Developing the Foundation for Novel Light-Responsive Materials: Tuning Physical Properties of Conjugated Polymer Systems by Illumination

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NON-TECHNICAL SUMMARY Stimuli-responsive materials alter their structure or properties according to changes in their environment. This research program will examine novel stimuli-responsive polymers whose function and properties can be controlled by exposure to light. This is promising because light can be applied remotely without physical contact, its intensity can be tuned with great fidelity, and it can be used to pattern the materials for specific uses. Unfortunately, there are only a few compounds that can be introduced into polymers that are light responsive. This research program will provide the foundation to develop a broad range of new light-responsive materials based on polymer moleculaes that can be electrically active. This increase in available light-sensitive and -patternable polymers will offer the opportunity for new applications using controlled illumination and significantly extend the practicality of light-responsive materials. Workforce development and training of the next generation of scientists and engineers prepared to tackle the grand challenges in materials research will be realized through this integrated research-and-education program and also by engaging public high-school students in hands-on research over summer periods, providing exceptional preparation for college. Further impact will result from the completion of experiments at the neutron facilities at national laboratories (ORNL and NIST) where the students participating in this project will acquire hands-on experience in a multi-user facility. This project will also further develop the sustainable research infrastructure in Tennessee and will be implemented to enhance the participation of underrepresented groups in research.TECHNICAL SUMMARYThe overarching goal of this research program is to develop a fundamental understanding of the mechanism by which photon absorption by conjugated polymers (CP) alters their macroscopic physical properties in order to provide guidelines by which this phenomenon can be controlled and exploited to realize new stimuli-responsive materials with targeted properties. The completion of this research program will provide a comprehensive understanding of how photon absorption by a conjugated polymer alters its configuration, morphology, dynamics and thermodynamics in blends and solutions. Correlation of local electronic and structural changes to the macroscopic dynamic response of the blends in the presence and absence of light will probe the fundamental processes that hierarchically guide the change in macroscopic behavior of conjugated polymer blends as a result of photon absorption. Examination of both CP solutions and blends will provide guidelines to control this functional response on a molecular level and offer a fundamental understanding of the structural and electro-optical processes that control this phenomenon. The experimental protocol, analysis, and interpretation are also designed to be applicable to a broad range of conjugated polymers and CP/non-CP blends. Neutron scattering will be used as a primary tool to determine the structure, depth profile, and phase behavior of the CP blends and solutions of interest. The use of neutrons simplifies the variation in experimental conditions from the presence to the absence of light, as the illumination of the sample with a floodlit beam of light will not impact the detection of the scattered neutrons, unlike a similar light scattering experiment.This suite of experimental results will then be interpreted to elucidate guidelines to enable the rational design and control of novel light-responsive materials with targeted properties. This research program will therefore provide a fundamental understanding of the mechanism by which local photon absorption translates over multiple length scales to a variation in macroscopic physical properties with the goal of providing strategies by which this unexpected phenomenon can be manipulated and directed to produce new light-responsive materials.