Shape Changing Stimuli-Responsive Multicomponent Molecular Bottlebrushes in Solution and at Interfaces

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PART 1: NON-TECHNICAL SUMMARYMolecular bottlebrush polymers are a class of chain-like molecules composed of a very long polymer backbone with densely grafted shorter molecules. These polymers exhibit intriguing properties and could be used, e.g., in manufacture of advanced materials, lubrication for friction reduction, drug delivery for medication. Their shapes are governed by the length ratio of backbone and side chains and the interactions of side chains with themselves and their environment. External stimuli have been shown to trigger the shape change of brush polymers from wormlike to globular, which mimics the folding and unfolding behavior of natural proteins. In this project the PI will design, prepare, and study multicomponent brush polymers that can individually change their shapes in solutions and at interfaces upon application of external stimuli. The fundamental understanding of the properties and behavior of such giant molecules under various conditions will potentially impact many technologies, including targeted delivery of substances (e.g., medications) and environmentally responsive foams and emulsions. The research program will provide a platform for training postdoctoral researchers, graduate and undergraduate students, and thus will have broader societal impact beyond the research itself. Outreach activities will be directed to stimulate the interest of high school students toward STEM fields and to broaden the science horizons of the students at the University of Tennessee Knoxville.PART 2: TECHNICAL SUMMARYThis project is aimed at synthesizing multicomponent molecular bottlebrush polymers that can display shape changes in response to external stimuli and understanding how various molecular parameters affect their shape changing behavior in dilute and moderately concentrated solutions and at interfaces. Specifically, the research program will utilize previously developed synthetic strategies to prepare stimuli-responsive multicomponent brush polymers via state-of-the-art synthesis techniques, characterize their changes in molecular dimension and conformation (shape) upon application of external stimuli in dilute and moderately concentrated aqueous solution, under external fields, and at interfaces, elucidate the effects of various molecular parameters on shape-changing behavior, and reveal the unique properties of brush polymers under different conditions. A series of multicomponent molecular bottlebrush polymers with various chemical compositions, molecular weights, molecular architectures, and narrow dispersities will be made. They will be investigated by multidetector size exclusion chromatography (SEC) for molecular weights and dimensions, dynamic and static light scattering (DLS and SLS) for molecular sizes under different conditions, atomic force microscopy (AFM) and transmission electron microscopy (TEM) for direct visualization on substrates, and small angle neutron scattering (SANS) for in situ study of brush dimensions and conformations in solutions. The knowledge gained from this research project will be used to guide the design and synthesis of functional brush polymers for potential applications in delivery of substances and stimuli-responsive foams and emulsions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.