Flow-Induced Structures in Lyotropic Chromonic Liquid Crystals

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

Non-technical Description: Liquid crystals are highly sensitive to external influences, including electric fields, magnetic fields, or mechanical stresses. The tunable properties of liquid crystals that result from this sensitivity have enabled revolutions in display technology and optical sensors. Over the past decade, a new class of liquid crystals has gained increasing attention, so-called lyotropic chromonic liquid crystals. These are water-based bio-compatible materials that therefore offer novel opportunities in biosensing and microfluidic applications. To fully harness their vastly unexplored potential, it needs to be understood how these liquid crystals respond to flow. Such an understanding, however, is currently lacking. Remarkably, flow can induce large-scale ordered structures. This project explores how these structures spontaneously emerge and how they can be controlled by tuning the flow and material properties. Integrated into the research is a comprehensive outreach plan that includes lectures for high-school students and teachers, research internships for undergraduates, and laboratory workshops for women high-school students. The project will present live science and art performances that will integrate visual, audio and dance elements to engage a broad audience in genuine scientific dialogue. Technical Description: The research probes the conditions under which self-organized structuring can be achieved in flowing nematic lyotropic chromonic liquid crystal solutions. Using a combination of advanced microscopy techniques, stability analyses, and numerical simulations, the project addresses how instabilities of the director field can trigger flow structuring and how these unstable configurations relax into macroscopic domains. In particular, two steady-state flow-induced textures are investigated: a periodic stripe pattern that occurs for planar surface anchoring conditions when the alignment is parallel to the flow direction and a band texture that emerges for a planar alignment perpendicular to the flow direction. Excitingly, the periodic stripe pattern is chiral: its mirror image cannot be superimposed on the original. This is remarkable, as the liquid crystalline units themselves are achiral, and achiral nematic liquids are generally expected to form achiral structures. The project aims to reveal the mechanism for the mirror symmetry breaking. By establishing the role of the surface anchoring conditions, the flow, and the material properties for the selection of characteristic length scales and macroscopic textures, the work will open the path to exploit flow as a simple and non-invasive pathway to intricate ordered structuring of complex fluids. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.