RUI: Orientational Relaxation of Chromophore Order in Nonlinear Optical Block Copolymers

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TECHNICAL:Nonlinear optical materials for applications in optical signal processing is extended to polymers, which offer greater compositional flexibility than conventional crystalline materials. Optical functionality in a polymer is incorporated by blending a chromophore with a transparent polymer host and electrically poling the material to induce a noncentrosymmetric ordering of chromophores. Research to date has largely been confined to homopolymer hosts, which offer limited options for tuning the chromophore micronenvironment. A promising alternate approach to achieving stable dipolar ordering is to selectively encapsulate the chromophore in one domain of a block copolymer. In this project, second harmonic generation and polarized absorption spectroscopy experiments will be used to make detailed measurements of the poling-induced order parameter and the post-poling orientational relaxation times of chromophores encapsulated in block copolymer domains, using the PS-b-P4VP block copolymer as a model system. Covalent and hydrogen-bonding schemes for selective chromophore encapsulation will be used to investigate orientational relaxation as a function of bonding mode. This model system will help probe to what extent the disparate requirements for poling and relaxation can be decoupled through appropriate choice of block copolymer system.NON-TECHNICAL:Nonlinear optical materials are integral to applications such as fiber optic data transmission for Internet-based communication. Traditional materials are crystalline, which are limited both in cost of fabrication and ultimate bandwidth capability. Polymeric materials are an alternative that offer flexibility in design and cost, but their long-term stability in deployed devices has not been fully established. One promising polymer category is that of block copolymers, which are effectively ordered combinations of chemically distinct polymers on the nanoscale. This research will utilize laser-based experiments to measure the long-term stability of block copolymer materials that have the potential for use in telecommunications devices. The project will employ physics and chemistry undergraduates in a vigorous interdisciplinary research program at Drew University. This will provide them with valuable experience in thin-film characterization, lasers, and related photonic technologies, all of which are in demand by high-technology industries and graduate training programs. Students will also benefit from interacting with collaborators at major research institutions, including the Johns Hopkins University and the University of Wisconsin.