Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session H30: Organization and Dynamics of Functional Liquid Crystals, Polymers, and Biological Assemblies IFocus
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Sponsoring Units: GSOFT DPOLY DBIO Chair: Cecilia Leal, University of Illinois at Urbana-Champaign Room: BCEC 162B |
Tuesday, March 5, 2019 2:30PM - 2:42PM |
H30.00001: Assembling and organizing block copolymer nanostructures with the aid of liquid crystals Chinedum Osuji, Youngwoo Choo, Manesh Gopinadhan, Masafumi Fukuto, Ruipeng Li, Dennis Ndaya, Reuben Bosire, Yekaterina Rokhlenko, Ken Kawamoto, Jeremiah Johnson, Rajeswari Kasi Attaching mesogens to block copolymer backbones (BCP) can result in a rich interplay of self-assembly on multiple lengthscales, and provides new opportunities to control nanostructure development. We examine the self-assembly and directed-self assembly under magnetic fields of LC BCPs and BCP-analogous macromolecules containing mesogens. We observe a rich phase behavior, including the formation of gyroid morphologies and highly asymmetric phase diagrams, and we encounter systems with structural periodicities as small as ~6 nm. We consider the phase behavior and field alignment of a cylinder-forming system in the presence of labile mesogens that swell the LC block. The system transitions from hexagonal cylinders to FCC spheres beyond a critical mesogen concentration. Despite the isometric nature of the cubic lattice, the system aligns with the [100] axis parallel to the applied magnetic field, resulting in a degenerate, fiber-like texture. We speculate that this response may originate from symmetry breaking due to the action of the field that leads to a 2-step ordering process of the spherical microdomains. Alternatively, the response may indicate the presence of an unexpected magnetic easy axis in this cubic system. |
Tuesday, March 5, 2019 2:42PM - 2:54PM |
H30.00002: Bipolar to Radial Drop Transitions in the Presence of Novel Surfactants Jake Shechter, Benjamin Strain, Linda Oster, Jessica Sleator, FNU Manisha, Uma Sridhar, Juan De Pablo, Sankaran Thayumanavan, Jennifer Ross Liquid crystals (LCs) are a class of molecules that can form a variety of phases that can be influenced by external interactions. We are interested in controlling the phase of a liquid crystal droplet by controlling the interface between the organic liquid crystal (5CB) and the aqueous surfactant medium. This is an interesting physical system because the molecules at the surface can alter the phase of the LC throughout the interior by balancing the elastic energy of splay, twist, and bend against the interfacial tension. Here, we test the effects of novel amphiphiles, in the presence of SDS, on the phase of the LC droplets. We have synthesized molecules with various triggerable stimuli, such as pH, light, and protein binding. To help us understand the dynamics of the phase changes, we compare our experiments to simulations. We find that the phase transition is triggered by the addition of SDS, but not the novel surfactants. The concentration at which the phase transition occurs does not appear to depend on the droplet size, but does depend on the novel surfactant in the solution. Interestingly, we find a hysteresis in the concentration of the phase transition, from bipolar to radial and back again, that depends on the novel surfactant used. |
Tuesday, March 5, 2019 2:54PM - 3:06PM |
H30.00003: Physical insights on the self-assembly of myelin sheaths: what drives healthy lamellar stacks to disrupted inverted hexagonal phase Roy Beck, Rona Shaharabani Myelin sheath is a multilamellar complex of various lipids and proteins that surrounds axons and acts as an insulating layer for proper nerve conduction. In multiple sclerosis (MS), the myelin structure is disrupted impairing its function. Previous studies showed that MS is correlated with a small lipid composition variation and a reduction in the adhesive myelin basic protein (MBP). We show that such alterations result in structural instabilities and phase transition from a lamellar to inverted hexagonal phase, in accordance with pathological in vivo studies. Moreover, alteration in local environmental conditions, such as elevated salinity and temperature, drive the myelin system further into the inverted hexagonal phase [2]. Finally, we will demonstrate that the self-assembly of such complex system presents ion-specific structural modulation that is physiologically relevant. Since the etiology and recovery pathways of MS are currently unclear, these findings delineate novel functional roles to dominant constituents in cytoplasmic myelin sheaths. |
