Droplet Initiated Rupture of High Viscosity Jets to Create Uniform Emulsions

Abstract

Creating highly monodisperse emulsions of high viscosity fluids has long been a challenging task. Even with the advent of micro-engineered emulsification systems such as membranes and microchannels obtaining a good degree of uniformity is hampered as these systems are very prone to jetting. We present a method of increasing the range at which uniform droplets can be produced by the use of droplet initiated jet rupture. In this method, a third, low viscosity inner phase, is introduced in the dispersed phase forcing the dispersed phase to form a shell around each drop and effectively reverts the system from jetting to dripping. Formulations are chosen so that the resulting core-shell droplets are unstable and soon rupture to form highly monodisperse emulsions. The rate of internal droplet production is found to be the governing parameter in the system and must be below a critical frequency. This frequency is found to be well predicted by Plateau–Rayleigh instability theory of jet rupture, where the perturbations caused by internal drops are at a wavelength larger than the circumference of the would-be jet. This method is easy to implement in conventional microfluidic designs and equipment and greatly facilitates the ability to produce very uniform emulsions of high viscosity.