Collaborative Research: Solution Processing with Entropy-Controlled Stratification of Architecturally-Complex Polymer Blends

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A variety of consumer products are manufactured by using solvents to deposit a thin polymer film on a surface, including anti-fouling coatings, membranes for water purification, and electronic devices. Solvent-based manufacturing processes are attractive because they are fast, inexpensive, and scalable to large areas. However, as the solvent evaporates, the polymers arrange themselves in ways that are difficult to predict or control. This collaborative research award develops new solvent-based manufacturing processes where different types of polymers are spontaneously sorted into layers according to their size and shape. This unique approach can be used to decouple the surface and bulk properties of the film, allowing for independent optimization of each attribute. Furthermore, the polymers can be degradable to facilitate their disassembly and recyclability. As a result, the principles established through this research can facilitate the development of high-performing polymer films for end-use applications in biomedical devices, desalination and filtration systems, and devices for clean energy, which greatly impacts society and the U.S. economy. Laboratory research engages graduate and undergraduate students and is complemented by education and outreach programs that include new modules for undergraduate and graduate courses at collaborating institutions; short courses and symposia for the broader scientific community; activities that teach science to the blind and visually impaired; and a student exchange program between the two institutions.The goal of this collaborative research project is to develop solution deposition processes that produce vertical stratification of bottlebrush copolymers and linear homopolymers in thin films. The research tasks are designed to test the hypothesis that bottlebrush copolymers are entropically attracted toward the vapor-liquid interface, leading to "bottlebrush-on-top" stratification for a broad range of material chemistries and processing conditions. Importantly, by leveraging these entropic effects during processing, the bottlebrush copolymer additives can be synthesized with "high energy" polar, ionic and hydrogen-bonding moieties. Such chemistries are critical for tuning a range of surface and interfacial properties, including wettability, friction, fouling resistance, adhesion strength, degradability, conductivity, and stimuli-responsiveness. The research plan examines the interplay between materials design (polymer architecture, chemistry) and processing variables (evaporation rate, diffusion rates) on stratification profiles, using existing models for vertical stratification of colloidal particles to guide experimental design. The collaboration consists of synthesis of a set of bottlebrush copolymer additives and characterization of transport-related parameters. The systematic research plan involves preparation and characterization of 400 independent samples, evenly split between the two institutions. Significantly, the principles established by this research redefines what types of polymers are characterized as "surface active" and transforms current approaches to surface engineering in polymeric materials.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.