title: Elastocapillary coalescence of plates and pillars.
abstract: When a fluid-immersed array of supported plates or pillars is dried, evaporation leads to the formation of menisci on the tips of the plates or pillars that bring them together to form complex patterns. Building on prior experimental observations, we use a combination of theory and computation to understand the nature of this instability and its evolution in both the two- and three-dimensional setting of the problem. For the case of plates, we explicitly derive the interaction torques based on the relevant physical parameters associated with pillar deformation, contact-line pinning/depinning and fluid volume changes. A Bloch-wave analysis for our periodic mechanical system captures the window of volumes where the two-plate eigenvalue characterizes the onset of the coalescence instability. We then study the evolution of these binary clusters and their eventual elastic arrest using numerical simulations that account for evaporative dynamics coupled to capillary coalescence. This explains both the formation of hierarchical clusters and the sensitive dependence of the final structures on initial perturbations, as seen in our experiments. We then generalize our analysis to treat the problem of pillar collapse in three dimensions, where the fluid domain is completely connected and the interface is a minimal surface with the uniform mean curvature. Our theory and simulations capture the salient features of experimental observations in a range of different situations and may thus be useful in controlling the ensuing patterns.
authors: School of Engineering and Applied Sciences , Wyss Institute for Bio-inspired Engineering, Harvard University , Cambridge, MA 02138, USA.
authors: Z
authors: Z
authors: Wei
authors: School of Engineering and Applied Sciences , Wyss Institute for Bio-inspired Engineering, Harvard University , Cambridge, MA 02138, USA ; Emergent Complexity in Physical Systems Laboratory (ECPS) , École Polytechnique Fédérale de Lausanne , Lausanne 1015, Switzerland.
authors: T M
authors: TM
authors: Schneider
authors: Department of Mechanical and Aerospace Engineering , Seoul National University , Seoul 151-744, Korea.
authors: J
authors: J
authors: Kim
authors: Department of Mechanical and Aerospace Engineering , Seoul National University , Seoul 151-744, Korea.
authors: H-Y
authors: HY
authors: Kim
authors: School of Engineering and Applied Sciences , Wyss Institute for Bio-inspired Engineering, Harvard University , Cambridge, MA 02138, USA ; Kavli Institute for Nano-Bio Science and Technology , Wyss Institute for Bio-inspired Engineering, Harvard University , Cambridge, MA 02138, USA.
authors: J
authors: J
authors: Aizenberg
authors: School of Engineering and Applied Sciences , Wyss Institute for Bio-inspired Engineering, Harvard University , Cambridge, MA 02138, USA ; Department of Physics , Wyss Institute for Bio-inspired Engineering, Harvard University , Cambridge, MA 02138, USA ; Kavli Institute for Nano-Bio Science and Technology , Wyss Institute for Bio-inspired Engineering, Harvard University , Cambridge, MA 02138, USA.
authors: L
authors: L
authors: Mahadevan
keywords: cluster formation; instability; liquid meniscus; surface tension