Tadej Emeršič
University of Luxembourg
Acoustically Energized Dynamics of Liquid Crystals
The optical properties of liquid crystals are fundamental to display, diagnostic, and sensing technologies, typically controlled using electric fields. In this seminar, I will demonstrate how acoustic fields can serve as an alternative tool for manipulating liquid crystals, offering new ways to control their structure and dynamics.
My talk will consist of two parts. In the first part, I will show the effects of acoustic fields on the molecular orientation and optical response of thermotropic nematic liquid crystals confined in microfluidic channels. We will see how acoustic forces alone, as well as in combination with fluid flow, give rise to previously unknown stable nematic morphologies that do not exist at equilibrium. These new structures are mapped onto a state diagram as a function of flow strength and acoustic field intensity. In the second part of my talk, I will shift the focus to lyotropic chromonic liquid crystals (LCLCs), which exhibit a fundamentally different response to acoustics compared to thermotropic liquid crystals. A key advantage of LCLCs is their ability to form a biphasic state, where nematic droplets in a shape of tactoids are surrounded by an isotropic phase. While their equilibrium properties are well understood, a major open question is how they behave under out-of-equilibrium conditions. I will demonstrate how acoustic activation induces diverse responses in nematic tactoids, including stretching, bending, splitting, merging, spontaneous rotation, and locomotion. Furthermore, I will show how carefully designed acoustic pulses can drive topological transformations, converting a tactoid into a long-lived toroidal droplet with elevated elastic energy. Our findings provide new insights into the behavior of acoustically energized liquid crystals in both the pure nematic and biphasic states, opening new avenues for the controlled manipulation of nematic fluids and droplets.
