Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session F50: Chirality in Polymers and Soft Matter III: Networks, Lyotropics and ColloidsFocus
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Sponsoring Units: DPOLY GSOFT DBIO Chair: Gregory Grason, University of Massachusetts Amherst Room: BCEC 252B |
Tuesday, March 5, 2019 11:15AM - 11:51AM |
F50.00001: Emergence of large-scale chirality in photonic crystals in insects and butterflies Invited Speaker: Gerd Schroeder-Turk The biological world is filled with chiral structures, formed from a soup of building blocks that usually include both achiral and chiral molecules. In this talk, I will focus on chiral structures that emerge at the scale of hundreds of nanometers in solid insect nanostructures, and that then act as biophotonic crystals. Of particular interest in this context are the Gyroid nanosolids that form in several butterflies, as highly ordered 3D network-like porous materials, and which then contribute in particular to green coloration. I will review in particular what we understand (and not understand) about the formation of these structures; in this context, the fortuitous discovery of a butterfly nanostructure in Thecla Opisena is noteworthy. It appears to show a time-frozen snapshot of various stages of the formation which allows us to infer properties of the formation from high-resolution electron and X-ray tomography images. |
Tuesday, March 5, 2019 11:51AM - 12:03PM |
F50.00002: Chiral Gyroidal Thin Films from Block Copolymer Self-Assembly as Structural Directing Templates for Fabrication of Mesostructured Crytalline Inorganic Materials Qi Zhang, Fei Yu, Ulrich Wiesner It has always been a challenge to fabricate crystalline materials with well-defined mesopores, which could find applications in microelectronics and catalysis. Block copolymer self-assembly offers a scalable, facile pathway to intricate mesostructures. We present on the use of amphiphilic triblock terpolymer co-assembly with additives to prepare high-temperature stable, mesoporous thin-film templates with chiral alternating gyroid structures (GA). This mesoscale chirality emerges from the calcination and preservation of only one of the interpenetrating GA domains and is inaccessible via conventional top-down approach. The resulting mesoporous molds can be backfilled with a wide range of inorganic materials to direct their mesostructures. Upon melting via transient laser heating on the nanosecond time scale, crystallized materials conformally fill the 3D continuous mesopores and inherit the chirality, without destroying the underlying template. Template removal yields mesoporous, crystalline inorganic materials, with optional epitaxy on the substrate. |
Tuesday, March 5, 2019 12:03PM - 12:15PM |
F50.00003: New Spontaneously Chiral 3D Network Structures in Thermotropic Liquid Crystals Goran Ungar, Huanjun Lu, Yaxin Li, Xiang-bing Zeng Spontaneous mirror symmetry breaking has been discovered recently in bicontinuous cubic phases [1], as well as in a special isotropic melt phase [2] of achiral rod-like mesogens. While the double gyroid Ia-3d phase is always achiral, the triple network cubic, previously given the Im-3m spacegroup, is always chiral. More recently in such compounds another chiral phase was found [3], turning out to be the so-called “SmQ”. This phase has previously been found only in enantiopure chiral compounds, and its structure was unclear. Now we find that it is also bicontinuous, with two isochiral networks of orthogonal twisted columns [3]. We have also re-examined the triple-network phase; due to its now recognised chirality, a new lower-symmetry spacegroup is assigned, resulting in a new structural model, still a triple network. It thus turns out that all known bicontinuous phases formed by transverse-lying rods in networks segments feature induced chirality, which is cancelled only in the racemic double gyroid. |
Tuesday, March 5, 2019 12:15PM - 12:27PM |
F50.00004: Self-assembly of chiral networks in achiral block copolymer systems using coarse-grained simulations Poornima Padmanabhan, Natalie Buchanan, Krysia Browka Ordered network materials, such as the double gyroid, are comprised of two interwoven networks embedded in a matrix and can be formed via the self-assembly of block copolymers. Using a triblock copolymer, one can form an alternating gyroid thereby breaking network symmetry and resulting in a structurally chiral morphology. In this talk, we investigate the self-assembly of model achiral block copolymers into gyroid morphologies using coarse-grained molecular simulation. By co-assembling with a selective homopolymer, the thermodynamic stability of the morphology is further improved. The geometric topology is quantified, and the effect of varying volume fraction on net chirality is explored. |
Tuesday, March 5, 2019 12:27PM - 12:39PM |
