Effect of Surface Texture on Freezing in Nanopores: Surface-Induced versus Homogeneous Crystallization

Coasne, Benoît

doi:10.1021/la5041213

Cited by 6 publications

(6 citation statements)

References 53 publications

(133 reference statements)

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“…Surface premelting is also observed in nanoporous materials, and melting temperature was related to the size of pores. A roughly proportional function is shown between the melting temperature and reciprocal of averaged pore-size, as predicted by Gibbs-Thomson equation [29], which is consistent with the experimental reports using nuclear magnetic reso-nance (NMR) [30] and X-ray diffraction techniques [31] and the atomistic simulation studies [32][33][34][35]. These studies enriched our knowledge of the melting in nanoporous materials.…”

Section: Introductionsupporting

confidence: 86%

Surface premelting/recrystallization governing the collapse of open-cell nanoporous Cu via thermal annealing

Wang

Zhang

Deng

et al. 2018

Phys. Chem. Chem. Phys.

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We systematically investigate the collapse of a set of open-cell nanoporous Cu (np-Cu) materials with the same porosity and shape but different specific surface areas, during thermal annealing, by performing large-scale molecular dynamics simulations. Two mechanisms govern the collapse of np-Cu. One is direct surface premelting, facilitating the collapse of np-Cu, when the specific surface area is less than a critical value (∼2.38 nm-1). The other is recrystallization followed by surface premelting, accelerating the sloughing of ligaments and the annihilation of voids, when the critical specific surface area is exceeded. Surface premelting results from surface reconstruction by prompting localized "disordering" and "chaos" on the surface, and the melting temperature reduces linearly with the increase of the specific surface area. Recrystallization is followed by surface premelting as the melting temperature is below the supercooling point, where a liquid is unstable and instantaneously recrystallizes.

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Section: Introductionsupporting

confidence: 86%

Surface premelting/recrystallization governing the collapse of open-cell nanoporous Cu via thermal annealing

Wang

Zhang

Deng

et al. 2018

Phys. Chem. Chem. Phys.

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show abstract

“…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%

“…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: ■ Summary and Conclusionmentioning

confidence: 83%

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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“…Obviously, it modifies the molecular arrangement of the confined oxygen in comparison to bulk and as a consequence the elastic behavior is altered. Simulations have shown that the structure of the pore surface and hence its interaction with the adsorbate influence also the phase behavior of adsorbate (see ref for adsorbed argon).…”

Section: Measurements and Analysismentioning

confidence: 99%

Oxygen in Nanopores: A Study on the Elastic Behavior of Its Solid Phases

2016

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In this article we present an ultrasonic study on the elasticity of oxygen confined to nanoporous Vycor glass. During cooling of the completely filled sample, we observe abrupt changes of the shear modulus indicating phase transitions of the adsorbed oxygen. However, also outside of these transition ranges the elasticity of the confined oxygen changes and this temperature dependence does not in the least correspond to the temperature dependence for bulk oxygen. Measurements with only an adsorbed oxygen layer on the pore walls reveal that this layer behaves solidlike already above the bulk melting temperature, T m,bulk, which was not observed for other adsorbates in previous measurements. The values for the shear modulus of the confined oxygen are higher than the shear modulus of both γ-, β-, and α-oxygen, in particular for the surface layer. We show that the enhancement of the shear modulus of adsorbed substances cannot directly be inferred from the strength of the interaction between adsorbate and pore surface. A weak interaction between adsorbed molecules seems to strengthen the impact of the pore walls. Our study indicates the possibility to modify elastic properties through nanoconfinement and it evidences the complexity of the elastic behavior in nanopores.

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Effect of Surface Texture on Freezing in Nanopores: Surface-Induced versus Homogeneous Crystallization

Cited by 6 publications

References 53 publications

Surface premelting/recrystallization governing the collapse of open-cell nanoporous Cu via thermal annealing

Surface premelting/recrystallization governing the collapse of open-cell nanoporous Cu via thermal annealing

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

Oxygen in Nanopores: A Study on the Elastic Behavior of Its Solid Phases

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