THRUST AREA: Polymer Nanocomposites

Brian C. Benicexicz, Ph.D
Departments of Chemical Engineering and Chemistry & Biochemistry
Polymer Nanocomposites Research Team, USC NanoCenter

Overview
Over the last four years, our research team has developed unique capabilities for synthesizing polymer nanocomposites containing custom-made, synthetic platelet materials. We have a broad array of characterization tools, including X-ray scattering, atomic force microscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy, for characterizing material microstructure. We have key instruments for evaluating material end-use performance (Figure 1), including dynamic mechanical analysis (mechanical properties), electrochemical impedance analysis (capacitance and energy storage), and a home-built system for measuring gas permeation rates through polymer films. We will soon have a research-grade microcompounder for processing as little as 5 g of an “as-made” polymer nanocomposite into fiber and film samples for mechanical, electrochemical, and gas barrier characterization. Using these capabilities, we are pursuing three main avenues of research: (1) in-house development of PET nanocomposites for food packaging, (2) polystyrene-based nanocomposites for energy storage (funded by the US Air Force), and (3) joint development of other polymer nanocomposites with company partners including Michelin, MeadWestvaco, and PBI Performance Products.

Background and History
In April 2002, Eastman Chemical donated its intellectual property portfolio in the area of polymer nanocomposites to the University of South Carolina. Since then, the USC Office of Research and the NanoCenter have invested almost $700,000 in funding and equipment to establish the Polymer Nanocomposites Research Team (a research thrust area of the USC NanoCenter) to develop new knowledge, technology, and experience built upon the Eastman IP donation. In April 2004, USC was awarded $3.5 million from the State to establish the Polymer Nanocomposites Research Center of Economic Excellence (PNC-RCoEE). The University has since received matching fund pledges totaling $3.5 million. With the PNC-RCoEE fully funded, the University has carried out a search for the PNC-RCoEE Endowed Professor and is currently negotiating with top candidates. These investments show that cutting-edge research in polymer nanocomposites is one of the highest priorities for the NanoCenter, the University, and the State.

Current Research
Our research team has developed a unique approach to research in polymer nanocomposites: we synthesize custom-made layered materials (clays and other inorganic solids) with surface chemical groups tailored for compatibility with PET or other target polymers. Some of our synthetic platelets, including metal phosphonates, (Figure 2, left) and hectorite, are composed of stacked platelets with face surfaces covered by covalently-bound organic functional groups (phenyl, carboxyl, alkyl, and others). Other synthetic layered materials, including layered perovskites and magadiite (Figure 2, center and right), can be exfoliated in water and subsequently functionalized with desired organic groups. In principle, the organic groups on the platelet faces can be tailored to maximize compatibility with target polymers, leading to the ability to exfoliate high aspect ratio platelets in hydrophobic polymers like PET. In thermodynamic terms, the polymer prefers intimate contact with a hydrophobically-modified platelet surface (via covalently attached organic groups), rather than with the more hydrophilic “native” platelet surface. This approach also offers other advantages, including ability to synthesize platelets with enormous aspect ratios (length-to-thickness), and tighter control over composition and purity compared to natural clays.

Our team has a two-fold strategy for capitalizing on the potential of these custom-made synthetic layered materials. First, we are trying to develop a complete in-house program for synthesis, characterization, and performance evaluation of PET-based nanocomposites. Second, we have worked to develop collaborations with partners in industry and defense agencies for joint development of other kinds of polymer nanocomposites.

PET Nanocomposites. In the area of PET-based nanocomposites, our team is one of a few academic groups in the nation having a complete system for making PET nanocomposites by in situ polymerization. We exfoliate platelets into water or ethylene glycol (or mixtures), and then introduce these platelet suspensions directly into bishydroxyethyl terephthalate (BHET, the monomer for PET). Elevated temperature and vacuum strip out water and excess glycol, followed by batch polymerization to produce PET-platelet nanocomposites. These materials are ground to a uniform granule size and then subjected to a second “solid-state” polymerization to raise the PET molecular weight. We use melt flow indexing to estimate PET molecular weight relative to commercial PET samples. The whole process typically takes a minimum of three days to produce about 150 g of PET-platelet nanocomposite.

Once we have synthesized a PET nanocomposite, we use the melt flow indexer to estimate the degree of polymerization and to produce a thick fiber sample. We measure mechanical properties via DMA and barrier properties via gravimetric water uptake. After installation of our microcompounder and film line in the second quarter of 2007, we will be able to produce PET nanocomposite film and fiber samples and subject them to uniaxial extension. We will then be able to assess the gas barrier performance of these nanocomposites using our gas permeation system.

