GOALI: Development of Transferable Force Fields for Phase Equilibria and Simulation Studies of Aggregation and Solvation in Microheterogeneous Fluids

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ABSTRACTGOALI: Development of Transferable Force Fields for Phase Equilibriaand Simulation Studies of Aggregation and Solvationin Microheterogeneous FluidsAccurate knowledge of the phase equilibria and other thermophysical properties of complex fluidmixtures is of enormous fundamental and practical importance. The success of molecular simulation in predicting thermophysical properties and in advancing our understanding of the relationship between molecular architecture and macroscopic observable depends on the availability of efficient simulation algorithms and accurate force fields. The goals of the proposed research are to develop three levels of transferable force fields and of biased Monte Carlo methods. The first-level force field, called TraPPE-UA (transferable potentials for phase equilibria united atom), employs the united-atom representation for alkyl segments and simple Lennard-Jones and Coulombic terms. In the second level, called TraPPE{EH (explicit hydrogen), all atoms including alkyl group hydrogens and somelone-pair electron and bond-center sites are treated explicitly. In the third-level, called TraPPE-pol (polarizable), both the van der Waals and electrostatic interactions can respond to changes in the environment. Whereas the first level is designed for simplicity and computational efficiency with good accuracy, the second level is aimed at improved accuracy for mixtures of non-polar or a polar non-hydrogen-bonding compounds. The third level is directed solely at the highest possible level of accuracy and transferability. The project will extend the TraPPE-UA force field to alkynes; alkene oxides; 5-membered homo- and hetero-aromatic rings; halogenated hydrocarbons; primary, secondary, and tertiary hydrofluoro alcohols, ethers, and oxides; and silicon and phosphorous containing functionalities. The TraPPE-EH force field will be extended to cyclic alkanes, alkenes, and arenes. An the development of the TraPPE-pol force field will be continued with common parameters for water, alkanes, alcohols, and ethers.In addition to force field development, this project also addresses novel simulation strategiesfor first principles simulations of phase equilibria. Molecular simulations using the transferableforce fields will be employed as engineering tool to predict thermophysical properties of a variety of systems, thereby adding to the available experimental database. The simulations provide microscopic-level information for complex chemical systems, thereby giving new physical insight into how molecular architecture and composition determine macroscopic phenomena. In particular, simulations will be carried out to investigate (i) homogeneous nucleation phenomena, (ii) interfacial properties, aggregation, and solubilities in mixtures containing non-ionic surfactants, and (iii) miscibility in monomer/oligomer/polymer systems. The broader impacts of the proposed work include the development of transferable force fields, advanced algorithms, and software packages that are made freely available through print publications, a web interface, and GNU General Public Licenses. These tools are eagerly awaited by a large research community. Furthermore, the proposed project will have a major impact on various educational, training, and mentoring activities and will allow continued outreach. This project will project from extensive collaboration of a tight university-industry team consisting of the PI, two graduate students, and Drs. Ross and Caldwell of 3M Central Research, St. Paul, MN.