Effect of salt concentration on Tg and ionic conductivity in PEG-PU/NaSCN complexes
P.H. Huh, M.G. Choi, K.Y. Lee, N.J. Jo, J.O. Lee
Dept. of Polymer Sci. & Eng. Pusan National University,Keumjeong-ku, Pusan 609-735, Republic of Korea.
Solid polymer electrolytes based on poly(ethylene glycol)-polyurethane (PEG-PU) complexed with NaSCN salt have been prepared by the solvent casting method. A poly(ethylene glycol)-polyurethane (PEG-PU) material (PEG:MDI:BD = 2:1:2) was synthesized with a typical two-step condensation reaction. Effects of the salt concentration on the ionic conductivity (s ) and glass transition temperature (Tg) of the complex electrolytes thus prepared were investigated by using the alternating current (AC) impedance spectroscopy, differential scanning calorimetry (DSC) and dynamic mechanical thermal analyzer (DMTA). Both s and Tg values measured exhibited similar tendencies to have a maximum point within the range studied, probably due to two opposite effects, i.e., the increased number of carrier ions and decreased chain mobility (or increased Tg) caused by the increase in salt concentration. The highest conductivity on the order of 10-7 Scm-1 was obtained at about [O]/[Na+]=20 (0.75 mol salt per kg matrix polymer). Comparison of thermal and dynamic Tgís by DSC and DMTA, respectively, for PEG-PU/NaSCN complexes at different salt contents were also carried out for reference. The results obtained were morphologically confirmed with the atomic force microscope (AFM).