Clustering of micropillars in soft solids*

Surface stresses can deform soft solids. Recent experiments have explored this effect using a compliant material textured with an array of cuboid micropillars. Elastocapillarity can cause isolated pillars to flatten and become rounded. Interestingly, when pillar arrays are sufficiently dense, clustering and long-range pattern formation is observed. We investigate this behavior with both theory and finite element simulations, probing the clustering transition as a function of pillar geometry and the thickness of the base layer. We compare this clustering effect to related instabilities observed in soft solids and discuss how our results can be used to guide experimental design.