  In this paper, we study experimentally and theoretically the dynamics of
liquid plugs in rectangular microchannels for both unidirectional and cyclic
pressure forcing. In both cases, it is shown that the transition between
quasi-static and dynamic film deposition behind the liquid plug leads to a
dramatic acceleration of the plug, rapidly leading to its rupture. This
behaviour proper to channels with sharp corners is recovered from a reduced
dimension model based on previous theoretical and numerical developments. In
addition, it is shown for cyclic periodic forcing that the plug undergoes
stable periodic oscillations if it remains in the quasi-static film deposition
regime during the first cycle, while otherwise it accelerates cyclically and
ruptures. The transition between these two regimes occurs at a
pressure-dependent critical initial length, whose value can be predicted
theoretically.
