Dynamics of a PEG based polymer gel Electrolyte: A combined frequency dependent dielectric relaxation and Time-resolved fluorescence spectroscopic study

Abstract

• Industrially relevant polymer gel electrolyte studied via dielectric relaxation and time-resolved fluorescence spectroscopy. • Relaxation dynamics monitored by using non-reactive fluorescent probe coumarin153. • Prominent impact of polymer concentration on solution dynamics. • Decoupling of probe solvation dynamics from medium viscosity and probe rotational dynamics. • Signatures of temporal heterogeneity in these polymer gel electrolyte systems observed. Here we investigate the dynamics of a polyethylene glycol ( P E G ) based polymer gel electrolyte (PGE) media and its dependence on polymer concentration and temperature via frequency dependent dielectric relaxation (DR) and time-resolved fluorescence (TRF) spectroscopic measurements. The polymer gel electrolyte system consists of propylene carbonate (PC; organic solvent), lithium perchlorate ( L i C l O 4 ; electrolyte) and P E G 300 (polymer). The impact of polymer on the dynamics of the medium has been monitored via gradually increasing the polymer concentration in the PGE media keeping the P C / L i C l O 4 molar ratio (11.2) unchanged. Coumarin 153 ( C 153 ), a well-known fluorescent probe molecule, has been employed as a local reporter for the fluorescence based experiments. Although the static dielectric constant of the medium decreases systematically upon addition of P E G 300 in the electrolyte media, no such systematic variation with polymer concentration in the fractional power dependence of the measured average DR time with medium viscosity is observed for these electrolyte systems. Steady state fluorescence measurements in these PGE systems indicate substantial effect of polymer addition on the organic electrolyte system, while no signature of spatial heterogeneity has been detected up to 40 wt% polymer concentration. Interestingly, fractional power dependence, similar to DR findings, of average rotational time for C 153 on the medium viscosity has been observed for both the processes, one by varying temperature of the medium at a fixed polymer concentration and other by changing the polymer concentration at a fixed temperature. Surprisingly, the average solvation time shows negative power dependence to the temperature reduced medium viscosity.