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How droplets sit and splash on soft surfaces

How droplets behave on hard surfaces is well known. For example, static droplets in equilibrium sit with a contact angle given by Young’s law, and impacting droplets splash when they hit a surface at speeds above a critical velocity. However, they behave very differently on soft surfaces. Young’s law breaks down, droplets interact with each other — e.g. they spontaneously slide across flat surfaces to coalesce with nearby droplets, and splashing of impacting droplets is significantly suppressed. I will show several experimental examples of this, and explain how we can understand this theoretically.