Tuesday, March 5, 2019 3:06PM - 3:42PM |
H30.00004: Mechanics and Ion Transport in Dynamic Polymer Networks based on Metal-Ligand Coordination in Polymeric Ionic Liquids Invited Speaker: Rachel Segalman Polymers that contain ionic liquid constituent retain many of the properties of ionic liquids including ionic conductivity. Further, the polymerized cation (such as imidazolium) forms transient ligand bond interactions with dissolved metal ions allowing them to conduct while also forming a dynamic network. Dynamic polymer networks based on metal-ligand coordination are promising materials to accomplish such decoupling due to the transient nature of the coordination interaction. The general system of interest comprises a metal salt mixed in a polymeric medium with ligands located either along the backbone or on pendant side-chains. The molecular design of these materials allows for precise and independent control over the nature and concentration of ligand and metal, the salt dissolution, and the binding energy between the ligand and metal, all of which shown to be critical for controlling bulk ion conduction and polymer mechanics. Salt dissociation is universally governed by coordination number, equilibrium constant, and initial salt and ligand concentrations. Salt dissociation is enhanced by larger equilibrium constants and higher cation valency. The sensitivity of the ionic conductivity on equilibrium constant, coordination number, and the ratio of cation to anion diffusion coefficients is much higher for monovalent salts compared to divalent or trivalent salts. In a model system composed of poly(ethylene oxide) with tethered imidazole moieties that facilitate salt dissociation of both nickel (II) bis(trifluoromethylsulfonyl)imide (NiTFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), the nickel-imidazole interactions physically crosslink the polymer, increase the number of elastically active strands, and dramatically enhance the modulus while allowing Li+ to conduct quickly through the matrix. |
Tuesday, March 5, 2019 3:42PM - 3:54PM |
H30.00005: Orientation of hard semiconducting nanoparticles by soft lyotropic lipid constructs Dylan Steer, Joseph C Flanagan, Marilyn Porras Gomez, Moonsub Shim, Cecilia Leal Quantum nanorods (QnR) are fluorescent nanoparticles with tunable optoelectronic properties depending on size and shape. These properties make them attractive in many biotechnology applications but due to their hydrophobic nature they are often hybridized by a shell of soft amphiphilic molecules. Anisotropic nanocrystals have orientation dependent properties, however controlling QnR alignment when drying from an organic solvent is difficult. We investigate the ability of amphiphilic molecules that are mostly known as stabilizers of QnRs in water to act as a matrix to guide QnR orientational order. Lipids are amphiphilic molecules that rapidly assemble into hierarchic liquid crystalline structures with various levels of positional and orientational order. These structures rapidly experience phase transitions depending on lipid composition, relative humidity, and temperature. Here we use glancing-incidence small angle X-ray diffraction (GI-SAXS) and fluorescence microscopy to study the co-assembly of lipid – QnR composites in highly concentrated regimes. Conditions are found to promote either the separation into lipid and highly ordered QnR domains, or the mixture of these components into a single phase with distinct structural characteristics. |
Tuesday, March 5, 2019 3:54PM - 4:06PM |
H30.00006: Elementary smectic ordering of “gapped” DNA duplexes Prabesh Gyawali, Rony Saha, Mirek Salamonczyk, James Gleeson, Antal Istvan Jakli, Hamza Balci, Samuel Sprunt We used small angle X-ray scattering and optical microscopy to study the liquid crystalline behavior of “gapped” DNA duplexes in aqueous solution. Our previous work1 revealed the occurrence of a smectic-A phase for DNA concentrations in the range ~230 to ~300 mg/ml and for a single-strand “gap” between duplexes of 20 thymine bases. Here we describe evidence for two coexisting/competing smectic-A-like layer structures, whose relative population varies with temperature and “gap” length. Smectic layering occurs for gap lengths down to 4 bases but disappears when the gap is reduced to 2 bases. Transitions from smectic to cholesteric/nematic state are observed as a function of temperature. |
