@article{bhattacharya_coasne_hung_gubbins_2009, title={Modeling Micelle-Templated Mesoporous Material SBA-15: Atomistic Model and Gas Adsorption Studies}, volume={25}, ISSN={["0743-7463"]}, DOI={10.1021/la801560e}, abstractNote={We report the development of a realistic molecular model for mesoporous silica SBA-15, which includes both the large cylindrical mesopores and the smaller micropores in the pore walls. The methodology for modeling the SBA-15 structure involves molecular and mesoscale simulations combined with geometrical interpolation techniques. First, a mesoscale model is prepared by mimicking the synthesis process using lattice Monte Carlo simulations. The main physical features of this mesoscale pore model are then carved out of an atomistic silica block; both the mesopores and the micropores are incorporated from the mimetic simulations. The calculated pore size distribution, surface area, and simulated TEM images of the model structure are in good agreement with those obtained from experimental samples of SBA-15. We then investigate the adsorption of argon in this structure using Grand Canonical Monte Carlo (GCMC) simulations. The adsorption results for our SBA-15 model are compared with those for a similar model that does not include the micropores; we also compare with results obtained in a regular cylindrical pore. The simulated adsorption isotherm for the SBA-15 model shows semiquantitative agreement with the experimental isotherm for a SBA-15 sample having a similar pore size. We observe that the presence of the micropores leads to increased adsorption at low pressure compared to the case of a model without micropores in the pore walls. At higher pressures, for all models, the filling proceeds via the monolayer-multilayer adsorption on the mesopore surface followed by capillary condensation, which is mainly controlled by the mesopore diameter and is not influenced by the presence of the micropores.}, number={10}, journal={LANGMUIR}, author={Bhattacharya, Supriyo and Coasne, Benoit and Hung, Francisco R. and Gubbins, Keith E.}, year={2009}, month={May}, pages={5802–5813} }
 @inbook{coasne_czwartos_gubbins_hung_sliwinska-bartkowiak_2007, title={Confinement effects on freezing of binary mixtures}, volume={160}, ISBN={9780444520227}, ISSN={0167-2991}, url={http://dx.doi.org/10.1016/s0167-2991(07)80086-3}, DOI={10.1016/s0167-2991(07)80086-3}, abstractNote={We report molecular simulations and experimental measurements of the freezing and melting of mixtures confined in nanopores. Dielectric relaxation spectroscopy was used to determine the experimental phase diagram of mixtures confined in activated carbon fibers. Grand Canonical Monte Carlo simulations combined with the parallel tempering technique were used to model the freezing of several Lennard - Jones mixtures in graphite slit pores. The effect of confinement is discussed for mixtures having a simple solid solution or an azeotropic solid - liquid phase diagram. We also investigate how the competition between the wall -fluid and fluid - fluid interactions affects the freezing temperature of the confined system. The structure of the crystal phase in the simulations is also investigated by means of positional and bond-orientational pair correlation functions and bond-order parameters.}, booktitle={Studies in Surface Science and Catalysis}, publisher={Elsevier}, author={Coasne, Benoit and Czwartos, Joanna and Gubbins, Keith E. and Hung, Francisco R. and Sliwinska-Bartkowiak, Malgorzata}, year={2007}, pages={667–674} }
 @inproceedings{hung_coasne_gubbins_siperstein_thommes_sliwinska-bartkowiak_2006, title={A Monte Carlo study of capillary condensation of krypton within realistic models of templated mesoporous silica materials}, volume={160}, DOI={10.1016/s0167-2991(07)80021-8}, abstractNote={We present a detailed simulation study of the hysteresis loop in conical pores and in cylindrical pores with periodic constrictions to understand how the non-uniformity of the pore diameter along the pore axis would affect the hysteresis loop. The shape and size of the loop in the conical pores (with and without closed ends) are modified by the cone angle because of the change in the curvature of the menisci at the pore ends. In periodically constricted cylindrical pores, the shape and size of the hysteresis loop are not significantly altered by the pore length or by the presence of a closed end because condensation and evaporation in this type of pore occur in the individual pore sections. Similar hysteresis loops have been found in experimental studies, suggesting that structures of the type modelled here occur in real materials.