Experimental evaluation of Marangoni stress and surfactant concentration at interface of contaminated single spherical drop using spatiotemporal filter velocimetry. (December 2017)

• Record Type: Journal Article
• Authors: Hosokawa, Shigeo; Masukura, Yuya; Hayashi, Kosuke; Tomiyama, Akio
• Is Part Of: International journal of multiphase flow. Volume 97(2017)
• Page Start: 157
• Page End: 167
• Publication Date: 2017-12
• Subjects: Drop -- Marangoni effect -- Spatiotemporal filter velocimetry -- Surfactant -- Interface; Multiphase flow -- Periodicals; Écoulement polyphasique -- Périodiques; Multiphase flow; Periodicals; 620.1064
• DOI: 10.1016/j.ijmultiphaseflow.2017.08.007
• Languages: English
• ISSNs: 0301-9322

Abstract

Highlights: Spatiotemporal filter velocimetry is extended to boundary–fitted measurement regions (BF-SFV). BF-SFV enables us to measure velocity distribution in the vicinity of an interface accurately. Interfacial velocity and interfacial shear stress can be evaluated from the measured velocity distribution. Distributions of the Marangoni stress, interfacial tension and surfactant concentration at the interface are successfully estimated from the accurate velocity distributions. Abstract: Spatiotemporal filter velocimetry (SFV) was extended to Lagrangian measurements with boundary-fitted measurement areas, and was applied to flows about single spherical drops of glycerol-water solution falling in stagnant silicon oil under clean and contaminated conditions to examine its applicability to the estimation of the Marangoni stress and surfactant concentration at a moving interface. Effects of bulk concentration of surfactant on the velocity field, the Marangoni stress and the surface concentration of surfactant were discussed from the measured data. As a result, we confirmed that accurate velocity distribution in the vicinity of the interface measured by SFV enables us to evaluate interfacial velocity and interfacial shear stresses and to estimate the Marangoni stress, interfacial tension and surfactant concentration at the interface with the assumption of negligible surface viscosity. The flow inside the drop and the interfacial velocity become weak due to the Marangoni stress caused by the gradient of surfactant concentration at the interface as the bulk concentration of surfactant increases. These results demonstrate that SFV is of great use in experimental analysis of adsorption and desorption kinetics at a moving interface.