The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Alexander V Neimark - One of the best experts on this subject based on the ideXlab platform.
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adsorption induced deformation of mesoporous solids macroscopic approach and density functional theory
Langmuir, 2011Co-Authors: Gennady Y Gor, Alexander V NeimarkAbstract:We present a theoretical study of the deformation of mesoporous solids during adsorption. The proposed thermodynamic model allows one to link the mechanical stress and strain to the solvation pressure exerted by the adsorbed molecules on the pore wall. Two approaches are employed for calculation of solvation pressure as a function of adsorbate pressure: the macroscopic Derjaguin-Broekhoff-de Boer theory of capillary condensation, and the microscopic density functional theory. We revealed that the macroscopic and microscopic theories are in quantitative agreement for the pores >8 nm diameter within the whole range of adsorbate pressures. For smaller pores, the macroscopic theory gradually deteriorates, and the density functional theory extends the thermodynamic model of adsorption-induced deformation to the nanometer scales.
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adsorption induced deformation of mesoporous solids
Langmuir, 2010Co-Authors: Alexander V NeimarkAbstract:The Derjaguin−Broekhoff−de Boer theory of capillary condensation is employed to describe deformation of mesoporous solids in the course of adsorption−desorption hysteretic cycles. We suggest a thermodynamic model, which relates the mechanical stress induced by the adsorbed phase to the adsorption isotherm. Analytical expressions are derived for the dependence of the solvation pressure on the vapor pressure. The proposed method provides a description of nonmonotonic hysteretic deformation during capillary condensation without invoking any adjustable parameters. The method is showcased drawing on the examples of literature experimental data on adsorption deformation of porous glass and SBA-15 silica.
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bridging scales from molecular simulations to classical thermodynamics density functional theory of capillary condensation in nanopores
Journal of Physics: Condensed Matter, 2003Co-Authors: Alexander V Neimark, Peter I Ravikovitch, Aleksey VishnyakovAbstract:With the example of the capillary condensation of Lennard-Jones fluid in nanopores ranging from 1 to 10 nm, we show that the non-local density functional theory (NLDFT) with properly chosen parameters of intermolecular interactions bridges the scale gap from molecular simulations to macroscopic thermodynamics. On the one hand, NLDFT correctly approximates the results of Monte Carlo simulations (shift of vapour–liquid equilibrium, spinodals, density profiles, adsorption isotherms) for pores wider than about 2 nm. On the other hand, NLDFT smoothly merges (above 7–10 nm) with the Derjaguin–Broekhoff–de Boer equations which represent augmented Laplace–Kelvin equations of capillary condensation and desorption.
G Backx - One of the best experts on this subject based on the ideXlab platform.
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effects on the fluid interface fluctuations due to the interaction potential form exponential interactions
Physical Review B, 1998Co-Authors: Georgios Palasantzas, G BackxAbstract:In this work, we investigate nonlocal effects (associated with exponential interactions) on the fluctuation properties of liquid films that completely wet random rough surfaces. It is found that the potential form and effective range could have significant impact on the real space fluctuation properties. The rms interface amplitude shows a complex dependence as a function of the potential effective range b which is characterized by a maximum at length scales smaller than the liquid film thickness. Comparisons with results obtained within the Derjaguin approximation shows that the nonlocal effects are more pronounced for slowly decaying interactions.
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Fluid interface fluctuations within the generalized Derjaguin approximation
Physical Review B, 1997Co-Authors: Georgios Palasantzas, G BackxAbstract:The fluctuation properties of fluid interfaces bounded by rough surfaces are investigated within a linear generalization of the Derjaguin approximation. In the thick-film regime, the interface roughness amplitude is lower in magnitude from that obtained in the Derjaguin approximation. Nevertheless, for large healing lengths z the power-law asymptotic behavior s w;z 22 , which is observed in the Derjaguin approximation, is still preserved. Moreover, the rms local interface slope r is shown to attain small values for film thicknesses larger than the substrate roughness amplitude and to follow an asymptotic power-law behavior r;z 22 for large z. @S0163-1829~97!07436-5# Wetting phenomena of fluids on solid substrates have been an important topic of applied and fundamental research for more than a century. However, the understanding of the complexity of these phenomena is still incomplete, since wetting is highly sensitive to roughness and chemical contaminants of the solid substrates. 1‐4 In general, these types of surface disorder can have a dramatic influence on interfacial processes which are of experimental and technological interest. Various theoretical treatments 2‐4 of the influence of surface roughness on the wetting properties of liquids have been performed within the so-called Derjaguin approximation. 5 In fact, this approximation accounts for replacing the local disjoining pressure P d by that of a uniform film of thickness h(r)2z(r) @z(r) and h(r) are, respectively, the substrate and liquid-vapor surface/interface profile functions# for small substrate roughness amplitudes, and then linearize the disjoining pressure around the average film thickness « that would exist on a flat surface. 3 The average thickness « is given by the relation Dm5P d(«), with Dm the chemical potential difference between the liquid and vapor phases, and the liquid-vapor interface fluctuations are described by the
Georgios Palasantzas - One of the best experts on this subject based on the ideXlab platform.
