Double symmetry breaking in filamentous colloidal tactoids

Abstract

Understanding the dynamics of liquid crystalline tactoids under external forces is of great importance due to their potential applications in optics, medical devices, and displays. However, only recently have tactoids started to be studied systematically under external forces, particularly under extensional flow. Here, we subject tactoids to a shear flow field and study their deformation dynamics under varying conditions of shear and time scales. Using amyloids and nanocellulose to form tactoids from model filamentous colloids with opposite sequences of chirality amplification (left-handed mesoscopic → right-handed cholesteric for amyloids; right-handed mesoscopic → left-handed cholesteric for nanocellulose), we show a complex deformation mechanism in their shape and internal structure under shear flow. When tactoids deform perpendicularly to their long axis, a double symmetry breaking occurs in both their contour shape, with the emergence of a kink, and the orientation of their nematic field. We further show that the mesoscopic chirality of the building blocks directs the position of the kink, with the macroscopic tactoid asymmetry being mirrored when inverting the mesoscopic chirality of the constitutive filamentous colloids, e.g., from the left-handed amyloids to the right-handed nanocellulose.