Tuesday, March 5, 2019 4:06PM - 4:18PM |
H30.00007: Lipid-driven Crystallization of Block Copolymers in Lipid-Polymer Alloys Yoo Kyung Go, Cecilia Leal Tailoring crystallinity of blocks in crystalline-crystalline diblock copolymers (BCPs) is a route to gain control over the material’s optical and mechanical properties. One methodology that has successfully tuned BCPs crystallinity is to include additives to the assembly.[1] In this work, we investigate the crystallization behavior of BCPs as tuned by the addition of a biological lipidic component. We adopted 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) as an additive to induce crystallization-driven self-assembly of poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO). Herein, we scrutinize the effects of the lipids on crystallization of each block in PCL-b-PEO at multiple length scales by IR spectroscopy, differential scanning calorimetry, wide-angle X-ray scattering, small-angle X-ray scattering, and polarization optical microscopy. We discovered that DPPC and BCPs assemble in a uniform alloy with a lamellar structure at the mesoscale. Within this structure, the lipid can enhance crystallinity of PCL while suppressing that of PEO. The crystalline domains appear tubular at the nanoscale and the alloy displays large platelet morphologies at the microscale compared to pure neat polymeric systems. [1] ACS Nano 2015, 9, 4, 3627-3640 |
Tuesday, March 5, 2019 4:18PM - 4:30PM |
H30.00008: Molecular Dynamics Simulations of Elastic Capsomeres Self Assembling into a Virus Capsid Lauren Nilsson, Jayanath Chamindu Kadupitige, Martin Jarrold, Vikram Jadhao Viruses are an important class of soft biological materials that are capable of self-assembling into capsids that are often icosahedral-shaped. However, this self-assembly process is not completely understood in part due to the arduousness and simulation cost of correlated investigations between experiments and rigid-body models of constituent capsomere subunits. Experimentally-informed, hybrid OpenMP/MPI parallelized molecular dynamics simulations of a coarse-grained model composed of elastic capsomeres are used to investigate the assembly pathway of heterogeneous icosahedral viruses, focusing on Hepatitis B virus (HBV) as a first application. Simulation results are correlated to data from charge detection mass spectrometry. Based on the time-dependent mass spectrums and steady-state phase diagrams associated with the self-assembly of HBV at 5-100 micromolar protein and 100-500 millimolar salt concentrations, we propose that the formation of both 90- and 120-capsomere (T3, T4) structures in HBV can be attributed to relatively low bending modulus of HBV capsomeres (10-15 kB T). Further, HBV self-assembly exhibits hierarchical features for small (<120 capsomere) icosahedral structures. |
Tuesday, March 5, 2019 4:30PM - 4:42PM |
H30.00009: Luminescent Liquid Crystals Based on Platinum(II) Complexes xingtian Hao, Haiyan Peng, Xiaolin Xie Luminescent liquid crystals, which hold outstanding optical anisotropy, fluidity and intrinsic photoluminescence characteristic, show a great potential to be widely applied in liquid crystal display, organic light-emitting diode, optical information storage, etc. Yet, it still remains a big challenge to enhance and tune the luminescent properties. Herein, we report a highly luminescent liquid crystals based on platinum(II) complexes. These complexes are able to relax from the excited state back to the ground state through spin-forbidden transitions, giving rise to distinct photochemical and photophysical features in comparison with traditional organic fluorophores. Flexible side chains are found to play a significant role in enabling the liquid crystal phase due to the strong intermolecular interaction between the complex’s square-planar structure. |
Tuesday, March 5, 2019 4:42PM - 4:54PM |