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effects on the fluid interface fluctuations due to the interaction potential form exponential interactions
Physical Review B, 1998Co-Authors: Georgios Palasantzas, G BackxAbstract:In this work, we investigate nonlocal effects (associated with exponential interactions) on the fluctuation properties of liquid films that completely wet random rough surfaces. It is found that the potential form and effective range could have significant impact on the real space fluctuation properties. The rms interface amplitude shows a complex dependence as a function of the potential effective range b which is characterized by a maximum at length scales smaller than the liquid film thickness. Comparisons with results obtained within the Derjaguin approximation shows that the nonlocal effects are more pronounced for slowly decaying interactions.
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Fluid interface fluctuations within the generalized Derjaguin approximation
Physical Review B, 1997Co-Authors: Georgios Palasantzas, G BackxAbstract:The fluctuation properties of fluid interfaces bounded by rough surfaces are investigated within a linear generalization of the Derjaguin approximation. In the thick-film regime, the interface roughness amplitude is lower in magnitude from that obtained in the Derjaguin approximation. Nevertheless, for large healing lengths z the power-law asymptotic behavior s w;z 22 , which is observed in the Derjaguin approximation, is still preserved. Moreover, the rms local interface slope r is shown to attain small values for film thicknesses larger than the substrate roughness amplitude and to follow an asymptotic power-law behavior r;z 22 for large z. @S0163-1829~97!07436-5# Wetting phenomena of fluids on solid substrates have been an important topic of applied and fundamental research for more than a century. However, the understanding of the complexity of these phenomena is still incomplete, since wetting is highly sensitive to roughness and chemical contaminants of the solid substrates. 1‐4 In general, these types of surface disorder can have a dramatic influence on interfacial processes which are of experimental and technological interest. Various theoretical treatments 2‐4 of the influence of surface roughness on the wetting properties of liquids have been performed within the so-called Derjaguin approximation. 5 In fact, this approximation accounts for replacing the local disjoining pressure P d by that of a uniform film of thickness h(r)2z(r) @z(r) and h(r) are, respectively, the substrate and liquid-vapor surface/interface profile functions# for small substrate roughness amplitudes, and then linearize the disjoining pressure around the average film thickness « that would exist on a flat surface. 3 The average thickness « is given by the relation Dm5P d(«), with Dm the chemical potential difference between the liquid and vapor phases, and the liquid-vapor interface fluctuations are described by the
G Betz - One of the best experts on this subject based on the ideXlab platform.
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on the Derjaguin offset in boundary lubricated nanotribological systems
Langmuir, 2013Co-Authors: Stefan J Eder, A Vernes, G BetzAbstract:We performed molecular dynamics simulations of boundary-lubricated sliding, varying the boundary lubricant type, its molecular surface coverage, the substrate roughness, and the load. The resulting load versus friction behavior was then analyzed to study how changes in lubricant type, coverage, and roughness affect the extrapolated friction force at zero load, the so-called Derjaguin offset. A smooth-particle-based evaluation method by the authors, applied here for the first time to visualize the sliding interface between the two layers of boundary lubricant, allowed the definition and calculation of a dimensionless normalized sliding resistance area, which was then related to the Derjaguin offset. This relationship excellently reflects the molecular surface coverage, which determines the physical condition of the lubricant, and can differentiate between some lubricant-specific frictional properties.
Joel Chevrier - One of the best experts on this subject based on the ideXlab platform.
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tuning near field radiative heat flux through surface excitations with a metal insulator transition
Physical Review Letters, 2012Co-Authors: P J Van Zwol, L Ranno, Joel ChevrierAbstract:The control of heat flow is a formidable challenge due to lack of good thermal insulators. Promising new opportunities for heat flow control were recently theoretically discovered for radiative heat flow in near field, where large heat flow contrasts may be achieved by tuning electronic excitations on surfaces. Here we show experimentally that the phase transition of ${\mathrm{VO}}_{2}$ entails a change of surface polariton states that significantly affects radiative heat transfer in near field. In all cases the Derjaguin approximation correctly predicted radiative heat transfer in near field, but it underestimated the far field limit. Our results indicate that heat flow contrasts can be realized in near field that can be larger than those obtained in far field.