Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D13: Liquid Crystal Defect Cores: Order Parameters, Regularization, and StabilizationInvited
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Sponsoring Units: DSOFT Chair: Daniel Beller, Johns Hopkins University; Jorge Vinals, University of Minnesota Room: Room 238 |
Monday, March 6, 2023 3:00PM - 3:36PM |
D13.00001: Molecular Self-Assembly in Topological Defects of Liquid Crystals Invited Speaker: Nicholas Abbott Topological defects in liquid crystals (LCs) have been used to organize colloidal dispersions and template polymerizations, leading to a range of elastomers and gels with complex mechanical and optical properties. However, little is understood about molecular-level assembly processes within the cores of topological defects. This presentation will describe how nanoscopic environments defined by LC topological defects can selectively trigger processes of molecular self-assembly. By using fluorescence microscopy, cryogenic transmission electron microscopy and super-resolution optical microscopy, key signatures of molecular self-assembly of amphiphilic and polymeric molecules in topological defects are observed - including cooperativity, reversibility, and controlled growth of the molecular assemblies. By using polymerizable amphiphiles, we demonstrate preservation of molecular assemblies templated by defects, thus providing insights into the nanoscopic structure of the cores of topological defects. We also find that molecular self-assembly can select for and stabilize specific types of defects, leading to soft matter that is exquisitely responsive to the presence of particular classes of synthetic and biological lipids. |
Monday, March 6, 2023 3:36PM - 4:12PM |
D13.00002: Reconfigurable assembly of topological defects in smectic liquid crystals confined at 3D-printed curved surfaces Invited Speaker: Mohamed Amine Gharbi The fabrication of assembled structures of topological defects in liquid crystals has attracted a lot of attention during the last decade. This interest stems from the potential of these defects in a wide range of technological applications, including in the field of nanotechnology. Different techniques can be employed to create large areas of engineered defects in liquid crystals. Some of them include the use of mechanical shearing, chemical surface treatment, external fields, or geometric confinement. The technique of 3D printing has recently emerged as a new powerful method to fabricate novel patterning topographies that other microfabrication techniques cannot make. In particular, the creation of confining substrates with curved topographies. In this work, we show the advantages of using 3D-printed curved surfaces to confine smectic liquid crystals and engineer new structures of topological defects [1,2]. Additionally, we demonstrate the ability of these defects to act as a scaffold for assembling nanomaterials [2]. We also discuss the limitations of this approach and explain the relationship between the spontaneous assembly of defects and the concentration of dispersed nanomaterials. |
Monday, March 6, 2023 4:12PM - 4:48PM |
D13.00003: Portraits of Topological Defects in Static, Driven, and Active Nematic Liquid Crystals Invited Speaker: Rui Zhang Topological defects are important for regulating the structural, optical, and rheological properties of liquid crystals. Current research interests in liquid crystal defects are motivated by their potential applications as a template to direct self-assembly and their autonomous motion capabilities in active liquid crystals. However, our understanding of their structures in driven and active systems is limited by their microscopic size and transient behavior. Therefore, simulations can provide a convenient platform to elucidate their emergence, structures, and dynamics. In this talk, I will discuss our recent efforts in employing different simulation methods combined with experiments to characterize disclination behaviors in nematic liquid crystal in static state, under driven flows, or driven by active stresses. First, we use molecular dynamics to examine nanoscopic structures and thermodynamics of disclinations and find that the molecular system can be well understood by continuum theories. We next combine continuum simulation and experiment to study the super-elastic properties of disclinations and their emergent structures in tumbling, lyotropic liquid crystals under a pressure-driven flow. Lastly, we predict a new symmetry breaking mechanism for self-propelling disclinations in active chiral nematics. As such, our multiscale simulations have provided a deeper understanding of topological defects in out-of-equilibrium nematic liquid crystals, which could facilitate their applications in sensing, photonics, material transport, and rheology. |
Monday, March 6, 2023 4:48PM - 5:24PM |
D13.00004: Fine structure of the defect cores in lyotropic chromonic liquid crystals Invited Speaker: Shuang Zhou The detailed structure of singularities of ordered field represents a fundamental problem in diverse areas of physics. At the defect cores, the deformations are so strong that the system explores states with symmetry different from that of an undistorted material. These regions are difficult to explore experimentally as their spatial extension is very small, a few molecular lengths in the condensed matter. Here we explore the cores of disclinations in the so-called chromonic nematics that extend over macroscopic length scales accessible for optical characterization. We demonstrate that the amplitude S and the phase n (the director) of the order parameter vary along both the radial and azimuthal directions, in contrast to the classic models in which S varies only with the distance from the centre and n depends only on the azimuthal coordinate. This unexpected core structure is explained by a strong coupling of the phase and amplitude of the order parameter in the free energy. |
Monday, March 6, 2023 5:24PM - 6:00PM |
D13.00005: Shape-morphing of topological liquid crystal elastomer kirigami Invited Speaker: Vianney K Gimenez-Pinto We investigate the actuation of laser-cut liquid crystal elastomer (LCE) samples imprinted with topological defects in their director microstructure and a director splay/twist along sample thickness. These topological LCE kirigami samples exhibit a rich variety of actuation behavior, including a bio-mimetic fluttering butterfly; accordion folds; bending, right-handed and left-handed twist coexisting in one sample; among others. Via finite-element elastodynamics, we simulate this actuation behavior and monitor strain distribution in the sample, observing the time-evolution of high-strain regions given by the topological defects within the custom-cut macroscopic geometry. |
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