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Capillary breakup of armored liquid filaments
Posted by Jesse Pritchard
Here is an article on the capillary breakup of armored liquid filaments, which are liquid columns wherein superhydrophobic particles reside on the liquid-air interface rather than in the bulk of the filament. The authors (Zou, Lin and Ji) conducted experiments using a high-speed camera to analyse the effects of the interfacial powder coverage on the filament breakup dynamics for a variety of powder sizes and how this related to a control experiment using 'pure liquid', for which there are established power-laws governing the minumum filament radius at points in time before pinch-off.
It was found that the thinning process for the filament can be split into three stages: (i) the armored liquid stage, (ii) the transition stage, and (iii) the liquid stage. The bulk of the work is on the dynamics of the armored liquid stage, in which the filament thins uniformly with an increased effective surface tension owing to the presence of the powder, and so maintains a larger minimum filament radius than its powder-less counterpart. The authors have found their own scaling law that governs the minimum filament radius during this stage and have a established a model that well approximates experiments with well-reasoned assumptions on the geometry of the system. When the minimum filament radius approaches the order of the average particle radius, the transition stage begins as the particles cause local deformation of the interface, increasing curvature and accelerating the thinning process. This continues until a time in which thinning can be modelled using power laws for 'pure liquids' in the final stages of thinning before capillary breakup, known as the liquid stage.