The breakup of a liquid filament is both a modern research topic of interest and a classical hydrodynamic stability problem of considerable importance for industries working on the development of printing and optical devices. This breakup mechanism is known as the Plateau-Rayleigh instability and occurs due to surface tension acting as a restoring force to minimise the overall energy of the system. However, when such slender threads rest on a solid surface, the wetting conditions and geometric constraints affect the subtle interplay with hydrodynamics, adding complexity to the system. This includes the motion of the contact lines, governed by the friction and surface forces, and result in a deviation from the equilibrium angle, thus affecting the outcome of the Plateau-Rayleigh instability. Additionally, we are interested in initial states shaped as liquid rings. The subtle interplay between each of these effects and the timescales over which they act makes the breakup pathway difficult to predict and consequently to control. Here, we show how by means of dielectrowetting, we able to produce the initial states of the liquid ring films. We study the dynamics and resultant breakup modes of toroidal films from an experimental and theoretical approach. We base the analysis on the stability of the morphology of the droplet coupled with the dynamics of a film. We observe from the experiments, the competition of the breakup modes and compare these findings against the theoretical analysis. This allows us to elucidate the subtle role that both static and dynamic wettability play in the evolution of the system. Finally, we demonstrate by means of dielectrowetting, how the selection mechanism can be altered to generate the patterns of droplets of well-defined dimensions and arrangement in a reversible and predictable manner.
Élfego Ruiz Gutiérrez is a Postdoctoral Research Associate and member of the Institute for Multiscale Thermofluids at the University of Edinburgh. He did his undergraduate degree and Masters in Physics at the National Autonomous University of Mexico and his PhD in Physics at Northumbria University. Currently, he has been working as a PDRA for 3 years. His research interests are in capillary flows that undergo phase change, are subject to heat and mass transfer or electric fields.