Short-Time Dynamics of Partial Wetting (original) (raw)

Dynamics of wetting: from inertial spreading to viscous imbibition

Journal of Physics: Condensed Matter, 2009

We report the influence of the nature of boundaries on the dynamics of wetting. We review some work recently published and highlight new experimental observations. Our paper begins with the spreading of drops on substrates and demonstrates how the exponents of the spreading laws are affected either by the surface chemistry or by the droplet shape. We then discuss the imbibition of completely and partially wetting fluids into channels and over microtextured surfaces. Starting with the one-dimensional imbibition of completely wetting liquids in tubes and surface textures, we show that (i) shape variations of channels change the power-law response of the imbibition and (ii) the geometrical parameters of a surface roughness change the spreading behavior. For partially wetting fluids, we observe directionally dependent spreading: polygonal wetted domains can be obtained. We conclude with a tabular summary of our findings, allowing us to draw connections between the different systems investigated, and shed light on open questions that remain to be addressed.

Universality in dynamic wetting dominated by contact-line friction

Physical Review E, 2012

We report experiments on the rapid contact line motion present in the early stages of capillary driven spreading of drops on dry solid substrates. The spreading data fails to follow a conventional viscous or inertial scaling. By integrating experiments and simulations, we quantify a contact line friction (µ f), which is seen to limit the speed of the rapid dynamic wetting. A scaling based on this contact line friction is shown to yield a universal curve for the evolution of the contact line radius as a function of time, for a range of fluid viscosities, drop sizes and surface wettabilities.

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.

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.

Kinetics of Wetting and Spreading of Droplets over Various Substrates

Langmuir : the ACS journal of surfaces and colloids, 2017

There has been a substantial increase in the number of publications in the field of wetting and spreading since 2010. This increase in the rate of publications can be attributed to the broader application of wetting phenomena in new areas. It is impossible to review such a huge number of publications; that is, some topics in the field of wetting and spreading are selected to be discussed below. These topics are as follows: (i) Contact angle hysteresis on smooth homogeneous solid surfaces via disjoining/conjoining pressure. It is shown that the hysteresis contact angles can be calculated via disjoining/conjoining pressure. The theory indicates that the equilibrium contact angle is closer to a static receding contact angle than to a static advancing contact angle. (ii) The wetting of deformable substrates, which is caused by surface forces action in the vicinity of the apparent three-phase contact line, leading to a deformation on the substrate. (iii) The kinetics of wetting and sprea...

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.

PHYSICAL REVIEW LETTERS Wetting Dynamics of the Edge of a Spreading Drop

We report the first explicit measurement on the profile of a spreading edge of nonvolatile liquid, in support of the theory of Hervet and de Gennes on a one-dimensional thin spreading edge. From the laser light interference patterns, the meniscus shape of the edge was reconstructed and the advancing dynamic contact angle was measured. The meniscus shape and the contact angle are in good agreement with their theory. The meniscus shape obtained at several different capillary numbers can be collapsed into one dimensionless curve, using their scaling laws.

Capillary spreading of a droplet in the partially wetting regime using a diffuse-interface model

Journal of Fluid Mechanics, 2007

The spreading of a liquid droplet on a smooth solid surface in the partially wetting regime is studied using a diffuse-interface model based on the Cahn--Hilliard theory. The model is extended to include non-90$^{\circ}$ contact angles. The diffuse-interface model considers the ambient fluid displaced by the droplet while spreading as a liquid. The governing equations of the model for the axisymmetric case are solved numerically using a finite-spectral-element method. The viscosity of the ambient fluid is found to affect the time scale of spreading, but the general spreading behaviour remains unchanged. The wettability expressed in terms of the equilibrium contact angle is seen to influence the spreading kinetics from the early stages of spreading. The results show agreement with the experimental data reported in the literature.

Thin Films in Partial Wetting: Internal Selection of Contact-Line Dynamics

Physical review letters, 2015

When a liquid touches a solid surface, it spreads to minimize the system's energy. The classic thin-film model describes the spreading as an interplay between gravity, capillarity, and viscous forces, but it cannot see an end to this process as it does not account for the nonhydrodynamic liquid-solid interactions. While these interactions are important only close to the contact line, where the liquid, solid, and gas meet, they have macroscopic implications: in the partial-wetting regime, a liquid puddle ultimately stops spreading. We show that by incorporating these intermolecular interactions, the free energy of the system at equilibrium can be cast in a Cahn-Hilliard framework with a height-dependent interfacial tension. Using this free energy, we derive a mesoscopic thin-film model that describes the statics and dynamics of liquid spreading in the partial-wetting regime. The height dependence of the interfacial tension introduces a localized apparent slip in the contact-line ...

Dynamics of a Complete Wetting Liquid Under Evaporation

Understanding Complex Systems, 2013

We describe a simple model of a contact line under purely diffusive evaporation and complete wetting condition taking into account the divergent nature of evaporative flux near the contact line as proposed by Deegan et al. [1] by using electrostatic analogy. We show the existence of a precursor film at the edge of the liquid and generalize Tanner's law accounting for evaporative effects. We apply this model to the problem of evaporation of a liquid droplet and partly recover the dynamics of spreading and retraction found in experiments [2].