The contacting of multiple liquid phases is a complex process, and one that is difficult to study experimentally. Liquid dispersion studies in stirred tanks and high shear mixers frequently involve the use of surfactants without a strong physical understanding of how the surfactants affect the mechanics of droplet production and breakup. In this study, experiments are performed using the axisymmetric laminar jet system. The breakup of a laminar axisymmetric jet is a well-studied fluid dynamics phenomenon. Despite the extensive literature on jet breakup, the impact of surface active agents on jet breakup has received limited attention.

An extensive series of experiments with water-air and oil-water jet systems with and without surfactants has been performed, varying fluid flow rate, jet diameter, jet bulk viscosity, surfactant type, and surfactant concentration. Surfactants were found to significantly affect the breakup of laminar liquid jets. Significant effects on both the length of jets and the size of resulting droplets are reported. In general, the effect of surfactants is to reduce the interfacial tension of the system in question, which results in longer jet breakup lengths and larger diameter droplets. However, the interfacial tension alone is insufficient to explain the physics of the jet breakup phenomena. Several breakup mechanisms were identified, and the regimes in which each operates vary not only due to jet geometry and velocity, but on the interfacial properties as well. The effect of surfactants on the breakup phenomena differs in each of these distinct breakup regimes.

A mechanistic model for the prediction of breakup length for surfactant laden jets is presented. This model results in good agreement between predicted and experimentally observed values over a wide variety of surfactant concentrations and jet conditions and was shown to be useful for both the oil-water and water-air systems, within the axisymmetric jetting regime.