Marangoni Flow of Films Composed of Ag and Au Nanostructures
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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. After mechanical agitation, Ag nanoparticles embedded in a film are driven from the organic-aqueous interface. A reddish-brown film, verified by transmission electron microscopy to contain uniformly dispersed Ag nanoparticles, is observed to spontaneously climb the interior surface of a glass vial. This phenomenon is recorded by a video recorder, and a measurement of the distance traveled by the film front versus time is extracted. Surface tension gradients due to the surfactant concentration, temperature, and electrostatic potential across immiscible fluids are known to drive interface motion; this well-known phenomenon is termed Marangoni flow. 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 Marangoni flow is measure in the range about 0.01 to about 1 s-1 from a fit to the relative film front distance traveled versus time data. Such flow suggests that purposeful creation of interfacial tension gradients may aid in the transfer of 2-and 3-dimensional assemblies composed of various types of nanostructures to solid surfaces. With this goal, preliminary results will also be presented for film flow containing Au nanoparticles and nanorods.