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Thermodynamic and Glass Transition Behavior in Co2 – Polymer Systems Emphasizing the Surface Region

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Thermodynamic and Glass Transition Behavior in Co2 – Polymer Systems Emphasizing the Surface Region THERMODYNAMIC AND GLASS TRANSITION BEHAVIOR IN CO2 – POLYMER SYSTEMS EMPHASIZING THE SURFACE REGION DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Dehua Liu, M.S. ***** The Ohio State University 2006 Dissertation Committee: Approved by Professor David L. Tomasko, Advisor Professor L. James Lee ______________________________ Professor Isamu Kusaka Advisor Chemical Engineering Graduate Program ABSTRACT Applying carbon dioxide to polymer processing remains a very attractive and innovative research area, driven by its significant impacts on environmental concerns, scientific and technological advancement. Typical applications have progressed from traditional extraction, blending, particle formation, etc. to the cutting edge frontier in a number of fields, in particular biomedical devices and microelectronics. For example, the design of nanoscale drug devices using low temperature assembly of micro-/nano- structures or ‘dry’ lithography in nanofabrication. The introduction of CO2 not only revitalizes and redefines a variety of existing technologies, but also serves as a powerful tool to link various disciplines and create exciting innovations. Advancements in applications are supported by a thorough characterization and fundamental understanding of CO2 interaction with a polymer host. As the dissolution of CO2 occurs, the polymer experiences a range of property variations that usually facilitate processing and rationalize the use of CO2. Macroscopically, polymer swelling and reduction in glass transition (Tg), viscosity and interfacial tension are expected. Recently, the discovery of anomalous dynamics associated with the polymer surface and thin films imposes a new challenge and opportunity for CO2 in terms of its possible effects. In this work, the interaction between CO2 and polymer, including both bulk phase and thin film, has been systematically addressed and modeled. ii A novel technique ADSA (Axisymmetric Drop Shape Analysis) is adopted to determine the CO2-induced polymer dilation. The method is shown to be a potent tool to study volumetric property of a gas-pressurized system over a wide range of temperature and pressure. In this study, the dilation isotherms of PMMA and Poly(lactide-co- glycolide) (PLGA) were measured over a wide range of temperature and pressure. In addition, with property estimations from a group contribution method, ADSA can be used to evaluate the characteristic parameters of an equation of state (EOS) by fitting the EOS to measured volumetric data. The real value of an EOS as a process design tool is the ability to describe all thermodynamic properties, not just those it has been fit to. The experimental swelling data were modeled using the Sanchez-Lacombe equation of state (SLEOS) and the correlated interaction parameter between gas and polymer decreases linearly with the increasing temperature. Then the SLEOS was successfully used to predict the CO2 sorption and Tg depression using the interaction parameter fit by swelling data. To demonstrate a CO2 application in pharmaceutical formulation, a drug solid dispersion was manufactured in this work by injecting carbon dioxide into an extruder. The effects of carbon dioxide on the thermal and rheological properties of drug and polymer, including PVP-VA 64, Eudragit® E100 and EC 20 cps, were studied. The minimum operation temperature could be shifted downward up to 30oC which offers an opportunity for processing thermally-labile materials. In order to clarify the deviation of the polymer surface Tg from its bulk value, and especially the influence of CO2, an Atomic Force Microscopy (AFM)–based visualization method was developed, in which the gold nanoparticles were deposited onto the surface iii of a polymer thin film and the embedding profile of those particles was used to probe the surface mobility at annealing conditions. The results of monodisperse PS are consistent with literature reports, namely, a region with enhanced mobility occurring near the surface even at conditions below bulk Tg. Moreover, CO2 further reduces the temperature where the dynamic enhancement is observed, and broadens the surface mobility layer. Finally, efforts toward revealing the underlying mechanism of surface Tg reduction were made. A thermodynamic model that is capable of profiling the mass density near the surface and mapping the entropy distribution was developed by combining gradient theory, the Gibbs-DiMarzio Tg criterion and SLEOS. It clearly shows that, even at temperatures lower than bulk Tg, there is a surface liquid-like layer with reduced density at the scale of 1nm