Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S05: Liquid Crystals IILive
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Sponsoring Units: DSOFT Chair: Youness Diouane, International School for Advanced Studies Room: 05 |
Thursday, March 18, 2021 11:30AM - 11:42AM Live |
S05.00001: Nematic Colloids at Liquid Crystal-Air Interfaces via Photopolymerization Xiaoshuang Wei, Nicholas Sbalbi, Laura Bradley Liquid crystals (LCs) have been shown to control the organization and location of colloidal assemblies ranging from chain-like to hexagonal structures. Most systems that exploit LC-mediated assembly for producing colloidal superstructures require the use of pre-synthesized particles or temperature-induced phase separation. Here, we demonstrate simultaneous synthesis and assembly of colloidal assemblies at LC-air interfaces. Polymer colloids are produced by photopolymerization of an acrylate monomer mixed in a non-reactive liquid crystal. Colloids spontaneously form ordered assemblies that cover the entire area of the LC-air interfaces. Systematic experiments varying the reaction time were conducted to monitor the growth and assembly. Our results demonstrate the design rules for producing nematic colloids at LC interfaces via photopolymerization which can offer opportunities for the preparation of large-scale LC-templated interfacial superstructures. |
Thursday, March 18, 2021 11:42AM - 11:54AM Live |
S05.00002: Absence of nematic quasi-long-range order in two-dimensional liquid crystals with three director components Youness Diouane The Lebwohl-Lasher model describes the isotropic-nematic transition in liquid crystals. In two dimensions, where its continuous symmetry cannot break spontaneously, it is investigated numerically since decades to verify, in particular, the conjecture of a topological transition leading to a nematic phase with quasi-long-range order. We use scale invariant scattering theory to exactly determine the renormalization group fixed points in the general case of $N$ director components ($RP^{N-1}$ model), which yields the Lebwohl-Lasher model for $N=3$. For $N>2$ we show the absence of quasi-long-range order and the presence of a zero temperature critical point in the universality class of the $O(N(N+1)/2-1)$ model. For $N=2$ the fixed point equations yield the Berezinskii-Kosterlitz-Thouless transition required by the correspondence $RP^1\sim O(2)$. |
Thursday, March 18, 2021 11:54AM - 12:06PM Live |
S05.00003: Nematic bits and logic gates Ziga Kos Topological field structures in nematic liquid crystals are known to share analogies with superconducting quantum mater. While the experimental control of orientation and dynamics of nematic structures has been developed, little is known how such structures could be used for information storage and computation. We introduce nematic bits [1] by using a quaternionic mapping [2,3] from nematic defects to a Bloch sphere. By using electric fields, we show in theory and simulation how logic gates could be applied to nematic bits, analogous to Pauli, Hadamard and other quantum gates. We also show Bell-like correlations and nematic discord in two nematic bit ensambles, opening a pathway towards non-classical computational strategies in topological soft matter systems. |
Thursday, March 18, 2021 12:06PM - 12:18PM Live |
S05.00004: Lipid islands on liquid crystal shells Anjali Sharma, Deepak Gupta, Giusy Scalia, Jan Lagerwall Combining a self-closing spherical topology, dual closely spaced liquid-liquid interfaces, and fluid long-range order, liquid crystal (LC) shells are exquisite reporters of delicate self-organization processes occurring at their interfaces. Conversely, the LC actively influences such processes, its 3D bulk elasticity triggering novel 2D surface ordering phenomena. Here we show that lipids adsorbing onto LC shells phase separate and form condensed monolayer islands, inducing a locally distorted LC director field that reveals their presence with high contrast in polarizing microscopy. Lipids transfer through the shell, forming secondary islands that are attracted to primary islands via nematic elasticity. The mutual interaction between LC shells and adsorbed lipid monolayers, revealed via LC birefringence, provides an unconventional means of detecting natural lipids. This turns LC shells into a valuable platform for studying liposome adsorption on soft hydrophobic substrates, and it may be useful in low-cost minimum-resource biosensing. It also opens new avenues in making 'patchy' colloidal particles with directionally programmed interactions. |
