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 Y07: Liquid Crystals II |
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Sponsoring Units: DSOFT Chair: Cecilia Leal, University of Illinois at Urbana-Champaign Room: Room 130 |
Friday, March 10, 2023 8:00AM - 8:12AM |
Y07.00001: Interplay between Nanoparticle-Induced and Substrate-Induced Ionic Effects in Molecular Liquid Crystals Yuriy Garbovskiy The future progress of liquid crystal science and technology relies on the development of new liquid crystal materials exhibiting advanced properties. A promising way to produce tunable multifunctional materials involves the dispersion of nanoparticles in molecular liquid crystals. As a rule, an electric field induced reorientation of liquid crystals is used to control the properties of such materials. This reorientation can be altered by ions present in molecular liquid crystals in minute quantities. Because ions can interact with both nanoparticles and substrates of a liquid crystal cell, it is important to understand how such interactions can affect the electrical properties of liquid crystals. This report presents a discussion of ionic effects induced by nanoparticles and substrates in molecular liquid crystal. Both experimental and theoretical results are presented. Substrate-induced ionic effects dominate if relatively thin samples are used to measure the electrical properties of molecular liquid crystals doped with nanoparticles. Nanoparticle-enabled ionic phenomena become more pronounced if thicker samples are utilized. In any real situation, the combined effect of substrates and nanoparticles on the behavior of ions in molecular liquid crystals should be considered. |
Friday, March 10, 2023 8:12AM - 8:24AM |
Y07.00002: Nanoparticle assembly in smectic-A to nematic phase transition at undulated surfaces Jane Bernadette Denise M Garcia, Mackenzie O'Keefe, Mohamed Amine Gharbi, Daniel A Beller Topological defects in liquid crystals are effective templates for nanoparticle (NP) assembly. In a hybrid-aligned smectic-A (SmA) liquid crystal, NPs assemble at the cusp defects of focal conic domains (FCDs). Adding two-dimensional undulations to one of the confining surfaces stabilizes defects in the nematic phase, as well, suggesting routes to patterned and switchable NP assembly at the SmA-nematic phase transition. We model how NPs assemble in the SmA-to-nematic phase when one of the hybrid-aligned surfaces has 2D undulations, using a multi-step Landau-de Gennes free energy minimization scheme accounting for smectic FCD configurations and elasticity. We show that the NPs assemble sequentially at defects and confining surfaces, with the assembly sequence dependent on NP surface anchoring. We explore how the curvature of the undulated surface influences to this sequential assembly. We also examine how the presence of NP assemblies affects, in turn, the defect structures that arise in the SmA-nematic phase transition. |
Friday, March 10, 2023 8:24AM - 8:36AM |
Y07.00003: Calculation of Electrical Transport Property for Liquid Binary CuxAg1-x Alloys Asma Harun, Ratan Chandra Gosh The electric transport properties named Electrical resistivity of liquid binary CuxAgx-1 alloys is calculated using the extended Ziman’s formula developed by Faber and Ziman at 1423 K. We have seen the behavior of alloys changing the concentration of both Copper and Silver. Form factor,Vij(q), and partial structure factor, Sij(q), are the key ingredients of this calculation. For Vij(q), we have chosen Bretonnet-Silbert (BS) pseudo-potential with Ichimaru-Utsumi (IU), and Vashishta-Singwi (VS) local field correction functions. For structure factor, Sij(q), we have chosen linearized Weeks-Chandler-Andersen (LWCA) thermodynamic perturbation theory. Calculated results of electrical resistivity comparing with the available experimental data suggest that the choice of VS local field correction function in the potential is important than IU local field correction function. It is also observed that the applied theory with both local field correction functions works well for Ag-rich alloys than those of Cu-rich alloys. To explain the resistivity of Cu-rich alloys more accurately a further study with more sophisticated theory is required. |
Friday, March 10, 2023 8:36AM - 8:48AM |
Y07.00004: Structures, Thermodynamics and Dynamics of Topological Defects in Gay–Berne Nematic Liquid Crystals Yulu HUANG, Weiqiang WANG, Jonathan K Whitmer, Rui Zhang As a consequence of broken symmetry, topological defects are ubiquitous across different physical systems, and are thereby important for understanding a wide variety of phenomena in physics. In nematic liquid crystals, topological defects exhibit unique optical signatures and can segregate impurities, showing their promise as molecular carriers and nano-reactors. Therefore, understanding defect structures and dynamics in liquid crystals is essential for their further applications. In this work, we study the structure and dynamics of topological defects in Gay–Berne nematic liquid crystals by molecular dynamics simulations. The elastic bend-to-splay ratio is measured using two independent measurements, showing good agreement with literature. Next, we study defect annihilation event, and find that their trajectories are consistent with experiments and hydrodynamic simulations. We further examine the thermodynamics of the system before and after defect annihilation, the result of which can be used to estimate the elastic constant of the nematic. Finally, we study defect motion under a temperature gradient and find that defects tend to propel into hotter area. Taken together, our work has provided molecular roots of continuum theory and simulations and proposed an alternative control parameter for defect transport. |
