last update: July 05, 2000
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STC-ERSP Program Details
Principal Investigator: Peter J. Rossky Project Title: Molecular structure and dynamics at the CO2/water interface (#7) Phone/Fax: 512-471-3555 / 512-471-1624 E-mail: rossky@mail.utexas.edu Research Plan Connectivity Outreach Components Requested Budget Allocation - Year 1 Plans for Additional Funding Research Plan Overall objectives Molecular-based theories and simulation will be used to calculate interfacial properties at the CO2-aqueous solution interface. We will determine the interrelationships between the degree and energy of surfactant adsorption, interfacial tension, surfactant conformation at the interface and the force of interaction between stabilized surfaces. A hierarchy of theories and simulation will be utilized for the phases, including a mean-field (Poisson-Boltzmann) approach, RISM-based integral equations, and fully detailed computer simulations. We will develop a mechanistic understanding of interfacial structure and surfactant behavior which will guide experimental studies of these interfacial properties. Relation to overall objectives of the Center The possibility of designing surfactants for interfaces between CO2 and aqueous solutions offers new opportunities in materials science, protein/polymer chemistry, separation science and environmental science. A rigorous fundamental understanding of the relationship between interfacial properties and surfactant structure is a prerequisite to the rational design and synthesis of surfactants for CO2. The key objective here is to determine how the variation of chemical constituents in the "CO2-philic" and "CO2-phobic" (anchor) segments of a surfactant influences both the energetics and conformational behavior of surface active molecules, leading to experimentally observed adsorption and interfacial tensions. Approach and Year 1-Year 5 timelines Years 1-2: Initial interfacial studies will use a mean-field approach based upon lattice fluid self-consistent field theory combined with the Poisson-Boltzmann equation applied to the aqueous/CO2 interface in the presence of surfactant. The structure of and interactions between interfaces with various surfactants will be evaluated. The approach includes the effects of solvent compressibility which are of paramount importance. Initial simulation studies will focus on the water/CO2 interface per se, and its variation with CO2 density. This is an essential element in developing the larger framework for interpreting surfactant behavior. Years 2-4: Simulation studies of individual and multiple single and dichain surfactants at the water/CO2 interface will be carried out to obtain free energetics and conformational details. Both apparently good surfactants and those that are (surprisingly) poor will be studied in order to elucidate underlying principles. The data will also be used to evaluate the expected results of neutron scattering and the corresponding signatures of these structures in NMR. More detailed non-simulation, but fully molecular, integral equation theory will be applied to describe solvent-surfactant interactions. Focus will be on the extended reference interaction site method (XRISM) and polymer RISM. Aqueous phases including electrolytes and polyelectrolytes will be included. Years 3-5: The most rigorous, and likewise computer intensive treatment, will be full computer simulation of the unconstrained multicomponent system. A key goal is to use the results of the various simplified theories and of simulation to determine the minimal model needed for a predictive theoretical approach. At the same time, results will be compared with experiment and such a comparison will continue to be used to guide the experimental programs. Thrust area of this proposal Thrust Area B : Molecular Dynamics and Computer Simulation Connectivity Collaborators, multi-institutional, multi-disciplinary components The theoretical work will be carried out under joint direction of Keith Johnston (UT, Chem. Eng.) and Peter Rossky (UT-Chemistry). Coordination with experiment is thus assured through the interfacial tension and surfactant adsorption experimental studies by Johnston. The work will be coordinated with the studies of solvation by CO2 to be described thoroughly in the simulation studies of binary systems by Berkowitz, Gubbins, Hall, and Sanchez. In particular, the ability to directly calculate NMR (Johnson, Samulski, Wallen) and neutron (Wignall, Cochran, Fulton) data from simulation will make exceptionally close connection to experimental thrusts. The results of the theoretical studies will be of special interest to those studying the interactions between microemulsion and emulsion droplets experimentally (by Cochran, Fulton, Webber, Wignall and by Kelly and Carbonell), as well as to those focusing specifically on the issue wetting and de-wetting (Wallen, Grant, Roberts, Carbonell). Related work in other thrust areas (Listed in section just above) Sharing of resources (students, supplies, equipment, etc.) The postdoctoral student will be jointly directed by Keith Johnston and Peter Rossky, so that experimental and theoretical studies will be effectively coordinated. The workstation will be available not only for these theoretical studies but also for analysis of experimental data. Workstation cycles will be coordinated with those available on other STC workstations to maximize throughput of computationally intensive calculations. Outreach Components Suggested K-12 Outreach Ideas Through David Haase, Rossky has already initiated development of relationship between this STC and a very successful outreach program in Austin (Young Scientists classroom) with the goal of expanding that program. This connection is expected to benefit both programs greatly. Requested Budget Allocation - Year 1 Personnel salaries
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