Millimeter-sized objects floating on the liquid surface distort the interface by their weight, which in turn attracts them towards each other. This phenomenon called Cheerios Effect is found in the clumping of cereals in a breakfast bowl and ends up being a profoundly encouraging course towards controlled self-assembly of colloidal particles at the water surface.
In a new study, scientists at the University of Twente, studied capillary attraction between levitating droplets, maintained in an inverse Leidenfrost state above liquid nitrogen. The droplet skates across the surface, just like the ‘water strider’ insect can walk over water. Using one droplet, the effect is already remarkable.
The effect is remarkable with the single droplet, but with two droplets, they would start behaving like bouncing billiard balls. The reason- they would start moving in orbits- has to do with surface tension.
The weight of one droplet mutilates the state of the liquid surface, making the other bead move. This resembles general relativity, wherein the mass of one celestial object impact the orbits of others by the curvature of space-time.
When the droplets get colder, the circumstances change and it also changes the speed and interaction. As a result, small friction takes place.
From that moment, the droplet leaves the similarity to the planet orbits: the orbit of droplets will be spirally shaped, as the scientists show in their calculations and simulations.
What if many droplets are released on the surface?
It seems fascinating, though complex, next step.
Scientists noted, “The way the movement of the droplet is controlled, could be a way of moving vulnerable biological examples and manipulate them without the need of putting them into a container or tube, risking contamination. The sample is even deep-frozen ‘on the move’.”
The study– published in the journal Nature Communications- conducted in collaboration with scientists from Max Planck – University of Twente Center for Complex Fluid Dynamics.