First steps in the spreading of a liquid droplet (original) (raw)
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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.
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.
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.
Spreading of a non-Newtonian liquid drop over a horizontal plane
Chemical Engineering Science, 2010
The spreading of a drop of non-Newtonian (power-law) liquid over a horizontal solid substrate is analyzed theoretically through energy approach method in the case of complete wetting. In this approach we have used the physical and geometrical reasoning and finally obtained a relation between the rate of spreading and bottom radius of the drop. It is shown that spreading rate of shear thickening liquid is more than that of a Newtonian liquid while shear thinning liquid is having slower rate than the latter one.
Model of inertial spreading and imbibition of a liquid drop on a capillary plate
AIChE Journal, 2017
We outline a low-order Lagrangian model for the inertial dynamics of spreading and imbibition of a spherical liquid cap on a plane featuring independent cylindrical capillaries without gravity. The analysis predicts the relative roles of radial and axial kinetic energy, reveals the critical Laplace number beyond which the drop oscillates, and attributes the exponent of the initial power-law for contact patch radius vs time to the form of capillary potential energy just after the water sphere touches the plate.
Spreading of non-Newtonian liquids over solid substrates
Journal of Colloid and Interface Science, 2003
The spreading of drops of a non-Newtonian liquid (Ostwald-de Waele liquid) over horizontal solid substrates is theoretically investigated in the case of complete wetting and small dynamic contact angles. Both gravitational and capillary regimes of spreading are considered. The evolution equation deduced for the shape of the spreading drops has self-similar solutions, which allows obtaining spreading laws for both gravitational and capillary regimes of spreading. In the gravitational regime case of spreading the profile of the spreading drop is provided.
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...
Effect of interfacial mass transport on inertial spreading of liquid droplets
Physics of Fluids
In this work, the early time dynamics of low-viscosity liquid drops spreading in their saturated vapor on partially wetting surfaces are investigated by lattice Boltzmann numerical simulations. Attention is paid to the effect of vapor transport through condensation on the spreading process. We observe that the condensation current resulting from the slight supersaturation of the liquid vapor near the dynamic wetting meniscus contributes to the motion and affects the spreading dynamics. Our results indicate that, in order to properly capture the initial dynamics of inertial spreading of a relatively volatile liquid drop, it is important to account for the vapor transport through condensation in the immediate vicinity of the contact line. A direct qualitative and quantitative comparison with experimental data of spontaneously wetting liquid drops is presented.
On the motion of Newtonian and non-Newtonian liquid drops
Scientia Iranica, 2012
In the present study, the motion of Newtonian and non-Newtonian liquid drops has been investigated experimentally. In order to investigate the effect of bulk fluid on drops, we have used water and air, as two fluids with different properties, and various industrial and biological applications. Image processing is utilized to analyze the images obtained by a high speed camera. The research has been separated into two parts. The first part has been devoted to the experiments in which air is the bulk fluid, and the second is related to the experiment carried out in water. The range of Reynolds number is, approximately, 50 < Re < 500. The major concern of the present study is the size variation of drops and its effect on the drag coefficient. It is proved that the period of size variation of a drop does not vary with properties. Rheological aspects of the problem have also been considered. In air with small density and viscosity, addition of non-Newtonian characteristics to the fluid causes the behavior of the drop to undergo dramatic changes. However, in water, a denser and more viscous bulk fluid, the behavior of Newtonian and non-Newtonian drops (at least for shear thinning fluids) looks the same. (B. Firoozabadi).