Accelerated spreading of inviscid droplets prompted by the yielding of strongly elastic interfacial films

Abstract

ReuseThis article is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs (CC BY-NC-ND) licence. This licence only allows you to download this work and share it with others as long as you credit the authors, but you can't change the article in any way or use it commercially. More information and the full terms of the licence here: https://creativecommons.org/licenses/ TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. AbstractThe complexity associated with droplets spreading on surfaces has attracted significant interest for several decades. Sustained activity results from the many natural and manufactured systems that are reliant on droplet-substrate interactions and spreading. Interfacial shear rheology and its influence on the dynamics of droplet spreading has to date received little attention. In the current study, saponin -aescin was used as an interfacial shear rheology modifier, partitioning at the air-water interface to form a strongly elastic interface (G'/G" ~ 6) within 1 min aging.The droplet spreading dynamics of Newtonian (water, 5 wt% ethanol, 0.0015 wt% N-dodecyl -D-glucopyranoside) and non-Newtonian (xanthan gum) fluids were shown to proceed with a time-dependent power-law dependence of ~ 0.50 and ~ 0.10 (Tanner's law) in the inertial and viscous regimes of spreading, respectively. However, water droplets stabilized by saponinaescin were shown to accelerate droplet spreading in the inertial regime with a depreciating time-dependent power-law of 1.05 and 0.61, eventually exhibiting a power-law dependence of ~ 0.10 in the viscous regime of spreading. The accelerated rate of spreading is attributed to the potential energy as the interfacial film yields as well as relaxation of the crumpled interfacial film during spreading. Even though the strongly elastic film ruptures to promote droplet spreading, interfacial elasticity is retained enhancing the dampening of droplet oscillations following detachment from the dispensing capillary.

Synergy between Composite Nanoparticles and Saponin β-Escin to Produce Long-Lasting Foams

“…A saponin β-escin drop was placed in the sealed quartz cuvette to minimize any influence of droplet evaporation during the measurement, and the droplet volume was also maintained by the autodispensing pump controlled on feedback by the Theta software. 41 Foam Studies. To prepare foams stabilized by saponin βescin and CPs, 10 mL of 1 wt % CP suspension containing 0.01 wt % saponin β-escin in 0.55 M Na 2 SO 4 was added to a 40 mL glass vial.…”

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

“…However, the observation of stages I and III will be possible as the surface tension is the main driving force and the macroscopic droplets and substrates can be used. In fact, there are many experimental evidences that the spreading process on flat substrates can be divided into several stages [11][12][13][14].…”

“…(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].…”