@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} }
 @inbook{sliwinska-bartkowiak_dudziak_radhakrishnan_gubbins_2002, title={Freezing in Mesopores: Aniline in Silica Glasses and MCM-41}, ISBN={9780444512611}, ISSN={0167-2991}, url={http://dx.doi.org/10.1016/s0167-2991(02)80169-0}, DOI={10.1016/s0167-2991(02)80169-0}, abstractNote={We report a study of the freezing of aniline in silica porous materials, using dielectric relaxation spectroscopy and light transmission measurements. The porous materials include controlled pore glasses with pore sizes H in the range 7.5 to 50 nm, Vycor glass (H = 4.1 nm) and MCM-41 (H = 2.8 nm). The freezing temperature is lowered due to the confinement, and in the larger pores crystallization occurs. In the MCM-41 material no crystallization is observed; instead a glassy phase is formed at low temperatures. In Vycor the experiments indicate a mixture of microscopic domains of crystal and glass at low temperature. The results are consistent with recent molecular simulation results.}, booktitle={Characterization of Porous Solids VI, Proceedings of the 6th International Symposium on the Characterization of Porous Solids (COPS-VI)}, publisher={Elsevier}, author={Sliwinska-Bartkowiak, M. and Dudziak, G. and Radhakrishnan, R. and Gubbins, K.E.}, year={2002}, pages={467–474} }
 @article{radhakrishnan_gubbins_sliwinska-bartkowiak_2002, title={Global phase diagrams for freezing in porous media}, volume={116}, ISSN={["0021-9606"]}, DOI={10.1063/1.1426412}, abstractNote={Using molecular simulations and free energy calculations based on Landau theory, we show that freezing/melting behavior of fluids of small molecules in pores of simple geometry can be understood in terms of two main parameters: the pore width H* (expressed as a multiple of the diameter of the fluid molecule) and a parameter α that measures the ratio of the fluid-wall to the fluid–fluid attractive interaction. The value of the α parameter determines the qualitative nature of the freezing behavior, for example, the direction of change in the freezing temperature and the presence or absence of new phases. For slit-shaped pores, larger α values lead to an increase in the freezing temperature of the confined fluid, and to the presence of a hexatic phase. For pores that accommodate three or more layers of adsorbate molecules several kinds of contact layer phase (inhomogeneous phases in which the contact layer has a different structure than the inner layers) are observed. Smaller α values lead to a decrease in the freezing temperature. The parameter H* determines the magnitude of shift in the freezing temperature, and can also affect the presence of some of the new phases. Results are presented as plots of transition temperature vs α for a particular pore width. Experimental results are also presented for a variety of adsorbates in activated carbon fibers (ACF) covering a wide range of α values; the ACF have slit-shaped pores with average pore width 1.2 nm. The experimental and simulation results show qualitative agreement.}, number={3}, journal={JOURNAL OF CHEMICAL PHYSICS}, author={Radhakrishnan, R and Gubbins, KE and Sliwinska-Bartkowiak, M}, year={2002}, month={Jan}, pages={1147–1155} }
 @article{sliwinska-bartkowiak_dudziak_sikorski_gras_gubbins_radhakrishnan_2001, title={Dielectric studies of freezing behavior in porous materials: Water and methanol in activated carbon fibres}, volume={3}, ISSN={["1463-9076"]}, DOI={10.1039/b009792f}, abstractNote={We report both experimental measurements and molecular simulations of the melting and freezing behavior of two dipolar fluids, water and methanol, in activated carbon fibres. Differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DS) were used to determine the melting point in these porous materials. The melting point was found to be very sensitive to the relative strength of the fluid–wall interaction compared 
 to the fluid–fluid interaction. Monte Carlo simulations and the Landau free energy formalism were used to determine the shift in the melting point, Tm, for simple fluids in pores having weakly attractive and strongly attractive walls. The strength of the interaction of the fluid with the pore wall is shown to have a large effect on the shift in Tm, with Tm being 
 reduced for weakly attracting 
 walls and elevated for strongly attracting walls.}, number={7}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Sliwinska-Bartkowiak, M and Dudziak, G and Sikorski, R and Gras, R and Gubbins, KE and Radhakrishnan, R}, year={2001}, pages={1179–1184} }
