Dynamics of millimeter-sized particles on low-friction interfaces – Anaïs Gauthier (Institut de Physique de Rennes)

The motion of millimeter-sized objects trapped at the liquid-air interfaces is an everyday-life phenomenon, seen in the clumping of cereals in a bowl or that of bubbles at the surface of a sparkling liquid. The deformation of the interface typically generates attractive forces between the particles, while friction with the underlying liquid slows down them down, so that the motion of particles is rarely faster than a few millimeters per second.

In this presentation, we will consider the dynamics of particles placed on two unusual interfaces, on which the friction is extremely small. 

The first interface is an evaporating bath of liquid nitrogen. When deposited on the cryogenic bath, ambient temperature particles are maintained in levitation by the vapour escaping from the interface. We will show that in this system, the particles spontaneously self-propel and move in straight lines at a velocity of a few cm/s. We will explain this phenomenon, and study the orbiting motion that appear when two particles approach each other.

The second interface is an horizontal soap film. Here, the particles weight deform macroscopically the film, which generates an attractive force typically one hundred times greater than the one measured at the liquid/air interface. In addition, the particles suck in the liquid within the film, which profoundly changes the film thickness distribution over time. Going further into this, we hope to explain the improved mechanical properties of soap films charged in particles.