PMMA-based polymer gel electrolytes containing NH4PF6: Role of molecular weight of polymer

The effect of the molecular weight of polymethylmethacrylate (PMMA) on the conductivity and viscosity behavior of proton conducting polymer gel electrolytes containing ammonium hexafluorophosphate (NH4PF6) in propylene carbonate (PC) has been studied. The addition of PMMA having molecular weights: 15,000; 120,000; 350,000; 996,000 results in an increase in conductivity and gels with conductivity higher than the corresponding liquid electrolytes have been obtained. The maxima observed in the variation of conductivity with PMMA concentration shifts towards higher concentrations of PMMA with an increase in the molecular weight of PMMA. The increase in conductivity with PMMA addition also depends upon the molecular weight of PMMA and has been found to be more for gels containing PMMA with lowest molecular weight (15,000). The increase in conductivity at low concentrations of PMMA is due to an increase in free ion concentration with the dissociation of ion aggregates, whereas the decrease in conductivity at higher concentrations of PMMA, is due to the exponential increase in viscosity, which lowers mobility and as a result conductivity decreases. These gels show high value of conductivity (∼10−2 S/cm at 25 °C) which does not vary with time and shows only a small increase over the 20–100 °C temperature range and is desirable for their potential use in applications.