 @article{sliwinska-bartkowiak_radhakrishnan_gubbins_2001, title={Effect of confinement on melting in slit-shaped pores: Experimental and simulation study of aniline in activated carbon fibers}, volume={27}, ISSN={["1029-0435"]}, DOI={10.1080/08927020108031356}, abstractNote={Abstract We report both experimental and molecular simulation studies of the melting behavior of aniline confined within an activated carbon fiber having slit-shaped pores. Dielectric relaxation spectroscopy is used to determine the transition temperatures and also the dielectric relaxation times over the temperature range 240 to 340 K. For the confined system two transitions were observed, one at 298 K and a second transition at 324 K. The measured relaxation times indicate that the low temperature phase (below 298 K) is a crystalline or partially crystalline solid phase, while that above 324 K is a liquid-like phase; for the intermediate phase, in the range 298–324 K, the relaxation times are of the order 10−5s, which is typical of a hexatic phase. The melting temperature of the confined system is well above that of bulk aniline, which is 267 K. The simulations are carried out using the Grand Canonical Monte Carlo method together with Landau free energy calculations, and phase transitions are located as state points where the grand free energies of two confined phases are equal. The nature of these phases is determined by analysis of in-plane pair positional and orientational correlation functions. The simulations also show two transitions. The first is a transition from a two-dimensional hexagonal crystal phase to a hexatic phase at 296 K; the second transition is from the hexatic to a liquid-like phase at 336 K. Confinement within the slit-shaped pores appears to stabilize the hexatic phase, which is the stable phase over a wider temperature range than for quasi-two-dimensional thin films.}, number={5-6}, journal={MOLECULAR SIMULATION}, author={Sliwinska-Bartkowiak, M and Radhakrishnan, R and Gubbins, KE}, year={2001}, pages={323–337} }
 @article{sliwinska-bartkowiak_dudziak_gras_sikorski_radhakrishnan_gubbins_2001, title={Freezing behavior in porous glasses and MCM-41}, volume={187}, DOI={10.1016/S0927-7757(01)00637-9}, abstractNote={We report experimental measurements of the melting and freezing behavior of fluids in nano-porous media. The experimental studies are for nitrobenzene in the silica based pores of controlled pore glass (CPG), Vycor and MCM-41. Dielectric relaxation spectroscopy was used to determine melting points and the orientational relaxation times of the nitrobenzene molecules in the bulk and the confined phase. It was found that the confined fluid freezes into a single crystalline structure for average pore diameters greater than 20 σ, where σ is the diameter of the fluid molecule. For average pore sizes between 20 and 15 σ, part of the confined fluid freezes into a frustrated crystal structure with the rest forming an amorphous region. For pore sizes smaller than 15 σ, even the partial crystallization did not occur.}, number={2001 Aug. 31}, journal={Colloids and Surfaces. A, Physicochemical and Engineering Aspects}, author={Sliwinska-Bartkowiak, M. and Dudziak, G. and Gras, R. and Sikorski, R. and Radhakrishnan, R. and Gubbins, Keith}, year={2001}, pages={523–529} }
 @article{sliwinska-bartkowiak_dudziak_sikorski_gras_gubbins_radhakrishnan_kaneko_2001, title={Freezing behavior in porous materials: Theory and experiments}, volume={75}, number={4}, journal={Polish Journal of Chemistry}, author={Sliwinska-Bartkowiak, M. and Dudziak, G. and Sikorski, R. and Gras, R. and Gubbins, K. E. and Radhakrishnan, R. and Kaneko, K.}, year={2001}, pages={547–555} }
 @article{sliwinska-bartkowiak_dudziak_sikorski_gras_radhakrishnan_gubbins_2001, title={Melting/freezing behavior of a fluid confined in porous glasses and MCM-41: Dielectric spectroscopy and molecular simulation}, volume={114}, ISSN={["0021-9606"]}, DOI={10.1063/1.1329343}, abstractNote={We report both experimental measurements and molecular simulations of the melting and freezing behavior of fluids in nanoporous media. The experimental studies are for nitrobenzene in the silica-based pores of controlled pore glass, Vycor, and MCM-41. Dielectric relaxation spectroscopy is used to determine melting points and the orientational relaxation times of the nitrobenzene molecules in the bulk and the confined phase. Monte Carlo simulations, together with a bond orientational order parameter method, are used to determine the melting point and fluid structure inside cylindrical pores modeled on silica. Qualitative comparison between experiment and simulation are made for the shift in the freezing temperatures and the structure of confined phases. From both the experiments and the simulations, it is found that the confined fluid freezes