@article{long_palmer_coasne_shi_sliwinska-bartkowiak_gubbins_2020, title={Reply to the 'Comment on "Pressure enhancement in carbon nanopores: a major confinement effect"' by D. van Dijk, Phys. Chem. Chem. Phys., 2020, 22, DOI: 10.1039/C9CP02890K}, volume={22}, ISSN={["1463-9084"]}, DOI={10.1039/c9cp04289j}, abstractNote={In his 'Comment' van Dijk points out that the local pressure at a point r in an inhomogeneous thermodynamic system, like other thermodynamic properties, is not uniquely defined; one must make an operational definition that involves deciding how to assign the intermolecular forces between pairs of molecules to the point r. This non-uniqueness difficulty is well known, and was discussed in our paper. It was discussed in detail in the 1950 paper of Irving and Kirkwood, and in many books and papers since then. We reply to these comments, and note that an average of the local pressure over a region of space may yield a well-defined pressure. We also discuss other possible ways to quantify the adsorption compression effect near an attractive wall. van Dijk also suggests that the non-uniqueness difficulty can be avoided by using the pressure of the uniform bulk fluid in equilibrium with the pore. While this pressure is well-defined, it only reflects the intermolecular forces in the bulk phase, and gives no information about the behavior in the pore.}, number={17}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Long, Yun and Palmer, Jeremy C. and Coasne, Benoit and Shi, Kaihang and Sliwinska-Bartkowiak, Malgorzata and Gubbins, Keith E.}, year={2020}, month={May}, pages={9826–9830} }
 @article{diallo_jazdzewska_palmer_mamontov_gubbins_sliwinska-bartkowiak_2013, title={Dynamics of nanoconfined water under pressure}, volume={88}, ISSN={["2470-0053"]}, DOI={10.1103/physreve.88.022316}, abstractNote={We report a study of the effects of pressure on the diffusivity of water molecules confined in single-wall carbon nanotubes (SWNT) with average mean pore diameter of ~16 Å. The measurements were carried out using high-resolution neutron scattering, over the temperature range 220≤T≤260 K, and at two pressure conditions: ambient and elevated pressure. The high pressure data were collected at constant volume on cooling, with P varying from ~1.92 kbar at temperature T=260 K to ~1.85 kbar at T=220 K. Analysis of the observed dynamic structure factor S(Q,E) reveals the presence of two relaxation processes, a faster diffusion component (FC) associated with the motion of "caged" or restricted molecules, and a slower component arising from the free water molecules diffusing within the SWNT matrix. While the temperature dependence of the slow relaxation time exhibits a Vogel-Fulcher-Tammann law and is non-Arrhenius in nature, the faster component follows an Arrhenius exponential law at both pressure conditions. The application of pressure remarkably slows down the overall molecular dynamics, in agreement with previous observations, but most notably affects the slow relaxation. The faster relaxation shows marginal or no change with pressure within the experimental conditions.}, number={2}, journal={PHYSICAL REVIEW E}, author={Diallo, S. O. and Jazdzewska, M. and Palmer, J. C. and Mamontov, E. and Gubbins, K. E. and Sliwinska-Bartkowiak, M.}, year={2013}, month={Aug} }
 @article{long_śliwińska-bartkowiak_drozdowski_kempiński_phillips_palmer_gubbins_2013, title={High pressure effect in nanoporous carbon materials: Effects of pore geometry}, volume={437}, ISSN={0927-7757}, url={http://dx.doi.org/10.1016/j.colsurfa.2012.11.024}, DOI={10.1016/j.colsurfa.2012.11.024}, abstractNote={Abundant experimental evidence suggests that adsorbates confined in nanoporous materials exhibit high pressures, such as high pressure crystal structures, high pressure chemical reactions, and the deformation of pore walls due to the adsorbate. We report molecular simulation studies of the pressure tensor for simple adsorbates (e.g. argon) in carbon nanopores of slit, cylindrical and spherical geometries. We find that for modest bulk phase pressures of 1 bar or less, the pressures parallel to the pore walls (tangential pressure) is of the order 104–105 bar, while the pressure normal to the wall is of the order of 103 bar, and can be positive or negative depending on the pore size. Moreover, we find that the pore geometry has a large effect on the structure of the adsorbate and thus on the in-pore pressure because of the curvature that determines the strength of the adsorbate–wall interaction. For the same pore size, temperature and bulk pressure, the in-pore tangential pressure is the largest in spherical pores, followed by that in cylindrical pores and slit pores. We also study the normal pressure of carbon tetrachloride and water confined in activated carbon fibers by molecular simulations and experiments. The pressure acting on the pore wall is found to be of the order of several thousand bar by both methods. Experiments also find that the pore can be expanded or contracted, depending on pore width, as we predict by molecular simulation.