Thursday, March 18, 2021 12:18PM - 12:30PM Live |
S05.00005: The crucial role of a functional group position in the self-assembly of lyotropic chromonic liquid crystals Jonghee Eun, Jiyong Cheon, Sung-Jo Kim, Tae Joo Shin, Joonwoo Jeong Plank-like lyotropic chromonic liquid crystal (LCLCs) molecules self-assemble face-to-face via non-covalent interactions in water. These aggregates may align to exhibit lyotropic liquid crystalline phases according to the temperature and concentration. Additives such as salt and polymers also affect the aggregate structure and resulting phase behavior. Here, utilizing the representative LCLC, Sunset Yellow FCF (SSY), we report the effects of intrinsic additives, i.e., byproducts of SSY synthesis. First, combining various characterization techniques, including Liquid Chromatography, Mass spectroscopy, and X-ray scattering, we unveil how and why the purification of commercially available SSY affects its aggregate structures and phase behaviors. We further focus on the byproduct impurities that resemble SSY but differ from SSY in the number and location of sulfonate groups. Experimental characterization and quantum chemistry calculation suggest that the sulfonate group near SSY's aromatic core distorts its planar shape, thus disrupt the aggregate formation and the resultant nematic phase. |
Thursday, March 18, 2021 12:30PM - 12:42PM Live |
S05.00006: Nanoscale crystalline order in lyotropic solution of supramolecular hollow cylinders Ningdong Huang, Goran Ungar Nanoscale 3D order is observed in the lyotropic columnar phase of supra-molecular aggregates by ionic planar oligomers. The meso-scopic structure and dynamics of the supramolecular LLC are characterized by polarized optical microscope, Cryo-TEM and X-ray scattering experiments. We observe the formation of tubular aggregates or columns with diameter about 15 nms of which the morphology remains almost unchanged with concentration. The columns are further bundled into hexagonal columnar phase which swells with decreasing concentration. Fiber diffraction on concentrated solutions display Bragg reflection arcs, indicating 3D crystalline order at nanometer scale and interlock between the columns. As concentration drops, the reflection arcs gradually fade but remain visible even at surface to surface separation about 8nm, suggesting effective inter-column correlation across rather long distances. Concomitant weakening of intra-column order upon dilution is evident in the dynamics of the supramolecular columns probed by X-ray Photon Correlation Spectroscopy. The 3D order in the supramolecular solutions is analogous to ordered column phase of thermotropic liquid crystals. The results and underlying mechanism are compared to semi-crystalline phase of covalently bonded DNAs. |
Thursday, March 18, 2021 12:42PM - 12:54PM Live |
S05.00007: Stability of binary colloidal crystals immersed in a cholesteric liquid crystal Setarehalsadat Changizrezaei, Colin Denniston We model a number of both closed-packed and non-closed-packed crystals inside a cholesteric liquid crystal (LC) with different pitch values and nematic LC through the Landau–de Gennes free-energy method. We investigated the anisotropic interactions between particles with heterogeneous boundary conditions inside both nematic and cholesteric liquid crystals [1]. The results show that it is energetically favorable for the particles to remain in a plane parallel to the far-field director in a nematic liquid crystal, while for particles immersed in a cholesteric there are multiple energy minima, not all located in the same plane. Therefore, We became interested in investigating the stability of binary crystals [2]. The results indicate that body-centered-cubic (BCC) crystals have a lower-energy lattice defect structure than the diamond crystal. Furthermore, it is shown that a pair of binary colloids can be self-assembled into a stable face-centered-cubic lattice structure inside a nematic LC, as it has the lowest energy comparing to diamond and BCC crystals. |
Thursday, March 18, 2021 12:54PM - 1:06PM Live |
