Polymerized ionic liquids are a promising class of versatile solid-state electrolytes for applications ranging from electrochemical energy storage to flexible smart materials that remain limited by their relatively low ionic conductivities compared to conventional electrolytes. Here, we show that the in situ polymerization of the vinyl cationic monomer, 1-ethyl-3vinylimidazolium with the bis(trifluoromethanesulfonyl)imide counteranion, under nanoconfinement within 7.5 ± 1.0 nm diameter nanopores results in a nearly 1000-fold enhancement in the ionic conductivity compared to the material polymerized in bulk. Using insights from broadband dielectric and Raman spectroscopic techniques, we attribute these results to the role of confinement on molecular conformations, ion coordination, and subsequently the ionic conductivity in the polymerized ionic liquid. These results contribute to the understanding of the dynamics of nanoconfined molecules and show that in situ polymerization under nanoscale geometric confinement is a promising path toward enhancing ion conductivity in polymer electrolytes.

Polymerized ionic liquids are advantageous for numerous applications such as batteries, dye- sensitized solar cells, and fuel cells. The combination of thermal and electrochemical stability, non- flammability, and ionic conductivity of ionic liquids; the mechanical properties of polymers; and also the decoupling of ionic and segmental dynamics make polymerized ionic liquids promising alternatives to traditional polymer electrolyte solutions. However, their intrinsic ionic conductivities are typically too low for many applications. This shortfall may be improved with proper chemical design of the polymer backbone and ionic groups as well as nanoscale confinement of the polymer chains, which has been hypothesized to increase the free volume of the diffusing ion. This study investigates the confinement effects of poly(1-ethyl-3-vinylimidazolium) bis(trifluoromethylsulfonyl)imide polymerized ionic liquid within mesoporous silica membranes using broadband spectroscopy to probe charge transport and polymer dynamics. Confinement is achieved by in situ free-radical polymerization of the vinyl- imidazolium monomer within the various sized pores. The progression of monomer conversion and polymerization kinetics is observed as a function of pore diameter and thermolytic initiator concentration using Fourier transform infrared spectroscopy. The interplay of the nanoscale confinement and ionic conductivity are discussed in terms of the current understanding of charge transport and dynamics in confined polymerized ionic liquids.