Seminar über aktuelle Fragen zur Dynamik komplexer Fluide: Part 1: Electrically controlled evolution of breath figures, Part 2: Electrowetting on soft substrates

Seminar über aktuelle Fragen zur Dynamik komplexer Fluide

  • Date: Nov 9, 2018
  • Time: 10:15 AM - 11:15 AM (Local Time Germany)
  • Speaker: Dr. Ranabir Dey
  • Twente University, Enschede, The Netherlands
  • Location: Max-Planck-Institut für Dynamik und Selbstorganisation (MPIDS)
  • Room: SR 0.77
  • Host: DCF
  • Contact:
Understanding condensation of vapor on functionalized surfaces is scientifically challenging and simultaneously technologically relevant (heat transfer, fog harvesting, desalination systems etc.). We show that an electric field in an electrowetting (EW) configuration with structured electrodes can be used to actively control the pattern of drops condensing onto otherwise at hydrophobic surfaces (breath figures). EW strikingly modifies the breath figure pattern by aligning drops and by inducing coalescence. Numerical calculations reveal that the drop alignment and enhanced coalescence are governed by the drop-size-dependent evolution of the electrostatic energy landscape that is imposed by the electrode pattern and the applied voltage. Such EW-controlled migration and coalescence of condensate drops significantly alter the statistical characteristics of the ensemble of droplets. Specifically, the evolution of the drop size distribution displays self-similar characteristics that significantly deviate from classical breath figures on homogeneous surfaces once the electrically induced coalescence cascades set in beyond a certain critical drop size. Finally, we also show that ac-EW with structured electrodes modifies the final gravity-driven shedding of drops. The unique droplet pattern evolution under EW, coupled with the enhanced shedding, can eventually lead to significantly enhanced net heat transfer.

The interconnection between the deformation of a soft substrate and the electrically induced wetting of a sessile drop on the same remains far from being well understood. Here, we explain the electrically modulated wetting behaviour of drops on soft dielectric films of varying elasticities. We also provide a simplistic description of the displacement profiles for the deformation of a soft dielectric film surface, due to the interfacial electro-elastocapillary interaction triggered by the electrowetted sessile droplet. We also discuss here the behaviour of soft super hydrophobic striped substrates during droplet electrowetting. We use a combination of confocal microscopy and semi-analytical methods to describe the deformation of the flexible structures during droplet (electro-) wetting.
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