Poly(ethylene oxide)-polyurethane/poly(acrylonitrile) semi-interpenetrating polymer networks for solid polymer electrolytes: vibrational spectroscopic studies in support of electrical behavior

Studies on solid polymer electrolyte systems based on semi-interpenetrating polymer networks of poly(ethylene oxide)-polyurethane and poly(acrylonitrile) (PEO-PU/PAN) doped with lithium trifluoromethanesulfonate (LiCF₃SO₃) is reported. Room temperature FT-IR analysis indicates a salt solvation process that occurs predominantly in the polyether segments of the semi-IPNs and incorporation of salt is also seen to favor a morphological change in the matrix with a transition from semi-crystalline to amorphous phase. From the relative band areas a critical concentration (C_c) of salt can be identified where concentration of ionic species, morphology and amount of transient crosslinks is optimal to impart maximum conductivity, which is in agreement with the room temperature conductivity results. Thermal analysis of the semi-IPN lends further support to this observation. The temperature dependence of conductivity is found to follow the Arrhenius behavior at low temperatures (∼ upto 328 K) and VTF dependence at higher temperatures. This crossover in temperature dependent conductivity is attributed to the change in the phase morphology of the semi-IPNs beyond the crystalline melting temperature (T_m1) of the polyether segments.