Surfactant Driven Marangoni Spreading in the Presence of Predeposited Insoluble Surfactant Monolayers

Abstract

When an insoluble surfactant is deposited on the surface of a thin fluid film, stresses induced by surface tension gradients drive Marangoni spreading across the subphase surface. The presence of a predeposited layer of an insoluble surfactant alters that spreading. In this study, the fluid film was aqueous, the predeposited insoluble surfactant was dipalmitoylphosphatidylcholine (DPPC), and the deposited insoluble surfactant was oleic acid. An optical density-based method was used to measure subphase surface distortion, called the Marangoni ridge, associated with propagation of the spreading front. The movement of the Marangoni ridge was correlated with movement of surface tracer particles that indicated both the boundary between the two surfactant layers and the surface fluid velocities. As the deposited oleic acid monolayer spread, it compressed the predeposited DPPC monolayer. During spreading, the surface tension gradient extended into the predeposited monolayer, which was compressed nonuniformly, from the deposited monolayer. The spreading was so rapid that the compressed predeposited surfactant could not have been in quasi-equilibrium states during the spreading. As the initial concentrations of the predeposited surfactant were increased, the shape of the Marangoni ridge deformed. When the initial concentration of the predeposited surfactant reached about 70 A2/molecule, there was no longer a Marangoni ridge but rather a broadly distributed excess of fluid above the initial fluid height. The nonuniform compression of the annulus of the predeposited monolayer also caused tangential motion ahead of both the Marangoni ridge and the boundary between the two monolayers. Spreading ceased when the two monolayers reached the same final surface tension. The final area per molecule of the DPPC monolayer matched that expected from the equilibrium DPPC isotherm at the same final surface tension. Thus, at the end of spreading, there was a simple surface tension balance between the two distinct monolayers.

Flow profiles near receding three-phase contact lines: influence of surfactants

“…These stagnant caps change the rise velocity and flow field in and outside the bubble. A similar process is observed in the coalescence dynamics of drops [26][27][28][29] with liquid pools. In evaporating drops, the natural convection due to thermal Marangoni effects 30 is modified for drops containing more than one component, 31 e.g., additional surfactants, 32,33 particles, 34 or salt.…”

Dual‐Channel Flexible Strain Sensors Based on Mechanofluorescent and Conductive Hydrogel Laminates

“…To make the hydrogel layer fluorescent, the commercial Rhodamine B (RB) was covalently grafted onto the chemically crosslinked PHEAA network via an esterification reaction (Figure S2, Supporting Information). [39,40] After that, the densely stacked carbon nanotubes (CNTs) film, which was produced by the reported Marangoni spread [41,42] and capillary force induced compression of multiwall CNTs, was transferred onto the other side of the PDMS film. [43,44] Trilayer structure of the as-prepared RB-PHEAA/PDMS/CNTs film was clearly evidenced by the SEM images (Figure 1b), which shows that these three layers are bonded tightly.…”

Surfactant spreading in a two-dimensional cavity and emergent contact-line singularities

“…The aim of this study is to describe the interfacial and bulk transient flows produced by self-induced Marangoni spreading of surfactant in a confined geometry. Exogenous surfactant added to the interface spreads, compressing the endogenous surfactant ahead of it (Grotberg, Halpern & Jensen 1995;Sauleda et al 2021). Since the surfactant monolayer is laterally confined, the surfactant concentration rises at the pinned contact lines, while Marangoni stresses drive further surfactants towards the stationary boundary.…”