Center for Applied Mathematics Colloquium
Droplets and droplet motions surround us. Our harvests depend on rain drops. We sweat, we shower and we drink. Drops enable the protein content of our bodily fluids to be measured and our silicon chips to be fabricated. Yet, droplet motions are still poorly understood. Despite a century of study, the spectrum of the supported drop has only recently been published. A free (unsupported) drop of inviscid liquid held by surface tension oscillates at natural frequencies with characteristic mode shapes (the Rayleigh spectrum). These are capillary waves governed by a wave equation. The Rayleigh spectrum is quantized by its spherical domain, which also makes it highly degenerate. When the drop is put in contact with a solid support, symmetry breaks, degeneracies split and the Rayleigh spectrum unfolds. In our model, two parameters relating to conditions at the liquid/solid/gas contact-line control the unfolding. Drawing parallels to the Schrödinger equation, a periodic table of mode shapes emerges much like that of the chemical elements. In this talk, we tell the story of this spectral unfolding and its surprising consequences.