Abstract
The famous two-balloon experiment involves two identical balloons filled
up with air and connected via a hollow tube, and upon onsetting the
experiment one of the balloons shrinks and the other expands. Here, we
present the liquid version of that experiment. We use superhydrophobic
(SHP) substrates to form spherical droplets and connect them with a
capillary channel. Different droplet sizes, substrates of different
hydrophobicities, and various channel pathways are investigated, and
morphometric parameters of the droplets are measured through image
processing. In the case of SHP substrates the pumping is from the
smaller droplet to the larger one, similar to the two-balloon
experiment. However, if one or both of the droplets are positioned on a
normal substrate the curvature radius will indicate the direction of
pumping. We interpret the results by considering the Laplace pressures
and the surface tension applied by the channel at the connecting points.