H30.00010: Effect of Lipid Headgroup on Polymer-Lipid Bilayer Association Wenjia Zhang, Frank Bates, Timothy Lodge Cell membrane composition plays an important role in binding to polymers. We have investigated the effect of lipid headgroup on the interaction between model membranes and amphiphilic and biocompatible diblock and triblock polymers composed of ethylene oxide and propylene oxide. Large unilamellar phospholipid vesicles were used as model membranes to mimic the lipid bilayer structure of cell membranes. The composition of the lipid headgroup was manipulated by altering the amount of phosphatidylcholine and phosphatidylglycerol in the lipid bilayers, thereby varying the molar ratio of choline to glycerol headgroups. Polymer binding to lipid bilayers was quantified by pulsed-field-gradient NMR, which differentiated the polymers bound to lipid bilayers from free polymers based on their distinct diffusivities. It was observed that polymer binding significantly increases as the concentration of glycerol in the lipid bilayer increases, which could be due to the hydrogen bonds formed between poly(ethylene oxide) and the glycerol group of phosphatidylglycerol. |
Tuesday, March 5, 2019 4:54PM - 5:06PM |
H30.00011: Spontaneous and diverse morphological transitions of nematic liquid crystal oligomer micro-droplets Wei-Shao Wei, Yu Xia, Sophie Ettinger, Shu Yang, A. G. Yodh Viruses and pollen grains are known for their diverse morphologies and surface patterns, which play important roles to their functions. It begs the questions how the patterns were originated and then evolved. Here, we report the spontaneous morphological transformations from micro-droplets, consisting of polydispersed nematic liquid crystal oligomers (NLCOs) suspended in water, to a strikingly rich set of nematic structures, including roughened spheres, flowers, and filamentous structures. We investigate the interplay of elasticity and interfacial tension within the drop as a function of temperature, surfactant concentrations, and the LCO chain length distribution. We show that heterogeneity of LCO chain length is a feature leading to segregation of LCOs within the micro-droplet. The transformed morphologies are highly uniform in size and can be locked via UV curing. The study of synthetic systems offers a first attempt to understand the origin of complex morphologies in biological world. |
Tuesday, March 5, 2019 5:06PM - 5:18PM |
H30.00012: Design Diblock Copolymers for More Efficient Encapsulation Bilin Zhuang, Minh Tuan Nguyen, Freda C.H. Lim The encapsulation of active molecules is often a crucial step in pharmaceutical and consumer care formulation processes. Diblock copolymers, with the right chemical structures, are potentially effective in encapsulating various hydrophobic active molecules. A model that predicts the encapsulation efficiency of diblock copolymers would therefore be helpful to guide the design of the diblock copolymers so that the encapsulation of specific active molecules can be maximized. Here, by combining group contribution method and self-consistent-field theory, we develop a model for computing the encapsulation free energy of drug molecules by diblock copolymers in a solution, based on the chemical structures of the constituents in the system. We systematically explore how the encapsulation free energy and the resulting morphology of the encapsulates depend on the variation in the chemical structures of the diblock copolymers. |
Tuesday, March 5, 2019 5:18PM - 5:30PM |
H30.00013: Deciphering and Engineering Reentrant Phase Transition of Intrinsically Disordered Proteins Priya Banerjee Formation of intracellular RNA- and protein-rich granules (RNP granules) are primarily driven by liquid phase condensation of Intrinsically Disordered Proteins (IDPs). What are the molecular driving forces that control the material properties and morphology of RNP granules? Using mixtures of multivalent charged IDPs and RNA that display reentrant phase behavior, we show that (a) the condensed phase is predominantly droplet-like under equilibrium conditions, and (b) the material properties are primarily tuned by the charge regulated electrostatic interactions. Unexpectedly, hollow condensates are formed under non-equilibrium conditions by RNA influx into RNP droplets1. We propose that this spontaneous morphological transformation of RNP droplets is actuated by RNA-mediated mixing phase transition at the droplet center. By controlling the RNA inflow using simple microfluidic designs, complex patterns of hollow condensates can be generated stochastically. Our results suggest that cellular processes that can drive an active RNA influx into RNP droplets, such as transcription, can spatiotemporally control their material properties and morphology. |
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