Tactoids Large and Small: Impact of an Electric Field

by Prof. Paul Van Der Schoot

Department of Applied Physics and Science Education, Eindhoven University of Technology, The Netherlands
at Biological and soft-matter physics

Thu, 29 Feb 2024, 12:10
ZOOM only - Meeting ID: 830 2741 1678, Passcode: 345123 (link attached)


Tactoids are spindle-shaped droplets of a nematic phase in co-existence with an isotropic host phase, found in fluid dispersions of rod-like colloids. Recent experiments on aqueous dispersions of chitin nanocrystals show that an electric AC field can massively stretch tactoids albeit only if sufficiently they are large. [1] See Figure 1. We present a thermodynamic model for tactoids, where the degree of curvature of the bipolar director field, as well as the aspect ratio of the droplets, are free to adjust to optimize the sum of the elastic, surface, and Coulomb energies. Contrary to observation, we find that in equilibrium tactoids do not elongate hugely in response to an electric field but rather make the director field more uniform. [2] These findings are supported by particle-based Monte Carlo simulations. [3] Invoking a dynamical model based on the relaxation in a free energy landscape we do find reasonable agreement with available experimental data if (i) the director field is bipolar in the absence of the field and (ii) its anchoring to the interface responds more slowly than the overall droplet shape. In that case, we find very long-lived, highly elongated droplets that eventually relax back to more modest aspect ratios. [4]

[1] L. Metselaar et al. Phys. Rev. E 2017, 96, 022706.
[2] A. Safdari, R. Zandi and P. van der Schoot, Phys. Rev. E 2021, 103, 062703.
[3] A. Kuhnhold and P. van der Schoot, J. Chem. Phys. 2022, 156, 104501.
[4] A. Safdari, R. Zandi and P. van der Schoot (submitted) 2023. ArXiv:2401.09642.

Join Zoom Meeting

Meeting ID: 830 2741 1678
Passcode: 345123

Created on 28-12-2023 by Granek, Rony (rgranek)
Updaded on 28-02-2024 by Granek, Rony (rgranek)