How the polymer electrolyte PEO/LiTFSI penetrates narrow pores*

We investigate if and how the ionic conductivity and chain mobility of a polymer electrolyte is affected during imbibition and following imbibition in nanopores. To this end, the archetypal polymer electrolyte poly(ethylene oxide) (PEO)/LiTFSI is employed and nanoporous alumina is the confining medium. Overall the results of the evolution of conductivity in the PEO/LiTFSI polymer electrolytes suggest that the time-dependence of dc-conductivity during flow is dictated by the adsorption of polymer chains at the pore walls. They further show that at the early stages of imbibition the effective viscosity is reduced below the bulk value. It seems that at such early stages the pore walls act as lubricants for the chain segments and ions. At much later stages, polymer adsorption takes place. The time scale of adsorption is very long—much longer than chain diffusion and certainly much longer than the segmental relaxation. Adsorption involves several unfavorable configurations of the polymer chains that inevitably affect the ion dynamics by (i) increasing the effective viscosity (higher T_g) and (ii) by reducing the number of mobile ions. These results are important in the design of confined polymer electrolytes.