Effects of surfactants on the retraction of viscous liquid sheets*

In several industrial applications including polymer processing and curtain coating, liquid sheets (thin films of liquid with two free surfaces) are extruded out of nozzles or dies. These sheets often have rectangular cross-sections with circular ends that contract or retract towards each other under the action of surface tension forces. Liquid sheets ejected from spray nozzles in agriculture and in many other applications commonly have surfactants present at the free surface (air-liquid interface) either by design or as contaminants. Earlier studies have shown that the presence of surfactants at the free surface alters the dynamics of free films and filaments, either by changing the breakup dynamics or by averting end pinching (Wee et al., Phys. Rev. Fluids, 2022; Kamat et al., JFM 2020). In this talk, we will report the results of a study investigating the effect of surfactants on the retraction dynamics of liquid sheets and extend the previous works of others on systems with clean interfaces (Notz and Basaran, JFM, 2004; Savva and Bush, JFM, 2009; Pierson et al., Phys. Rev. Fluids, 2020; Deka and Pierson, Phys. Rev. Fluids, 2020).