Elongation of Tactoids in the presence of an electric field

Tactoids are spindle-shaped droplets of a nematic phase suspended in the co-existing isotropic phase. They are found in dispersions of a wide variety of elongated colloidal particles, including actin, fd virus, carbon nanotubes, vanadium peroxide, and chitin nanocrystals. Recent experiments on tactoids of chitin nanocrystals dispersed in water show that electrical fields can strongly elongate tactoids, but only if the tactoids have a sufficiently large volume. We explain this by extending the Oseen-Frank elastic model of Kaznacheev et al. [1] and Prinsen et al. [2] to partially bipolar tactoids and evaluate the level of elongation of the tactoids as a function of the surface tension, elastic constants, volume, and electric field strength. By invoking a free-energy-based relaxational dynamics, we also describe the time evolution after switching on the electric field, confirming that, counterintuitively, large tactoids take more time to elongate to their equilibrium value in an electric field than small ones do.
[1] A. Kaznacheev et al., The Nature of prolate shape of tactoids in lyotropic inorganic liquid Crystals, JETP 95, (2002), 57.
[2] Peter Prinsen et al, 2003, Shape and director-field transformation of tactoids