Charge Transport and Dynamics of 2D-Confined Polymerized Ionic Liquids

Abstract

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.