Novel Solid-State Polymer Electrolyte Consisting of a Porous Layer-by-Layer Polyelectrolyte Thin Film and Oligoethylene Glycol

A novel solid-state polymer electrolyte was constructed using layer-by-layer (LbL) polyelectrolyte assembly of linear poly(ethylenimine) (LPEI) and poly(acrylic acid) (PAA), combined with a plasticization step using oligoethylene glycol dicarboxylic acid (OEGDA). This composite film exhibits a relatively high ionic conductivity of 9.5 × 10-5 S/cm at 25 °C and 22% relative humidity. Detailed characterization of the composite was undertaken using grazing-angle Fourier transform infrared (GA-FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and impedance spectroscopy. After immersing the LPEI/PAA films into OEGDA aqueous solutions, the films exhibited a swelling behavior and increased surface roughness indicative of porosity induced by reorganization of ionic interactions between LPEI and PAA in acidic solution. This internal porous structure allows inclusion of OEGDA within the multilayer and increased ionic conductivity under ambient conditions due to the combined effects of plasticization of the LbL matrix by atmospheric water as well as the added mobility of ions in molten OEGDA within the composite.