Statistical Physics Perspective on Droplet Spreading in Reactive Wetting Interfaces

Droplet spreading is a fascinating phenomenon. Especially when the droplet spreads, reacts, and dissolves on and into metal substrates. This reactive wetting mainly occurs at high temperatures, with a vast number of applications in industry and material science. It is common to monitor and study the process using a side-view projection of the droplet, focusing on the dynamics and shape of its contact line. However, when the spreading is monitored top-view, rich and non-trivial spatio-temporal patterns are revealed during different stages of the process. These patterns call for a different type of study of the perimeter of the entire droplet. Statistical physics is the natural candidate to perform such tasks, using tools developed for the study of kinetic roughening of advancing interfaces. In this review, we demonstrate the use of these tools, the growth, roughness, and persistence exponents, to study the spreading of mercury droplets on metal-on-glass at room temperature, which by itself is a unique experimental system at this range of temperatures. The universality of the results is discussed in comparison with similar patterns of reactive wetting at high temperatures.