S05.00008: Hydrodynamic theory of p-atic liquid crystals Niladri Sarkar, John J Toner, Luca Giomi We formulate a comprehensive hydrodynamic theory of two dimensional liquid crystals having p-fold rotational symmetry often referred to as |
Thursday, March 18, 2021 1:06PM - 1:18PM Live |
S05.00009: Anisotropic disclination cores in nematic liquid crystals modelled by a computational Maier-Saupe field theory Cody Schimming, Jorge Vinals We develop a computational model based on a field theory extension of the Maier-Saupe molecular model of a uniaxial, nematic liquid crystal. A tensor order parameter is defined as the second moment of an orientational probability distribution, leading to a free energy that is not convex within the isotropic-nematic coexistence region, and that goes to infinity if the eigenvalues of the order parameter become non-physical. An elastic free energy is added which is an expansion in spatial gradients of the order parameter up to third order, allowing for parametric control over the anisotropy and elasticity of the liquid crystals. Computations of the spatial profile of the order parameter are presented for nematic disclinations in two dimensions. We compare the simulation results to recent experiments and show good agreement. |
Thursday, March 18, 2021 1:18PM - 1:30PM Live |
S05.00010: Weakly compressible smectic-isotropic model: coalescence, flows and focal conic defects Eduardo Vitral, Perry H. Leo, Jorge Vinals Curvature driven phenomena in soft matter involves both complex geometry at small scales and anisotropies associated with material symmetries. For instance, smectic liquid crystals consist of layers of molecules than can bend and form focal conic defects. We previously proposed a phase field model to study a smectic-isotropic interface, and our numerical results have shown morphological transitions from focal conics to conical pyramids, which are also observed in experiments on smectic films. Interface equations were derived from the model, revealing the role of the Gaussian curvature on local equilibrium and resulting morphologies. We generalize this model to allow for phases of different density ρ, adding a penalty to the energy for deviations from preferred ρ values, with a multiplying constant that controls the strength of the coupling between the smectic order parameter ψ and ρ. We show that if this constant is large enough, ψ becomes approximately conserved, whereas if the constant is too small, ψ moves almost independently of ρ. Numerical results explore the possibility of coalescence between two stacks of smectic layers, and also interactions between focal conics due to flows. We show how these resulting flows are driven by both curvatures and interface compressibility. |
Thursday, March 18, 2021 1:30PM - 1:42PM Live |
S05.00011: Difference in the interaction of nano-diameter rod and tubular particles with a disclination line in a nematic liquid crystal Meenu Murali, Hakam Agha, Ales Mrzel, Giusy Scalia Defects created by the nematic liquid crystal (LC) due to the presence of particles, spherical as well as rod-shaped, generate strong forces, inducing also particle trapping into a defect line. However, even in presence of particles such as carbon nanotubes (CNTs), not expected to create defects, even if in elongated bundles, we observe trapping into a 1/2 LC defect line but with differences in the dynamics compared to aggregates of rod-shaped Mo6S2I8 nanowires. The reason is attributed to the topological difference of the particle shapes. Even if both types have cylindrical shape, the hollow nature of CNTs make them not homotopically equivalent to the Mo6S2I8 nanowires and this inequivalence holds also for the LC around them. The nanowires induce defects in the LC close-by their surfaces. In contrast, multi-wall CNTs, being hollow, do not form defects even close to their ends. However, structural tube bending, as observed in the used multi-wall CNTs, presumably due to the ultrasound dispertion treatment, together with the strong planar anchoring of LC at their bare surfacs, induces deformations in the LC, enabling attraction forces with the defect line. |
Thursday, March 18, 2021 1:42PM - 1:54PM Live |
