Acoustically powered active liquid crystals*

Active nematics are materials composed of mobile, elongated particles that can transform energy from the environment into a mechanical motion. Current experimental realizations of the active nematics are of biological origin and include cell layers, suspensions of elongated bacteria in liquid crystal, and combinations of bio-filaments with molecular motors. In this talk, we report the discovery of a fully synthetic active nematic system comprised of a lyotropic chromonic liquid crystal externally energized by ultrasonic waves. This synthetic active liquid crystal is free from biological degradation and variability, exhibits stable material properties, and enables a precise and rapid control of activity over an extended range. The energy of the acoustic field is converted into microscopic extensile stresses that disrupt long-range nematic order and give rise to an undulation instability, proliferation of topological defects, and the development of turbulent-like stress. We also reveal the emergence of unconventional free-standing persistent vortices in the nematic director field at high activity levels. Development of active nematic systems with stable and well-controlled material properties and turnable topological dynamics is crucial for both investigating the complex phenomenology of active nematics and unlocking their potential practical applications.