Marjolein Dijkstra (Utrecht University) From twist-bend and splay-bend nematic phases to baby skyrmions and polar blue phases in systems of colloidal bananas

Using simulations, we demonstrate that the exotic biaxial, twist-bend (TB), and splay-bend (SB) nematic phases of hard banana-shaped particles, which are metastable with respect to an overly stable smectic phase, can be stabilized by polydispersity in particle length or by curvature in particle shape [1]. In addition, we find that TB phases transition towards SB phases via a novel twist-splay-bend (TSB) phase with a director field precessing around an elliptical cone [2].

While the TB phase has been widely observed in thermotropic bent-core mesogens, the SB phase remains elusive to date. Here, we show the first observation of SB phases in colloidal systems of smoothly curved SU-8 rods [3] and in systems of polydisperse bent silica rods [4] thereby verifying that polydispersity and particle curvature can indeed stabilize SB phases.

Finally, we demonstrate that these achiral banana-shaped particles governed by purely excluded volume interactions can also stabilize polar blue phases comprising of chiral skyrmion filaments with a nematic orientational field that are entangled with a 3D network of topological defect lines. In addition, these systems can stabilize quasi-2D layers of isolated skyrmions and high-density lattices of skyrmions under confinement.  

References

[1] M. Chiappini, T. Drwenski, R. van Roij, and M. Dijkstra, Phys. Rev. Lett. 123, 068001 (2019)

[2] M. Chiappini and M. Dijkstra, Nature Communications 12, 2157 (2021).

[3] C. Fernández-Rico, M. Chiappini, T. Yanagishima, H. de Sousa, D.G.A.L. Aarts, M. Dijkstra, and R.P.A. Dullens, Science 369, 950 (2020).

[4] R. Kotni, A. Grau-Carbonell, M. Chiappini, M. Dijkstra, A. van Blaaderen, Nature Communications 13, 7264 (2022).