Friday, March 10, 2023 8:48AM - 9:00AM |
Y07.00005: Ferroelectric nematic liquids with conics Oleg D Lavrentovich, Priyanka Kumari, Bijaya Basnet Spontaneous electric polarization of solid ferroelectrics follows the direction of crystallographic axes. Domains of differently oriented polarization are divided by boundary defects, called domain walls (DWs), which are predominantly flat. Here we demonstrate that DWs are shaped as conic sections in a ferroelectric nematic (NF) liquid crystal, which is a fluid with no crystallographic axes. The conics bisect the angle between two neighboring polarization fields to avoid electric charges. The remarkable bisecting properties of conic sections, known for millennia, find their material realization as intrinsic features of fluid ferroelectrics. The findings could be helpful in designing patterns of electric polarization and space charge. |
Friday, March 10, 2023 9:00AM - 9:12AM |
Y07.00006: Programming Liquid Crystal Director Fields Using Spatially Varying Magnetic Fields Zhe Liu, Yvvone Zagzag, Chinedum Osuji, Randall D Kamien, Jay Kikkawa Magnetic fields can be used to control the director orientation in liquid crystals. The resulting anisotropic texture is implicitly associated with anisotropy of material properties, including dielectric permittivity and elasticity. Here we show that the director field of a small molecule LC can be spatially programmed by employing magnetic microstructures. Microstructured ferromagnetic materials, such as cobalt, distort the uniformity of a background field and cause spatial variation of field strength and direction. Mesogens confined between surfaces with homeotropic anchoring undergo a Freedericksz transition to a planar configuration above a critical field strength set by the sample thickness and anchoring energy. In this configuration, the local variation in field strength due to the Co magnetic microstructures results in a readily observable spatial variation of the LC director field that is encoded or programmed by the magnetic field. We explore various geometrical arrangements of cobalt microstructures and the director field configurations that result from the magnetic field patterns formed by these arrays. We reconcile the results using simulations of the spatial variation of the magnetic field and LC director field. This approach enables the generation of bespoke director field patterns, with inverse design methodologies connecting required magnetic array geometries to desired director field patterns. The embedded local control of material properties provides a feasible route to spatially programming material function. |
Friday, March 10, 2023 9:12AM - 9:24AM |
Y07.00007: Applications of the Peach-Koehler force in liquid crystals Cheng Long, Jonathan V Selinger In solids, external stress induces the Peach-Koehler force, which drives dislocations to move. Similarly, in liquid crystals, an external angular stress creates an analogous force, which drives disclinations to move [1]. Calculating the angular stress at a disclination in a liquid crystal is often challenging due to the effects of boundary conditions. In this work, we argue that the relevant angular stress can be identified by expanding the total angular stress around a disclination as a Laurent series, and eliminating the divergent stress from the disclination itself. We demonstrate this method by applying the Peach-Koehler force theory to two different problems: (a) Array of disclinations in a liquid crystal cell with patterned substrates, as the experiment of Babakhanova [2]. (b) Pair of disclinations in a long capillary tube with homeotropic anchoring. Our Peach-Koehler force theory predicts the positions of the disclinations for both problems, and the predictions are consistent with the results of minimizing the total free energy. |
Friday, March 10, 2023 9:24AM - 9:36AM |
Y07.00008: Electric field induced interfacial instability in a ferroelectric nematic liquid crystal Marcell T Máthé, Antal Jakli, Agnes Buka, Peter Salamon, László Péter, Bendegúz Farkas The investigation of the external magnetic or electric fields induced surface instabilities in fluids are not only interesting and spectacular but also a widely used part of physics, like the electric field induced Rayleigh instability which is the basic mechanism of electrospinning. After the recent discovery of polar nematic materials, which have a ferroelectric nematic phase, an obvious question arises: Can a new type of electric field driven surface instability be observed in these materials? We investigated the response of a ferroelectric nematic liquid crystal to electric fields in various geometries. In our experiments, we observed pattern formation as a consequence of an electric field induced surface instability. We characterize the effect and provide a model to explain the basic mechanism of the pattern formation observed in ferroelectric nematic droplets with free surface exposed to electric fields. |
