Impact of solvent granularity and layering on tracer hydrodynamics in confinement

Bollinger, Jonathan A.; Carmer, James; Jain, Avni; Truskett, Thomas M.

doi:10.1039/c6sm02093c

Cited by 6 publications

(6 citation statements)

References 61 publications

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“…The anisotropic behavior is believed to be due to the heterogeneous arrangement of ions in the solid crystals as well as to the strong interactions between diffusing molecules and the calcite surfaces. Recent studies , also suggested that the complex diffusion mechanism in confinement is not solely based on the static properties of the systems, such as one-dimensional free energy profiles, but also on its dynamic evolution, such as density fluctuations.…”

Section: Introductionmentioning

confidence: 99%

Transport Mechanism of Guest Methane in Water-Filled Nanopores

et al. 2017

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We computed the transport of methane through 1 nm wide slit-shaped pores carved out of selected solid substrates using classical molecular dynamics simulations. The transport mechanism was elucidated via the implementation of the well-tempered metadynamics algorithm, which allowed for the quantification and visualization of the free energy landscape sampled by the guest molecule. Models for silica, magnesium oxide, alumina, muscovite, and calcite were used as solid substrates. Slit-shaped pores of width 1 nm were carved out of these materials and filled with liquid water. Methane was then inserted at low concentration. The results show that the diffusion of methane through the hydrated pores is strongly dependent on the solid substrate. While methane molecules diffuse isotropically along the directions parallel to the pore surfaces in most of the pores considered, anisotropic diffusion was observed in the hydrated calcite pore. The differences observed in the various pores are due to local molecular properties of confined water, including molecular structure and solvation free energy. The transport mechanism and the diffusion coefficients are dependent on the free energy barriers encountered by one methane molecule as it migrates from one preferential adsorption site to a neighboring one. It was found that the heterogeneous water distribution in different hydration layers and the low free energy pathways in the plane parallel to the pore surfaces yield the anisotropic diffusion of methane molecules in the hydrated calcite pore. Our observations contribute to an ongoing debate on the relation between local free energy profiles and diffusion coefficients and could have important practical consequences in various applications, ranging from the design of selective membranes for gas separations to the sustainable deployment of shale gas.

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Section: Introductionmentioning

confidence: 99%

Transport Mechanism of Guest Methane in Water-Filled Nanopores

et al. 2017

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“…where we reintroduced the two-dimensional packing fraction ϕ 2D = n 0 πσ 2 /4 and the natural time scale t 0 = σ/v th We further simulate particles using a steep Weeks-Chandler-Andersen (WCA) potential as used in Ref. [55,56], which captures many properties of dense atomistic liquids [57]. The particle-particle interactions are defined as u pp (r) = 4 [(σ/r) 48 − (σ/r) 24 ] + for r ≤ 2 1/24 σ and u pp (r) = 0 for r ≥ 2 1/24 σ, where r and σ are the inter-particle separation and particle diameter, respectively.…”

Section: Supplemental Materials 1 Zwanzig-mori Equations Of Motion An...mentioning

confidence: 99%

“…[55,56], which captures many properties of dense atomistic liquids [57]. The particle-particle interactions are defined as u pp (r) = 4 [(σ/r) 48 − (σ/r) 24 ] + for r ≤ 2 1/24 σ and u pp (r) = 0 for r ≥ 2 1/24 σ, where r and σ are the inter-particle separation and particle diameter, respectively.…”

Section: Zwanzig-mori Equations Of Motion and Relaxation Timementioning

confidence: 99%

Diverging Time Scale in the Dimensional Crossover for Liquids in Strong Confinement

Mandal

Franosch

2017

Phys. Rev. Lett.

