Dynamics of a Spreading Nanodroplet: A Molecular Dynamic Simulation (original) (raw)
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Statics and dynamics of drops spreading on a liquid-liquid interface
Physical Review Fluids, 2020
The spreading of drops on surfaces is ubiquitous and has relevance to many technological applications. In this work, we present two-dimensional numerical simulations of the surface tension driven spreading of drops dispensed on a fluid-fluid interface. A comprehensive picture describing the equilibrium shapes of the drops is provided in the form of a state diagram. We show that the analysis of kinetics of drops that spread symmetrically on the fluid-fluid interface reveal several interesting features: (i) the existence of a single length scale that describes the spreading process, (ii) the power law dependence of the temporal variation of the geometrical parameters of the spreading drop, (iii) the linear dependence of the power law exponents on the equilibrium enclosing angle of the liquid drop, (iv) a strong dependence of the power law exponents on the spreading coefficient, and (v) a collapse of the spreading kinetics data into a master curve. Though restricted to two dimensions, our analysis provides a rationale for explaining experimentally determined power law exponents which have been reported to vary over a wide range and hence to understand the universal nature of the spreading process.
Molecular dynamics simulations of spontaneous spreading of a nanodroplet on solid surfaces
Fluid Dynamics Research, 2011
The dynamics of spontaneous spreading of nano-sized droplets on solid surfaces were investigated using molecular dynamics simulations. The spreading behavior was analyzed in terms of the temporal evolution of instantaneous spreading diameter and contact angle for surfaces with different wetting characteristics. The computational model was validated through qualitative comparison with existing numerical and experimental data, including correlations for the variation of dynamic contact angle and spreading diameter. The results indicated that the spreading dynamics are mainly governed by surface and viscous forces. The spontaneous spreading process on a wettable surface can be described by three different stages, namely the initial, intermediate and final stages. The initial stage is characterized by the development of a precursor film, which moves ahead of the droplet, whereas the intermediate and final spreading stages are governed by a balance between surface and viscous forces. Simulations were used to develop correlations for the temporal variation of contact angle and spreading diameter for wettable, partially wettable and non-wettable surfaces. These correlations were found to be closer to those based on the molecular kinetic model than to those based on the hydrodynamic model. The results were further analyzed to obtain correlations for the effect of droplet size on the spreading parameters. These correlations indicated that the normalized spreading diameter and contact angle scale with non-dimensional drop diameter as D m /D 0 ∝ D −0.6±0.04
Molecular dynamics simulations of nanodroplet spreading on solid surfaces, effect of droplet size
Fluid Dynamics Research, 2010
Molecular dynamics simulations were performed to study the spreading characteristics of nano-sized droplets on solid surfaces. The spreading behavior was analyzed in terms of the temporal evolution of the dynamic contact angle and spreading diameter for wettable, partially wettable and nonwettable surfaces. The computational model was validated through qualitative comparison with the measurements of Bayer and Megaridis, and through comparison with existing correlations. The comparison based on the ratio of
Size Effect on Nano-Droplet Spreading on Solid Surface
Molecular dynamics simulations were performed to study the spreading characteristics of nano-sized droplets on solid surfaces. The spreading behavior was analyzed in terms of the temporal evolution of the dynamic contact angle and spreading diameter for wettable, partially wettable and nonwettable surfaces. The computational model was validated through qualitative comparison with the measurements of Bayer and Megaridis, and through comparison with existing correlations. The comparison based on the ratio of
The Role of the Solid Substrate on the Spreading Kinetics of a Liquid Droplet
WIT transactions on engineering sciences, 2003
Classic hydrodynamic wetting theory leads to a linear relationship between spreading speed and the capillary force, being determined only by the surface tension of the liquid and its viscosity. The theory appears in good agreement with results generated from experiments conducted on the spreading of Polydimethylsiloxanes, PDMS on soda-lime glass substrate and fails to account for the behavior of other liquids. The spreading kinetics of three different liquids (PDMS 1000cp, hexadecane and glycerin) was determined on three different solids, namely, soda-lime glass, polymethylmethacrylate (PMMA) and polystyrene (PS), which exhibit different critical wetting energies. The results are summed up in two themes; equilibrial spreading and kinetics. PDMS is found to exhibit complete spreading on all three different solids at similar rate for glass and PS, but at much lower rate on PMMA. Hexadecane, a low surface energy liquid, was noted to exhibit equilibrial wetting that is proportional to t...
Droplet spreading on liquid–fluid interface
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018
We studied the early time dynamics of viscous drop spreading on a liquid-fluid interface. Unlike spreading on solid substrate, a drop deforms at the base as it spreads on a liquid-fluid interface. Hence the dynamics are seen to deviate from the classical power law of spreading. Experimental observations allowed us to establish a simple empirical expression to predict the temporal growth of the contact radius. Further, inertial oscillations were observed for spreading of less viscous liquid drop that can be described by the inertial capillarity model.
Langmuir, 2010
We study the spontaneous wetting of liquid drops on FCC solid substrates using large-scale molecular dynamics simulations. By varying the solid lattice parameter, five different drop/solid dynamic systems are investigated. It is shown that the results are in agreement with the molecular-kinetic theory (MKT) describing the dynamics of wetting. Moreover, it is established that the microscopic parameters resulting from fits using the MKT, the so-called molecular jump frequency at equilibrium and the jump length, correspond to the values that can be estimated directly from the simulations. This agreement strongly supports the validity of the MKT at the microscopic scale.
Droplet Spreading: Partial Wetting Regime Revisited
Langmuir, 1999
We study the time evolution of a sessile liquid droplet, which is initially put onto a solid surface in a non-equilibrium configuration and then evolves towards its equilibrium shape. We adapt here the standard approach to the dynamics of mechanical dissipative systems, in which the driving force, i.e. the gradient of the system's Lagrangian function, is balanced against the rate of the dissipation function. In our case the driving force is the loss of the droplet's free energy due to the increase of its base radius, while the dissipation occurs due to viscous flows in the core of the droplet and due to frictional processes in the vicinity of the advancing contact line, associated with attachment of fluid particles to solid. Within this approach we derive closed-form equations for the evolution of the droplet's base radius, and specify several regimes at which different dissipation channels dominate. Our analytical predictions compare very well with experimental data.
Dynamics of Spreading of Liquid Microdroplets on Substrates of Increasing Surface Energies
Langmuir, 1998
By spatially resolved single-wavelength ellipsometry, we investigate the spreading on a solid substrate of low molecular weight trimethyl-terminated poly(dimethylsiloxane) droplets. Especially, we focus our study on the dependence of the diffusion coefficient of the first molecular layer on the substrate surface energy, characterized by the critical surface tension γc measured for the alkane series. Our experimental data show that the diffusion coefficient D calculated from the film length reaches a maximum value for surfaces of intermediate energies. This result is shown to be consistent with the predictions of the available theoretical approaches and agrees quite well with molecular dynamics simulations reported in the third part of the paper.