}, journal={Colloids and Surfaces A: Physicochemical and Engineering Aspects}, publisher={Elsevier BV}, author={Long, Yun and Śliwińska-Bartkowiak, Małgorzata and Drozdowski, Henryk and Kempiński, Mateusz and Phillips, Katherine A. and Palmer, Jeremy C. and Gubbins, Keith E.}, year={2013}, month={Nov}, pages={33–41} }
 @article{long_palmer_coasne_sliwinska-bartkowiak_jackson_mueller_gubbins_2013, title={On the molecular origin of high-pressure effects in nanoconfinement: The role of surface chemistry and roughness}, volume={139}, ISSN={0021-9606 1089-7690}, url={http://dx.doi.org/10.1063/1.4824125}, DOI={10.1063/1.4824125}, abstractNote={Experiments and simulations both suggest that the pressure experienced by an adsorbed phase confined within a carbon nanoporous material can be several orders of magnitude larger than the bulk phase pressure in equilibrium with the system. To investigate this pressure enhancement, we report a molecular-simulation study of the pressure tensor of argon confined in slit-shaped nanopores with walls of various models, including carbon and silica materials. We show that the pressure is strongly enhanced by confinement, arising from the effect of strongly attractive wall forces; confinement within purely repulsive walls does not lead to such enhanced pressures. Simulations with both the Lennard-Jones and Barker-Fisher-Watts intermolecular potentials for argon-argon interactions give rise to similar results. We also show that an increase in the wall roughness significantly decreases the in-pore pressure due to its influence on the structure of the adsorbate. Finally, we demonstrate that the pressures calculated from the mechanical (direct pressure tensor calculations) and the thermodynamic (volume perturbation method) routes yield almost identical results, suggesting that both methods can be used to calculate the local pressure tensor components in the case of these planar geometries.}, number={14}, journal={The Journal of Chemical Physics}, publisher={AIP Publishing}, author={Long, Yun and Palmer, Jeremy C. and Coasne, Benoit and Sliwinska-Bartkowiak, Malgorzata and Jackson, George and Mueller, Erich A. and Gubbins, Keith E.}, year={2013}, month={Oct}, pages={144701} }
 @article{palmer_gubbins_2012, title={Atomistic models for disordered nanoporous carbons using reactive force fields}, volume={154}, ISSN={["1873-3093"]}, DOI={10.1016/j.micromeso.2011.08.017}, abstractNote={Optimization of disordered nanoporous carbons (DNCs) for specific applications remains a challenge due to the difficulty in accurately characterizing their nanostructures with current experimental methods. We describe how atomistic simulation techniques can be used to build structural models of DNCs and subsequently elucidate the structure–function relationship in these complex porous materials. In particular, two state-of-the-art approaches that use methods based in statistical mechanics to predict the structure of DNCs are described. The quench molecular dynamics method is a pseudo-mimetic approach that captures the effect of synthesis temperature on the structural morphology of disordered carbons, while the hybrid reverse Monte Carlo method is a reconstruction approach that builds realistic replicas of DNCs from experimental diffraction data. Both of these methods use reactive force fields to capture the formation and disassociation of chemical bonds during the simulations, allowing for the structural and porous features of DNCs to be predicted. We describe the principles behind these methods and provide illustrative examples that demonstrate their utility in modeling DNCs. Finally, we also discuss their current limitations and future avenues for improving their predictive capabilities.}, journal={MICROPOROUS AND MESOPOROUS MATERIALS}, author={Palmer, Jeremy C. and Gubbins, Keith E.}, year={2012}, month={May}, pages={24–37} }