F50.00005: Chirality from segments to domain shapes in ordered block copolymer networks Abhiram Reddy, Ishan Prasad, Gregory Grason Multi-continuous structures offer an attractive route to devise functional materials where three dimensional microphase geometry can influence transport, mechanical, and optical properties. BCPs, assemble into a variety of such network phases, provide the ability to tune the properties of the network structures. Recently, it has been shown that underlying the inhomogeneous spatial density profiles of BCP domains, are intra-domain segment orientation textures that couple to the domain geometry. Here, we will quantify chirality at different length scales in these self-assembled systems and ask specifically what is the coupling of domain geometry on local segment twist. To this effect, we define two measures of chirality at global (inter-node dihedral rotation at the network scale) and local (cholesteric ordering at segment scale) and study their correlation in network morphologies self-assembled from ABC terpolymers. We use SCFT to show how these chiral order parameters change upon varying volume fraction, interblock repulsion and network symmetry. This study forms the basis to understand the thermodynamics of chirality transfer from chiral interactions at the segment scale to controllable chiral network symmetries at the mesodomain scale. |
Tuesday, March 5, 2019 12:39PM - 12:51PM |
F50.00006: Lyotropic Liquid Crystals: The Emergence of Chiral Structures Mohan Srinivasarao, Kathik Nayani, Jung Ok Park, Jinxin Fu, Rui Chang Crystallization of tartrates by Pasteur provided the first glimpse of spontaneous mirror-symmetry breaking, and that led to the foundation of stereochemistry as a discipline. A consequence of mirror-symmetry breaking is optical activity, and since the time of its discovery by Biot in the early 1800s, has fascinated scientist. Since those early studies, the appearance of macroscopic chirality from both chiral and achiral molecules has been of interest. In this talk, we discuss the appearance of macroscopic chiral structures from a class of liquid crystals, referred to as lyotropic liquid crystals under various conditions. |
Tuesday, March 5, 2019 12:51PM - 1:03PM |
F50.00007: A different kind of Lyotropic Liquid Crystalline Phase: The case of Orange-II and gamma-Cyclodextrin Germano Iannacchione, Jung Ok Park, Mohan Srinivasarao Liquid crystallinity, either thermotropic or lyotropic, arises from species which are either rod or disk shaped. Lyotropic systems occur when an asymmetrically shaped species is dissolved in a solvent at a concentration high enough to force the formation of an anisotropic phase. For either case, the asymmetrically shaped species can be built solely from covalent bonds, where no additional assembling process is required for the species to have an appropriate aspect ratio. Here, we report on the formation of a different kind of lyotropic liquid crystal formed by the non-covalent association of two species, g-cyclodextrin and a dye molecule, Orange II, in water as the solvent. This system is different in that it requires two different compounds that self-assemble to build a larger species with geometrical asymmetry. In an effort to understand the complexation and the formation of the liquid crystalline phase, we present data on UV-Visible spectra, conductometric titrations, fluorescence spectroscopy as well as heat capacity measurements on the formation of the anisotropic structure in water solutions. The studies point to a stoichiometry of 2 dye molecules per g-cyclodextrin, that eventually form a rodlike entity, giving rise to the formation of a liquid crystalline phase. |
Tuesday, March 5, 2019 1:03PM - 1:15PM |
F50.00008: Microdomain morphology, curvature and twist in colloidal membranes of bidisperse rod mixtures Douglas Hall, Joia Miller, Joanna Robaszewski, Michael F Hagan, Zvonimir Dogic, Gregory Grason Long and short rod-like viral particles condense into a single-layer membrane driven by a dextran depletant. The organization of the micron-sized rods is more easily probed experimentally than nanometer scale structures in phospholipid membranes, yet both systems are described by liquid crystalline models. In the colloidal membrane system, rods microphase separate and form circular raft domains with self-limiting domain size in equilibrium, much larger than the range of rod-rod interactions. Recent experimental evidence shows that the intra-membrane domain boundaries discriminate between long-rod and short-rod sides, so that short-rod rafts twist significantly more than long-rod rafts. Also, long-rod rafts are unstable to asymmetric and concave morphologies. We develop a model to describe the microstructure and thermodynamic effects of the intra-rod domain edge, and we predict a thermodynamic coupling between domain edge curvature and rod-tilt. This coupling is achiral and distinct from the aspects of raft formation previously captured by a chirality driven model. We argue that this curvature/tilt coupling should exist in any model of phase-separating membranes as a coupling between in-plane tilt and second-derivatives of composition. |
Tuesday, March 5, 2019 1:15PM - 1:27PM |
F50.00009: Microphase Separation and Stability of Chiral Rafts in Colloidal Membranes Chaitanya Joshi, Joia Miller, Arvind Baskaran, Gregory Grason, Zvonimir Dogic, Michael F Hagan, Aparna Baskaran Colloidal membranes are an experimental system composed of rod-like chiral particles that are driven by depletion interactions to self-assemble into one-rod-length thick monolayers. Their large size enables the study of behaviors that cannot be visualized in lipid bilayers, as they are described by the same continuum theory. Membranes formed from a mixture of short right-handed rods and long left-handed rods exhibit microphase separation, wherein one rod species forms finite-sized rafts floating in a background membrane of the other rod species. This system exhibits complex membrane-mediated interactions between rafts, which depend on the depletant concentration and the chirality of the rods. In this talk I will present a Ginzburg-Landau theory that explains the existence and interactions of rafts. Consistent with recent experiments, we find that decreasing the background chirality allows rafts to form with either right-handed (in the direction preferred by chirality) or left-handed (counter to the preferred direction) twist. Further, pairs of like-twisted rafts have repulsive interactions, while pairs of oppositely-twisted rafts have attractive interactions. The theory allows for a mechanistic understanding of these behaviors. |