which may serve as the origin of enhanced mobility. The layer is temperature and CO2 pressure dependent, and its thickness is in good agreement with experimental determinations and molecular simulations. The associated fast mobility could penetrate into the polymer bulk phase at the scale of tens of nanometers via intramolecular chain connection and intermolecular entanglement. iv To my daughter Jiaqi To my wife Jun v ACKNOWLEDGMENTS First, I would like to express my sincere thanks to my advisor, Dr. David L. Tomasko, who has been very enlightening, supportive and encouraging with me throughout my study at the Ohio State University. Only with his exceptional insight and guidance could I accomplish this dissertation. I also desire to take this opportunity to thank Dr. Isamu Kusaka for his help on surface Tg modeling. His keen view and skill of thermodynamics always amazes me, and more importantly keeps me on the right track for solving problems. I am grateful to Dr. L. James Lee for his suggestions on surface Tg, and for serving on my PhD committees of qualifier, candidacy and oral defense. I appreciate very much a number of interesting discussions with Dr. Hongbo Li, and collaboration of surface Tg measurement with Dr. Yong Yang. I am also thankful to Dr. Geert Verreck and his team in Janssen Pharmaceutica for productive collaboration and financial aid that enables the application of CO2 to manufacturing drug solid dispersion. My whole group deserves my many thanks, which helped me and leaves me so many precious memories, especially, Mike Noon for his experimental help and Max Wingert for discussions. I like to express my gratitude to Paul Green, Leigh Evrard and Carl Scott for their efforts of machining and equipment repair/maintenance. vi Finally, I want to thank my entire family for their love and support. In particular, my wife, Jun, who leads me through all these years with her endless love and support; and my daughter, Jiaqi, who brings in tremendous joy and enjoys going to school with me and asking me questions I can not answer. vii VITA December 16, 1975……………………....… Born – Dongying, P. R. China 1996………………………………………… B.S., Chemical Engineering TianJin Institute of Technology, P. R. China 1999………………………………………… M.S., Chemical Engineering TianJin University, P. R. China 1999 – 2001………………………………… Research Scholar Petroleum University of China, P.R. China 2001 – present………………….…………… Graduate Research Assistant Chemical & Biomolecular Engineering The Ohio State University PUBLICATIONS [1] Verreck, G.; Decorte, A.; Heymans, K.; Adriaensen, J.; Cleeren, D.; Jacobs, A.; Liu, D.; Tomasko, D.; Arien, A.; Peeters, J.; Rombaut, P.; Van den Mooter, G.; Brewster, M. E, “The effect of pressurized CO2 as a temporary plasticizer and foaming agent on the hot stage extrusion process and extrudate properties of solid dispersions of itraconazole with PVP-VA 64”, European Journal of Pharmaceutical Science, 2005, 26(3-4), 349-358 [2] Liu D., Li H., Noon M., Tomasko D. L., “CO2-Induced PMMA Swelling and Multiple Thermodynamic Property Analysis Using SLEOS”, Macromolecules, 2005, 38(10), 4416 [3] Han X., Zeng C., Wingert M. J., Liu D., Tomasko D. L., Koelling K. W., Lee, L. J., “Effect of Clay Surface Modification on the Polymer Nanocomposite Foam Structure” Proceedings of NSF DMII Grantees Conference, Scottsdale, AZ, 2005 viii [4] Yang Y., Liu D., Lee, L. J., Tomasko D. L., “Three-Dimensional Assembly of Polymer Micro-/Nanostructures at Low Temperatures”, 20th Annual Meeting of Polymer Processing Society, paper 239, June 2004 [5] Yang Y., Liu D., Lee, L. J., Tomasko D. L., “Investigation of Polymer Surface Dynamics Under CO2 Using Atomic Force Microscopy”, 20th Annual Meeting of Polymer Processing Society, paper122, June 2004 [6] Yang, Y., Liu D., Lee, L. J., Tomasko D. L., “Micro/nanoscale Bonding and Surface Glass Transition Temperature of Polymers under Carbon Dioxide”, Annual Technical Conference - Society of Plastics Engineers, 2004, 62(3), 3095- 99 [7] Liu D., Li H., Han X., Wingert M. J., Tomasko D. L., Koelling K. W., Lee, L. J., “Polymer Nanocomposite Foams Prepared by Environmentally Benign Carbon Dioxide” Proceedings of NSF DMII Grantees Conference, Dallas, TX, 2004 [8] Tomasko D. L., Li H., Liu D., Han X., Wingert M. J., Koelling K. W., Lee, L. J., “A Review of CO2 Applications in the Processing of Polymers”, Industrial & Engineering Chemistry Research, 2003, 42(25), 6431 [9] Tomasko D. L., Han X., Liu D., Gao W., “Supercritical Fluid Applications in Polymer Nanocomposites” Current Opinion in Solid State & Materials Science, 2003, 7(4-5), 407 [10] Yuan C.; Xu Y., Wang Y., Liu D., Chai Y., Cao T., “Polymer microgels prepared by emulsifier-free emulsion polymerization of unsaturated polyesters and styrene” Journal of Applied Polymer Science, 2000, 77(14), 3049-3053 FIELDS OF STUDY Major Field:
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