Experimental investigation of phase inversion in a stirred vessel using LIF

A non-intrusive dye tracing technique, laser-induced fluorescence (LIF), has been applied to investigate phase inversion in concentrated immiscible organic-aqueous liquid dispersions. The phase inversion process from oil-in-water (o/w) dispersion to water-in-oil (w/o) dispersion has been recorded by a high-speed video camera. Apart from phase inversion, secondary dispersion, drop coalescence and breakup mechanisms, have also been observed in great detail. The experimental results demonstrate that phase inversion is a gradual phenomenon: the process occurs only over 1–2 s, may not occur globally and depends on the local phase distribution. During phase inversion, two opposing pairs of processes, namely drop coalescence and break-up, and the inclusion and escape of small drops in larger drops, play a key role in phase inversion. The structure of the dispersion is extremely complex and a great number of secondary dispersions and multi-dispersions appear during phase inversion, which include water–oil–water secondary dispersions.