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 W07: Liquid Crystals I |
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Sponsoring Units: DSOFT Chair: Chaitanya Joshi, Tufts University Room: Room 130 |
Thursday, March 9, 2023 3:00PM - 3:12PM |
W07.00001: Focal conic array in patterned microchannels near the smectic phase transition Sean Hare It is known that the liquid crystalline smectic-A phase has geometric defects, called focal conic domains, whose size and positions are heavily influenced by their boundaries. Focal conic defects can be recovered when heated to the nematic (or cholesteric) phase, and cooled back to smectic. This phenomenon of memory of defects is also seen in reverse, with the orientation of defects in the nematic phase being “remembered” upon cooling to smectic[1] or toron-like defects in the cholesteric phase reversibly transforming into focal conics[2]. We demonstrate that the extent to which an array of focal conic domains can be recovered depends on the maximum heating temperature, and we seek to understand how much this memory is affected by the phase transition itself or by further heating above the phase transition. To do this, we compare a nematic system with a weakly chiral system in which the positions of focal conic domains are induced by a patterned microchannels with curved boundaries and show that, for our particular system, it is possible to quantify the geometric memory. To this purpose, we identify a quantitative measurement of “memory” for focal conic domains in smectic A liquid crystals that undergo a transition to either nematic or cholesteric liquid crystals. |
Thursday, March 9, 2023 3:12PM - 3:24PM |
W07.00002: Nematic-to-isotropic phase transition at prepatterned topological defects Nilanthi P Haputhanthrige, Miao Jiang, Hao Chen, Xiayu Feng, Maxim O Lavrentovich, Oleg D Lavrentovich, Qihuo Wei, Yubin Guo Topological defects play an important role in phase transitions in condensed matter. We explore the nematic-to-isotropic transition in an array of topological defects generated by a pre-patterned director field. Isotropic islands nucleate either at the defect cores or away from them, depending on the rate of temperature increase. The isotropic nuclei appearing at the ±1/2 |
Thursday, March 9, 2023 3:24PM - 3:36PM |
W07.00003: Phase equilibrium and dynamics in mixture of 5CB/dimethyl phthalate isotropic one-phase state Ryoko Shimada, Osamu Urakawa, Tadashi Inoue, Hiroshi Watanabe Phase equilibrium and dynamics were examined for a mixture of 5CB with dilute dimethyl phthalate (DMP; wDMP = 3.1 wt%). The mixture was in an isotropic one-phase state at temperatures T above a critical temperature TIN (~ 27.0°C). This TIN was described well by a simple model of free energy contributed from a Flory-Huggins type mixing entropy and a Landau-de Gennes type nematic interaction, suggesting that the phase separation in the mixture was triggered by the nematic transition of 5CB and thus the orientation fluctuation of 5CB molecules is coupled with the composition fluctuation. This coupling affected the dielectric relaxation time τε reflecting the orientation fluctuation of 5CB molecules: In a high-T asymptote (T > TIN +10°C), τε of the mixture was close to that of pure 5CB, which suggested no significant effect of the above coupling on the 5CB dynamics in the mixture at such high T. However, in a significantly wide range of T between TIN and TIN +10°C where the mixture was still in the isotropic one-phase state, τε increased on cooling much more significantly compared to τε in that high-T asymptote. The kinematic viscosity ν of the mixture exhibited a qualitatively similar increase in the same range of T, but this increase was weaker than that of τε. This difference between τε and ν is discussed on site in relation to the coupling of the orientation and the composition fluctuations. |
Thursday, March 9, 2023 3:36PM - 3:48PM |
W07.00004: Measures of chirality in the framework of atom-atom potentials Petr V Shibaev, Mihir Shetty Recently, different chirality measures were suggested to quantify the ability of chiral molecules to twist a nematic phase (twisting power). In this presentation, some of these measures are reviewed, and a few novel methods are suggested and considered. They are based on intermolecular interaction calculations within the framework of atom-atom potentials which are widely used in quantum chemistry, molecular dynamics calculations, etc. The novel chirality measures originate from calculating intermolecular interactions between a single chiral molecule and a small cluster of aligned non-chiral rods surrounding the chiral molecule. We consider different chiral “components” of intermolecular interactions (torques, forces, and energies) and discuss their applicability as chirality measures of the chiral molecule. The torque seems to be one of the most convenient chirality measures. Analytical calculations are made for the cases of atomic chirality and atropoisomers. The latter case correlates well with experimental data on helical pitch measurements. |
Thursday, March 9, 2023 3:48PM - 4:00PM |
