ELECTROCHEMICAL CONTROL OF BLOCK COPOLYMER SELF-ASSEMBLY

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

ABSTRACT Considerable theoretical and experimental effort has led to an understanding of the effect of conventional variables such as temperature and pressure on the self-assembly of block copolymers. In this project one uses electrochemical potential to control the formation of block copolymer nanostructures, which represents a significant departure from the conventional approach because these systems are inherently out of equilibrium. This study is motivated by both a lack of fundamental understanding of the coupling between electric fields and self assembly in soft matter, and the practical advantages that arise due to ease with which electric fields can be controlled and applied. The systems of interest are ferrocene containing block copolymers. Preliminary data indicate that these organometallic block copolymers respond reversibly to electric potentials of 2 V/cm: the ordered state is stable near the positive electrode and the disordered stare is stable near the negative electrode. This is in sharp contrast to previous attempts to use electric fields to control block copolymer self assembly wherein fields as high as 105 V/cm are needed to induce irreversible changes in microstructure alignment. The required block copolymers will be synthesized by anionic polymerization. A fraction of the ferrocene (Fc) groups on the chain, which are in the uncharged state under normal conditions after synthesis, will be oxidized to ferrocenium (Fc+) in the presence of a suitable counterion (e.g. Fc+NO3). The polymer will be dissolved in an electrolyte and placed in an electrochemical cell. Reversible transformations between Fc and Fc+ and the concomitant electric current will be used to drive nanostructure formation. The self-assembly of a wide range of block copolymers will be studied by spatially resolved, in situ UV via spectroscopy, birefringence and small angle X-ray and neutron scattering. Efforts will be made to identify systems that order and disorder completely and rapidly in response to changes in the applied electric fields. Broader Impact The PI is a member of the Committee on Student Diversity and Academic Development at Berkeley since 2001. In 1974, the committee established the Professional Development Program (PDP) to encourage students from disadvantaged groups to enroll in all degree programs in substantial numbers. The PI has published an article in Research Advocate (a Berkeley publication) that is aimed at connecting faculty who are interested in broadening the impact of their scientific activities with PDP run programs that would benefit from their participation. To increase the broader impact of this proposal, the PI will participate in a recently established PDP run program at Willard Middle School. 45 % of the students in Willard are African American. In this program, faculty and PDP staff members are invited to the classrooms to learn about the current science and math curriculum, and to discuss possible additions to the curriculum with teachers. The PI will propose demonstrations based on current electro-active polymers, and how this can be used to create artificial muscles.