Abstract
Chirality, ubiquitous in complex biological systems, can be controlled and quantified in synthetic materials such as cholesteric liquid crystal (CLC) systems. In this work, we study spherical shells of CLC under weak anchoring conditions. We induce anchoring transitions at the inner and outer boundaries using two independent methods: by changing the surfactant concentration or by raising the temperature close to the clearing point. The shell confinement leads to new states and associated surface structures: a state where large stripes on the shell can be filled with smaller, perpendicular substripes, and a focal conic domain (FCD) state, where thin stripes wrap into at least two, topologically required, double spirals. Focusing on the latter state, we use a Landau–de Gennes model of the CLC to simulate its detailed configurations as a function of anchoring strength. By abruptly changing the topological constraints on the shell, we are able to study the interconversion between director defects and pitch defects, a phenomenon usually restricted by the complexity of the cholesteric phase. This work extends the knowledge of cholesteric patterns, structures that not only have potential for use as intricate, self-assembly blueprints but are also pervasive in biological systems.
3 More- Received 5 July 2017
DOI:https://doi.org/10.1103/PhysRevX.7.041029
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Liquid crystals are widely known for their use in flat-panel electronic displays found in many gadgets, from digital watches to large televisions. These liquid-crystal displays (LCDs) make use of the unique way rodlike molecules in the liquid crystal interact with light and align with one another. Altering their organization can modify both of these properties, facilitating their use for other technologies. Here, we develop and exploit a platform that lets us produce and transform a wealth of intricate structures including both new and previously reported states, making the dynamic study of transitions between these patterns accessible for the first time.
We focus on cholesteric liquid crystals, a phase where the molecules are arranged in a helical fashion. We confine the cholesteric within onionlike spherical shells, sandwiched between two layers of water, produced using microfluidics. In this arrangement, topological defects—areas where the cholesteric order is ill defined—are required. Using two independent mechanisms, we precisely manipulate both the thickness of the shells and the orientation of the cholesteric molecules at the interfaces, therefore altering the topology of the system. This results in a series of complex states, where stripes form organized, hierarchical patterns on the shell surfaces. By shining light on this structure, we can study transitions between these patterns.
Our methods can be used in systems with differing topologies, such as droplets or tori, to further investigate the nature of cholesteric defects. Such a comprehensive study could also lay the groundwork for using topological defects in liquid crystals to design nanostructures.