NC STATE UNIVERSITY

1. CMC Addition of silica Molar fraction of surfactant, XS Surfactant removal Reduced density, rr T=192 K T=290 K Freezing of LJ CCl4 confined in multi-walled carbon nanotubes (carbon walls not shown). T=140 K Active site (-COOH) Ammonia (NH3) evaporation of water Surfactant Concentration in the Pore Bulk Surfactant Concentration Surfactant Concentration Department of Chemical Engineering NC STATE UNIVERSITY 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 to important new insights. Currently our interest is focused on several systems: (a) Micellar and reverse micellar solutions - their phase 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-15,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 separations, and in new technologies based on CO2 solvent applications. Nano-porous materials play a prominent role in chemical processing, particularly in separations 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. Front Row: (left to right)Laurel Andersen, Francisco Hung, Keith E. Gubbins, Lauriane Scanu, Supriyo BhattacharyaBack Row: (left to right)Coray Colina, Jorge Pikunic, Naresh Chennamsetty, Heath Turner, Martin Lisal, Flor Siperstein, John Brennan Front Row: (left to right) Flor Siperstein, Supriyo Bhattachrya, Lauriane Scanu, Gerhard H. Findenegg (visitor) Keith E. Gubbins, Francisco Hung Back Row: (left to right) Jorge Pikunic, Henry Bock, Coray Colina, Alberto Striolo, Erik Santiso Naresh Chennamsetty Current Research Realistic Molecular Models for Nanoporous Carbons Jorge Pikunic Freezing and Melting Behavior of Fluids Confined in Porous Materials Francisco R. Hung Molecular Modeling of Polymer Systems: Prediction of Phase Behavior and Surfactant Aggregation Coray M. Colina Molecular Simulation of Surfactant Systems: Cosurfactant Effects and Adsorption Naresh Chennamsetty Modeling the Synthesis of Ordered Mesoporous Materials using Lattice Monte Carlo Simulations Supriyo Bhattacharya Saccharose-based carbon heated at 400°C Saccharose-based carbon heated at 1000°C Micelles formed in CO2 with surfactants consisting of CO2-philic and CO2-phobic components. Phase diagram for PTAN-b-PVAC in CO2. Symbols are experimental points. Lines predicted with the SAFT EOS on this work. Nitrogen adsorption at 77 K (simulation results) Freezing of LJ CCl4 confined in MCM-41 (pore walls in black). Water Adsorption and Phase Transitions in Carbon Pores Alberto Striolo Initial and final configurations in interfacial NVT simulations showing the surfactant rich and poor regions in equilibrium Surfactant-Silica LiquidCrystals as Precursors for Ordered Mesoporous Materials Flor R. Siperstein B Chemical Reactions in Confined Geometries Heath Turner Phase behavior of scCO2/surfactant/water systems using Lattice Monte Carlosimulations* Lauriane F. Scanu C A Volume expansivity versus pressure for carbon dioxide modeled as a two center Lennard-Jones plus point quadrupole (2CLJQ). Continuous lines predicted by the Span-Wagner EOS, dashed lines by 2CLJQ EOS and symbols from NPT Monte Carlo simulations (this work). Ammonia synthesis, N2+3H2  2NH3, in a chemically activated carbon Molecular Modeling of Self-Assembled Nanostructures on Surfaces and in Narrow Pores Henry Bock Pore width determines the pressure at which capillary condensation occurs. What is the effect of pore connectivity? Aqueous Surfactant Solution in the Bulk Aqueous Surfactant Solution in Confinement B T*=0.29 Ammonia conversion tends to increase due to electrostaticinteractions with the COOH groups on the carbon surface. C A B Synthesis mechanism T* phase boundary T* Observed structures cmc Surfactants contain a CO2-phobic head (red) and a CO2-philic tail (yellow). They phase separate at low density (rr <1.4). At rr1.4, they form micelle or are individually solubilized depending on the density and concentration with respect to the CMC curve. T*=0.26 Observed structures When water is adsorbed in narrow pores there is evidence of a disorder-to-order transition at 298K. Is this a first-order phase transition? * In collaboration with Prof. Carol K. Hall The phase diagram is obtained from a mean-field approximation of a modified lattice gas model. Water as solvent causes a lower critical point and a decrease of the cmc with increasing temperature at low temperatures. Water as solvent causes an inverse temperature behavior of surfactant adsorption from solution, i.e. the adsorbed amount increases with increasing temperature. Ammonia synthesis, N2+3H2  2NH3, in a slit carbon pore Silica/Surfactant concentration