S05.00012: Molecular Packing in Double Gyroid Cubic Phases Revealed via Resonant Soft X-ray Scattering Yu Cao, Mohamed Alaasar, Asritha Nallapaneni, Miroslaw Salamonczyk, Peter Marinko, Ewa Gorecka, Feng Liu, Natasa Vaupotic, Chenhui Zhu The bicontinuous double gyroid phase is one of the nature’s most symmetric and complex structures, the electron density map of which was established long ago. By utilizing small-angle X-ray scattering (SAXS), resonant soft X-ray scattering (RSoXS) at the carbon K-edge and model-dependent tensor based scattering theory, we have not only elucidated morphology but also identified molecular packing in the double gyroid phases formed by molecules with different shapes, i.e. rod-like vs taper-shaped, thus validating some of the hypothetical packing models and disproving others. The spatial variation of molecular orientation through the channel junctions in the double gyroid phase can be either continuous in the case of anisotropic channels or discontinuous in the case of isotropic channels depending on the molecular structure and shape. |
Thursday, March 18, 2021 1:54PM - 2:06PM Live |
S05.00013: Mechanogeometry of nanowrinkling in biological cholesteric liquid crystal surfaces Ziheng Wang, Phillip Servio, Alejandro Rey The chiral fibrous architecture is found in chitin (insects), cellulosics (plants), and collagen I (cornea and bone of mammals) and is a solid analogue of that of cholesteric liquid crystals. The surface and interfaces of biological plywoods are distinguished by hierarchical topographies and nanowrinkling. We presented a theory to model the emergence of these surfaces and interfaces using liquid crystal-based shape equations that directly connect material properties with geometric wrinkling. The model applies to liquid crystal precursors of the plywood solid analogues. The theory focuses on wrinkling geometry and mechanics, as well as the mechanogeometry relationships (topology of stress curves and curvature of the wrinkles). We showed that anchoring is a versatile surface morphing mechanism with a rich surface bending stress field, two ingredients behind many potential multifunctionalities. |
Thursday, March 18, 2021 2:06PM - 2:18PM Live |
S05.00014: Interaction of tilted liquid crystal skyrmions Ayhan Duzgun, Avadh Saxena Skyrmions are topologically protected defect structures which also exhibit particle-like behaviors. Cholesteric liquid crystals (LC) confined between parallel substrates can host such LC skyrmions as well as other static solitons. There, a background alignment provided by external electric field or surface anchoring stabilizes the barrel-shaped skyrmions against shrinking or expansion. When the alignment is perpendicular to the plane of the LC cell, skyrmions are axisymmetric and upright and the interaction between two nearby skyrmions is that of soft-disk repulsion. However, when the background alignment is tilted, the directors also get tilted and the skyrmion takes a radially anisotropic form. The tilted skyrmion is topologically equivalent to the upright one but the interaction between two skyrmions is quite different. In this work we investigate this interaction in a variety of cases. |
Thursday, March 18, 2021 2:18PM - 2:30PM Live |
S05.00015: Switching and hopping of hopfions in chiral liquid crystals Jung-Shen Tai, Jin-Sheng Wu, Ivan I Smalyukh Hopfions are 3D particle-like knotted field configurations. Realized in liquid crystals and predicted to exist in magnets, a hopfion is the higher dimensional analog of widely studied 2D skyrmions, stimulating fundamental and technological interest. Recently, a new type of particle-like lattice-forming 3D topological soliton, dubbed heliknoton [1], was realized in the helical background of chiral liquid crystals and was predicted to exist in chiral magnets [1,2]. We demonstrate how hopfions and heliknotons inter-transform smoothly between one another when the background field of the host medium is switched by an electric field between uniform and helical states, with myriads of different energetically stable embodiments of Hopf-fibration-like topology with and without applied electric fields. At intermediate field, Hopfions embedded in a heliconical background were also observed. Furthermore, under a modulating electric field, we find that the hopfions (heliknotons) oscillate between the two flavors and display activated hopping-like motion in a 3D bulk. This emergent behavior of topological solitons emerges from a periodic reorientation of the molecular alignment field that breaks the time reversal symmetry. |
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