Pojman, John A. - Louisiana State University

个人简介

Bachelor's Degree(s): Georgetown University, 1984 PhD: University of Texas at Austin, 1988 PostDoc: Brandeis, 1988-90

研究领域

Nonlinear Chemical Dynamics in Polymeric Systems Nonlinear chemical dynamics is the study of systems away from equilibrium that can exhibit spatial and temporal self-organization, such as oscillating reactions, chemical waves, Turing patterns and chaos. There are two reasons to study nonliner chemical dynamics. The are intrinsically interesting. Secondly, because they could be useful. We propoose that there are three ways we can use Nonlinear Dynamics with Polymers to accomplish something useful: 1) Create a dynamic system that can do something useful. A good example is Ron Siegel's pulsatile drug delivery based on an oscillating reaction created with hysteresis in permeability with pH for a hydrogel. 2) Use a dynamic system to create a nonequilbrium product, such as a functional gradient material, that would not be accessible by traditional methods, e.g., isothermal frontal polymerization We have done much work with IFP.. 3) Use a dynamic system to create a product that may be accessible by traditional methods but the dynamic approach has specific practical advantages. This is what we try to do with frontal polymerization. Identifying New Forms of Feedback in Polymer Chemistry To create systems that exhibit oscillations, propagating fronts and complex spatial pattern formation, we need to identify positive feedback in polymer chemistry. The simplext example is autocatalysis: A + B --> 2A +P In the case above, the reaction rate is not the highest at the start of the reaction, but midway through the process. If reaction is performed in an unstirred medium with B present everywhere, then a drop of A can start a propagation front of reaction. This type of "small molecule" autocatalysis is unknown in polymer chemistry. We are working to find examples. The two most common forms of autocatalysis are the "gel effect" in free-radical chain growth polymerization and thermal feedback, present in any exothermic reaction. The "gel effect' occours because the viscosity increases during free-radical polymerization, and this high viscosity can reduce the rate of termination in the chain grown process, resulting in a net increase in rate. Frontal Polymerization Frontal polymerization is a localized reaction that propagates through the coupling of the Arrhenius dependence of the rate of an exothermic polymerization with thermal transport. We mostly study free-radical polymerization systems because of the large heat release and because the thermal initiator provides a large energy of activation. Fronts are ignited with a heat source or UV light, and the reaction autonomously spreads throughout the sample. A dimethacrylate polymerization front. We have two goals with frontal polymerization: The first is to study unusual dynamical phenomena. Fronts do not necessarily propagate as flat fronts but can oscillate or propagate as a helix, which is called a "spin mode". A front propagating as a "spin mode": Left: visible image. Right: IR image. Our second goal is to develop practical uses for frontal polymerization. We have two patents issued and two pending. We have made great progress in creating systems with low front temperature and good shelf life. These could be used for rapid repair. Rapid repair with frontal polymerization. A hole was drilled in block of polyethylene. The resin and filler were placed into the hole. The front was ignited with a heat lamp, and in seconds a rock-hard material was formed. We are exploring new chemisties that can be cured frontally, including cationically-cured epoxy resins and thiol-acrylate systems. One of the major problems of using frontal polymerization is that the fronts can quench from heat loss. Our greatest challenge is to create an isothermal frontal polymerization, perhaps by coupling a polymerization to a propagating front of non-polymer chemistry. Or, we will need to find an isothermal autocatalytic reaction involving a polymerization reaction. Microencapsulation Our frontal polymerization work led us to microencapsulating peroxides and other catalysts to obtain long shelf lives with rapid reaction at elevated temperature. We are developing novel methods for producing microcapsules and microspheres for “cure on demand" for epoxy resins and free-radical systems. Microspheres containing a polymerization catalyst. Effective Interfacial Tension Miscible fluids can exhibit a transient or effective interfacial tension when brought in contact. Using spinning drop tensiometry, we were the first to conclusively measure an effective interfacial tension and to observe a capillary instability. We study systems that have a critical solution temperature. For example, isobutyric acid (IBA) and water are miscible above 27 ¾C but form two phases below that temperature. To create a miscible drop of isobutyric acid-rich solution, we create a drop of IBA below 27 ¾C and then rapidly raise the temperature. Thermal equilibrium is reached quickly, leaving a drop of a miscible fluid. By changing the rotation rate, we can observe capillary instabilities and measure the EIT from the drop’s diameter. Left: A breakup of a drop of IBA-rich fluid after the rotation rate in the tensiometer was rapidly decreased. We have developed an experiment (MFMG) for the International Space Station to study the behavior of miscible fluids in the absence of buoyancy-driven convection. We currently are studying other miscible systems using microfluidics and spinning drop tensiometry.

