Our research program is aimed at understanding, at the molecular level, the behavior of nano-dimensional fluids and solids. The underlying theme of our work is to develop molecular models that accurately describe the materials and systems of interest. These models are then used in molecular simulations and theories to interpret experimental results, and to predict behavior that is not accessible to experiment. Experimental studies complement the molecular simulation work, and comparison of the two frequently leads important new insights.

Currently our interest is focussed on two several kinds of system:

• (a) Micellar and reverse micellar solutions – their phase behavior, thermodynamics, surface properties and structure.
  
• (b) Nano-porous materials (solid materials having pores of nanometer dimension), such as templated mesoporous materials (MCM-41, SBA, etc), activated carbons, carbon buckytubes, aerogels and xerogels, silicas, etc.
• (c) Chemical reactions in nano-scale systems, where strong intermolecular interactions are important (porous materials as nano-scale reactors, reactions in supercritical fluids, etc.).

Micellar solutions are important in separtions, and in new technologies based on CO₂ solvent applications. Nano-porous materials play a prominent role in chemical processing, particularly in separation and as catalysts and catalyst supports. They can also form the basis of future technologies, involving energy storage, as nano-reactors, as sensors, fabrication of small devices of molecular dimensions, etc. Both the yield and rate of chemical reactions are strongly affected by the reduced dimensionality of nano-scale systems, and experimental studies are very difficult at this scale.

Carbon dioxide is an attractive alternative solvent, since it is environmentally benign, inexpensive and widely available. Recently CO₂-philic surfactants and polymers have been developed that open the way to new CO₂-based technologies, including cleaning processes, and the formation of coatings, thin films, polymer blends, etc. However, further development is hindered by a lack of understanding of the thermodynamics, phase equilibria, and surface properties of these novel systems. In this project molecular simulations and theories will be used to develop a basic understanding of the underlying principles governing phase changes, microscopic structure, and other properties. This project is supported by the NSF Center for Environmentally Responsible Solvents and Processes, and will involve two stages: (a) development of an understanding of phase equilibria and thermodynamics for binary and ternary mixtures involving CO₂ as the solvent; and (b) developing realistic molecular models that describe the self-assembly phenomena (formation of micelles and reverse micelles) observed in some systems, and use of these models to predict how micellization changes with the state conditions and chemical species involved. The results of these calculations, and the direction of the research program, will be coupled with experimental studies being undertaken for these systems at NCSU and at UNC-CH.

Little is known of the influence of confinement in porous media on liquid-liquid, liquid-solid and solid-solid phase separation and equilibria. We are interested in knowing the effects on the phase diagram and any critical points, the nature of the transitions and the structure of solid phases. Experimental studies are difficult because of long-lived metastable states and poorly characterized materials. In this area projects are available to study gas-liquid, liquid-liquid and solid-liquid equilibria, and also the kinetics of phase separation. Opportunities are available to participate in experimental work with groups with whom we collaborate.

Buckytubes are a novel form of carbon tubule, which can be made with tightly controlled pore size in the range 1-10 nm; MCM-41 is a new aluminosilicate with cylindrical pores whose size can be adjusted within a similar range. These materials offer exciting possibilites for highly selective separations, and for energy storage. Molecular models developed in our group provide a good description of the existing experimental data. With further refinement they can be used to design optimal adsorption systems for fuel storage, separations and pollutant removal. Of particular interest is the design of optimal systems for (a) removal of trace amounts of contaminants and pollutants from gas and water streams, and (b) storage of hydrogen and methane.