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Wetting on Soft Surfaces

The wetting of rigid surfaces has a long history, and is now fairly well understood. Soft surfaces might be expected to wet in a similar fashion as sessile droplets don’t really change the surface, other than making a few tiny deformations. In particular, this is at the contact line, where the droplets' surface tension pulls up a microscopic 'wetting ridge’ on the substrate surface. However, despite the tiny size of this ridge, it can have a big influence on how sessile droplets behave. For example, I will show how its presence can control how droplets slide across soft surfaces, and how stretching the substrate can lead to strongly asymmetric wetting. Furthermore, I will show how experimental imaging of this ridge gives us a novel way to characterise surface properties of the solid.