  The droplet size in emulsions is known to affect the rheological properties
and plays a crucial role in the many applications of emulsions. Despite its
importance, the underlying mechanisms governing droplet size in emulsification
remain poorly understood. We investigate the average drop size and size
distribution upon emulsification with a high-shear mixer for model oil-in-water
emulsions stabilized by a surfactant. The size distribution is found to be a
log-normal distribution, resulting from the repetitive random breakup of drops.
High-shear emulsification, the usual way of making emulsions, is therefore
found to be very different from turbulent emulsification given by the
Kolmogorov-Hinze theory for which power-law distributions of the drop size are
expected. In agreement with this, the mean droplet size does not follow a
scaling with the Reynolds number of the emulsification flow, but rather a
capillary number scaling based on the viscosity of the continuous phase.
