last update: March 21, 2001
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STC-ERSP Program Details Principal Investigator: R.J. Spontak Project Title: Phase behavior of Blends (Former Prog #22) Research Plan Connectivity Outreach Components Additional Comments Requested Budget Allocation - Year 1 Plans for Additional Funding Research Plan Overall objectives Spontak proposes to identify or design multiphase polymer systems composed of (i) two or more homopolymers, (ii) a homopolymer and a block copolymer, (iii) two homopolymers and a block copolymer, or (iv) a single block copolymer that will be subjected to high-pressure CO2 with and without custom-synthesized CO2-philic/phobic surfactants. By systematically varying the pressure and temperature of the CO2 and subsequently altering the density and solvent/plasticizing efficacy of CO2, the effect of high-pressure CO2 on both phase behavior and morphological development can be ascertained through the use of in-situ scattering and microscopy techniques, as well as complementary ex-situ analysis. Results will be compared to theoretical predictions from equation-of-state models for multicomponent polymer systems. Systems in which CO2 serves as a slightly selective solvent (i.e., those containing fluorinated polymers), as well as those that can be continuously extruded, will be of particular interest in this study. Relation to overall objectives of the Center Since most efforts thus far regarding the utilization of high-pressure CO2 in polymer processing have focused on plasticization-induced changes in viscosity and the glass transition temperature, the effect of high-pressure CO2 on phase behavior and morphology development in multicomponent polymer systems remains poorly understood. This project will reveal, for instance, the dependence of the Flory-Huggins interaction parameter on CO2 pressure. Such fundamental information can subsequently be used to better understand the role of CO2 on intermolecular interactions at high-pressure, and is prerequisite to the theoretical modeling of multicomponent polymer systems in the presence of high-pressure CO2 Discerning the effect of high-pressure CO2 on phase separation kinetics will also yield insight into the molecular dynamics of unstable multiphase systems as a function of CO2 density. Knowledge of phase behavior, as well as phase stability, will also be of tremendous value in the design of continuous processes (e.g., extrusion) that will be aimed at generating novel polymer morphologies, including microcellular foams. Approach and Year 1-Year 5 timelines Years 1-2: Identify relevant multiphase polymer systems (UCST and LCST) or custom-synthesize new homopolymers/block copolymers for study. Match chemistry of one block with existing or synthesizable CO2-philic/phobic block copolymers to ensure that surfactants can be used. Examine simple binary systems of homopolymers by SANS at Oak Ridge National Laboratory and by spectrophotometry at the Center. Quantify shifts in phase boundaries and develop a modified Sanchez-Lacombe theory to accommodate high-pressure CO2. Use the Random Phase Approximation to ascertain the CO2 pressure dependence of the Flory-Huggins interaction parameter. Set up high-pressure optical cell for visualization of multicomponent polymer systems in high-pressure CO2. Years 2-3: Extend initial study to include (i) block copolymers that serve as compatibilizers for the homopolymers studied and (ii) CO2-philic/phobic block copolymers to improve solubility in CO2. Use high-pressure optical cell to correlate CO2 density with flow characteristics and morphology development under shear flow. Compare results obtained with materials produced through extrusion. Vary compositions of multicomponent polymer systems and examine systems rich in the CO2-philic/phobic copolymer to ascertain the self-association behavior of these copolymers in microemulsions. Years 2-5: Continue developing multicomponent polymer systems on the basis of initial findings. Use the results of this work to guide theoretical modeling efforts and other processes utilizing high-pressure CO2. Prepare new materials and systems on an as-needed basis. Collaborate with other investigators requiring the expertise gained in this study. Thrust area of this proposal Thrust Area C: Rate Processes Connectivity Collaborators, multi-institutional, multi-disciplinary components Some homopolymers and copolymers may not be commercially available and will require the synthetic talents of DeSimone (UNC-CH). This will certainly be the case for the CO2-philic/phobic block copolymers required here. Wignall (ORNL) will use SANS to study the scattering behavior of homogeneous systems to discern Flory-Huggins interaction parameters as functions of temperature and pressure. Khan (NCSU) will use his high-pressure magnetorheometer to study the rheological properties of our CO2-solvated blends in dynamic and steady modes, and will employ the single- and (proposed) twin-screw extruders for large-volume production and foaming operations. Assistance from Hall (NCSU) and Sanchez (UT-Austin) will be sought to modify existing equation-of-state thermodynamic models to extract molecular interaction parameters from multicomponent polymer data in the presence of high-pressure CO2, and to develop a predictive tool for future design use. Small-angle light scattering will be required for in-situ phase separation studies will be conducted in collaboration with Rubinstein (UNC-CH). High-pressure calorimetry will be performed with Roberts (NCSU) to ascertain the extents of mixing and plasticization in the proposed multicomponent/phase systems. We shall work with Johnson (UT-Austin) to develop an inter-institutional effort to study polymer morphologies in the presence of high-pressure CO2. Related work in other thrust areas Researchers in Thrust A (Interfacial and Colloid Science in Compressible Media) will prepare some of the specialty (co)polymers required in this study and will help us understand the self-association behavior of CO2-philic/phobic block copolymers. Researchers in Thrust B (Molecular Thermodynamics and Computer Simulations) will extend existing thermodynamic models for multicomponent polymer systems to include compressible fluids. Researchers in Thrust C (Rate Processes) will use information obtained here for the study of multicomponent foaming operations. Sharing of resources (students, supplies, equipment, etc.) The student responsible for this project will employ materials synthesized by other researchers in the Center and will be intimately involved in efforts pertaining to the self-association of CO2-philic/phobic block copolymers in high-pressure CO2 and foaming operations. The student will work closely with the other PIs mentioned above. Outreach Components Suggested K-12 Outreach Ideas Spontak and the student will visit local schools to discuss and demonstrate some basic principles of polymers as useful materials and emulsification. We also intend to develop a short computer visualization to show these ideas over the Web to undergraduates majoring in chemistry, chemical engineering, materials science and engineering, and physics. Khan and Spontak plan to present a workshop on polymer thermodynamics and rheology during one summer and will touch upon results obtained from the present study. Additional Comments Please contact me (Spontak) if others need information regarding multiphase polymer systems and the effect of high-pressure CO2 on such systems, or the self-assembly behavior of block copolymers in (non)selective solvents. Anyone interested in using the high-pressure optical cell should also contact me. Requested Budget Allocation - Year 1 Personnel salaries
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