Nanoscale Resolution of Electric-Field Induced Motion in Ionic Copolymer Films

The development of ionic block copolymers with a tuneable elctromechanical response to applied electric fields stands to benefit a range of fields including biomimetic devices, flexible electronics, solid electrolytes for energy storage, and nanofluidics. Currently, this area lacks a thorough understanding of how chemical structure, morphology, and counterions dictate electromechanical processes such as expansion, contraction, or ion mobility of these systems on the nanoscale. Our research probes the electromechanical response of ionic block copolymer systems on the nanoscale using neutron reflectometry to elucidate the factors that govern these processes. We have designed and implemented a custom environmental chamber capable of applying electric fields while allowing the in situ collection of reflectivity data. Results indicate that the choice of counterion dictates whether expansion or contraction occurs in these films. Experimental results were compared directly to computational models mimicking the physical samples. These findings establish the drastic impact counterion identity has on electromechanical response and outlines the importance of pushing the resolution of experimental measurements to a length scale that converges with computational efforts.