}, booktitle={Characterization of porous solids vii - proceedings of the 7th international symposium on the characterization of porous solids (cops-vii), aix-en-provence, france, 26-28 may 2005}, author={Hung, F. R. and Coasne, B. and Gubbins, Keith and Siperstein, F. R. and Thommes, M. and Sliwinska-Bartkowiak, M.}, year={2006}, pages={153–160} }
 @article{coasne_gubbins_hung_jain_2006, title={Adsorption and structure of argon in activated porous carbons}, volume={32}, ISSN={["1029-0435"]}, DOI={10.1080/08927020600675707}, abstractNote={Molecular simulations are used to investigate the adsorption and structure of argon in ordered and disordered models of porous carbons. The ordered porous carbon (model A) is an assembly of regular slit pores of different sizes, while the disordered porous carbon (model B) is a structural model that reproduces the complex pore shape and pore connectivity of saccharose-based porous carbons. The same pore size distribution is used for models A and B so that we are able to estimate, for similar confinement effects, how the disorder of the porous material affects the adsorption and structure of the confined fluid. Adsorption of argon at 77.4 K in the two models is studied using Grand Canonical Monte Carlo simulations. The structure of the confined fluid is analyzed using crystalline bond order parameters and positional or bond orientational pair correlation functions. The filling pressure for the assembly of slit pores is much lower than that for the disordered porous carbon. It is also found that the isosteric heat of adsorption for the ordered porous model overestimates that for the disordered porous model. The results suggest that the agreement between models A and B would be improved if the same density of carbon atoms were used in these two models. Strong layering of Ar is observed at all pressures for model A. The confined phase is composed of liquid-like layers at low-pressures, which crystallize into well-defined hexagonal 2D crystals after complete filling of the pores. The structure of argon in the disordered porous carbon strongly departs from that in the slit pore model. Although its structure remains liquid-like overall, argon confined in model B is composed of both crystalline clusters and amorphous (solid or liquid) nano-domains.}, number={7}, journal={MOLECULAR SIMULATION}, author={Coasne, Benoit and Gubbins, Keith E. and Hung, Francisco R. and Jain, Surendra K.}, year={2006}, month={Jun}, pages={557–566} }
 @article{coasne_hung_pellenq_siperstein_gubbins_2006, title={Adsorption of Simple Gases in MCM-41 Materials: The Role of Surface Roughness}, volume={22}, ISSN={["0743-7463"]}, DOI={10.1021/la051676g}, abstractNote={This paper reports the development and testing of atomistic models of silica MCM-41 pores. Model A is a regular cylindrical pore having a constant section. Model B has a surface disorder that reproduces the morphological features of a pore obtained from an on-lattice simulation that mimics the synthesis process of MCM-41 materials. Both models are generated using a similar procedure, which consists of carving the pore out of an atomistic silica block. The differences between the two models are analyzed in terms of small angle neutron scattering spectra as well as adsorption isotherms and isosteric heat curves for Ar at 87 K and Xe at 195 K. As expected for capillary condensation in regular nanopores, the Ar and Xe adsorption/desorption cycles for model A exhibit a large hysteresis loop having a symmetrical shape, i.e., with parallel adsorption and desorption branches. The features of the adsorption isotherms for model B strongly depart from those observed for model A. Both the Ar and Xe adsorption branches for model B correspond to a quasicontinuous pore filling that involves coexistence within the pore of liquid bridges and gas nanobubbles. As in the case of model A, the Ar adsorption isotherm for model B exhibits a significant hysteresis loop; however, the shape of the loop is asymmetrical with a desorption branch much steeper than the adsorption branch. In contrast, the adsorption/desorption cycle for Xe in model B is quasicontinuous and quasireversible. Comparison with adsorption and neutron scattering experiments suggests that model B is too rough at the molecular scale but reproduces reasonably the surface disorder of real MCM-41 at larger length scales. In contrast, model A is smooth at small length scales in agreement with experiments but seems to be too ordered at larger length scales.