Molecular simulation of nanoparticle diffusion at fluid interfaces

Cheung, David L.

doi:10.1016/j.cplett.2010.06.074

Cited by 27 publications

(23 citation statements)

References 36 publications

(50 reference statements)

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“…3b as ξ c and is larger than the drag computed from the MD simulations. The interfacial width is the likely source of the discrepancy: the sphere in these simulations is partly in contact with lower density fluid in the interfacial zone which exerts less force, as has also been found by [7,8].…”

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confidence: 84%

“…The drag on smaller, nanometer-sized colloidal particles has been addressed theoretically, using molecular dynamics (MD) simulations of spherical rigid or structureless particles at an atomistically fluctuating liquid interface to calculate the surface diffusivity from the mean square displacement. For liquid/vapor interfaces in Lennard-Jones (LJ) systems [7][8][9], the expected increase of surface diffusivity with displacement into the vapor is found, and for a water/polydimethylsiloxane interface [10] the diffusivity was intermediate between the simulated bulk diffusion coefficients.…”

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confidence: 99%

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Diffusivity and hydrodynamic drag of nanoparticles at a vapor-liquid interface

Koplik

Maldarelli

2017

Phys. Rev. Fluids

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Measurements of the surface diffusivity of colloidal spheres translating along a vapor/liquid interface show an unexpected decrease in diffusivity, or increase in surface drag (from the Stokes-Einstein relation) when the particles situate further into the vapor phase. However, direct measurements of the surface drag from the colloid velocity due to an external force find the expected decrease with deeper immersion into the vapor. The paradoxical drag increase observed in diffusion experiments has been attributed to the attachment of the fluid interface to heterogeneities on the colloid surface, which causes the interface, in response to thermal fluctuations, to either jump or remain pinned, creating added drag. We have performed molecular dynamics simulations of the diffusivity and force experiments for a nanoparticle with a rough surface at a vapor/liquid interface to examine the effect of contact line fluctuations. The drag calculated from both experiments agree and decrease as the particle positions further into the vapor. The surface drag is smaller than the bulk liquid drag due to the partial submersion into the liquid, and the finite thickness of the interfacial zone relative to the nanoparticle size. Contact line fluctuations do not give rise to an anomalous increase in drag.When a colloid particle breaches the interfacial zone between two adjoining immiscible fluid phases the interfacial energy of the particle changes, because the area of the fluid interface decreases and the contact areas of the particle with the bounding fluid phases are altered. For a particle which only partially wets both adjoining fluids, the change in interfacial energy is at a minimum when the colloid partially straddles both adjoining phases. For example, for a spherical colloid of radius R at a vapor/liquid interface of interfacial tension γ (Fig. 1a), the minimum free energy relative to the vapor phase is [1] ∆F = −πγR 2 (1 + cos θ) 2 where the contact angle θ is measured through the liquid. For particles of large enough size, ∆F can overwhelm the typical thermal energy k B T and the particle becomes trapped, as thermal fluctuations cannot dislodge the particle from the interface. Monolayers of strongly adsorbed colloids at the fluid interfaces of foams and emulsions provide steric barriers to coalescence of the dispersed phase, and find applications as foam and emulsion stabilizers (e.g. Pickering emulsions). Particle stabilized foams and emulsions are also used for the fabrication of colloid-based solid foams, gels, and bijels, and crystalline monolayers find applications as superhydrophobic or antireflection coatings, and templates for micro and nanostructured materials [2]. Central to these applications is the surface organization of the colloids, which is a balance between interparticle attractive and repulsive forces, external forces applied parallel to the interface, and the viscous resistance or surface drag due to the hydrodynamic motion of the colloids along the fluid surface. As we explain, the surface drag is not w...

