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Molecules Structure Properties Functions |
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A major focus of our research has been on the Density Functional Theory (DFT) for complex molecular systems. The free-energy functionals developed in our group have been successfully used to describe the microscopic structure and thermodynamic properties of colloidal dispersions, block copolymers, polymer and polyelectrolyte brushes, polymer composites, liquid crystals, telechelic and multivalent polymers, and confined DNA/RNA. In addition to DFT, we use advanced liquid-state theories and various molecular simulation techniques, including Monte Carlo, molecular and Langevin dynamics, to study equilibrium and off-equilibrium phase transitions in colloidal dispersions, charge/polymer-regulated colloidal forces, gas adsorption in porous materials, and protein folding in confined geometries. In collaboration with experimental groups, our theoretical investigations provide insights for discovery of a novel porous material for hydrogen storage, development of new methods for separation of large DNA molecules and protein folding, and design of a new procedure for protein refolding based on dynamic control. |
Density Functional Theory (DFT) Fundamentals |
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Research |
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DFT provides a unifying computational method for describing the microscopic structures and phase behavior of soft-condensed matter. The method is rooted in quantum mechanics but shares mathematical similarity with a number of classical theories in statistical mechanics. |
DFT Applications |
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Milestones:
· van der Waals (1893) Nobel Prize (1910) · Thomas-Fermi (1920s) Nobel Prize (1938) · Onsager (1949) Nobel Prize (1968) · Hohenberg and Kohn (1964) Nobel Prize (1998) · Mermin (1965)-Ebner-Saam-Stroud (1976) |
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· Surface tension and interfacial behavior · Gas adsorption · Materials characterization · Wetting transitions · Solvation · Surface forces · Freezing and melting transitions · Phase behavior of liquid crystals · Structure and phase behavior polymeric materials and composites · Molecular self-assembly · Transport through ion channels · Lipid bilayers · Biomacromolecular crowding · Kinetics of phase transitions · Off-equilibrium phase transitions ·
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Phase Transition in Colloidal Dispersions |
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Colloidal dispersions exist in a variety of natural and industrial settings and exhibit rich and diverse equilibrium and off-equilibrium properties. A quantitative understanding of the solvent-mediated colloidal forces and phase behavior is required for many practical applications of colloids, but it also consists of a major challenge in the statistical mechanics of complex fluids.
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Protein Adsorption and Stability |
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Proteins fold in a confined space not only in vivo, i.e., folding assisted by molecular chaperones and chaperonins in a crowded cellular medium, but also in vitro as in the industrial production of recombinant therapeutic proteins. By using Langevin dynamics simulations, we demonstrated that a cage of moderate size and hydrophobicity optimizes both the protein folding yield and kinetics of structural transitions. Similar conclusions were reached by molecular simulation for the folding of a β-barrel protein in the presence of model surfactants or temperature-sensitive polymers. The simulation results provide insights for the development of a new strategy for protein refolding in periodic mesoporous organosilica (PMO), which enables high-yield refolding at high protein concentrations (e. g. > 1 mg/ml for lysozyme). The simulation also helps to develop a new procedure to control the kinetic pathways of protein folding by using a thermally-responsive polymer that varies its hydrophobicity concomitant with the protein structural changes.
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Other Works |
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Some other projects over the past few years include self-diffusion of methane in single-walled carbon nanotubes, activated carbons for separation of hydrogen and carbon dioxide, porous materials for hydrogen storage, surface-facilitated separation of long DNA molecules, and phase behavior of asphaltene-containing crude oils. Among numerous challenges before prevalent utilization of hydrogen energy, a pressing task is to produce and store hydrogen gas efficiently. According to our molecular simulations, a novel class of carbonaceous material called graphitic carbon inverse opal (GCIO) may provide excellent sorbents for hydrogen storage at room temperature. The simulation results may inspire broad interests for practical demonstration of the exciting hydrogen-storage capability of the novel material. Also related to gas storage and separation, we investigated the separation efficiency and diffusion properties of gas mixtures in nanostructured materials. For the prevention of undesired asphaltene precipitations during oil recovery and refinery processes, we developed a new thermodynamic model that provides a good prediction of asphaltene precipitation over wide temperature, pressure and composition intervals.
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