Liquid triboelectrification by sliding droplets

M1/3A internship proposal 2021-2022

Soft Matter Science and Engineering Laboratory, (SIMM)

Address: ESPCI, 10 Rue Vauquelin 75005 Paris

Chair: Etienne Barthel

Supervisors: Jean COMTET (jean.comtet (arobase) espci.fr) https://blog.espci.fr/jcomtet/

Scientific description :

The universally-known triboelectric effect results in the charging of solid surfaces following mechanical contact. This ubiquitous phenomenon has macroscopic consequences, both mundane and fundamental (tribo-charging leads to dust aggregation, which might be responsible for initial planetary formation [1]). Very recently, triboelectricity has also seen a surge of interest in the context of the development of novel energy harvesting devices with exceptional performances [2]. However, the origin of this surface charging remains fundamentally misunderstood, being indistinctively attributed to the transfer of minute quantities of electrons, ions or matter between surfaces [3].

Tribocharging of a hydrophobic solid surface upon sliding of a liquid drop.Tribocharging of a hydrophobic solid surface upon sliding of a liquid drop.

In this internship, we will focus on the particularly peculiar case of liquid triboelectrification in which the sliding motion of water drops on hydrophobic surfaces leads to a macroscopic separation of charges, with the deposition of permanent negative charges onto the solid surface and to the positive charging of the drop [2], [4], [5] (See Figure). These observations suggest that negative surface charges developing at the solid/liquid interface in the drop get trapped at the solid/air interface during forced droplet dewetting [6], [7]. This raises a number of questions, related to (i) the interplay between dynamic effects occurring at the moving contact line with charge dynamics at the solid/liquid interface and (ii) the physicochemical nature of the deposited charges.

The intern will first perform macroscopic charge measurements on sliding droplets of controlled pH and ionic strength. He will then couple these measurements with techniques based on ellipsometry, to probe and reveal the presence of a molecular liquid film of solvated charges at the rear of the sliding drop. These measurements will help us gain novel fundamental physical insights on the underlying mechanisms at play during the peculiar liquid triboelectrification.

Keywords : Triboelectricity, Drops, Soft Matter, Surface Charges
Techniques/methods in use : Electrical measurements, Fast Camera, Ellipsometry
Applicant skills : Soft Matter, Hydrodynamics, Taste for Experimental Work

[1] T. Steinpilz et al., “Electrical charging overcomes the bouncing barrier in planet formation,” Nature Physics, vol. 16, no. 2, pp. 225–229, 2020. [2] W. Xu et al., “A droplet-based electricity generator with high instantaneous power density,” Nature, vol. 578, no. 7795, pp. 392–396, 2020. [3] D. J. Lacks and T. Shinbrot, “Long-standing and unresolved issues in triboelectric charging,” Nature Review Chemistry, 2019. [4] Q. Sun et al., “Surface charge printing for programmed droplet transport,” Nat. Mater., 2019. [5] N. Miljkovic, D. J. Preston, R. Enright, and E. N. Wang, “Electrostatic charging of jumping droplets,” Nature Communication, vol. 4, pp. 1–9, 2013. [6] A. Z. Stetten, D. S. Golovko, S. A. L. Weber, and H. J. Butt, “Slide electrification: Charging of surfaces by moving water drops,” Soft Matter, vol. 15, no. 43, pp. 8667–8679, 2019. [7] M. D. Sosa et al., “Liquid-polymer triboelectricity: Chemical mechanisms in the contact electrification process,” Soft Matter, vol. 16, no. 30, pp. 7040–7051, 2020.

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Practical information

Sciences et Ingénierie de la Matière Molle

Soft Matter Enginering and Science Laboratory - UMR 7615

10 rue Vauquelin
75231 PARIS CEDEX 05
FRANCE

  • Chair : E. Barthel
  • Vice Chairs : J.B. d’Espinose & G. Ducouret
  • Administration : F. Decuq, M.-T. Mendy & M. Hirano-Courcot
  • Communication : A. Hakopian & M. Ciccotti
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