 @article{śliwińska-bartkowiak_drozdowski_kempiński_jażdżewska_long_palmer_gubbins_2012, title={Structural analysis of water and carbon tetrachloride adsorbed in activated carbon fibres}, volume={14}, ISSN={1463-9076 1463-9084}, url={http://dx.doi.org/10.1039/C2CP22111J}, DOI={10.1039/c2cp22111j}, abstractNote={We report X-ray diffraction studies of water and carbon tetrachloride adsorbed in nanoporous activated carbon fibres. The fibres are built of turbostratic nanoparticles separated by quasi two-dimensional voids, forming narrow slit-shaped pores. In order to determine the structure of water within the pores and its influence on the fibres' structure, mean interatomic and intermolecular distances have been estimated from the positions of the maxima of the normalized angular distribution functions obtained by X-ray diffraction. We observe a cluster arrangement of the water molecules, as well as significant changes in the interlayer distance of the carbon nanoparticles upon adsorption of both water and carbon tetrachloride. The results suggest that very high pressures arise within the pores, as has been observed in molecular simulations, and this may give rise to the large change in electronic properties of the fibres after adsorption of guest molecules. The in-pore pressure normal to the pore walls is estimated from the experimental data, and is found to be positive and of the order 4000 bar. Molecular simulation results for the normal pressure component are presented for both water and carbon tetrachloride in carbon slit pores, and are in general agreement with the experiments. For both fluids the normal pressure is an oscillating function of pore width.}, number={19}, journal={Physical Chemistry Chemical Physics}, publisher={Royal Society of Chemistry (RSC)}, author={Śliwińska-Bartkowiak, Małgorzata and Drozdowski, Henryk and Kempiński, Mateusz and Jażdżewska, Monika and Long, Yun and Palmer, Jeremy C. and Gubbins, Keith E.}, year={2012}, pages={7145} }
 @article{long_palmer_coasne_sliwinska-bartkowiak_gubbins_2012, title={Under pressure: Quasi-high pressure effects in nanopores}, volume={154}, ISSN={["1873-3093"]}, DOI={10.1016/j.micromeso.2011.07.017}, abstractNote={Phenomena that occur only at high pressures in bulk phases are often observed in nanopores, suggesting that the pressure in such confined phases is large. We develop two models to study the pressure tensor of an argon nanophase confined in carbon micropores by molecular simulation, and show that the in-pore tangential pressure is positive and on the order of 104 bar, while the normal pressure can be positive or negative depending on pore width, with a magnitude of ∼103 bar at ambient bulk pressure. We find that the in-pore tangential pressure is very sensitive to the bulk pressure, suggesting that it should be possible to control the former over wide ranges in laboratory experiments. We also report results for porous materials other than carbon, and show that the pressure enhancement is smaller for pores with weakly attractive walls (e.g. silica and oxides), but larger for more strongly attractive walls (e.g. mica).}, journal={MICROPOROUS AND MESOPOROUS MATERIALS}, author={Long, Yun and Palmer, Jeremy C. and Coasne, Benoit and Sliwinska-Bartkowiak, Malgorzata and Gubbins, Keith E.}, year={2012}, month={May}, pages={19–23} }
 @article{palmer_moore_brennan_gubbins_2011, title={Adsorption and diffusion of argon in disordered nanoporous carbons}, volume={17}, ISSN={["1572-8757"]}, DOI={10.1007/s10450-010-9308-0}, number={1}, journal={ADSORPTION-JOURNAL OF THE INTERNATIONAL ADSORPTION SOCIETY}, author={Palmer, Jeremy C. and Moore, Joshua D. and Brennan, John K. and Gubbins, Keith E.}, year={2011}, month={Feb}, pages={189–199} }
 @article{palmer_moore_roussel_brennan_gubbins_2011, title={Adsorptive behavior of CO2, CH4 and their mixtures in carbon nanospace: a molecular simulation study}, volume={13}, ISSN={["1463-9084"]}, DOI={10.1039/c0cp02281k}, abstractNote={Using molecular simulation, four types of nanoporous carbons are examined as adsorbents for the separation of CO(2)/CH(4) mixtures at ambient temperature and pressures up to 10 MPa. First, the adsorption selectivity of CO(2) is investigated in carbon slit pores and single-walled carbon nanotube bundles in order to find the optimal pore dimensions for CO(2) separation. Then, the adsorptive properties of the optimized slit pore and nanotube bundle are compared with two realistic nanoporous carbon models: a carbon replica of zeolite Y and an amorphous carbon. For the four carbon models, adsorption isotherms and isosteric heats of adsorption are presented for both pure components and mixtures. Special attention is given to the calculation of excess isotherms and isosteric heats, which are necessary to assess the performance of model nanoporous materials in the context of experimental measurements. From these results, we discuss the impact that variables such as pore size, pore morphology, pressure and mixture composition have on the performance of nanoporous carbons for CO(2) separation.