a necessary mechanical property from a processing standpoint. A gel-sol transition was observed at ca. 110°C where both viscoelastic moduli reduce themselves by a factor 100, reporting the formation of a fluid system with G″>G'.