Study of drop-interface coalescence using piezoimaging

A novel technique for monitoring drop/homophase coalescence in liquid-liquid dispersions having an opaque or turbid dispersion medium has been developed and described in this paper. This technique is based on using a piezotransducer to monitor the process of coalescence of a drop at a liquid-liquid interface. The piezotransducer signal observed when coalescence occurs has two distinct parts. This study shows that the first part of the signal is due to interfacial instability, while the second part of the signal is due to a transient jet which is ejected into the homophase during coalescence. The effects of interfacial tension, homophase viscosity, and surfactant concentration in the dispersion medium on the observed signal are studied. Several other potential applications of the technique such as measuring the rate of phase separation are also discussed.