This paper considers the interaction between two droplets placed on asubstrate in immediate vicinity. We show here that when the two droplets are ofdifferent fluids and especially when one of the droplet is highly volatile, awealth of fascinating phenomena can be observed. In particular, the interactionmay result in the actuation of the droplet system, i.e. its displacement over afinite length. In order to control this displacement, we consider dropletsconfined on a hydrophilic stripe created by plasma-treating a PDMS substrate.This controlled actuation opens up unexplored opportunities in the field ofmicrofluidics. In order to explain the observed actuation phenomenon, wepropose a simple phenomenological model based on Newton's second law and asimple balance between the driving force arising from surface energy gradientsand the viscous resistive force. This simple model is able to reproducequalitatively and quantitatively the observed droplet dynamics.
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