CAREER: Connecting the Wetting and Rheological Behaviors of Polymer Grafted Nanoparticles in Polymer Melts

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

National Science Foundation - Division of Chemical &Transport Systems Particulate & Multiphase Processes Program (1415) ABSTRACT Proposal Number: 0644890 Principal Investigator: Green, David L. Affiliation: University of Virginia Main Campus Proposal Title: CAREER: Connecting the Wetting and Rheological Behaviors of Polymer Grafted Nanoparticles in Polymer Melts Intellectual Merit: Recent advances in grafting polymer brushes to nanoparticles surfaces permit the formulation of a wide range of advanced polymer nanocomposites in which the brush serves to prevent particle aggregation. Through recent NSF-supported research, the PI was one of the first to fundamentally connect the wetting of the brush to the uniform dispersion of nanoparticles for a model system of polydimethylsiloxane (PDMS)-grafted silica nanospheres in PDMS melts. The PDMS-grafted nanoparticles in that study were formulated by an established "grafting to" method that entailed the covalent attachment of pre-formed polymer chains directly to the nanoparticle surface. The "grafting to" method enabled the study of the impact of low-to-moderate PDMS graft densities on nanoparticle Dispersion. The research will to employ atom transfer radical polymerization (ATRP), a recently developed "grafting from" methodology, to construct polystyrene (PS) and polymethylmethacrylate (PMMA) brushes monomer-by-monomer from the surface of monodisperse silica nanoparticles. The "grafting from" technique permits the synthesis of polymer brushes over a wider range of graft densities than the "grafting to" method. Ultimately, this set of experiments will produce systematic data that will permit quantification of the strength of attraction between nanoparticles as well as the relevant time- and length-scales that control the gelation process. Broader Impacts: Broader impacts are three-fold. First, the calibration of self-consistent models to experimental data will permit the prediction of physical properties such as the interparticle spacing that could then be used to optimize a range of materials properties. Second, formulation of well-designed model systems will permit physicists, colloidal scientists, and rheologists to study and quantify gelation phenomena to facilitate comparisons of experimental data across of wide range of laboratories. Third, the proposed research provides an excellent medium for achieving the educational and outreach goal of exposing more students to a career in science and engineering. To this end, the PI will seek funds for a summer program to expose secondary school teachers to cutting-edge research in his lab, create demonstrations to introduce students to the fascinating properties of nanoparticles, and utilize the Research Experience for Undergraduates program to establish a pipeline of underrepresented students for engineering graduate study at the University of Virginia. By targeting these programs to specific geographic areas and populations, the PI hopes to increase the number of woman and minority PhDs in chemical engineering.