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Electrowetting-induced droplet jumping over topographically structured surfaces

Merdasi, A ; Sharif University of Technology | 2019

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  1. Type of Document: Article
  2. DOI: 10.1088/2053-1591/ab2955
  3. Publisher: Institute of Physics Publishing , 2019
  4. Abstract:
  5. We analyze the process of electrowetting-induced jumping of droplets away from a substrate with a geometric heterogeneity in the form of a cone and compare the results with those of a flat substrate in different wettabilities and hydrophobicities. Our results reveal that the droplet dynamics can be enhanced through applying a topographic heterogeneity. However, increasing the height of the cones does not always provide a better condition for the jumping and there is an optimum value for the height of the cones. The enhancement is due to the fact that more liquid flowing affects the pressure gradient within the droplet leading to a higher jumping velocity. It is shown that for the flat surface most of the kinetic energy can be converted into the oscillations of the droplet during retraction and would not contribute to the droplet jumping. The substrate contact angle has a significant effect on the jumping height of the droplet. As the contact angle increases, the maximum value of jumping height increases. Also, for the heterogeneous substrate, the surface energy decreases faster. By drawing a diagram, we specify regions that a droplet as a function of the substrate contact angle and the height of the cone at a constant Ohnesorge number is separated from the substrate. The results indicate that by reducing Ohnesorge number, the separation of the droplet occurs at smaller equilibrium contact angles. When the height of the cones becomes larger than the optimum value, the pinning of the droplet in the cone region gradually dominate and the energy barrier for the separation increases and a more hydrophobic substrate for the separation is required. The effect of Ohnesorge number on the optimum value has been discussed
  6. Keywords:
  7. Droplet ; Electrowetting ; Structured substrates ; Contact angle ; Hydrophobicity ; Kinetic energy ; Kinetics ; Separation ; Substrates ; Wetting ; Droplet dynamics ; Electro wetting ; Heterogeneous substrates ; Hydrophobic substrate ; Jumping ; Structured substrate ; Structured surfaces ; Substrate contact ; Drops ; Electrowetting
  8. Source: Materials Research Express ; Volume 6, Issue 8 , 2019 ; 20531591 (ISSN)
  9. URL: https://iopscience.iop.org/article/10.1088/2053-1591/ab2955