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Bouncing under AC electric field and Coulombic attraction suggest charge transfer between biopolymer microcapsules

Nishant Nair1, Clément de Loubens1,*, Romain Lhermerout2, Benjamin Cross2, and Hugues Bodiguel1

  • *Contact author: clement.de-loubens@univ-grenoble-alpes.fr
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Phys. Rev. Fluids 11, 073701 – Published 13 July, 2026

DOI: https://doi.org/10.1103/tf2x-ktb1

Abstract

We report a striking bouncing phenomenon exhibited by pairs of ≃100µm biopolymer microcapsules subjected to a low-frequency AC electric field. The bouncing occurs at twice the applied frequency, suggesting that its origin lies in polarization-induced charge transfer during capsule-capsule contact. This interpretation is supported by the observation that, once the field is removed, the capsules spontaneously attract each other with a force consistent with Coulombic interaction between oppositely charged objects. A minimal toy model incorporating electrophoretic driving and Coulombic attraction captures semiquantitatively the observed dynamics. These findings provide direct experimental evidence of charge transfer in microcapsule suspensions and offer insights into the anomalous gel-like properties of these non-Brownian systems at low volume fractions.

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Phys. Rev. Fluids 11, 073701– Published 13 July, 2026
  • Received 19 September 2025
  • Accepted 23 June 2026
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