W07.00005: Emerging Topological Structures in Nematic Moiré Patterns Xinyu Wang, Juan Chen, Jinghua Jiang, Chenhui Peng, Rui Zhang Topological defects are of fundamental interest to soft matter physics, particle physics, and mathematics. In liquid crystals, they are also of practical importance in sensing, photonics, and directed self-assembly of colloids and molecules. Rational design of topological defects with arbitrary morphology and periodicity could enable more practical applications of topological defects, which remains a challenge to date. Inspired by the moiré pattern, here we combine simulations and experiments to study nematic liquid crystal cells confined by two identical surface patterns. By a mechanical twist, we observe a rich variety of highly tunable, novel topological structures, which are sensitive to system geometries; the corresponding cross-polarized images are distinct from isotropic moiré patterns. Simulations also show that the Frederiks transition voltage is approximately 10% lower in nematic moiré patterned cells than in conventional planar twisted cells. As such, the proposed simple mechanical twist method shows the promise of designing and tuning arbitrary, external-field-responsive, mesoscopic structures and optical patterns in liquid crystals and beyond, which can facilitate applications in defect-templated self-assembly, display, imaging, and photonic devices. |
Thursday, March 9, 2023 4:00PM - 4:12PM |
W07.00006: Electro-optical switching of a single component ferroelectric nematic material at room temperature. Alex Adaka, Rony Saha, Pawan Nepal, Parikshit Guragain, Kelum Perera, James T. Gleeson, Robert J. Twieg, Antal Jakli The study of ferroelectric nematic liquid crystal materials has gained worldwide significance. The liquid crystal materials with ferroelectric nematic properties at room temperature have applications that are of fundamental importance in various industries that hold promise for new technologies including high-density power storage or sub-millisecond switching information displays. Here we present the measurements of the physical properties of a single component ferroelectric nematic material RT11165 with electro-optical switching properties down to room temperature. Various characterization techniques such as differential scanning calorimetry (DSC), x-ray scattering, dielectric spectroscopy, polarizing optical microscopy (POM), ferroelectric polarization and electro-optical measurements, were employed to characterize the physical properties of the material. |
Thursday, March 9, 2023 4:12PM - 4:24PM |
W07.00007: High-Temperature Mesomorphic Glassy Liquid Crystals with Exclusive Cholesteric Mesomorphism Benjamin D Carlson, Mitchell Anthamatten, Shaw H Chen Glassy liquid crystals (GLCs) are a unique class of materials that can preserve their spontaneously ordered liquid crystalline state upon cooling through the glass-transition temperature. We are studying a series of GLCs with high morphological stability that display exclusive mesomorphism of the nematic and cholesteric type over a broad temperature range. The ability to process these compounds into well-ordered, nm and µm thick films with large area monodomains, opens the door for a wide range of compact, robust optical applications. Improvements in chemical synthesis alongside the selection of the core and pendant groups allow these materials to be scaled up to gram-level while retaining thermal and optical properties. Resulting films offer near perfect circular polarization that is tunable from the near-UV to the mid-IR via simple mixing of enantiomers. Thermal gravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC) reveal that transition temperatures remain unchanged upon the mixing enantiomers. This enables the versatile design of durable circular polarizers, notch filters, and polarization control devices across different spectral regions and high-temperature environments. |
Thursday, March 9, 2023 4:24PM - 4:36PM |
W07.00008: Nematronics: Reciprocal coupling between ionic currents and nematic dynamics Chau Dao, Jeffrey C Everts, Miha Ravnik, Yaroslav Tserkovnyak Adopting a spintronics-inspired approach, we study the reciprocal coupling between ionic charge currents and nematic texture dynamics in a uniaxial nematic electrolyte. Assuming quenched fluid dynamics, we construct the analogs to spin torque and spin pumping in nematic electrolytes. Based on the principle of least dissipation of energy, we derive the adiabatic "nematic torque" exerted by ionic currents on the nematic director field as well as the reciprocal motive force on ions due to the orientational dynamics of the director. We discuss several simple examples that illustrate the potential functionality of this coupling, as well as propose how one could measure the coupling strength. Exploring further applications based on this physics could foster the development of nematronics -- nematic iontronics. |
Thursday, March 9, 2023 4:36PM - 4:48PM |
W07.00009: Effects of Mesostructured Ionic Liquids on Charge Transport Marvin Diaz Segura Ionic liquid crystals (ILCs) are a class of materials that are in the intersection of ionic liquids and liquid crystals. These materials typically consist of oppositely charged molecules with typically bulky ionic groups. Our work uses atomistic molecular simulations to explore the behavior of a novel ILC lithium salt to explore its ion conducting properties, and how these are mutually influenced by ion-pair binding and mesoscale structure. In particular, we analyze the relative mobility of Li+ ions and their larger counterions, and discuss the relevance of these results for the development of solid-state single-ion conducting materials for rechargeable batteries. |
