Exotic liquids crystals from colloidal banana self-assembly

The curvature of elongated microscopic building blocks, such as proteins or bacteria, plays an essential role in their self-assembly and functional properties. In the biological world, for instance, cell division relies on the ability of “banana-shaped” BAR proteins to generate curvature in cell membrane. At the molecular scale, banana-shaped molecules exhibit a range of fascinating liquid crystalline (LC) phases with supramolecular chirality and polarity, which play a role in the development of faster sensors and LC displays [1]. Experimental studies of how and why these phases form at the molecular level have remained challenging until very recently, as the time and length scales involved in these systems are extremely fast and small.

 

In this talk, I will present our recently developed system of colloidal banana-shaped particles, which has allowed the direct study of the structure and dynamics of exotic colloidal LC phases using confocal microscopy [2].  By carefully tuning the shape of the particles [2,3], we studied the effect of curvature in LC assembly, and elucidated the full phase behaviour of the particles. We found that while highly curved bananas only form isotropic phases,  less curved bananas exhibit a very rich phase behaviour including the elusive splay-bend nematic phase, whose very existence is finally experimentally established more than 40 years after its theoretical prediction. Finally, I will also discuss the effect of polydispersity in these systems [4], and show how this is a key ingredient for the formation of hierarchical liquid crystal phases, known as the colloidal vortices.

[1]   A. Jakli, et al., Rev. Mod. Phys., 90, 45004 (2018).

[2]   C. Fernández-Rico, et. al, Science, 369, 950-955 (2020).

[3]   C. Fernández-Rico, et. al, Adv. Mat., 31, 1807514 (2019).

[4]   C. Fernández-Rico, et. al, PNAS, 118, 33 (2021).