Atypical wetting behavior of binary mixtures of partial and total wetting liquids: leak-out phenomena

The wetting behavior of simple binary mixtures containing both partial and total wetting liquids is investigated on the commonly used substrates. The variation of the contact angle (CA) of the binary liquid with the composition (xP) on different solid surfaces is obtained. It is interesting to find that for the droplet which can exhibit self-propulsion, four different regimes can be identified in the CA-xP plot. Among them, the plateau regime where the CA remains a constant value in a certain concentration range is most intriguing. In contrast, for the droplet which cannot self-propel, the CA grows monotonously with the concentration of the partial wetting liquid. The leak-out phenomenon in which the droplet is surrounded by the precursor film is believed to occur in the plateau regime, and it is examined by observing the encounter of two miscible droplets by optical micro-scopy. The apparently noncontact repulsion between the moving and static droplets reveals the presence of the precursor film leaked out from the self-propelled droplet.

Automated summary

The wetting behavior of binary mixtures containing both partial and total wetting liquids on substrates is studied. The contact angle of the binary liquid on different solid surfaces varies with its composition. Four different regimes are identified in the contact angle-composition plot for self-propelled droplets, while the contact angle monotonously increases with the concentration of the partial wetting liquid for non self-propelled droplets. The leak-out phenomenon in the plateau regime, where the droplet is surrounded by the precursor film, is examined by observing the encounter of two miscible droplets using optical microscopy.