This study is concerned on the coalescence behavior of dimethyl disulfide drops and itsmother-phase at the planar interface of sodium hydroxide aqueous solutions. This phenomenon is an essential part of the well-known Merox process. Three surfactant types of non-ionic Tween 20, anionic sodiumdodecyl sulfate (SDS) and cationic cetyl trimethyl ammonium bromide (CTAB) were used to examine the effect of surfactants on the coalescence process. Critical micelle concentrations (CMC) of the surfactants in caustic solutions were obtained by the interfacial tensionmeasurement. The drop coalescence timesweremeasured using a high-speed digital camera. Itwas found that Tween 20 was the most effective surfactant in the reduction of interfacial tension for which the coalescence time was reduced by 85.2% under its CMC of 75.4mg/L. The results also revealed that increase in the concentration of surfactants promoted the interface deformation. Furthermore, the effects of physical properties of the phases on the coalescence timewere studied. Accordingly, a correlationwas proposed based on the obtained data in which effective parameters and physical properties were involved with a maximum deviation of 15.1% and an average deviation of 7.8%. The resultswere compared with the so far reported correlations for coalescence times.