}, number={1}, journal={LANGMUIR}, author={Coasne, B and Hung, FR and Pellenq, RJM and Siperstein, FR and Gubbins, KE}, year={2006}, month={Jan}, pages={194–202} }
 @inproceedings{bhattacharya_coasne_hung_gubbins_2006, title={Modeling triblock surfactant templated mesoporous silicas (MCF and SBA-15): A mimetic simulation study}, volume={160}, DOI={10.1016/s0167-2991(07)80068-1}, abstractNote={We have developed models for templated mesoporous silicas such as Mesostructured Cellular Foams and SBA-15. The first part of our work elaborates the effect of oil concentration on the pore morphology of the triblock surfactant templated mesoporous materials. Our Lattice Monte Carlo simulations mimic the synthesis process by equilibrating a mixture of triblock surfactant, oil, water and silica at a constant temperature and density. With increasing oil concentration, we find the pore geometry to change according to the sequence: cylinders → lamellae → mesocells, which is in qualitative agreement with experimental results. In the second part of our work, we develop realistic atomistic models of the SBA-15 material, starting from the mesoscale model obtained from Lattice Monte Carlo simulations. Both the pore surface heterogeneity and the micropores are derived from the mimetic simulations. The simulated TEM and pore size distribution of the model qualitatively resemble the real material.}, booktitle={Characterization of porous solids vii - proceedings of the 7th international symposium on the characterization of porous solids (cops-vii), aix-en-provence, france, 26-28 may 2005}, author={Bhattacharya, S. and Coasne, B. and Hung, F. R. and Gubbins, Keith}, year={2006}, pages={527–534} }
 @article{jazdzewska_hung_gubbins_sliwinska-bartkowiak_2005, title={An experimental study of melting of CCl4 in carbon nanotubes}, volume={7}, ISSN={["1463-9084"]}, DOI={10.1039/b510245f}, abstractNote={We report dielectric relaxation spectroscopy measurements of the melting point of carbon tetrachloride confined within open-tip multi-walled carbon nanotubes with two different pore diameters, 4.0 and 2.8 nm. In both cases, a single transition temperature well above the bulk melting point was obtained for confined CCl4. These results contrast with what was obtained in our previous measurements using carbon nanotubes with a pore diameter of 5.0 nm, where multiple transition temperatures both above and below the bulk melting point of CCl4 were observed. Our experimental measurements are consistent with our recent molecular simulation results (F. R. Hung, B. Coasne, E. E. Santiso, K. E. Gubbins, F. R. Siperstein and M. Sliwinska-Bartkowiak, J. Chem. Phys., 2005, 122, 144706). Although the simulations overestimate the temperatures in which melting upon confinement occurs, both simulations and experiments suggest that all regions of adsorbate freeze at the same temperature, and that freezing occurs at higher temperatures upon reduction of the pore diameter.}, number={22}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Jazdzewska, M and Hung, FR and Gubbins, KE and Sliwinska-Bartkowiak, M}, year={2005}, pages={3884–3887} }
 @article{sliwinska-bartkowiak_hung_santiso_coasne_dudziak_siperstein_gubbins_2005, title={Effect of Confinement on Freezing of CCl4 in Cylindrical Pores}, volume={11}, ISSN={0929-5607 1572-8757}, url={http://dx.doi.org/10.1007/s10450-005-5956-x}, DOI={10.1007/s10450-005-5956-x}, number={S1}, journal={Adsorption}, publisher={Springer Nature}, author={Sliwinska-Bartkowiak, Malgorzata and Hung, Francisco R. and Santiso, Erik E. and Coasne, Benoit and Dudziak, Grazyna and Siperstein, Flor R. and Gubbins, Keith E.}, year={2005}, month={Jul}, pages={391–396} }
