Wetting dynamics in two-liquid systems: Effect of the surrounding phase viscosity

Abstract

This paper reports the experimental results of a water droplet spreading on a glass substrate submerged in an oil phase. The radius of the wetted area grows exponentially over time forming two distinct regimes. The early time dynamics of wetting is characterized with the time exponent of 1, referred to as the viscous regime, which is ultimately transitioned to the Tanner's regime with the time exponent of 0.1. It is revealed that an increase in the ambient phase viscosity over three decades considerably slows down the rate of three-phase contact line movement. A scaling law is developed where the three-phase contact line velocity is a function of both spreading radius and mean viscosity, close to the geometric mean of the droplet and ambient fluids' viscosities. Using the proposed scaling and mean viscosity, all plots of spreading radius for different viscosity ratios collapse to a master curve. Furthermore, several cases with multiple rupture and spreading points, i.e., wetting in a nonideal system, are considered. The growth of an equivalent wetting radius in a multiple point spreading system is predicted by the developed scaling law.

Spreading, pinching, and coalescence: the Ohnesorge units

“…In general, ratios of the material properties of the inner and outer fluids can have an impact on the dynamics. This issue has been investigated for spreading [64,65], coalescence [50,65] and pinching [61] and we hope to be able to include these studies in the future.…”

Four stages of droplet spreading on a spherical substrate and in a spherical cavity: Surface tension versus line tension and viscous dissipation versus frictional dissipation

“…(33) and (34) of the combined theory [11,37]. However, it will be more instructive to divide the spreading process into several stages, each of which is characterized by a scaling law and the corresponding scaling exponent [11][12][13][14].…”

“…Although the spreading of liquid on solid substrates is a complicated phenomena where many factors come into play, the time evolution of spreading on a flat [3,4,[6][7][8][9][10] solid substrate is usually described by amazingly simple universal power laws. The most well-known law called Tanner's law, which describes the spreading on flat substrate, has been derived theoretically from several different approaches [3,7,8] and confirmed experimentally [8,[10][11][12][13][14] and numerically [15,16]. However, the wetting and spreading on a curved substrate [17][18][19][20][21] and the intrusion and spreading within a curved wall of cavity [22][23][24][25][26][27] attract less scientific attention even though they are also ubiquitous.…”

“…In fact, not only the power-law spreading but also the faster exponential and the finite time spreadings have been predicted [28,29] when the line tension dominates over the surface tension. However, it becomes well recognized that the spreading process is divided into several stages or regimes, each of which is characterized by different spreading exponents [11][12][13][14]. In fact, Tanner's hydrodynamic regime characterized by the viscous dissipation is believed to be preceded by the molecular-kinetic regime characterized by the frictional dissipation at the contact line [11,12] and the initial inertia spreading regime [33][34][35].…”

Induced-charge electrokinetic (ICEK) development and applications in microfluidics

“…Two-phase flow microfluidic devices have been widely used for chemical filtration, pharmacology and drug delivery (Azizian et al, 2019;Bazazi, Sanati-Nezhad, & Hejazi, 2018). When a leaky dielectric droplet immersed in another immiscible leaky dielectric liquid, four symmetric MVs are induced inside and outside the droplet (Lin, Skjetne, & Carlson, 2012).…”