Shaping colloidal bananas to reveal biaxial, splay-bend nematic, and smectic phases
By: Prof. Roel Dullens
From: Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Park Road, OX1 3QZ, Oxford, United Kingdom
At: Online - Zoom (https://videoconf-colibri.zoom.us/j/87223926284)
[2020-10-22]
Colloidal dispersions of rod-like particles are widely accepted as convenient model systemsto study the phase behavior of liquid-crystal forming systems, commonly found in LCDs. Thisis due to the fact that colloidal rods exhibit analogous phase behavior to that of elongatedmolecules, while they can be directly observed by optical microscopy. Recently, there hasbeen a surge of interest in the liquid crystalline behaviour of so-called bent-core, or banana-shaped, molecules. This is due to their ability to form exotic biaxial nematic phases such asthe twist-bend and splay-bend nematic phase, which may be of particular interest inherent totheir fast switching response in LCDs.
Here, we develop model “banana-shaped†colloidal particles with tunable dimensions andcurvature, whose structure and dynamics are accessible at the particle level. By heatinginitially straight rods made of SU-8 photoresist, we induce a controllable shape deformationthat causes the rods to buckle into banana-shaped particles. We elucidate the phasebehavior of differently curved colloidal bananas using confocal microscopy. Although highlycurved bananas only form isotropic phases, less curved bananas exhibit very rich phasebehavior, including biaxial nematic phases, polar and antipolar smectic-like phases, andeven the long-predicted, elusive splay-bend nematic phase.
