Janus Brushblock Copolymer Phase Behavior: Morphology and Thermodynamics

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

Part I: NON-TECHNICAL SUMMARY Specialty polymers that form precise and tailorable structures at the nanometer length scale (1/10000th of the width of a human hair) provide a route for developing useful porous membranes for selective water and gas purifications, as well as templates for patterning faster computer microprocessors with ever smaller components. This research program will educate the next generation of scientists and engineers in the guided design and development of such polymers, within an interdisciplinary research group situated at the interface between chemistry, chemical engineering, and materials science. Through combination of advanced polymer synthesis, detailed structural characterization at the nanoscale, and characterization of the resulting polymer properties, this project will reveal new molecular design rules for nonlinear polymers that lead to their spontaneous self-organization at length scales below 15 nanometers. These studies will provide American industry with technological knowledge that enables the development of innovative products that maintain global competitiveness. The educational outreach activities associated with this project will focus on the development of simple, visually attractive demonstrations featuring spontaneous self-organization of macroscopic materials into structures visible to the naked eye. These demonstrations will furnish opportunities for educating and exciting students at the K-12 and college levels, as well as the general public, about advanced technologies based on polymers. Part 2: TECHNICAL SUMMARY Block polymers self-assemble into a variety of nanostructured morphologies, as a consequence of the molecular frustration induced by coupling two or more immiscible polymer segments into a single macromolecule. A delicate thermodynamic balance governs the lowest degree of polymerization (N) at which an AB diblock polymer microphase separates, which then dictates the smallest microdomain size that can form. One potential block polymer application relies on their periodic microdomains as templates for advanced microelectronics and mesoporous inorganic materials with sub-15 nm features. A common approach to reducing diblock polymer domain sizes is to decrease N, while increasing the chemical incompatibility of the A and B segments. However, applications of these new materials often require costly development of new materials processing protocols. This project investigates the microphase separation behavior of Janus bottlebrush polymers, a nonlinear polymer architecture derived from covalently linking linear AB diblocks through their junctions, as a new means for driving AB diblocks to self-assemble at smaller length scales than their linear homologs. Using a combination of small-angle X-ray scattering, transmission electron microscopy, and rheological measurements, the phase behaviors of Janus bottlebrushes will be studied as a function of their compositions, the chemical incompatibility between the homopolymer arms, and the graft density of the bristles along the backbone.