The self-motion of liquid droplets on solid surfaces has attracted broadening attention in last few years. Self-propulsion of a liquid occurs when a surface tension gradient causes the liquid to flow. The difference in surface tension on either side of a liquid droplet produces a directional transport of the droplet through a second liquid or over a solid substrate. This phenomenon is known as the Marangoni effect. A classic example of Marangoni effect is wine tears on the wall of a glass. Due to different evaporation rates of alcohol and water, a gradient of surface tension is created on the glass wall which causes wine moves upward. In artificial systems, a similar effect can be achieved for a droplet sitting on a homogeneous surface if the droplet contains a species which adsorbs/react onto the surface. Droplet motion is then driven by the irreversible modification of the surface free energy which affects the interfacial energy on either side of the droplet —a so-called “chemical” Marangoni effect.<br/><br/>In this study, we present water born fluoro-silane mixtures showing a self-propulsion behavior on glass. The movement can surmount the gravity force and push the droplet uphill (Figure.1). The droplet moves on the glass surface and changes the glass surface energy instantly by chemically bonding a silane based nano-layer onto the surface. The droplet velocity changes with the concentration of the fluoro-silanes composition, the pH, the critic micelle concentrations (CMC) as well as the surface tension of the solution organo-silane solution. A water-based droplet motion system could be an exceptional model of the process of chemo–mechanical energy conversion with variety of applications in microfluidics and delivery systems. Therefore, the Marangoni effect will be discussed in term of binding mechanism to the glass substrate.

Self-propelled water based organo-silanes on glass

256th National Meeting (2018)

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