into a single crystalline structure for average pore diameters greater than 20σ, where σ is the diameter of the fluid molecule. For average pore sizes between 20σ and 15σ, part of the confined fluid freezes into a frustrated crystal structure with the rest forming an amorphous region. For pore sizes smaller than 15σ, even the partial crystallization did not occur. Our measurements and calculations show clear evidence of a novel intermediate “contact layer” phase lying between liquid and crystal; the contact layer is the confined molecular layer adjacent to the pore wall and experiences a deeper fluid–wall potential energy compared to the inner layers. We also find evidence of a liquid to “hexatic” transition in the quasi-two-dimensional contact layer at high temperatures.}, number={2}, journal={JOURNAL OF CHEMICAL PHYSICS}, author={Sliwinska-Bartkowiak, M and Dudziak, G and Sikorski, R and Gras, R and Radhakrishnan, R and Gubbins, KE}, year={2001}, month={Jan}, pages={950–962} }
 @article{radhakrishnan_gubbins_sliwinska-bartkowiak_2000, title={Effect of the fluid-wall interaction on freezing of confined fluids: Toward the development of a global phase diagram}, volume={112}, ISSN={["0021-9606"]}, DOI={10.1063/1.481745}, abstractNote={We report molecular simulation studies of the freezing behavior of fluids in nano-porous media. The effect of confinement is to induce spatial constraints as well as energetic heterogeneity on the confined fluid, thereby altering the bulk phase behavior drastically. We consider the effect of the fluid-wall interaction energy on the shift of the freezing temperature and on the fluid structure, using a novel approach to calculate the free energy surface based on Landau theory and order parameter formulation. Corresponding states theory is then used to map out the global freezing behavior of a Lennard-Jones (LJ) fluid in model slit-shaped pores of varying fluid-wall interaction strengths. Using LJ parameters fitted to thermophysical property behavior, we predict the qualitative freezing behavior for a variety of fluids and nano-porous materials, based on a global freezing diagram. We have attempted to verify these predictions by comparing with experimental data for several systems, and show that in these cases, the experimental observations and the predictions are in agreement.}, number={24}, journal={JOURNAL OF CHEMICAL PHYSICS}, author={Radhakrishnan, R and Gubbins, KE and Sliwinska-Bartkowiak, M}, year={2000}, month={Jun}, pages={11048–11057} }
 @article{sliwinska-bartkowiak_gras_sikorski_dudziak_radhakrishnan_gubbins_2000, title={Experimental and simulation studies of melting and freezing in porous glasses}, volume={128}, DOI={10.1016/s0167-2991(00)80017-8}, number={2000}, journal={Characterization of Porous Solids V}, author={Sliwinska-Bartkowiak, M. and Gras, J. and Sikorski, R. and Dudziak, G. and Radhakrishnan, R. and Gubbins, Keith}, year={2000}, pages={141–150} }
 @article{radhakrishnan_gubbins_1999, title={Free energy studies of freezing in slit pores: an order-parameter approach using Monte Carlo simulation}, volume={96}, ISSN={["0026-8976"]}, DOI={10.1080/00268979909483070}, abstractNote={We report a molecular simulation study of freezing transitions for simple fluids in narrow slit pores. A major stumbling block in previous studies of freezing in pores has been the lack of any method for calculating the free energy difference between the confined solid and liquid phases. Conventional thermodynamic integration methods often fail for confined systems, due to the difficulty in choosing a suitable path of integration. We use a different approach that involves calculating the Landau free energy as a function of a suitable order parameter, using the grand canonical Monte Carlo simulation method. The grand free energy for each phase can then be obtained by one-dimensional integration of the Landau free energy over the order parameter. These calculations are carried out for two types of wall—fluid interaction, a hard wall and a strongly attractive wall modelled on carbon. The grand free energy results for both cases clearly indicate a first order fluid to solid transition. In the case of the attr...}, number={8}, journal={MOLECULAR PHYSICS}, author={Radhakrishnan, R and Gubbins, KE}, year={1999}, month={Apr}, pages={1249–1267} }
