  Some members of the vegetal kingdom can achieve surprisingly fast movements
making use of a clever combination of evaporation, elasticity and cavitation.
In this process, enthalpic energy is transformed into elastic energy and
suddenly released in a cavitation event which produces kinetic energy. Here we
study this uncommon energy transformation by a model system: a droplet in an
elastic medium shrinks slowly by diffusion and eventually transforms into a
bubble by a rapid cavitation event. The experiments reveal the cavity dynamics
over the extremely disparate timescales of the process, spanning 9 orders of
magnitude. We model the initial shrinkage as a classical diffusive process,
while the sudden bubble growth and oscillations are described using an
inertial-(visco)elastic model, in excellent agreement with the experiments.
Such a model system could serve as a new paradigm for motile synthetic
materials.
