Short- and long-term avalanche dynamics in 1D-printed microfluidic crystals

We report arrays of monodisperse water-in-oil microdroplets printed onto a substrate in a form of a compact linear chain -- a 1D-crystal -- pinned at one end. The chain spontaneously collapses under capillary forces via a sequence of avalanche-like rearrangement waves, resembling the rearrangements in a flowing microfluidic crystal, yet limited by the hydrodynamic friction at the substrate. While the propagation of the subsequent waves, separated by highly ordered metastable states, is either accelerating or decelerating depending on the direction of collapse, the coarse-grained dynamics of multiple waves -- at moderate packing fractions $\phi$ -- is initially linear in time, before leveling off. We further demonstrate how the collapse can be prevented via the use of a roughened substrate. Our study provides insight into the short- and long-term avalanche dynamics in granular systems with free interfaces and opens way to precision-printing of microfluidic assays.