Tuesday, March 5, 2019 1:27PM - 1:39PM |
F50.00010: Light-Matter Interactions of Chiral Inorganic Nanomaterials Nicholas Kotov The studies of photonics phenomena in chiral inorganic nanoparticles (NPs) encompass sophisticated nanoscale constructs from metals, semiconductors, ceramics, and nanocarbons with multiple chiral geometries with characteristic scales from Ångströms to microns. What drives the rapid development of this field are the uniquely high values of optical anisotropy are attributed to resonances of incident electromagnetic radiation with plasmonic and excitonic states typical for metals and semiconductors as well as resonant states. Distinct similarities between the geometries and light-matter interactions involving chiral supramolecular and biological systems can also be traced. The analysis of these similarities with known biological, supramolecular, and liquid crystalline materials help us understand in greater depth the role of chiral asymmetry in Nature and accelerate the development of technologies based on chiroplasmonic, chiroexcitonic, and chiromagnetic effects. Technological prospects of chiral inorganic materials with current front-runners being biosensing, chiral catalysis, polarization optics and chiral photonics will be discussed in this talk. |
Tuesday, March 5, 2019 1:39PM - 1:51PM |
F50.00011: Exploiting shape to control percolation of grain boundaries in packings of ellipsoids on curved surfaces Zhaoyu Xie, Tim Atherton Packings of hard objects provide insights into the properties of crystals, glasses and granular media. When the packing occurs on a curved surface, it requires defects to accommodate the curvature. For identical spheres packed on a spherical surface, the packings are largely crystalline with grain boundaries or “scars”, while for sufficiently polydisperse spheres the packings typically form an amorphous state. We recently showed that these regimes can be connected by a percolation transition on the neighbor graph, whereby the scars grow as a function of particle size anisotropy. Here we show that manipulating particle shape can cause a similar transition. Ellipsoids of varying aspect ratio are packed on a spherical surface with scars at low aspect ratio; these scars elongate and disconnect the crystalline regions with increasing aspect ratio. The cluster growth and scaling are shown to agree with percolation theory. The influence on the cluster growth of interactions between the particle shape and the surface on which they are packed will also be presented, as well as prospects for the exploitation of other particle shapes, such as chiral particles, to control the transition. |
Tuesday, March 5, 2019 1:51PM - 2:03PM |
F50.00012: Formation of Twisted Bundles from Small Regular Arrays of Polymer Nanopillars Cheng Zeng, Isaac Bruss, Mohammad Shahjamali, Edvin Memet, Vinothan N Manoharan Elastocapillary assembly has been used to form twisted bundles in large arrays of nanopillars, often placed in square lattices. We study how the emergence of twisting can be controlled by both the dimensions of individual pillars and the local bundle geometry. Using direct laser writing, we fabricate nanopillars with high spatial resolution in arbitrary lattices. The bundles are composed of a central pillar surrounded by 4 to 7 outer pillars that are evenly spaced from one another. Although no chirality is programed into the design, we find that twisted bundles form under certain combinations of pillar spacing (D) and pillar height (H). Interestingly, we find that achiral bundles always form when D/H is small, even with long and flexible pillars. We find a transition from achiral to chiral bundles when D/H is 0.2 to 0.3. To understand this transition, we use a scaling model and numerical simulations. |
Tuesday, March 5, 2019 2:03PM - 2:15PM |
F50.00013: Chiral Self-Assembly of Flexible High Aspect Ratio Nanopillars Mohammad Shahjamali We present experimental self-assembly of high aspect ratio nanopillars into chiral clusters in response to capillary force. We take advantage of pillars with an aspect ratio of up to 500 with adjustable dimension, shape, porosity and two-dimensional arrangement fabricated by two-photon lithography and oxygen plasma etching. Using such freedom of design in combination with the kinetically controlled evaporation of a liquid, we devise systems where we can externally introduce five-fold disclination defects on the surface of clustered pillars due to geometrical frustration. In addition, we can kinetically control the number of assembled clusters per array and adjust the handedness of the twists in asymmetrical arrays of nanopillars. |
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