The effects of the addition of ionic liquid (IL) in pristine poly(ethylene oxide), PEO and polymer electrolyte (PEO + 10 wt.% LiClO4) membranes on melting temperature (T-m), degree of crystallinity (X-c) and crystallization kinetics (by DSC using isothermal technique and growth of spherulites observed under polarizing optical microscope) are reported. The addition of IL amorphocises both PEO and PEO + LiClO4 membranes resulted in corresponding decrease in the degree of crystallinity, T-m, and crystallization rate. The effect was more evident as the IL content in the membrane was increased. (C) 2013 Elsevier B.V. All rights reserved.