Distinct dynamical and structural properties of a core-softened fluid when confined between fluctuating and fixed walls

Krott, Leandro B.; Bordin, José Rafael

doi:10.1063/1.4824860

Cited by 32 publications

(47 citation statements)

References 68 publications

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“…41,42 Whereas, when the nanopore has at least one degree of freedom, given by the mobility of the plates in z direction, the anomalous behavior of the fluid disappears and distinct phase transitions are observed. [43][44][45][46] CS fluids confined in nanotubes also present interesting findings, similar to obtained in atomistic models for water, as the increase in diffusion coefficient and flux for narrow nanotubes associated to a layer to single-file transition and a discontinuity in the enhancement flow factor. [47][48][49] The drawback of these core-softened potentials is that due to the simplicity of the two length scales, they are not capable to reproduce the effects related to the third coordination shell of the anomalous fluid what might be relevant under confinement.…”

Section: Introductionsupporting

confidence: 77%

Effects of confinement on anomalies and phase transitions of core-softened fluids

Krott

Bordin

Barraz

et al. 2015

The Journal of Chemical Physics

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We use molecular dynamics simulations to study how the confinement affects the dynamic, thermodynamic, and structural properties of a confined anomalous fluid. The fluid is modeled using an effective pair potential derived from the ST4 atomistic model for water. This system exhibits density, structural, and dynamical anomalies, and the vapor-liquid and liquid-liquid critical points similar to the quantities observed in bulk water. The confinement is modeled both by smooth and structured walls. The temperatures of extreme density and diffusion for the confined fluid show a shift to lower values while the pressures move to higher amounts for both smooth and structured confinements. In the case of smooth walls, the critical points and the limit between fluid and amorphous phases show a non-monotonic change in the temperatures and pressures when the nanopore size is increase. In the case of structured walls, the pressures and temperatures of the critical points varies monotonically with the pore size. Our results are explained on basis of the competition between the different length scales of the fluid and the wall-fluid interaction.

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Section: Introductionsupporting

confidence: 77%

Effects of confinement on anomalies and phase transitions of core-softened fluids

Krott

Bordin

Barraz

et al. 2015

The Journal of Chemical Physics

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“…Also, the nanopore flexibility, with proper thermostatted walls, influences the dynamical, thermodynamical, and structural behavior of the confined fluid, 50, 51 and distinct results are obtained when the nanopore is rigid or flexible. 44,52 Nevertheless, the difference between the results in non-equilibrium simulations with frozen or thermostatted walls are monotonic, 50, 51 and a qualitative comparison between the cases is valid. Therefore, our model reflects the case of rigid confinement inside a solid nanopore, and the results should be considered in this scenario.…”

Section: The Model System and The Simulation Methodologymentioning

confidence: 96%

“…However, we should address that the nanopore flexibility can lead to distinct results. 30,44 Therefore, since the nanotube particles are not time integrated, the thermostat is applied only to the fluid particles. The reduced temperature in our simulations is defined as T * ≡ k B T/ε, where k B is the Boltzmann constant.…”

Section: The Model System and The Simulation Methodologymentioning

confidence: 99%

“…41,42 Recently, it has been suggested that core-softened potential models are able to capture some of the anomalous behavior even under confinement. [43][44][45][46][47] In fact, the behavior of the diffusion constant for nanoconfined water, attributed to the hydrogen bonds, 48 was obtained by pure volumetric effects in these isotropic anomalous fluids. 46 Motivated by this proposition, in this paper we use NEMD simulation in order to explore the connection between the enhanced particle flow and the fluid-fluid interaction potential for fluids confined inside a nanopore.…”

Section: Introductionmentioning

confidence: 99%

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Enhanced flow of core-softened fluids through narrow nanotubes

Bordin

Andrade

Diehl

et al. 2014

The Journal of Chemical Physics

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We investigate through non-equilibrium molecular dynamic simulations the flow of anomalous fluids inside rigid nanotubes. Our results reveal an anomalous increase of the overall mass flux for nanotubes with sufficiently smaller radii. This is explained in terms of a transition from a single-file type of flow to the movement of an ordered-like fluid as the nanotube radius increases. The occurrence of a global minimum in the mass flux at this transition reflects the competition between the two characteristic length scales of the core-softened potential. Moreover, by increasing further the radius, another substantial change in the flow behavior, which becomes more evident at low temperatures, leads to a local minimum in the overall mass flux. Microscopically, this second transition is originated by the formation of a double-layer of flowing particles in the confined nanotube space. These nano-fluidic features give insights about the behavior of confined isotropic anomalous fluids.

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“…To understand the effect of the confinement on the structural behaviour of supercritical fluid parallel to the walls, we examine the parallel components of RDF for each of these layers. The radial distribution function for each of these layers can be evaluated from [38,39]…”

Section: Structural Features Parallel To the Walls : Before And Aftermentioning

confidence: 99%

Structural behavior of supercritical fluids under confinement

Ghosh

Krishnamurthy

2018

Phys. Rev. E

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The existence of the Frenkel line in the supercritical regime of a Lennard-Jones (LJ) fluid shown through molecular dynamics (MD) simulations initially and later corroborated by experiments on argon opens up possibilities of understanding the structure and dynamics of supercritical fluids in general and of the Frenkel line in particular. The location of the Frenkel line, which demarcates two distinct physical states, liquidlike and gaslike within the supercritical regime, has been established through MD simulations of the velocity autocorrelation (VACF) and radial distribution function (RDF). We, in this article, explore the changes in the structural features of supercritical LJ fluid under partial confinement using atomistic walls. The study is carried out across the Frenkel line through a series of MD simulations considering a set of thermodynamics states in the supercritical regime (P=5000 bar, 240K≤T≤1500K) of argon well above the critical point. Confinement is partial, with atomistic walls located normal to z and extending to "infinity" along the x and y directions. In the "liquidlike" regime of the supercritical phase, particles are found to be distributed in distinct layers along the z axis with layer spacing less than one atomic diameter and the lateral RDF showing amorphous-like structure for specific spacings (packing frustration) and non-amorphous-like structure for other spacings. Increasing the rigidity of the atomistic walls is found to lead to stronger layering and increased structural order. For confinement with reflective walls, layers are found to form with one atomic diameter spacing and the lateral RDF showing close-packed structure for the smaller confinements. Translational order parameter and excess entropy assessment confirms the ordering taking place for atomistic wall and reflective wall confinements. In the "gaslike" regime of the supercritical phase, particle distribution along the spacing and the lateral RDF exhibit features not significantly different from that due to normal gas regime. The heterogeneity across the Frenkel line, found to be present both in bulk and confined systems, might cause the breakdown of the universal scaling between structure and dynamics of fluids necessitating the determination of a unique relationship between them.

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Distinct dynamical and structural properties of a core-softened fluid when confined between fluctuating and fixed walls

Cited by 32 publications

References 68 publications

Effects of confinement on anomalies and phase transitions of core-softened fluids

Effects of confinement on anomalies and phase transitions of core-softened fluids

Enhanced flow of core-softened fluids through narrow nanotubes

Structural behavior of supercritical fluids under confinement

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