Vapour-mediated sensing and motility in two-component droplets.

• Autores: N. J. Cira, M. Prakash, A. Benusiglio
• Localización: Nature: International weekly journal of science, ISSN 0028-0836, Vol. 519, Nº 7544, 2015, págs. 446-450
• Idioma: inglés
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• Resumen

  • Controlling the wetting behaviour of liquids on surfaces is important for a variety of industrial applications such as water-repellent coatings 1 and lubrication 2. Liquid behaviour on a surface can range from complete spreading, as in the 'tears of wine' effect 3,4, to minimal wetting as observed on a superhydrophobic lotus leaf 5. Controlling droplet movement is important in microfluidic liquid handling 6, on self-cleaning surfaces 7 and in heat transfer 8. Droplet motion can be achieved by gradients of surface energy 9-13. However, existing techniques require either a large gradient or a carefully prepared surface 9 to overcome the effects of contact line pinning, which usually limit droplet motion 14. Here we show that two-component droplets of well-chosen miscible liquids such as propylene glycol and water deposited on clean glass are not subject to pinning and cause the motion of neighbouring droplets over a distance. Unlike the canonical predictions for these liquids on a high-energy surface, these droplets do not spread completely but exhibit an apparent contact angle. We demonstrate experimentally and analytically that these droplets are stabilized by evaporation-induced surface tension gradients and that they move in response to the vapour emitted by neighbouring droplets. Our fundamental understanding of this robust system enabled us to construct a wide variety of autonomous fluidic machines out of everyday materials.