The dependence of morphology of solid polymer electrolyte membranes on transient salt type: effect of cation type

The structures of poly(N-vinyl pyrrolidone) (PVP) and poly(ether sulfone) composite membranes were investigated with transient salt addition. The effects of type and concentration of AgNO3 and Cu(NO3)(2) on membrane morphology were evaluated through attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, differential scanning calorimetry (DSC) and atomic force microscopy. Complex formation between carbonyl groups (on PVP chains) and Cu2+ or Ag+ decreases the strength of the carbonyl bond as evidenced through ATR-FTIR spectroscopy. The results indicate that the copper salts create more powerful interactions than the silver salts in the polymer matrix. DSC experiments reveal that the glass transition temperature of polymeric films containing silver or copper cations is lower than that of the PVP reference film. Comparison of the thermograms of PVP + AgNO3 and PVP + Cu(NO3)(2) shows that copper ions disrupt the polymer crystallinity more than silver ions. Therefore, DSC observations confirm the ATR-FTIR results in the case of the strength of the complexes formed. A morphological analysis of membrane surfaces reveals the existence of electrostatic interactions in the polymeric membrane structure. This is a result of the addition of salt to the casting solution, wrinkling the polymer chains including the surface layer, and accordingly the surface of the facilitated transport membranes is rougher than the initial PVP membrane. (C) 2010 Society of Chemical Industry