  We explore air invasion in an initially water-filled dead-end compliant
microchannel containing a constriction. The phenomenon is driven by the
pervaporation of the liquid present in the channel through the surrounding
medium. The penetration is intermittent, jerky, and characterised by a
stop-and-go dynamics as the bubble escapes the constriction. We demonstrate
that this sequence of arrest and jump of the bubble is due to an
elastocapillary coupling between the air-liquid interface and the elastic
medium. When the interface enters the constriction, its curvature strongly
increases, leading to a depression within the liquid-filled channel which
drives a compression of the channel. As the interface is forced to leave the
constriction at a given threshold, due to the ongoing loss of liquid content by
pervaporation, the pressure is suddenly released, which gives rise to a rapid
propagation of the air bubbles away from the constriction and a restoration of
the rest shape of the channel. Combining macroscopic observations and confocal
imaging, we present a comprehensive experimental study of this phenomenon. In
particular, the effect of the channel geometry on the time of arrest in the
constriction and the jump length is investigated. Our novel microfluidic design
succeeds in mimicking the role of inter-vessel pits in plants, which
transiently stop the propagation of air embolism during long and severe
droughts. It is expected to serve as a building block for further biomimetic
studies in more complex leaf-like architectures, in order to recover this
universal phenomena of intermittent propagation reported in real leaves.
