This collaborative project seeks to understand the phase behavior of binary mixed brushes composed of two distinct homopolymers randomly or alternately immobilized via covalent bonds on inorganic particles and to explore their applications in polymer nanocomposites. Mixed brushes are an intriguing class of environmentally responsive materials. To tap into their full potentials in various technological applications, it is necessary to understand their phase behaviors under different environmental conditions. In response to this need, an international collaborative team has been assembled and consists of Bin Zhao (a polymer chemist at University of Tennessee), Lei Zhu (a polymer physicist at Case Western Reserve University), and Feng Qiu and Ping Tang (theoreticians at Fudan University, China). By combining two different "living"/controlled polymerization techniques, the PIs will prepare mixed brushes with predetermined molecular weights, narrow polydispersities and controlled grafting densities from asymmetric difunctional initiator-terminated self-assembled monolayers immobilized on a variety of inorganic particles. The phase morphologies of mixed brushes will be systematically studied using both experimental and computer simulation approaches. The effects of various molecular parameters such as molecular weight and grafting density will be elucidated. The mixed brush-grafted particles will be used to make advanced polymer/inorganic nanocomposites with improved properties. The knowledge gained from this work could open up new opportunities in the preparation of novel nanostructured hybrid materials and the applications of binary mixed polymer brushes in technological uses.
This collaborative project brings together a group of scientists, graduate and undergraduate students with various backgrounds and expertise from three universities in the U.S. and China. Exchange of faculty and students between the two countries exposes them to different research environments and cultures, and enables them to gain international experience and global visions in science. This research provides a good opportunity to train students in polymer and organic synthesis, surface chemistry, as well as polymer physics. The PIs are committed to help science and engineering teaching in K-12 education by working with local high school teachers to develop new modules and lab experiments in science and technology classes with an emphasis on polymer surface chemistry. High school teachers and underrepresented, minority high school students will be hosted in the summer with the goals of improving high school teachers, teaching performance and enhancing student interest in science and engineering.
This Materials World Network project focuses on the phase morphology of binary mixed brushes composed of two distinct homopolymers randomly grafted via covalent bonds on inorganic particles. Our major goal is to achieve fundamental understanding of effects of molecular weight, surface free energy, grafting density, substrate geometry, and environmental conditions on the self-assembly behavior of two surface-tethered homopolymer brushes in nanoscale confined geometry. The gained knowledge from this work will be beneficial to technological applications of polymer hairy particles and nanocomposites. The intellectual merit of this project is realized through a national and international collaboration. Guided by the computer simulation and prediction by Fudan University, China, well-defined polymer brushes grafted on silica nanoparticles are synthesized by University of Tennessee at Knoxville. Nanoscale morphology is characterized using advanced transmission electron microscopy tomography at Case Western Reserve University. By varying a broad range of independent variables, such as molecular weight, chain disparity, grafting density, and particle size, rich information on the self-assembly behavior of end-tethered mixed polymer brushes are obtained. By comparing the phase behavior of mixed homopolymer brushes with neat diblock copolymers, mixed brushes are more difficult to phase separate. The obtained knowledge on basic science of mixed polymer brushes will help design patchy hairy particles for application in nanocomposites. The broader impacts of this project lies in the nature of international collaboration and education. First, this project exchanges scientists and students from different backgrounds including computer simulation, polymer synthesis, and advanced polymer morphology characterization. Second, research and education are all levels. High school students, undergraduate students, graduate students, and postdoc worked together with a hierarchical mentoring process. Especially, minority and female high school and undergraduate students are trained in the principal investigator’s lab. Third, Research results on the understanding of phase behavior of mixed polymer brushes are broadly disseminated via referred journal publications and conference presentations. In particular, a symposium on "Polymer Hairy Particles and Nanocomposites" was organized in the American Chemical Society national meeting in Indianapolis in 2013. A special issue on Hairy Particles will appear in Journal of Polymer Physics, Part B: Polymer Physics as the last issue in 2014.