Polystyrene Nanocomposites for Energy Storage. We recently received over $900,000 in funding from the Air Force to explore applications of polymer nanocomposites as high performance thin film capacitors. To address the Air Force's need for new high energy density storage systems for pulse power applications, this project will develop an entirely new class of light weight capacitors based on advanced polymer-platelet nanocomposite dielectrics (PPNDs). We will synthesize high permittivity inorganic platelet materials, covalently functionalize the platelet surfaces with organic groups, and prepare polymer nanocomposites incorporating these materials. In collaboration with researchers at Wright-Patterson AFB, we will characterize the electrochemical performance of these materials, evaluating the impact of functionalized platelets on dielectric material properties and prototype capacitor performance.

NSF Partnership for Innovation. This NSF-funded award ($600,000 over three years) will establish the Polymer Nanocomposites Manufacturing Partnership (PNMP), a joint effort of USC and polymer manufacturing companies located in or near South Carolina. The goal of the PNMP is to foster innovation in polymer manufacturing through (1) basic research in synthesis and characterization of layered (nano)materials, routes to their incorporation in polymer nanocomposites, and accelerated methods for evaluating nanocomposite performance; (2) joint University/industry development of polymer nanocomposite technology for near-term commercialization; and (3) workforce development through student involvement in research, cross-disciplinary education, and industrial internships. Specifically, the PNMP set up as many as four cross-disciplinary research teams of students, faculty, and industry representatives, each focused on the interests of one industrial partner. The PNMP includes four confirmed industrial partners: Eastman, Michelin, and PBI Performance Products, and MeadWestvaco. We are currently defining the scope of each partner’s project, and we plan to initiate research and educational activities of the PNMP in August 2007.

Program Development and Future Proposals. Building upon past investments, the University and the State continue to view polymer nanocomposites research as one the highest priorities for research growth as well as economic development. The State award to establish the Polymer Nanocomposites Research Center of Economic Excellence provides a solid foundation for future growth. A faculty search for a world leader to join us as the PNC Endowed Professor is currently under way. The research group of this leader, those of two new junior faculty hires, and elements of our current research groups, are slated to occupy one floor (about 23,000 gross ft2) of the Horizon I building currently under construction (for a live webcam view of contruction of the Horizon Center, see http://www.sc.edu/research/webcam.shtml.

Along the way, we have received advice and guidance from an Industrial Advisory Board composed of representatives from all of the major polymer manufacturing companies in South Carolina. This group will serve as the nucleus for developing a future NSF proposal to establish a Industry/University Cooperative Research Center (I/UCRC) in Polymer Nanocomposites.

Relevant Publications

1. "Pressure Induced Octahedral Tilting Distortion in Ba2YTaO6", Lufaso, M. W., Macquart, R. B., Lee, Y., Vogt, T., zur Loye, H.-C., Chem. Commun., 2006, 168-170.
2. “Quantitative Analysis of Montmorillonite Platelet Size by Atomic Force Microscopy”, H. J. Ploehn and C. Liu, Industrial & Engineering Chemistry 45, 7025-7034 (2006).
3. "Crystal Growth and Magnetic Properties of Lanthanide-Containing Osmium Double Perovskites, Ln2NaOsO6 (Ln = La, Pr, Nd)", Gemmill, W. R., Smith, M. D., Prozorov, R., zur Loye, H.-C., Inorg. Chem., 2005, 44, 2639-2646.
4. Gemmill, W. R., Smith, M. D., Mozharivsky, Y. A., Miller, G. J., zur Loye, H.-C., "Crystal Growth, Structural Transitions and Magnetic Properties of the Fluorite-Related Osmates: Sm3OsO7, Eu3OsO7 and Gd3OsO7", Inorg. Chem., 2005, 44, 7047-7055.
5. “Dendrimer-Mediated Synthesis of Platinum Nanoparticles: New Insights from Dialysis and AFM Measurements”, H. Xie, Y. Gu, and H. J. Ploehn, Nanotechnology 16(7), S492-S501 (2005).
6. “AFM Characterization of Dendrimer-Stabilized Platinum Nanoparticles”, Y. Gu, H. Xie, J. Gao, D. Liu, C. T. Williams, C. J. Murphy, and H. J. Ploehn, Langmuir 21(7), 3122-3131 (2005).
7. “Crystal Growth and Structure Determination of Novel Barium Rhodates: Stepping Stones Towards 2H-BaRhO3”, Stitzer, K. E., El Abed, A., Darriet, J., zur Loye, H.-C., J. Am. Chem. Soc., 2004, 126, 856-864.
8. “(NaLa2)NaPtO6: The First 2H-Perovskite Related Oxide with a Rare Earth Cation on the A-site”, Davis, M. J., Smith, M. D., zur Loye, H.-C., Inorg. Chem., 2003, 42, 6980-6982.
9. “Modeling the Effect of Plasticizer on the Viscoelastic Response of Crosslinked Polymers Using the Tube-Junction Model”, P. P. Simon and H. J. Ploehn (100%), Journal of Rheology 44(2), 169-183 (2000).
10. “Dynamic Mechanical Analysis of the Effect of Water on Glass Bead-Epoxy Composites”, J. Y. Wang and H. J. Ploehn, Journal of Applied Polymer Science 59(2), 345-357 (1996).