Molecular dynamics of a microscopic droplet on solid surface

Nieminen, Jouko; Abraham, D. B.; Karttunen, Mikko; Kaski, Kimmo

doi:10.1103/physrevlett.69.124

Cited by 115 publications

(97 citation statements)

References 21 publications

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“…If one of the dimensions of a fluid film is comparable to the size of the fluid molecules, a hydrodynamical description of the film is no longer justified [9,10,11]. In this case the discrete nature of the fluid becomes important and the fluid cannot be treated as a continuum in the confined direction.…”

Section: Introductionmentioning

confidence: 99%

Spreading in narrow channels

et al. 2007

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We study a lattice model for the spreading of fluid films, which are a few molecular layers thick, in narrow channels with inert lateral walls. We focus on systems connected to two particle reservoirs at different chemical potentials, considering an attractive substrate potential at the bottom, confining side walls, and hard-core repulsive fluid-fluid interactions. Using kinetic Monte Carlo simulations we find a diffusive behavior. The corresponding diffusion coefficient depends on the density and is bounded from below by the free one-dimensional diffusion coefficient, valid for an inert bottom wall. These numerical results are rationalized within the corresponding continuum limit.

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Section: Introductionmentioning

confidence: 99%

Spreading in narrow channels

et al. 2007

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“…As Ball observed over a decade ago [1], at that time there was hardly even a formative theory of such phenomena. Such theory must capture the experimentally determined diffusive behavior and, at the same time, explain how an extremely viscous, involatile material is transported from the reservoir to the precursor edge.A partial solution was first achieved by applying Molecular Dynamics to a droplet composed of spherical molecules with Lennard-Jones interactions [4]. The strength of these is adjusted to achieve sufficient involatility.…”

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confidence: 99%

Microscopic Model for Thin Film Spreading

2002

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A microscopic, driven lattice gas model is proposed for the dynamics and spatio-temporal fluctuations of the precursor film observed in spreading experiments. Matter is transported both by holes and particles, and the distribution of each can be described by driven diffusion with a moving boundary. This picture leads to a stochastic partial differential equation for the shape of the boundary, which agrees with the simulations of the lattice gas. Preliminary results for flow in a thermal gradient are discussed.PACS numbers: 68.08. Bc, 68.15+e, 64.60.Ht, 05.70.Np Spreading of involatile liquid drops on surfaces and fibers plays a significant role in many technologies, the efficient deployment of which requires detailed understanding of the underlying process [1,2]. Behavior at a macroscopic scale is accurately described by hydrodynamics [3], but experiments performed over the last 15 years or so have produced a surprise: in the case of complete wetting, the spreading drop, when examined on an atomic length scale in the direction normal to the substrate, is found to be preceded by a precursor film about one molecule thick; this can be followed laterally out to an extension of the order of 10 7 molecules diameter. At the horizontal resolving power of the technique used (ellipsometry), the precursor film is found to be flat and homogeneous. Its radius advances with time as √ t. Typical systems showing this class of behavior which can be investigated by ellipsometry are various silanes spreading over atomically flat Si(111) wafers with highly pure oxydised surfaces. With selected silanes, such systems even show dynamical layering with up to four superposed precursor films advancing as √ t, the layer directly in contact with the substrate being much faster than the others. As Ball observed over a decade ago [1], at that time there was hardly even a formative theory of such phenomena. Such theory must capture the experimentally determined diffusive behavior and, at the same time, explain how an extremely viscous, involatile material is transported from the reservoir to the precursor edge.A partial solution was first achieved by applying Molecular Dynamics to a droplet composed of spherical molecules with Lennard-Jones interactions [4]. The strength of these is adjusted to achieve sufficient involatility. Experimentally, the droplet is placed in contact with a substrate composed of much smaller units; this is therefore treated as a continuum for calculating the interaction of the spreading molecules with the substrate. Such a model shows a precursor film with the correct, diffusive behavior [4,5]. Monte Carlo (MC) lattice gas simulations in 3d [6,7] confirm this, and suggest a dual mechanism of matter transport involving on the one hand particles located in a supernatant layer directly placed above the precursor film, and on the other, holes in the precursor film itself. At the same time, essentially all the configurational change occurs at the boundary of the drop. However, so far these ideas just constitute a pictur...

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“…This has been observed in experiments [1,2,3,4] as well as simulation [5,6,7,8,9]. This foot grows diffusively with an effective diffusion constant D eff that depends on the square root of the initial radius R o of the droplet [10].…”

Section: Introductionmentioning

confidence: 71%

Liquid Nanodroplets Spreading on Chemically Patterned Surfaces

2006

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Controlling the spatial distribution of liquid droplets on surfaces via surface energy patterning can be used to control material delivery to specified regions via selective liquid/solid wetting. While studies of the equilibrium shape of liquid droplets on heterogenous substrates exist, much less is known about the corresponding wetting kinetics. We make significant progress towards elucidating details of this topic by studying, via large-scale atomistic simulations, liquid nanodroplets spreading on chemically patterned surfaces. A model is presented for lines of polymer liquid (droplets) on substrates consisting of alternating strips of wetting (equilibrium contact angle θ 0 ≃ 0 • ) and nonwetting (θ 0 ≃ 90 • ) material. Droplet spreading is compared for different wavelength λ of the pattern and strength of surface interaction on the wetting strips. For small λ, droplets partially spread on both the wetting and non-wetting regions of the substrate to attain a finite contact angle less than 90 • . In this case, the extent of spreading depends on the interaction strength in the wetting regions. A transition is observed such that, for large λ, the droplet spreads only on the wetting region of the substrate by pulling material from non-wetting regions. In most cases, a precursor film spreads on the wetting portion of the substrate at a rate strongly dependent upon interaction strength.

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Molecular dynamics of a microscopic droplet on solid surface

Cited by 115 publications

References 21 publications

Spreading in narrow channels

Spreading in narrow channels

Microscopic Model for Thin Film Spreading

Liquid Nanodroplets Spreading on Chemically Patterned Surfaces

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