Melting mechanism of monolayers adsorbed in cylindrical pores: The influence of the pore wall roughness

Kuchta, B; Firlej, Lucyna; Denoyel, Renaud; Rols, S.; Johnson, Mark R.; Coasne, Benoît

doi:10.1063/1.2916683

Cited by 6 publications

(6 citation statements)

References 26 publications

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“…The third open question is the role of surface roughness in the real materials. 74,75 The SANS experiments indicated significant roughness, 49 while our model silica is perfectly smooth, which could either promote or retard 2D ordering of the adsorbed methane depending on the exact nature of that roughness.…”

Section: Discussionmentioning

confidence: 81%

“…Finally, because the distinct layers are still amorphous, even after capillary condensation raises the density to near-liquid conditions, further densification cannot proceed without a structural reorganization that increases the free volume of each layer. The third open question is the role of surface roughness in the real materials. , The SANS experiments indicated significant roughness, while our model silica is perfectly smooth, which could either promote or retard 2D ordering of the adsorbed methane depending on the exact nature of that roughness.…”

Section: Discussionmentioning

confidence: 85%

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Quasi-Two-Dimensional Phase Transition of Methane Adsorbed in Cylindrical Silica Mesopores

et al. 2017

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Using Monte Carlo and molecular dynamics simulations, we examine the adsorption of methane in cylindrical silica mesopores in an effort to understand a possible phase transition of adsorbed methane in MCM-41 and SBA-15 silica that was previously identified by an unexpected increase in the adsorbed fluid density following capillary condensation, as measured by small-angle neutron scattering (SANS) [Chiang, W-S., et al., Langmuir 2016, 32, 8849]. Our initial simulation results identify a roughly 10 % increase in the density of the liquidlike adsorbed phase for either an isotherm with increasing pressure or an isobar with decreasing temperature and that this densification is associated with a local maximum in the isosteric enthalpy of adsorption. Subsequent analysis of the simulated fluid, via computation of bond-orientational order parameters of specific annular layers of the adsorbed fluid, showed that the layers undergo an ordering transition from a disordered, amorphous state to one with two-dimensional hexagonal structure. Furthermore, this two-dimensional restructuring of the fluid occurs at the same thermodynamic state points as the aforementioned densification and local maximum in the isosteric enthalpy of adsorption. We thus conclude that the densification of the fluid is the result of structural reorganization, which is signaled by the maximum in the isosteric enthalpy. Owing to the qualitative similarity of the structural transitions in the simulated and experimental methane fluids, we propose this hexagonal reorganization as a plausible explanation of the densification observed in SANS measurements. Lastly, we speculate how this structural transition may impact the transport properties of the adsorbed fluid.

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Section: Discussionmentioning

confidence: 81%

Section: Discussionmentioning

confidence: 85%

Quasi-Two-Dimensional Phase Transition of Methane Adsorbed in Cylindrical Silica Mesopores

et al. 2017

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“…For the melting process, only one, unsymmetrical, broad endothermic peak was observed for all filling fractions. Kuchta analyzed the influence of the pore wall roughness on the melting mechanism of monolayers adsorbed in cylindrical pores . It was suggested that, for heterogeneous pores, some adsorbed molecules are still trapped in strongly attractive adsorption sites even when the melting starts at a relatively low temperature.…”

Section: Resultsmentioning

confidence: 99%

Liquid−Solid Transition of Confined Water in Silica-Based Mesopores

et al. 2010

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Cooling and heating curves of water confined in partially filled Vycor porous glass were measured for both adsorption and desorption processes. One endothermic and two exothermic peaks were observed for almost all cases. The peak temperature and the enthalpy of the exothermic peak located below 232 K increased initially and then decreased with further increases in the filling factor. These abnormal changes were analyzed based on the liquid-solid transition of nanoconfined water using a core/shell model, and the initial adsorption process of water in this typical mesoporous material with disordered pores is discussed. In addition, an interesting observation is that different peak temperatures for the endothermic peak and an almost constant peak temperature for the exothermic peak were observed at the same filling factor obtained under different sample preparation conditions, that is, adsorption and desorption processes. To compare with the liquid-solid transition temperatures of confined water in fully filled silica-based mesopores of different pore radius, a parameter of the ratio of pore inner surface area to confined liquid volume is proposed in this paper. Referring to this parameter, the core part of confined water in silica-based nanopores has the same liquid-solid transition temperatures. This suggestion is valid for the freezing process of water confined in either fully filled ordered or fully or partially filled disordered pores. For the melting process, different linear changes of melting temperature with the ratio of pore inner surface area to liquid volume were observed for water in disordered and ordered pores.

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“…In spite of long history of these problems major results were obtained for idealized smooth surfaces of the solid. However, real surfaces are usually rough, so influence of geometry on adsorption and other thermodynamic processes is actively investigated in recent years [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

“…It was shown both experimentally [3] and theoretically [4] that the roughness can induce wetting transition at the conditions corresponding to the lack of wetting for smooth surface. Also, experiments with neutron scattering and Monte Carlo simulations show strong influence of the surface roughness on melting process [5]. In work [6] the review of intrusion and freezing in porous silica with both simple and disordered porous geometry is presented.…”

Section: Introductionmentioning

confidence: 99%

Random Process Theory Approach to Geometric Heterogeneous Surfaces: Effective Fluid–Solid Interaction

Khlyupin

Aslyamov

2017

J Stat Phys

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Realistic fluid-solid interaction potentials are essential in description of confined fluids especially in the case of geometric heterogeneous surfaces. Correlated random field is considered as a model of random surface with high geometric roughness. We provide the general theory of effective coarsegrained fluid-solid potential by proper averaging of the free energy of fluid molecules which interact with the solid media. This procedure is largely based on the theory of random processes. We apply first passage time probability problem and assume the local Markov properties of random surfaces. General expression of effective fluid-solid potential is obtained. In the case of small surface irregularities analytical approximation for effective potential is proposed. Both amorphous materials with large surface roughness and crystalline solids with several types of fcc lattices are considered. It is shown that the wider the lattice spacing in terms of molecular diameter of the fluid, the more obtained potentials differ from classical ones. A comparison with published Monte-Carlo simulations shows good qualitative agreement with the theory predictions. The work provides a promising approach to explore how the random geometric heterogeneity affects on thermodynamic properties of the fluids.

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Melting mechanism of monolayers adsorbed in cylindrical pores: The influence of the pore wall roughness

Cited by 6 publications

References 26 publications

Quasi-Two-Dimensional Phase Transition of Methane Adsorbed in Cylindrical Silica Mesopores

Quasi-Two-Dimensional Phase Transition of Methane Adsorbed in Cylindrical Silica Mesopores

Liquid−Solid Transition of Confined Water in Silica-Based Mesopores

Random Process Theory Approach to Geometric Heterogeneous Surfaces: Effective Fluid–Solid Interaction

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