Long-term instability of water in oil microdroplets.

Water in oil emulsions have a wide range of applications from chemical technology to microfluidics, where the stability of water droplets is of paramount importance. Here we describe and experimentally characterize a yet overlooked phenomenon, the dissolution of water in oil, which renders nanoliter-sized droplets unstable, resulting in their shrinkage and disappearance in a time scale of hours. The rate of dissolution is determined by the product of the diffusion coefficient and the saturation density of water in oil, which also provides a novel method to measure either of these parameters.