Effect of interfacial dilational rheology on the breakage of dispersed droplets in a dilute oil–water emulsion

Surfactants reduce the interfacial tension of oil–water and hence favor emulsification; however, attention has rarely been focused on the effect of interfacial dilational rheology on drop breakage. The aim of this work is to rheologically characterize the interfacial properties of oil–water droplets and the effect on drop breakage during emulsification. The dispersed holdups are fixed in dilute dispersion where breakage dominates during mixing. The total number of droplets, the square weighted (sqr-wt) mean diameter and the chord length distribution (CLD) are measured online using the focus beam reflectance method (FBRM). Variations in the dispersed droplets are further analyzed with the interfacial dilational modulus. For emulsions with surfactant concentrations below the critical micelle concentration (CMC), the interfacial tension decreases as the surfactant concentration increases, whereas the mean drop diameter initially shows an increasing trend and then decreases. However, for concentrations above the CMC, the interfacial tension rarely decreases, whereas the mean diameter of the dispersed phase continues to decrease, and the total number of droplets increases as the concentration of Span 80 continues to increase. This indicates that the interfacial dilational elasticity is a key factor that influences the pure breakage emulsification process and the related dispersed modality.