EFFECT OF SURFACTANTS ON COALESCENCE OF A DROP AT AN INTERFACE .I.

The coalescence of single drops at a plane interface has been studied experimentally for the system toluene-water. Novel techniques for forming single drops and cleaning the interface are described. It was found that coalescence was sensitive to minute quantities of surfactants, present either as impurities or deliberately added (sodium benzoate and lauryl sulfate). Toluene drops were more sensitive than water drops. After cleaning of the interface, rest times showed surprisingly reproducible behavior. If no surfactant was present in the interface, rest times were extremely short. Rest times decreased with drop size, except where there was a tendency for drops to be stable. Then small drops were more readily stabilized than large drops. The results are explained in terms of interface movement and a double-layer repulsion. © 1969.