 @article{czwartos_coasne_gubbins_hung_sliwinska-bartkowiak_2005, title={Freezing and melting of azeotropic mixtures confined in nanopores: experiment and molecular simulation}, volume={103}, ISSN={["1362-3028"]}, DOI={10.1080/00268970500200101}, abstractNote={The paper reports on a qualitative comparison between experimental measurements and molecular simulations of the freezing and melting of azeotropic mixtures confined in nanoporous materials. Dielectric relaxation spectroscopy was used to determine the experimental solid/liquid phase diagram of CCl4/C6H12 mixtures confined in activated carbon fibres. Grand Canonical Monte Carlo simulations combined with the parallel tempering technique were used to model the freezing of the azeotropic Lennard–Jones mixture Ar/CH4 in a graphite slit pore. The structure of the crystal phase in the simulations is investigated by means of positional and bond-orientational pair correlation functions and appropriate bond-order parameters. Both simulations and experiments show that the phase diagram of the confined mixture is of the same type as that for the bulk, but the solid/liquid coexistence lines are located at higher temperatures. The effect of confinement and of the wall/fluid interaction on the location of the azeotrope is discussed.}, number={21-23}, journal={MOLECULAR PHYSICS}, author={Czwartos, J and Coasne, B and Gubbins, KE and Hung, FR and Sliwinska-Bartkowiak, M}, year={2005}, pages={3103–3113} }
 @article{coasne_czwartos_gubbins_hung_sliwinska-bartkowiak_2005, title={Freezing of mixtures confined in a slit nanopore}, volume={11}, ISSN={["1572-8757"]}, DOI={10.1007/s10450-005-5941-4}, abstractNote={We report a Grand Canonical Monte Carlo study of the freezing/melting of Lennard-Jones A/B mixtures confined in a slit pore (H = 1.44 nm). The fluid/fluid interactions are chosen to model A = Ar and B = Kr. Fluid/wall interaction parameters are chosen so that the ratio of the wall/fluid to the fluid/fluid interactions for Kr and Ar is larger and smaller than 1, respectively. We find that the phase diagram of the confined mixture is of the same type than that for the bulk. The freezing temperature of confined mixtures rich in Kr is larger than the bulk. In contrast, we observe a decrease of the freezing temperature for mixtures rich in Ar. The confined crystal has a hexagonal structure (triangular symmetry), except for pure Ar where a square structure is observed.}, number={Suppl. 1}, journal={ADSORPTION-JOURNAL OF THE INTERNATIONAL ADSORPTION SOCIETY}, author={Coasne, B and Czwartos, J and Gubbins, KE and Hung, FR and Sliwinska-Bartkowiak, M}, year={2005}, pages={301–306} }
 @article{hung_gubbins_radhakrishnan_szostak_beguin_dudziak_sliwinska-bartkowiak_2005, title={Freezing/melting of Lennard-Jones fluids in carbon nanotubes}, volume={86}, ISSN={["1077-3118"]}, DOI={10.1063/1.1862786}, abstractNote={We report molecular simulation and experimental results for the freezing/melting behavior of Lennard-Jones fluids adsorbed in pores of cylindrical geometry, using simple models for multiwalled carbon nanotubes (MWNTs) of inner diameter 5nm. For cylindrical pores, our results for a D=9.7σff MWNT show no formation of regular three-dimensional crystalline structures. They also suggest that the outer layers experience an increase in the freezing temperature, while the inner layers provoke a depression in the freezing temperature with respect to the bulk freezing point. Dielectric relaxation spectroscopy shows a solid-fluid transition at 234K for CCl4 in these MWNTs that is in qualitative agreement with that determined in our simulations for the inner adsorbed layers.}, number={10}, journal={APPLIED PHYSICS LETTERS}, author={Hung, FR and Gubbins, KE and Radhakrishnan, R and Szostak, K and Beguin, F and Dudziak, G and Sliwinska-Bartkowiak, M}, year={2005}, month={Mar} }
