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

    Year: 2018

    Journal: Colloid Surf. A-Physicochem. Eng. Asp., Volume 554, OCT 5, page 326–333

    Authors: James, Emily; Tangparitkul, Suparit; Brooker, Anju; Amador, Carlos; Graydon, Andrew; Vaccaro, Mauro; Cayre, Olivier J.; Hunter, Timothy N.; Harbottle, David

    Organizations: Engineering and Physical Sciences Research Council (EPSRC); Procter & Gamble Ltd. (EPSRC iCASE) [12440605]

    Keywords: Droplet spreading; Interfacial shear elasticity; Yielding interfaces; Damped droplet oscillation

    The 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 beta-aescin was used as an interfacial shear rheology modifier, partitioning at the air-water interface to form a strongly elastic interface (G'/G '' similar to 6) within 1 min aging. The droplet spreading dynamics of Newtonian (water, 5 wt% ethanol, 0.0015 wt% N-dodecyl beta-D-glucopyranoside) and non-Newtonian (xanthan gum) fluids were shown to proceed with a time-dependent power-law dependence of similar to 0.50 and similar to 0.10 (Tanner's law) in the inertial and viscous regimes of spreading, respectively. However, water droplets stabilized by saponin beta-aescin 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 similar to 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.
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