}, number={9}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Palmer, Jeremy C. and Moore, Joshua D. and Roussel, Thomas J. and Brennan, John K. and Gubbins, Keith E.}, year={2011}, pages={3985–3996} }
 @article{long_palmer_coasne_sliwinska-bartkowiak_gubbins_2011, title={Pressure enhancement in carbon nanopores: a major confinement effect}, volume={13}, ISSN={["1463-9084"]}, DOI={10.1039/c1cp21407a}, abstractNote={Phenomena that occur only at high pressures in bulk phases are often observed in nanopores, suggesting that the pressure in such confined phases is large. We report a molecular simulation study of the pressure tensor of an argon nanophase within slit-shaped carbon pores and show that the tangential pressure is positive and large, while the normal pressure can be positive or negative depending on pore width. We also show that small changes in the bulk pressure have a large effect on the tangential pressure, suggesting that it should be possible to control the latter over wide ranges in laboratory experiments.}, number={38}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Long, Yun and Palmer, Jeremy C. and Coasne, Benoit and Sliwinska-Bartkowiak, Malgorzata and Gubbins, Keith E.}, year={2011}, pages={17163–17170} }
 @article{palmer_moore_brennan_gubbins_2011, title={Simulating Local Adsorption Isotherms in Structurally Complex Porous Materials: A Direct Assessment of the Slit Pore Model}, volume={2}, ISSN={["1948-7185"]}, DOI={10.1021/jz1015668}, abstractNote={A fundamental understanding of the behavior of fluids confined in structurally complex nanoporous materials is crucial to the development of improved technologies for environmental remediation and energy storage. We present a computational method for assessing the impact that confinement has on the properties of fluids in model porous materials. The proposed method is demonstrated by calculating pore-size-specific adsorption isotherms and adsorption selectivites in a structurally heterogeneous nanoporous carbon (NPC) model. The results from this method are used to test the predictions made by the ubiquitous slit pore (SP) model. In general, we find that the SP model does not qualitatively capture the behavior of the pore-size-specific adsorption isotherms and selectivites in the NPC structure. These qualitative differences provide significant insight into the origins of the well-known deficiencies of the SP model to predict the adsorption behavior of real NPCs.}, number={3}, journal={JOURNAL OF PHYSICAL CHEMISTRY LETTERS}, author={Palmer, Jeremy C. and Moore, Joshua D. and Brennan, John K. and Gubbins, Keith E.}, year={2011}, month={Feb}, pages={165–169} }
 @article{gubbins_liu_moore_palmer_2011, title={The role of molecular modeling in confined systems: impact and prospects}, volume={13}, ISSN={["1463-9084"]}, DOI={10.1039/c0cp01475c}, abstractNote={Molecular modeling at the electronic and atomistic levels plays an important and complementary role to experimental studies of confinement effects. Theory and atomistic simulation can provide fundamental understanding, determine the limits of well known macroscopic laws such as Kelvin's equation, provide predictions for systems that are difficult to study via experiment (e.g. adsorption of highly toxic gases), and can be used to gain detailed molecular level information that may not be accessible in the laboratory (e.g. the local structure and composition of confined phases). We describe the most important and useful methods that are based firmly on quantum mechanics and statistical mechanics, including ab intio and classical density functional theories, and Monte Carlo and molecular dynamics simulation. We discuss their strengths and limitations. We then describe examples of applications of these methods to adsorption and equilibrium properties, including testing the Kelvin equation, determination of pore size distributions and capillary phenomena. Applications to self and transport diffusion, including single-file and anomalous diffusion, and viscous flow in nanoporous materials are described. The use of these methods to understand confinement effects on chemical reactions in heterogeneous media is treated, including effects on reaction equilibria, rates and mechanism. Finally we discuss the current status of molecular modeling in this area, and the outlook and future research needs for the next few years. The treatment is suitable for the general technical reader.