Prof. Dr. Jordi Ignés-Mullol: Emerging phenomena and symmetry breaking at the interface between an active and a passive liquid crystal

I will present experimental studies of a biomimetic active nematic model system, which forms when filamentous tubulin microtubules cross-linked by kinesin molecular motors are condensed at the interface between the aqueous medium and an oil interface. Consumption of ATP leads to the emergence of long-range orientational order of the filaments and to self-sustained flows driven by the unbinding of topological defects. Despite the apparent chaotic dynamics, the system features intrinsic length and time scales that determine its adaptation to different interventions. When the oil is a thermotropic liquid crystal, we can use its viscous anisotropy to control active nematic flows using the passive phase as a handle, taking advantage of the hydrodynamic coupling between the interfaced fluids. I will show how, using a smectic-A thermotropic liquid crystal, we can change the geometry of the active flows, transform them from chaotic to pseudo-laminar, and promote the emergence of active spatiotemporal patterns. Throughout these processes, the intrinsic length and time scale of the active nematic manifest in different but crucial ways.