Mixed Rod-Coil Polymer Brushes Tailored for Controlled Surface Topography

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PART 1: NON-TECHNICAL SUMMARY: Polymers are long molecules that make up the many kinds of coatings, fabrics and plastics we use. Some polymers can be flexible and soft. Other polymers can be long and stiff. By combining stiff and flexible polymers in a single system formed on a surface, we have learned that we can make nanoscale spiky brush-like surfaces using careful temperature control and coating methods. The PI and his group plan to better understand this surface formation process by making new combinations of soft and stiff polymers, by using advanced tools to study their organization, and by employing computers to model the structure and to predict their behavior. This new way of making surfaces opens up many interesting applications. For example, the surface mimics the protein spikes present on virus surfaces that are used by nature to identify target cells, take part in the entry into the cell, and also to prevent identification by antibodies. These materials can be used to study the behavior of cells on topics ranging from how they work to the behavior of the immune system. Because the spikes are vertically aligned, they may also act as nanowires, so they can be used in energy production and storage systems like solar cells and batteries. Finally, these spikes may be piezoelectric, i.e. they could convert electrical energy to motion (or sound) and motion to electrical energy. This research program will also serve as a mechanism to teach students about polymers and materials science, create globally aware graduate students, and expose students to a collaborative environment. Graduate students will be able to work with the research groups of our collaborators as parts of teams and to take part in exchange visits. Lessons learned from these research programs will be used to teach K-12 students and to be applied in high school teachers' workshops. PART 2: TECHNICAL SUMMARY:Coil polymer brushes synthesized using living radical polymerization methods will be combined with rod brushes with high persistence lengths grown from surfaces made using a variety of living and pseudo-living chemistries. Phase separation aided by solvent processing and guided by nanolithography will be used to control in-plane structure. A variety of chemical and process methods will be used to limit macroscopic phase separation and thereby direct assembly of topographical and chemical structures. Brush growth will employ new, chemically tailored brush initiators for single chain and binary chain growth to form rod-coil mixed brush pairings. To direct brush structure and rod-coil phase separation, brush initiators will be patterned at length scales of a few 10s of nanometers using state-of-the-art lithography methods to control spacing of the brush spikes. Brush organization will be compared to computational predictions which will be used to guide both brush design and selection and to anticipate the resulting physical structure and aid characterization studies. Characterization of the brushes will be made using a selection of analytical methods including grazing incidence (GI) SAXS and WAXS, neutron reflectivity and resonant soft X-ray scattering (RSoXS) measurements. Studies of the conductivity and piezoelectric character of the rod-coil brush films will aid in our understanding of the mixed brush structure. Through collaborations, studies of these materials as cell membrane substrates, for targeted biomolecular binding, as piezoelectric and as conducting materials with unusual transport pathways, will also provide information about key length scales and rod-brush organization. .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.