 @article{radhakrishnan_gubbins_watanabe_kaneko_1999, title={Freezing of simple fluids in microporous activated carbon fibers: Comparison of simulation and experiment}, volume={111}, ISSN={["0021-9606"]}, DOI={10.1063/1.480261}, abstractNote={We study the freezing of CCl4 in microporous activated carbon fibers (ACF), using Monte Carlo simulation and differential scanning calorimetry (DSC). Microporous activated carbon fibers are well characterized porous materials, having slit-shaped pores due to the voids formed between graphitic basal planes. They serve as highly attractive adsorbents for simple nonpolar molecules, the adsorbent–adsorbate interaction being mostly dispersive (of the van der Waals-type). Recent molecular simulation studies have predicted an upward shift in the freezing temperature (ΔTf=Tf,pore−Tf,bulk>0) for simple fluids confined in such highly attractive carbon slit pores. Our DSC experiments verify these predictions about the increase in Tf. The results also indicate significant deviation from the prediction of ΔTf based on the Gibbs–Thomson equation (simple capillary theory). We employ a recently developed free energy method to calculate the exact freezing temperature in these confined systems using molecular simulation, in order to address the failure of the simple capillary theory.}, number={19}, journal={JOURNAL OF CHEMICAL PHYSICS}, author={Radhakrishnan, R and Gubbins, KE and Watanabe, A and Kaneko, K}, year={1999}, month={Nov}, pages={9058–9067} }
 @misc{gelb_gubbins_radhakrishnan_sliwinska-bartkowiak_1999, title={Phase separation in confined systems}, volume={62}, ISSN={["1361-6633"]}, DOI={10.1088/0034-4885/62/12/201}, abstractNote={We review the current state of knowledge of phase separation and phase equilibria in porous materials. Our emphasis is on fundamental studies of simple fluids (composed of small, neutral molecules) and well-characterized materials. While theoretical and molecular simulation studies are stressed, we also survey experimental investigations that are fundamental in nature. Following a brief survey of the most useful theoretical and simulation methods, we describe the nature of gas-liquid (capillary condensation), layering, liquid-liquid and freezing/melting transitions. In each case studies for simple pore geometries, and also more complex ones where available, are discussed. While a reasonably good understanding is available for phase equilibria of pure adsorbates in simple pore geometries, there is a need to extend the models to more complex pore geometries that include effects of chemical and geometrical heterogeneity and connectivity. In addition, with the exception of liquid-liquid equilibria, little work has been done so far on phase separation for mixtures in porous media.}, number={12}, journal={REPORTS ON PROGRESS IN PHYSICS}, author={Gelb, LD and Gubbins, KE and Radhakrishnan, R and Sliwinska-Bartkowiak, M}, year={1999}, month={Dec}, pages={1573–1659} }
 @article{sliwinska-bartkowiak_gras_sikorski_radhakrishnan_gelb_gubbins_1999, title={Phase transitions in pores: Experimental and simulation studies of melting and freezing}, volume={15}, ISSN={["0743-7463"]}, DOI={10.1021/la9814642}, abstractNote={We report both experimental measurements and molecular simulations of the melting and freezing behavior of simple fluids in porous media. The experimental studies are for carbon tetrachloride and nitrobenzene in controlled pore glass (CPG) and Vycor. Differential scanning calorimetry (DSC) was used to determine the melting point in the porous materials for each of the glass samples. In the case of nitrobenzene (which has a nonzero dipole moment), dielectric spectroscopy was also used to determine melting points. Measurements by the two methods were in excellent agreement. The melting point was found to be depressed relative to the bulk value for both fluids. With the exception of smallest pores, the melting point depression was proportional to the reciprocal of the pore diameter, in agreement with the Gibbs-Thomson equation. Structural information about the different confined phases was obtained by measuring the dielectric relaxation times using dielectric spectroscopy. Monte Carlo simulations were used to determine the shift in the melting point, T m , for a simple fluid in pores having both repulsive and strongly attractive walls. The strength of attraction to the wall was shown to have a large effect on the shift in T m , with T m being reduced for weakly attracting walls. For strongly attracting walls, such as graphitic carbon, the melting point increases for slit-shaped pores. For such materials, the adsorbed contact layer is shown to melt at a higher temperature than the inner adsorbed layers. A method for calculating the free energies of solids in pores is presented, and it is shown that the solid-liquid transition is first order in these systems.}, number={18}, journal={LANGMUIR}, author={Sliwinska-Bartkowiak, M and Gras, J and Sikorski, R and Radhakrishnan, R and Gelb, L and Gubbins, KE}, year={1999}, month={Aug}, pages={6060–6069} }