Marangoni Flow of Ag Nanoparticles from the Fluid−Fluid Interface

Abstract

Fluid flow is observed when a volume of passivated Ag nanoparticles suspended in chloroform is mixed with a water/ethanol (v/v) mixture containing acidified 11-mercaptoundecanoic acid. Following mechanical agitation, Ag nanoparticles embedded in a film are driven from the organic-aqueous interface. A reddish-brown colored film, verified by transmission electron microscopy to contain uniformly dispersed Ag nanoparticles, is observed to spontaneously climb the interior surface of an ordinary, laboratory glass vial. This phenomenon is recorded by a digital video recorder, and a measurement of the distance traveled by the film front versus time is extracted. Surface (interfacial) tension gradients due to surfactant concentration, temperature, and electrostatic potential across immiscible fluids are known to drive interface motion; this well-known phenomenon is termed Marangoni flow or the Marangoni effect. Experimental results are presented that show the observed mass transfer is dependent on an acid surfactant concentration and on the volume fraction of water in the aqueous phase, consistent with fluid flow induced by interfacial tension gradients. In addition, an effective desorption rate constant for the Marangoni flow is measured in the range of approximately 0.01 to approximately 1 s(-1) from a fit to the relative film front distance traveled versus time data. The fit is based on a time-dependent expression for the surface (interface) excess for desorption kinetics. Such flow suggests that purposeful creation of interfacial tension gradients may aid in the transfer of 2- and 3-dimensional assemblies, made with nanostructures at the liquid-liquid interface, to solid surfaces.

The dynamic mass transfer of surfactants upon droplet formation in coaxial microfluidic devices

“…Despite the fact that interfaces are usually partly covered with surfactant molecules because of unsaturated adsorption, it is assumed that Marangoni stresses are negligible during droplet formation, in accordance with previous studies (Baret et al, 2009;Steegmans et al, 2009;Wang et al, 2009;Xu et al, 2012). Firstly, the Marangoni flow is very slow compared with continuous-phase flow (Steegmans et al, 2009) since the rate of Marangoni flow is maximally roughly 1 μm ms À 1 , (Thutupalli et al, 2011, Johnson et al, 2008, while the rate of continuous-phase flow over the droplets is typically at the magnitude of 100 μm ms À 1 . Secondly, since the adsorption flux is proportional to the empty space on the interface, the depleted regions are supplied more rapidly.…”

The Dynamic Effects of Surfactants on Droplet Formation in Coaxial Microfluidic Devices

“…It is worth noting that when the interface is not fully covered or the surfactant monomers are distributed along the interface nonuniformly, local variations of interfacial tension can arise, leading to movement in a fluid interface and departure from the equilibrium tension, or “Marangoni stresses”. − Despite the fact that the interfaces in our experiment are usually partly covered with SDS monomers because of the unsaturated adsorption, we assume that Marangoni stresses are insignificant during droplet formation similar to previous studies. ,, First, the Marangoni flow is very slow relative to continuous-phase flow since Marangoni flow is maximally roughly 1 μm·ms –1 , , while the continuous-phase flow rate over the droplets is typically at the magnitude of 100 μm·ms –1 . Second, since the adsorption flux is proportional to the empty space on the interface, the depleted regions are supplied more rapidly.…”

Marangoni-driven film climbing on a draining pre-wetted film

“…On the other hand, if gravity may be neglected, the Marangoni stress balances the viscous stress in the film to produce a time (t) variation of spreading that scales as t 1/2 (He & Ketterson 1995), which is consistent with the Marangoni spreading on a horizontal strip (Jensen & Grotberg 1992, 1993. While there are many studies across a wide range of fields that describe a film climbing phenomenon (Fanton, Cazabat & Quéré 1996;Münch & Bertozzi 1999;Johnson et al 2008;Daripa & Paşa 2009;Fletcher & Holt 2011), the interplay of surface tension, viscous effects and gravity remains an open question: to the best of our knowledge, we are not aware of previous experimental studies of Marangoni spreading on a vertically draining pre-wetted film, and we show that the drainage of the pre-wetted film, where the thickness changes in time, affects the spreading.…”