Thursday, March 9, 2023 4:48PM - 5:00PM |
W07.00010: Flow-induced switching between blue phases Tadej Emersic, Rui Zhang, José A Martínez-González, Kushal Bagchi, Paul F Nealey, Juan J De Pablo Blue-phases (BPs) are highly ordered soft materials that appear in a narrow temperature range between the chiral nematic and the isotropic phases. BPs exhibit cubic arrangements of double-twist cylinders and disclination lines with characteristic length scales of the wavelength of visible light. Between BPI and BPII exist topological differences which are significantly responsible for their different dynamical response under external stimuli. Here we focus on the dynamic and out-of-equilibrium states of BPII under shear stresses in pressure-driven flow inside microfluidic channels. We show in experiments how precise tuning of the driving pressure on BPII with the lattice orientation (111) can be used to stabilize and manipulate a previously unresearched switching state between BPII and BPI. Combining experiments with simulations, we try to understand the dynamics of disclinations lines and how they are affected by hydrodynamic forces. We also characterize the sequence of all dynamical, flow-induced out-of-equilibrium regimes when subject to a pressure-driven flow in a microfluidic geometry with controlled anchoring conditions. |
Thursday, March 9, 2023 5:00PM - 5:12PM |
W07.00011: Magnetic Field Driven Configuration Transitions in Nematic Droplets Sophie Ettinger, Charlotte Slaughter, Sebastian H Parra, Peter J Collings, James M Kikkawa, Arjun G Yodh We experimentally study the director configuration evolution in a nematic liquid crystal (NLC) droplet in a uniform magnetic field. To date, the magnetic field driven transition from a radial configuration to an axial configuration has been predicted in theory and simulation, but has yet to be critically examined experimentally. To this end, we built an apparatus to observe NLC droplets in high-magnetic fields using polarized optical microscopy. Our observations reveal that the transformation from radial to axial configuration has two intermediary states: a "deformed radial" state and an "axial with defect" state. We examine these transition states through experiment and numerical simulation and discuss their characteristics in the context of current literature. Building on prior work, we develop a critical field model to describe the relationship between critical magnetic field and droplet radius for a droplet with finite anchoring strength. Finally, by identifying critical fields for a range of droplet sizes and surfactant concentrations, we use the model to estimate anchoring strength at a liquid-liquid interface for commonly used surfactants and concentrations. |
Thursday, March 9, 2023 5:12PM - 5:24PM |
W07.00012: Effects of GoldnanoUrchin nanoparticles on ion-transport and electro-optic response in nematic liquid crystal Rajratan Basu, Derek Gess A small quantity of GoldnanoUrchin nanoparticles (GUNP) was doped in a nematic liquid crystal (LC), and the nematic electro-optic switching was found to be significantly faster in the LC + GUNP hybrid than that of the pure LC. Additional studies revealed that the presence of GUNP reduced the free ion concentration in the nematic media by ion-trapping process. The reduction of mobile ions in the LC was found to have subsequent impacts on the LC’s conductivity and rotational viscosity, allowing the nematic director to respond faster as the electric field was turned on and off. |
Thursday, March 9, 2023 5:24PM - 5:36PM |
W07.00013: Dynamic Motion Control of Topological Defects in Nematic Liquid Crystals by Chemically Patterned Surfaces Xiao Li, Tejal Pawale, Sid Hashemi, Justin Swain, Giordano Tierra Chica The existence of topological defects (TDs) is ubiquitous in nature due to their occurrence at broad spatiotemporal scale, for instance, in subatomic particles or cosmology. The analogous nature of these defects makes it possible to apply the mathematics describing TDs formation and evolution to different disciplines and length scales. Liquid crystals have been considered as an ideal system for the defects investigation, due to the birefringence phenomena of LCs enabling direct visualization of such topological defects and a straightforward analyzation process. In addition to characterizing and analyzing the equilibrium morphology of LC topological defects, it is also of great interest to track and control the formation and annihilation of defects during thermodynamic processes. However, controlling the dynamic behavior of formed defects remains a challenge. Here, we confine the nematic LCs in a cell exhibiting surfaces with periodic anchoring conditions and surface topography at the interface of homeotropic and degenerate planar anchoring stripes. We explore the effects of patterned surface characteristics on defects dynamic motion, stabilization and annihilation by controlling the width of homeotropic/planar stripes along with the periodicity. |
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