J.W. Dugger, M. Chen, T.E. Long, Y. Fu, R. Kumar, B.S. Lokitz, J.F. Browning
Oak Ridge National Lab,
Keywords: ionic block copolymers, neutron reflectometry, electric field, actuator, tunable materials
Summary:One of the rapidly developing frontiers in research and engineering applications is focused on the rational design of materials that have targeted functionalities and tunable responses to external stimuli. Such materials stand to revolutionize how structural components are designed for applications including flexible electronics, biomimetic devices, nanofluidics, as well as separation chemistry. A chief obstacle to achieving this capability is the lack of a fundamental understanding of how chemical structure and morphology give rise to macromolecular properties. With this in mind, our research explores how polymer structure, counterion species, and film morphology affects the electromechanical response of materials when exposed to external electric fields. While the actuating behavior of materials such as Nafion have been commonly investigated, the literature lacks a thorough understanding of how the aforementioned factors drive the electrostatic and mechanical stresses that result in material deformation. Our research has investigated how thin film morphology and counterion species affect the electromechanical response of diblock copolymers containing charged imidazolium groups using neutron reflectometry. The sensitivity of neutron reflectometry to scattering length density as well as sub-nanometer changes in thickness make it an ideal tool for investigating polymer and counterion mobility under applied fields. To this end, we have designed a vacuum chamber capable of applying electric fields to thin films during reflectometry measurements. This chamber was used at the liquids reflectometer (BL-4B) at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) to explore the electromechanical response of ionic block copolymers.