Topological turbulence in confined chiral nematic fields

Active matter is today one of the fore-front topics in soft matter physics research, and also more generally in general natural sciences. Active agents –both biological and engineered- are at the core of active matter, exhibiting locomotion, rotation, and general motility at the expanse of using external energy provided by the environment, either via chemical energy or external fields. And being able to design, control and manipulate the activity of active agents (micro-swimmers) is at the core of modern active matter development. In this experimental and modelling project, we want to develop and explore a novel route for manipulating active agents by exposing them to anisotropic environment of (passive) complex nematic fluids, with special focus on topological turbulence, and actually more generally develop a novel type of engineered anisotropic active-passive matter. Specifically, we aim to use phoretic active colloids in the form of Janus particles (spheres, rods,…) that will be electrophoretically driven by external electric field, distinctly within an environment of the complex nematic fluid, creating novel active materials. We will start by developing single Janus particles in the nematic fluid driven by the electric field, continue with pair interaction and then expand to the collective motion of electrically propelled Janus particles in different confined nematic geometries. In parallel to experiments, theoretical-modelling framework will be developed that will be able to account for motile active particles within the passive nematic environment at the mesoscopic level. The distinct novelty of the work will be that the general motility of the active Janus particles will be controlled and strongly affected by the anisotropy and general structure of the surrounding nematic fluid, which is known to create long-range soft elastic interactions or potential on colloidal inclusion. We will design and use these nematic interactions –that are known to be susceptible to geometry, topology, chirality and material flow- to control and manipulate the active agents at the individual and collective level. The confining geometries for the designed anisotropic active-passive matter will include layers, droplets, cavities, but can be also expanded to arbitrary 3D printed patterns, such as fractals. The project will be implemented in the Soft matter group at the Josef Stefan Institute and Faculty of Mathematics and Physics at the University of Ljubljana, which is reknown for highest scientific standards [PRL 2020, 2x PRX 2019, Nature Comm 2019, Science Adv 2018, Nature Phys 2017, 2x Nature Comm 2017. More generally, this proposal is aimed at developing a novel active-passive responsive matter, that is more engineering and not biologically based, which in mid-turn and beyond this project can allow for rather direct transfer to various optical and photonic applications based on active matter and active matter phenomena, such as micro-motile light media, which today are non-existent. Finally, understanding active agents within anisotropic environment will offer a novel insight into various bio-relevant processes, opening routes for developments and applications in biosciences and medicine, including biophysics, of clear benefit to the society as a whole.