Storm in a Teacup: dynamics of micro-droplets on hot water surface
Hiizu Nakanishi, Department of Physics, Kyushu University, Fukuoka, Japan

When having a cup of hot tea or coffee, you may notice some white sheets of membrane floating around edge of a cup. They stay very close to the water surface and look almost sticky to it. Occasionally, splitting events run through them very fast to open slits about 1 mm width, and interesting patterns develop in the membranes. We made high speed video observations on this phenomenon and found that i) the white sheets of membrane consist of small droplets of the diameter about 10 $\mu\,{\rm m}$, ii) they are levitating above the water surface by about 10 $\mu\,{\rm m}$, iii) the splitting events are collective vanishing of the droplets, which propagates as a wave front of surface wave with the speed 1~2 m/s, iv) the collective vanishing events are triggered by surface disturbance caused by disappearance of a single droplet.