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We study a strongly interacting dense hard-sphere system confined between two parallel plates by event-driven molecular dynamics simulations to address the fundamental question of the nature of the 3D to 2D crossover. As the fluid becomes more and more confined the dynamics of the transverse and lateral degrees of freedom decouple, which is accompanied by a diverging time scale separating 2D from 3D behavior. Relying on the time-correlation function of the transversal kinetic energy the scaling behavior and its density-dependence is explored. Surprisingly, our simulations reveal that its time-dependence becomes purely exponential such that memory effects can be ignored. We rationalize our findings quantitatively in terms of an analytic theory which becomes exact in the limit of strong confinement.Introduction.-Transport of particles in nanoconfinement is of great scientific and industrial importance with applications in heterogeneous catalysis [1], oil recovery [2], or lubrication [3][4][5][6]. In recent years artificial nanoporous materials such as metal organic frameworks [7,8], zeolites [9,10], and biocompatible scaffolds [11] have also triggered many novel applications, including gas storage [12], repairing or regenerating tissues [11], size-selective molecular sieving [13], lab-on-a chip technology and nanofluidics [14,15]. The efficiency of such nanodevices often crucially depends on higher surface to volume ratio, such that the distance between the confining walls may even reach atomic scale [16], or the system effectively becomes quasi-2D. Nevertheless, despite its long history, a deep understanding of the transport mechanisms in nanoconfinement and how the dimensional crossover occurs dynamically is still far from satisfactory.Early theoretical studies on transport in nanoconfinement starting from Knudsen and Smoluchowski [17,18] focused on dilute hard-sphere gases where exact results could be obtained analytically in the low-density limit [17][18][19][20][21][22] by assuming particle-wall collisions as diffusive. In contrast, confinement effects on dense strongly interacting systems have only recently come into focus [23]. There, the simplest geometry to investigate the effects of strong confinement is a slit where fluid particles are restricted to a narrow space between two smooth parallel plates, but also tubes or spherical confinements have been realized experimentally [24][25][26]. Computer simulations and experiments for the planar confinement have revealed an exotic equilibrium phase behavior due to commensurable stacking [27][28][29][30][31][32][33][34] as well as the hexatic phases in the limit of quasi-2D confinement [35,36]. Confinement induced order-disorder phase transitions for certain nonpolar liquids have also been reported in several experiments [37], but the interpretation has been challenged in favor of a glass transition [38][39][40]. The structural properties of strongly confined liquids have been measured directly only recently by x-ray scattering [41,42].The structural changes by ...

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“…Molecular crowding has been recognised as an important factor (see, e.g. [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] and references therein), which strongly affects the behaviour of currents across the narrow channels, as well as the dynamics of individual molecules or probes, which move either due to thermal activation only, or are also subject to external constant forces. This latter case, i.e.…”

Section: Introductionmentioning

confidence: 99%

Tracer diffusion in crowded narrow channels

Bénichou

Illien

Oshanin

et al. 2018

J. Phys.: Condens. Matter

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We summarise different results on the diffusion of a tracer particle in lattice gases of hard-core particles with stochastic dynamics, which are confined to narrow channels-single-files, comb-like structures and quasi-one-dimensional channels with the width equal to several particle diameters. We show that in such geometries a surprisingly rich, sometimes even counter-intuitive, behaviour emerges, which is absent in unbounded systems. This is well-documented for the anomalous diffusion in single-files. Less known is the anomalous dynamics of a tracer particle in crowded branching single-files-comb-like structures, where several kinds of anomalous regimes take place. In narrow channels, which are broader than single-files, one encounters a wealth of anomalous behaviours in the case where the tracer particle is subject to a regular external bias: here, one observes an anomaly in the temporal evolution of the tracer particle velocity, super-diffusive at transient stages, and ultimately a giant diffusive broadening of fluctuations in the position of the tracer particle, as well as spectacular multi-tracer effects of self-clogging of narrow channels. Interactions between a biased tracer particle and a confined crowded environment also produce peculiar patterns in the out-of-equilibrium distribution of the environment particles, very different from the ones appearing in unbounded systems. For moderately dense systems, a surprising effect of a negative differential mobility takes place, such that the velocity of a biased tracer particle can be a non-monotonic function of the force. In some parameter ranges, both the velocity and the diffusion coefficient of a biased tracer particle can be non-monotonic functions of the density. We also survey different results obtained for a tracer particle diffusion in unbounded systems, which will permit a reader to have an exhaustively broad picture of the tracer diffusion in crowded environments.

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Impact of solvent granularity and layering on tracer hydrodynamics in confinement

Cited by 6 publications

References 61 publications

Transport Mechanism of Guest Methane in Water-Filled Nanopores

Transport Mechanism of Guest Methane in Water-Filled Nanopores

Diverging Time Scale in the Dimensional Crossover for Liquids in Strong Confinement

Tracer diffusion in crowded narrow channels

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