 @article{hung_coasne_santiso_gubbins_siperstein_sliwinska-bartkowiak_2005, title={Molecular modeling of freezing of simple fluids confined within carbon nanotubes}, volume={122}, ISSN={["1089-7690"]}, DOI={10.1063/1.1881072}, abstractNote={We report Monte Carlo simulation results for freezing of Lennard-Jones carbon tetrachloride confined within model multiwalled carbon nanotubes of different diameters. The structure and thermodynamic stability of the confined phases, as well as the transition temperatures, were determined from parallel tempering grand canonical Monte Carlo simulations and free-energy calculations. The simulations show that the adsorbate forms concentric molecular layers that solidify into defective quasi-two-dimensional hexagonal crystals. Freezing in such concentric layers occurs via intermediate phases that show remnants of hexatic behavior, similar to the freezing mechanism observed for slit pores in previous works. The adsorbate molecules in the inner regions of the pore also exhibit changes in their properties upon reduction of temperature. The structural changes in the different regions of adsorbate occur at temperatures above or below the bulk freezing point, depending on pore diameter and distance of the adsorbate molecules from the pore wall. The simulations show evidence of a rich phase behavior in confinement; a number of phases, some of them inhomogeneous, were observed for the pore sizes considered. The multiple transition temperatures obtained from the simulations were found to be in good agreement with recent dielectric relaxation spectroscopy experiments for CCl(4) confined within multiwalled carbon nanotubes.}, number={14}, journal={JOURNAL OF CHEMICAL PHYSICS}, author={Hung, FR and Coasne, B and Santiso, EE and Gubbins, KE and Siperstein, FR and Sliwinska-Bartkowiak, M}, year={2005}, month={Apr} }
 @article{coasne_hung_siperstein_gubbins_2005, title={Molecular simulation of gas adsorption in realistic models of silica nanopores}, volume={30}, ISSN={["1958-5934"]}, DOI={10.3166/acsm.30.375-383}, abstractNote={Cet article presente une etude par simulation moleculaire de l'adsorption de Xe a 195 K dans deux modeles atomiques des pores de silice MCM-41. Le modele A consiste en un pore cylindrique regulier a section constante. Le modele B presente un important desordre de surface qui reproduit les aspects morphologiques d'un modele obtenu par simulation sur reseau du processus de synthese des pores de MCM-41. L'isotherme d'adsorption pour le modele A comporte une large boucle d'hysteresis, typique de la condensation capillaire dans des nanopores reguliers. Au contraire, le processus d'adsorption/desorption pour le modele B a une allure quasi continue et quasi reversible. A cause de l'importante rugosite de surface du modele B, la chaleur d'adsorption isosterique pour cet echantillon est beaucoup plus grande que celle obtenue pour le pore cylindrique regulier. Dans la mesure du possible, les resultats sont compares a des donnees experimentales.}, number={4}, journal={ANNALES DE CHIMIE-SCIENCE DES MATERIAUX}, author={Coasne, B and Hung, FR and Siperstein, FR and Gubbins, KE}, year={2005}, pages={375–383} }
 @article{coasne_czwartos_gubbins_hung_sliwinska-bartkowiak_2004, title={Freezing and melting of binary mixtures confined in a nanopore}, volume={102}, ISSN={["1362-3028"]}, DOI={10.1080/00268970412331292678}, abstractNote={This paper reports on a Grand Canonical Monte Carlo study of the freezing and melting of Lennard–Jones Ar/Kr mixtures confined in a slit pore composed of two strongly attractive structureless walls. For all molar compositions and temperatures, the pore, which has a width of 1.44 nm, accommodates two contact layers and one inner layer. Different wall/fluid interactions are considered, corresponding to pore walls that have a larger affinity for either Ar or Kr. The solid/liquid phase diagram of the confined mixture is determined and results compared with data for the bulk mixture. The structure of the confined mixture is studied using 2D order parameters and both positional g(r) and bond orientational G6(r) pair correlation functions. It is found that in the confined solid phase, both the contact and inner layers have a hexagonal crystal structure. It is shown that the freezing temperature of the Ar/Kr confined mixture is higher than the bulk freezing point for all molar compositions. Also, it is found that the freezing temperature becomes larger as the ratio α of the wall/fluid to the fluid/fluid interactions increases, in agreement with previous simulation studies on pure substances confined in