Enhanced Electromechanical Responses in Films Containing Charged Di-block Copolymers

Thin films of dibock copolymers with an ionic block covalently linked to a deuterated neutral block were studied using in situ specular neutron reflectivity in applied voltages of varying magnitudes. Effects of applied voltages (0.5, 2, 5, and 7 kV in vacuum) at room temperature and 120^o C were studied. Analysis of the specular reflectometry data shows that electric field doesn’t affect the local structure at the room temperature. In contrast, local structural rearrangements were observed in the films at even 0.5 kV at 120^o C, which corresponds to electric field < 1V /μm. Such an enhanced electromechanical response of the film is attributed to the presence of bromine counterions, in agreement with previous theoretical studies. Overall, this work confirms the significant role played by counterions in affecting electromechanical responses of ionic diblock copolymers.