Chirality-induced helical self-propulsion of chiral liquid crystal droplets, by Takaki Yamamoto

202 Physics Bldg.

Artificial microswimmers have been intensively studied to understand the mechanism of the locomotion and collective behaviors of cells and microorganisms. Among them, most of the artificial microswimmers are designed to swim along the straight path. However, in biological systems, chiral dynamics such as circular and helical motions are quite common because of the chirality of their bodies. To understand the role of the chirality in the dynamics of microswimmers, we designed an experimental system [1] and the phenomenological model [2] of a self-propelled chiral liquid crystal (CLC) droplet dispersed in a surfactant solution which swims in a helical path driven by the Marangoni flow. In [1] and [2], we speculated that CLC droplets swim in helical paths due to the chiral coupling between translational motion induced by the Marangoni flow and rotational motion via the chirality of helical director fields in the CLC droplets. However, such a chiral coupling has not been verified by experimentally observing hydrodynamic flow which the CLC droplets produce. Thus, the mechanism of the helical motion of CLC droplets remains to be elucidated from the viewpoint of hydrodynamics.

In the experimental system of swimming CLC droplets, we recently found that, under a condition, the droplets do not exhibit translational motion but only rotational motion, driven by the concentration gradient of surfactant around the droplet, which occurs due to the effect of gravity [3]. In this study, to obtain a clue to the mechanism of the helical motion of CLC droplets from the viewpoint of hydrodynamics, we investigated the hydrodynamic flow around the rotating CLC droplets. Consequently, we revealed that a nontrivial rotational hydrodynamic flow appears around the rotating CLC droplets. While the mechanism of the rotation and the generation of the hydrodynamic flow is not fully understood, we would like to discuss these experimental results and the roles of chirality in active matter.

[1] T. Yamamoto and M. Sano, Soft Matter, 13, 3328 (2017).
[2] T. Yamamoto and M. Sano, Phys. Rev. E., 97, 012607 (2018).
[3] T. Yamamoto and M. Sano, under review.

Yakaki Yamamoto, visiting post-doc at Syracuse University

Host: Prof. Lisa Manning / Contact: Yudaisy Salomón Sargentón, 315-443-5960