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confidence: 99%

Diffusivity and hydrodynamic drag of nanoparticles at a vapor-liquid interface

Koplik

Maldarelli

2017

Phys. Rev. Fluids

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“…For typical values for the translational velocity U of order of 10 −3 ms −1 (values measured for capillary attraction 8–12 ), colloid densities of order 10 3 –10 4 kg m −3 , liquid density and viscosity of order 10 3 kg m −3 and 10 −3 kg m −1 s −1 , respectively, and surface tension of the order of 10 mNm −1 , colloid diameters should be less than approximately 10 μ m for Bo < 10 −2 and Re < 10 −2 which infers that the colloid size range which satisfies the restrictions of our study approach the colloid domain. For nanoparticles, the diffusion and forced motion of nanoparticles on fluid interfaces have been studied theoretically using molecular dynamics simulations 13,14 without gravity and low to order one Reynolds number, and noticeable meniscus curvature at the contact line was not observed, either as the colloids diffused along the surface or were forced to move by an external force.…”

Section: Introductionmentioning

confidence: 99%

The Translational and Rotational Dynamics of a Colloid Moving Along the Air-Liquid Interface of a Thin Film

Das

Koplik

Farinato

et al. 2018

Sci Rep

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This study examines the translation and rotation of a spherical colloid straddling the (upper) air/liquid interface of a thin, planar, liquid film bounded from below by either a solid or a gas/liquid interface. The goal is to obtain numerical solutions for the hydrodynamic flow in order to understand the influence of the film thickness and the lower interface boundary condition. When the colloid translates on a film above a solid, the viscous resistance increases significantly as the film thickness decreases due to the fluid-solid interaction, while on a free lamella, the drag decreases due to the proximity to the free (gas/liquid) surface. When the colloid rotates, the contact line of the interface moves relative to the colloid surface. If no-slip is assumed, the stress becomes infinite and prevents the rotation. Here finite slip is used to resolve the singularity, and for small values of the slip coefficient, the rotational viscous resistance is dominated by the contact line stress and is surprisingly less dependent on the film thickness and the lower interface boundary condition. For a colloid rotating on a semi-infinite liquid layer, the rotational resistance is largest when the colloid just breaches the interface from the liquid side.

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“…43 On the other hand, the diffusion properties and rotational relaxation of such particles at a liquid interface have yet to be quantified. Although such analysis is available for homogeneous particles, 44 the effect of surface heterogeneity on tuning the diffusivity and rotational motion has not been investigated. The translational motion of Janus nanoparticles at liquid interfaces is important to understand interfacial self-assembly processes and to use them as tracer elements in micro-and nanorheology, 45,46 while their orientational motion has implications for their use as catalysts e.g.…”

Section: Introductionmentioning

confidence: 99%

Molecular simulation of translational and rotational diffusion of Janus nanoparticles at liquid interfaces

Rezvantalab

Drazer

Shojaei-Zadeh

2015

The Journal of Chemical Physics

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We perform molecular dynamics simulations to understand the translational and rotational diffusion of Janus nanoparticles at the interface between two immiscible fluids. Considering spherical particles with different affinity to fluid phases, both their dynamics as well as the fluid structure around them are evaluated as a function of particle size, amphiphilicity, fluid density, and interfacial tension. We show that as the particle amphiphilicity increases due to enhanced wetting of each side with its favorite fluid, the rotational thermal motion decreases. Moreover, the in-plane diffusion of nanoparticles at the interface becomes slower for more amphiphilic particles, mainly due to the formation of a denser adsorption layer. The particles induce an ordered structure in the surrounding fluid that becomes more pronounced for highly amphiphilic nanoparticles, leading to increased resistance against nanoparticle motion. A similar phenomenon is observed for homogeneous particles diffusing in bulk upon increasing their wettability. Our findings can provide fundamental insight into the dynamics of drugs and protein molecules with anisotropic surface properties at biological interfaces including cell membranes.

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Molecular simulation of nanoparticle diffusion at fluid interfaces

Cited by 27 publications

References 36 publications

Diffusivity and hydrodynamic drag of nanoparticles at a vapor-liquid interface

Diffusivity and hydrodynamic drag of nanoparticles at a vapor-liquid interface

The Translational and Rotational Dynamics of a Colloid Moving Along the Air-Liquid Interface of a Thin Film

Molecular simulation of translational and rotational diffusion of Janus nanoparticles at liquid interfaces

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