nanopores. In the case of pore walls having a stronger affinity for Kr atoms (ε Ar/W<ε Kr/W), it is observed that both the contact and inner layers of the confined mixture undergo, at the same temperature, a transition from the liquid phase to the crystal phase. The freezing of Ar/Kr mixtures confined between the walls having a stronger affinity for Ar (ε Ar/W > ε Kr/W) is more complex: for Kr molar concentration lower than 0.35, we observe the presence of an intermediate state between all layers being 2D hexagonal crystals and all the layers being liquid. This intermediate state consists of a crystalline contact layer and a liquid-like inner layer. It is also shown that the qualitative variations of the increase of freezing temperature with the molar composition depend on the affinity of the pore wall for the different components. These results confirm that, in addition to the parameter α the ratio of the wall/fluid interactions for the two species, η=ϵAr/W/ϵKr/W, is a key variable in determining the freezing and melting behaviour of the confined mixture.}, number={19-20}, journal={MOLECULAR PHYSICS}, author={Coasne, B and Czwartos, J and Gubbins, KE and Hung, FR and Sliwinska-Bartkowiak, M}, year={2004}, month={Oct}, pages={2149–2163} }
 @article{hung_dudziak_sliwinska-bartkowiak_gubbins_2004, title={Freezing/melting behaviour within carbon nanotubes}, volume={102}, ISSN={["1362-3028"]}, DOI={10.1080/00268970410001670090}, abstractNote={We report a study of the freezing and melting of fluids confined within multi-walled carbon nanotubes with an internal diameter of 5 nm, using experimental measurements and molecular simulations. Dielectric relaxation spectroscopy was used to determine the experimental melting points and relaxation times of nitrobenzene and carbon tetrachloride within carbon nanotubes, and parallel tempering Monte Carlo simulations in the grand canonical ensemble were performed for confined carbon tetrachloride. The simulations show that the adsorbate forms concentric layers that solidify into quasi-two-dimensional hexagonal crystals with defects; highly defective microcrystalline regions are formed in the inner layers, owing to the strong geometrical constraints. Our simulations show no formation of common three-dimensional crystalline structures (fcc, hcp, bcc, sc or icosahedral) in confinement. The results suggest the presence of inhomogeneous phases (i.e., combinations of crystalline and liquid regions) within the pore over extended temperature ranges. Our results indicate that the outer layers of adsorbate solidify at temperatures slightly higher than the bulk freezing point, whereas the inner layers freeze at lower temperatures. The simulation results are in good agreement with the experimental measurements.}, number={2}, journal={MOLECULAR PHYSICS}, author={Hung, FR and Dudziak, G and Sliwinska-Bartkowiak, M and Gubbins, KE}, year={2004}, month={Jan}, pages={223–234} }
 @article{muller_hung_gubbins_2000, title={Adsorption of water vapor-methane mixtures on activated carbons}, volume={16}, ISSN={["0743-7463"]}, DOI={10.1021/la991312m}, abstractNote={We report grand canonical Monte Carlo simulation studies of adsorption for a molecular model of water and water vapor−methane mixtures on activated carbon pores. For pure water, the influence of the density of oxygenated sites in the carbons, and of the strength of the water−site interaction is investigated. It is shown that the site density has a profound influence on the adsorption at low and moderate pressures and that, except for very low site densities, capillary condensation does not occur. The adsorption of water is very slight for water−site interaction strengths below eHB/k < 3000 K but rises rapidly above this value. For water−methane mixtures, the adsorption behavior is also strongly dependent on the surface site density. Even for very low site densities, for example, n ∼ 0.05 site/nm2, water clusters form around sites and block a significant fraction of the surface to methane adsorption. This effect is significant for pores of width 2.0 nm. For pores of width 1.0 nm, the effect is much larger,...}, number={12}, journal={LANGMUIR}, author={Muller, EA and Hung, FR and Gubbins, KE}, year={2000}, month={Jun}, pages={5418–5424} }