Studies of Mixed Polymer Brushes Designed for Periodic In-Plane Order

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PART 1: NON-TECHNICAL SUMMARY Polymers are valuable materials in everyday life. These long-chain molecules are the basis of industries ranging from food packaging to medical device manufacture to the clothing we wear. Polymers are critical components in the nanotechnology revolution enabling the manufacture of microelectronics that make possible smart phones. This project studies mixed polymer brushes, that is, more than one kind of polymer chain tied to a surface. Unique features of polymer brushes compared to other polymer systems are that they are bound to a surface, extended perpendicular to the surface, and have a controlled thickness and controlled surface chemistry. We will study how mixtures of two brushes phase separate, like oil and water, and form structures smaller than possible with today's advanced patterning methods. Over length scales of a few nanometers the nature of a surface can be transformed from a rigid inorganic structure to one that is soft and organic. Computer models predict symmetrical, periodic structures that we will explore as new nanostructures, as new energy storage materials and as new materials for biotechnology applications. We will work with computer experts to improve their theory and models by providing information about how well their concepts correctly predict these new mixed brush coatings. The research program will engage students in polymer science and materials research, foster globally aware graduate students and train students to work in a collaborative environment. Graduate students will in turn serve as mentors and role models to undergraduate students from Cornell and other universities, while gaining supervisory skills. REU students from other schools with an emphasis on underrepresented students will participate in research during the summer months. The PI and graduate student volunteers will interact with high school teachers in an RET program and teachers' workshops. PART 2: TECHNICAL SUMMARY This fundamental research program will investigate the synthesis, processing and characterization of mixed polymer brushes designed to form controlled periodic spacings in the plane of the brush film. By using mixed polymer brushes of coil-coil and rod-coil architectures and harnessing their in-plane phase separation we will create patterned structures with controlled topography, porosity or multipath transport properties. Mixed polymer brushes will be synthesized using living radical polymerization of flexible coil polymers and Kumada chemistry of conjugated rod polymers. The in-plane phase separation process of dense brushes with controlled brush uniformity will be investigated. Studies will make use of new binary brush initiators developed using Passerini chemistry to form coil-type homopolymer, diblock copolymer and multiblock copolymer mixed brushes. The phase behavior and how it compares to computational predictions will be studied for homopolymer and block copolymer pairs with the goal of creating stable periodic structures. Computational materials science through our collaborations will be used to guide brush design and selection, to predict physical structure and to aid examination of the physical properties of these new materials. To achieve our goal of uniform long-range order in these brush layers, we will investigate solvent vapor annealing and thermal transient laser spike annealing in conjunction with guiding structures. Characterization of the brushes will be made using a variety of analytical methods including X-ray reflectometry, grazing incidence (GI) SAXS and WAXS, neutron reflectivity and STORM superresolution fluorescence microscopy measurements. Charge transport measurements will be carried out on new rod-coil mixed brushes. Each technique will provide information about the internal or surface organization of the material and will aid our understanding of the structures produced.