Friday, March 10, 2023 9:36AM - 9:48AM |
Y07.00009: Latex-Stabilized Cholesteric Liquid Crystal Coatings for Thermochromic Textiles Md Mostafa Cholesteric liquid crystals (CLCs) dispersed in commercial water-based latex varnish (CLC-Latex) are coated on yarns and fabrics. The CLC-latex coatings displayed bright and stable colors that change with temperature. The optical and stability properties of CLC-latex coated polyester fibers are better than found before using conventional polymer dispersed liquid crystals and comparable to that planar CLCs clads overcoated with polymer layer [1]. We also sprayed the CLC-Latex on fabrics and found them comparable with fabric coated by commercially available thermochromic liquid crystal inks. We find that the excellent brightness is due to the flattening of the phase separated CLC droplets during the water evaporation from the latex varnishes. These CLC-latex coatings are also durable, environmentally friendly, inexpensive, and easy to coat on fibers and fabrics. The resulting smart textiles could be used for numerous biosensing, medical and decorative applications. |
Friday, March 10, 2023 9:48AM - 10:00AM Author not Attending |
Y07.00010: Supramolecular meso-Trick - Ambidextrous Mirror Symmetry Breaking in a Liquid Crystalline Network with Tetragonal Symmetry Yu Cao, Mohamed Alaasar, Chenhui Zhu, Lei Zhang, Carsten Tschierske, Feng Liu Bi- and multi-continuous network phases are among nature's most complex structures in soft matter systems. Here a chiral bicontinuous tetragonal phase is reported as a new stable liquid crystalline intermediate phase at the transition between two cubic phases, the achiral double gyroid and the chiral triple network cubic phase with I23 space group, both formed by dynamic networks of helices. The mirror symmetry of the double gyroid, representing a meso-structure of two enantiomorphic networks, is broken at the transition to this tetragonal phase by retaining uniform helicity only along one network while losing it along the other one. This leads to a conglomerate of enantiomorphic tetragonal space groups, P41212 and P43212. Phase structures and chirality were analyzed by small-angle X-ray scattering (SAXS), grazing-incidence small-angle X-ray scattering (GISAXS), resonant soft X-ray scattering (RSoXS) at the carbon K-edge and model-dependent SAXS/RSoXS simulation. Our findings not only lead to a new bicontinuous network-type 3D mesophase but also reveals a mechanism of mirror symmetry breaking in soft matter by partial meso-structure racemization at the transition from enantiophilic to enantiophobic interhelical self-assembly. |
Friday, March 10, 2023 10:00AM - 10:12AM |
Y07.00011: Topological liquid crystal superstructures as structured light lasers Urban Mur Liquid crystals (LCs) form an extremely rich range of self-assembled topological structures with artificially or naturally created topological defects. Some of the main applications of LCs are various optical and photonic devices, where compared to their solid-state counterparts, soft photonic systems are fundamentally different in terms of unique properties such as self-assembly, self-healing, large tunability, sensitivity to external stimuli, and biocompatibility. Distinctly, inserting liquid crystals into the laser cavity allows for extensive control over the emitted light due to their high susceptibility to external fields and birefringent nature. Here we show that complex tunable microlasers emitting structured light can be generated from self-assembled topological LC superstructures containing topological defects inserted into a thin Fabry–Pérot microcavity. The topology and geometry of the LC superstructure determine the structuring of the emitted light by providing complex three-dimensionally varying optical axis and order parameter singularities, also affecting the topology of the light polarization. The microlaser can be switched between modes by an electric field, and its wavelength can be tuned with temperature. The proposed soft matter microlaser approach opens directions in soft matter photonics research, where structured light with specifically tailored intensity and polarization fields could be designed and implemented. |
Friday, March 10, 2023 10:12AM - 10:24AM Author not Attending |
Y07.00012: Formation and fluctuation of two-dimensional dodecagonal quasicrystals Uyen T Lieu, Natsuhiko Yoshinaga Patchy particles are the particles with anisotropic surface patterns or patches on specific positions on the surface. The interaction of such particles is not only dependent on the distance, but also on their mutual orientations. Therefore, the patchy particles are capable of organising themselves into complex structures, which are important for the generation of novel materials. One of the complex structures is quasicrystal. Quasicrystal are ordered structures lacking periodic translational symmetry. Quasicrystals may have 5-, 10-, 12-fold rotational symmetry while crystals possess 2-, 3-, 4-, and 6-fold rotational symmetry. The quasicrystal can be applied in various application such as advanced coatings, reinforced composites, magnetism. The quasicrystal is formed by nucleation and growth. However understanding on the mechanism, the growth of quasicrystal is still incomplete. |
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