REVIEW OF SOLUTAL MARANGONI SPREADING ON FREE SURFACE

Marangoni flow is the interfacial spreading driven by an uneven distribution of surface tension. While it consists a shear flow at the interface, it may also induce severe interfacial deformation in case of spreading on a thin film, and fluid convection in case of spreading on a thick layer. The surface tension gradient can be modulated by the nonuniform distribution of temperature or of solutes, such as surfactant molecules and components that are miscible with the substrate. Solutal Marangoni spreading has important applications in biomedical fields such as the drug delivery in human airways, as well as in advanced manufacturing fields such as the formation of particles with complex structure and surface coating. Some physicochemical processes of solute molecules can affect the dynamics of Marangoni spreading, for instance, the transport of molecules at the interface, the mass exchange between the droplet and the substrate, and the evaporation of volatile solutes at the free liquid surface, which modulate the surface tension gradient instantaneously. In addition, under the combined effects of the rheological properties of the liquids and the strong shear rate induced by Marangoni spreading, the fluids may exhibit a series of complex and interesting phenomena. Based on the review article on solutal Marangoni spreading published by Matar and Craster in 2009, this review summarizes works reported on solutal Marangoni spreading in recent years, including surfactant-assisted spreading with modulated solubility, Marangoni spreading at interface of miscible liquids, and on free surfaces of complex fluids, as well as Marangoni spreading due to selective evaporation of one component in a fluid mixture. Phenomena will be presented and the mechanisms will be discussed. Finally, this review will enumerate the applications of Marangoni spreading in emerging industrial fields to provide references for developing low-energy devices and production processes that utilize the physicochemical properties of liquids.