Polymers are long molecules having many unique properties different from metals and small-molecule liquids. They are widely used in our daily life in plastics, textile fibers and optical/medical devices. In my laboratory, we are interested in understanding the structural and morphological development and manipulation of complex polymer systems during preparation and processing in real time. The focus of our research projects is the design, preparation, characterization and application of nanostructured soft condensed materials, such as fibers (one-dimensional orientation), films (two-dimensional orientation) and bulk material systems (three-dimensional orientation). My current research interests are mainly focused on the use of nanostructured materials for energy, environmental and medical applications.
Polymer Crystallization: We are interested in fundamental research of polymer crystallization. One ongoing project is orientation-induced crystallization of entangled polymer chains. The behavior of orientation-induced crystallization in polymers under flow and deformation has been investigated using in-situ X-ray techniques. We propose that molecular orientation affects the crystallization behavior of polymer melts in two different aspects: thermodynamic and hydrodynamic. The thermodynamic effect involves the reduction of entropy in oriented chains, which favors the formation of primary nuclei with small size and large density that are mainly responsible for the increase of crystallization rate. The hydrodynamic effect generates the landscape of molecular orientation in chains with different molecular weights, which is responsible for the resultant morphology such as shish, kebab or spherulite.
Polymer Nanocomposites: We are developing varying chemical and physical pathways to disperse nanostructured molecules and nanosize particles (e.g. nanotubes and layered silicates) in the polymer matrix at the molecular level. We found that the structure, property and processing relationships are dramatically different in nanocomposites as compared to their neat resin counterparts.
Synchrotron X-ray Scattering and Diffraction Technology Development: One unique characterization tool developed in this laboratory is the simultaneous small-angle x-ray scattering (SAXS) and wide-angle x-ray diffraction (WAXD) technique using synchrotron radiation. Dedicated to polymer research, the Advanced Polymers Participating Research Team (AP-PRT) was formed in 1997 to develop a synchrotron X-ray scattering beamline (X27C) at the National Synchrotron Light Source, Brookhaven National Laboratory. This facility, the first of its kind in the U.S., was funded by Stony Brook (Prof. B. Chu and I are spokespersons), government and industrial laboratories. The primary focus of this PRT is to investigate polymer structure, morphology and dynamics from atomic (1-20 Å) to microscopic scales (20 - 1000 Å) in real time and/or in-situ using simultaneous SAXS/WAXD techniques.
Absorbable Polymers for Medical Applications, Drug Delivery and Tissue Engineering: We have developed several unique processing techniques to fabricate nanostructured materials including (1) nonwoven membranes consisting of nanosize fibers, and (2) nanosize particles (10 - 500 nm). FDA-approved biodegradable polymers such as polyglycolide (PGA) and polylactide (PLA) homo- and copolymers are the base materials for forming the nanostructured scaffolds. The biodegradation rate as well as the drug (DNA and medicine) release rate are functions of fiber/particle size, morphology, porosity and chemical compositions, which can be precisely controlled by processing parameters. The major goal of this research is for medical applications, drug delivery and tissue engineering.
Breakthrough Nanofibrous Membrane Technology for Water Purification: Together with Prof. Benjamin Chu, we are focusing on the use of breakthrough nanofibrous membranes for water purification. The major innovation of our nanofiber technology is that membranes made of nanofiber materials in the non-woven format have drastically improved the flux capacity (e.g. often with many times flux increase) and thereby permitting lower operating pressures but retaining their resistance to fouling. Better flux means less time to filter the same amount of water, which in turn decreases energy consumption and increases cost efficiency. Better resistance to fouling refers to the ability to avoid clogging of the membrane pores by foreign matter, such as oil, detergents, biomacromolecules and salts that can accumulate during the purification process. The fouling resistance of our filters requires additional considerations on chemical composition and surface modifications.