}, number={1}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Gubbins, Keith E. and Liu, Ying-Chun and Moore, Joshua D. and Palmer, Jeremy C.}, year={2011}, pages={58–85} }
 @article{moore_palmer_liu_roussel_brennan_gubbins_2010, title={Adsorption and diffusion of argon confined in ordered and disordered microporous carbons}, volume={256}, ISSN={["0169-4332"]}, DOI={10.1016/j.apsusc.2009.12.071}, abstractNote={We use a combination of grand canonical Monte Carlo and microcanonical molecular dynamics simulations to study the adsorption and diffusion of argon at 77 K and 120 K confined in previously generated models of a disordered bituminous coal-based carbon, BPL, and an ordered carbon replica of Faujasite zeolite (C-FAU). Both materials exhibit a maximum in the diffusion coefficient as well as anomalous (sub-diffusive) behavior in the mean-squared displacements at short times at some relative pressures. In BPL, the anomalous diffusion occurs at low relative pressures, due to the trapping of argon atoms in small pores. In C-FAU, the anomalous diffusion occurs at high relative pressures, due to competitive diffusion of atoms traveling through windows and constrictions which interconnect the pores. All diffusion eventually tends to Fickian diffusion at longer times.}, number={17}, journal={APPLIED SURFACE SCIENCE}, author={Moore, Joshua D. and Palmer, Jeremy C. and Liu, Ying-Chun and Roussel, Thomas J. and Brennan, John K. and Gubbins, Keith E.}, year={2010}, month={Jun}, pages={5131–5136} }
 @article{palmer_llobet_yeon_fischer_shi_gogotsi_gubbins_2010, title={Modeling the structural evolution of carbide-derived carbons using quenched molecular dynamics}, volume={48}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2009.11.033}, abstractNote={We develop morphologically realistic models for amorphous carbon using quenched molecular dynamics. We show that as the thermal quench rate is decreased, the model structures become more highly ordered, forming large graphene-like fragments and regularly shaped porous features. The evolution of these changes is compared with a series of carbide-derived carbons synthesized from crystalline TiC using different chlorination temperatures. In general, we find that the structural changes in the models are similar to those seen in experiment and that these changes have a significant impact on pore size distributions, specific surface areas, and adsorption isotherms, which are used to empirically characterize microporous carbons.}, number={4}, journal={CARBON}, author={Palmer, J. C. and Llobet, A. and Yeon, S. -H. and Fischer, J. E. and Shi, Y. and Gogotsi, Y. and Gubbins, K. E.}, year={2010}, month={Apr}, pages={1116–1123} }
 @article{palmer_brennan_hurley_balboa_gubbins_2009, title={Detailed structural models for activated carbons from molecular simulation}, volume={47}, ISSN={["0008-6223"]}, DOI={10.1016/j.carbon.2009.06.037}, abstractNote={A detailed atomistic model of Calgon Co.’s bituminous coal-based activated carbon (BPL) was developed using an adaptation of the Hybrid Reverse Monte Carlo method. The resulting model was a highly heterogeneous carbon structure that had features consistent with experimental X-ray diffraction measurements. The microstructure of the model was characterized and Grand Canonical Monte Carlo simulations were used to examine the adsorptive properties of the model. These findings were compared with experimental measurements taken on samples of the real material. The results showed that the model provides a realistic description of the BPL’s microstructure and accurately predicts adsorptive behavior over a wide range of state conditions.}, number={12}, journal={CARBON}, author={Palmer, J. C. and Brennan, J. K. and Hurley, M. M. and Balboa, A. and Gubbins, K. E.}, year={2009}, month={Oct}, pages={2904–2913} }