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Free-standing three-dimensional topological structures in geometrically confined chiral nematic liquid crystals: fundamentals and applications

Periodic Reporting for period 1 - TOPOZOO (Free-standing three-dimensional topological structures in geometrically confined chiral nematic liquid crystals: fundamentals and applications)

Reporting period: 2016-01-01 to 2017-12-31

The project aim at exploiting both the intrinsic robustness and wide diversity of topological structures that naturally appear in soft condensed matter systems such as liquid crystals in order to fabricate advanced materials, possibly reconfigurable, towards emerging photonics applications such as high-dimensional data storage and topological shaping of light at small scale. One of the foreseen application potential concerns write/read of high-dimensional memories, where topological diversity would allow large and robust information content in a small volume, a liquid crystal voxel. Our ambition is to establish the related experimental foundations, to develop techniques for on-demand reconfiguration the generated topological structures, and to bring proof-of-principle of a few applications that we foresee. To this aim, the project will focus on situations where the chirality of soft matter meets topology, by the use of chiral liquid crystals under the action of external fields tailoring their topological features. At the end of the project, the main conclusions are the elaboration and characterization of various chiral liquid crystals mixtures leading to novel static and dynamical structural behavior such as reconfigurable metastable defects structures in micro-droplets and microscopic continuously rotating soft engines powered by light in thin films.
After one year, we have developed various chiral liquid crystal mixtures whose internal chiral properties are optically addressable. Structural and optical characterization has been performed. The response to optical stimuli has been studied and has revealed the appearance of structures involving various topologies and symmetries. The dynamical response of the system has been found to exhibit a robust and unexpected behavior, which has been fully characterized: it corresponds to the original realization of a continuously rotating soft engine driven by light under fixed irradiation conditions. In practice, we experimentally studied the conditions of formation of various kinds of localized topological patterns in chiral nematic films with perpendicular boundary conditions, which behave as elastic quasi-particles sustained by light. We unraveled their stability depending on the composition of liquid crystal mixture (nature and relative concentrations of passive and/or active chiral dopants added to a passive nonchiral nematic liquid crystal host) and the irradiation conditions (beam size, beam power, polarization state of light, duration of excitation, etc.). We also revealed the emergence of asymmetric and dynamical patterns encoded at the molecular level. From an interpretation point of view, we proposed a simplified physico-chemical model for the discovered continuous, regular and unidirectional rotation of a localized chiral liquid crystal structure, which is based on the interplay between the twist of the supramolecular structure and the diffusion of the chiral molecular nano-motors through an inhomogeneous and chiral fluidic environment. We also demonstrated that the work produced by the revolving supramolecular structure can be harnessed into the rotation of a cargo.
The specific developed chiral liquid crystal mixtures represent a substantial progress in the sense that they exhibit a novel photo-induced orientational dynamics that is driven by the chirality of matter. The obtained results bring new knowledge in the field of physico-chemistry of soft condensed matter, have an impact in the physics of biological systems, and contribute to the development of molecular machines that are capable of transforming light into work continuously. We think that our work thus represents an important step in developing advanced mechanical motors, nano- and micro-robots, and synthetic muscles.
Snapshot of a 50µm-diameter rotating chiral supramolecular structure observed under the microscope b
Chiral nematic liquid crystal micro-droplet exhibiting complex topological structure