Wednesday  |  Allegheny  |  05:20 PM–05:40 PM

#13446, Contact Fronts and Air Entrainment During Impact of Liquid Drops and Soft Solids on Smooth Rigid Surfaces via the Virtual Frame Technique

Before an object can contact a surface during impact, it must drain the intervening fluid. Typically, for droplet impacts and soft solids, the air will fail to drain, and instead compress. However, the impact process takes place over fleeting timescales and diminutive length-scales, and is typically obscured by the impacting body, making direct observation difficult or impossible. Here we present a combination of the Virtual Frame Technique and Frustrated Total Internal Reflection that together enable the direct visualization of key stages of contact front formation and propagation during impact. These observations lead to fundamental insights into the dynamics of impact processes, and highlight the non-trivial influence of the physical properties of the fluid or material involved in the impact process, including the capillary velocity in fluid droplets and the Rayleigh velocity in elastomer impact. For the droplet, the imaging modality suggests that the fluid is skating on a nanometer-scale film of air during the highest velocity impacts, whereas for the elastomer, we observe a transition from elasticity- to inertially-dominated impact regimes. Perspectives on the limitations of these methods will be discussed at the conclusion of the talk.

John Kolinski   EPFL