Cavitation propagation in water under tension

Cavitation appears when pressure decreases below vapor pressure, generating vapor bubbles. It can be obtain in dynamical ways (acoustic, hydraulic) but also in quasi-static conditions. This later case is often observed in nature, in trees, or during the ejection of ferns spores [1]. We study the cavitation bubbles nucleation dynamics and its propagation in a confined microfabricated media. This later is an ordered array of microcavities made in hydrogel filled with water [2]. When the system is put into dry air, it dehydrates, water leaves the cavities and tension (negative pressure) builds in the cavities. This can be sustained up to a critical pressure (of order -20 MPa), then cavitation bubbles appear. We follow the dynamics using ultra high speed imaging. Events with several bubbles cavitating in a few microseconds could be observed along neighboring cells, showing a propagation phenomenon that we discuss.\\[4pt] [1] X. Noblin, N. O. Rojas, J. Westbrook, C. Llorens, M. Argentina, J. Dumais. The Fern Sporangium: A Unique Catapult. Science, 335, 1322, 2012.\\[0pt] [2] Tobias D. Wheeler and Abraham D. Stroock. The transpiration of water at negative pressures in a synthetic tree. Nature, 455, 208-212, 2008.