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Jiménez, Z.; Hoyle, C.; Lowe, A.; Pojman, J. A. "Photopolymerization Kinetics of Ionic Liquid Monomers Derived from Neutralization Reaction between Trialkylamines and Acid-Containing (Meth)Acrylates," J. Polym. Sci. Part A: Polym. Chem. 2007, 45, 3009-3021. Marszalek, J.; Pojman, J. A.; Aultman, K. L.; Hoyle, C.; Whitehead, J. B. "Humidity-Responsive Polymeric Films Based on Aot-Water Reverse Microemulsions," J. Appl. Polym. Sci. 2007, 106, 1957-1963. Zoltowski, B.; Chekanov, Y.; Masere, J.; Pojman, J. A.; Volpert, V. "Evidence for the Existence of an Effective Interfacial Tension between Miscible Fluids. 2. Dodecyl Acrylate-Poly(Dodecyl Acrylate) in a Spinning Drop Tensiometer," Langmuir 2007, 23, 5522-5531. Interfacial Tension between Miscible Fluids: Isobutyric Acid-Water and 1-Butanol-Water in a Spinning-Drop Tensiometer," Langmuir 2006, 22, 2569-2577. Binici, B.; Fortenberry, D. I.; Leard, K. C.; Molden, M.; Olten, N.; Popwell, S.; Pojman, J. A. "Spherically Propagating Thermal Polymerization Fronts," J. Polym. Sci. Part A: Polym. Chem. 2006, 44, 1387-1395. Nason, C.; Roper, T.; Hoyle, C.; Pojman, J. A."UV-Induced Frontal Polymerization of Multifunctional (Meth)Acrylates," Macromolecules 2005, 38, 5506-5512. McFarland, B.; Popwell, S.; Pojman, J. A. "Free-Radical Frontal Polymerization with a Microencapsulated Initiator: Characterization of Microcapsules and Their Effect on Pot Life, Front Velocity and Mechanical Properties," Macromolecules 2006, 39, 53-63. Lewis, L. L.; DeBisschop, C. S.; Pojman, J. A.; Volpert4, V. A. "Isothermal Frontal Polymerization: Confirmation of the Mechanism and Determination of Factors Affecting Front Velocity, Front Shape, and Propagation Distance with Comparison to Mathematical Modeling,"J. Polym. Sci. Part A Polym. Chem. 2005, 43, 5774-5786. Antrim, D.; Bunton, P.; Lewis, L. L.; Zoltowski, B. D.; Pojman, J. A. "Measuring the Mutual Diffusion Coefficient for Dodecyl Acrylate in Low Molecular Weight Poly(Dodecyl Acrylate) Using Laser Line Deflection (Wiener’s Method) and the Fluorescence of Pyrene," J. Phys. Chem. Part B 2005, 109, 11842-11849. Pojman, J. A.; Varisli, B.; Perryman, A.; Edwards, C.; Hoyle, C. "Frontal Polymerization with Thiol-Ene Systems,"Macromolecules 2004, 37, 691-693. Pojman, J. A.; Masere, J.; Petretto, E.; Rustici, M.; Huh, D.-S.; Kim, M. S.; Volpert, V. "The Effect of Reactor Geometry on Frontal Polymerization Spin Modes,"Chaos 2002, 12, 56-65. Mariani, A.; Fiori, S.; Chekanov, Y.; Pojman, J. A. "Frontal Ring-Opening Metathesis Polymerization of Dicyclopentadiene,"Macromolecules 2001, 34, 6539-6541. Fortenberry, D. I.; Pojman, J. A. "Solvent-Free Synthesis of Polyacrylamide by Frontal Polymerization,"J. Polym. Sci. Part A: Polym Chem. 2000, 38, 1129-1135. Pojman, J. A.; Epstein, I. R. "Nonlinear Chemical Dynamics in Polymeric Systems," Chaos, 1999, 9, 255-259. Washington, R. P; Misra, G. P.; West, W. W.; Pojman, J. A. "Polymerization Coupled to Oscillating Reactions: I. A Mechanistic Investigation and Numerical Simulation of Acrylonitrile Polymerization in the Belousov-Zhabotinsky Reaction in a Batch Reactor", J. Am. Chem. Soc. 1999, 121,7373-7380. McCaughey, B.; Pojman, J. A.; Simmons, C.; Volpert, V. A. "The Effect of Convection on a Propagating Front with a Liquid Product: Comparison of Theory and Experiments,"Chaos 1998, 8, 520-529. Chekanov, Y.; Arrington, D.; Brust, G.; Pojman, J. A. "Frontal Curing of Epoxy Resin: Comparison of Mechanical and Thermal Properties to Batch Cured Materials,"J. Appl. Polym. Sci. 1997, 66, 1209-1216. Bowden, G.; Garbey, M.; Ilyashenko, V. M.; Pojman, J. A.; Solovyov, S.; Taik, A.; Volpert, V. "The Effect of Convection on a Propagating Front with a Solid Product: Comparison of Theory and Experiments,"J. Phys. Chem. B 1997, 101, 678-686. Pojman, J. A.; Ilyashenko, V. M.; Khan, A. M. "Free-Radical Frontal Polymerization: Self-Propagating Thermal Reaction Waves,"J. Chem. Soc. Faraday Trans. 1996, 92, 2824-2836.