Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session R37: Liquid Crystals: Dimers and Liquid Crystal Applications |
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Sponsoring Units: GSOFT Chair: Antal Jakil, Kent State University Room: 340 |
Thursday, March 17, 2016 8:00AM - 8:12AM |
R37.00001: The twist-bend nematic phase of bent mesogenic dimers and its mixtures Michael Tuchband, Min Shuai, Keri Graber, Dong Chen, Leo Radzihovsky, Arthur Klittnick, Lee Foley, Alyssa Scarbrough, Jan Porada, Mark Moran, Eva Korblova, David Walba, Matthew Glaser, Joesph Maclennan, Noel Clark Binary mixtures of the twist-bend nematic-forming liquid crystal CB7CB with the prototypical rod-like liquid crystal 5CB exhibit a twist-bend nematic phase with properties similar to those reported for neat CB7CB. The linear dependence of the phase transition temperature on concentration indicates that these binary mixtures are nearly ideal. We confirm the presence of nanoscale modulations of the molecular orientation in the mixtures by freeze-fracture transmission electron microscopy (FFTEM). We devise and implement a statistical approach to quantitatively measure the ground state pitch of the twist-bend phase and its mixtures using FFTEM. The addition of 5CB generally shifts the measured ground-state pitch distributions towards larger pitch. The pitch apparently increases discontinuously at higher 5CB concentrations. [Preview Abstract] |
Thursday, March 17, 2016 8:12AM - 8:24AM |
R37.00002: Resonant soft X-ray scattering study of twist bend nematic phase Chenhui Zhu, Anthony Young, Cheng Wang, Alexander Hexemer, Quan Li, Oleg Lavrentovich, David Walba, Michael Tuchband, Min Shuai, Noel Clark Liquid crystals (LCs) form many interesting nano-scale structures, many of which can be probed with X-ray scattering techniques, typically hard X-rays due to its high penetrating power. However, in the hard X-ray regime, the scattering contrast of some LC nanostructures can be extremely low due to their weak electron density modulation. Here we show it is possible to use resonant soft x-rays to probe the helical pitch of the newly discovered twist bend nematic phase [1,2], which is purely a twist bend structure with no electron density modulation. The in-situ temperature dependent measurement will be presented and discussed. This work together with our previous study on the helical nanofilament B4 phase [3] shows the great potential of soft x-ray scattering in liquid crystals. [1] D. Chen, et al. \textit{PNAS}, DOI 1314654110 (2015). [2] V. Borshch, et al. \textit{Nat. Comm}., \textbf{4}, 2635 (2015). [3] C. Zhu, et al. \textit{Nano. Lett.} \textbf{15}, 3420 (2015). [Preview Abstract] |
Thursday, March 17, 2016 8:24AM - 8:36AM |
R37.00003: Dynamic Light Scattering on a Twist-Bend nematic Liquid Crystal Zeinab Parsouzi, Shaikh Shamid, Volodymyr Borshch, Pavan Challa, Gabriela Tamba, Georg Mehl, James Gleeson, Antal Jákli, Oleg Lavrentovich, David Allender, Jonathan Selinger, Samuel Sprunt We present a dynamic light scattering study performed on the uniaxial and twist-bend nematic (N$_{TB})$ phases of a liquid crystal dimer/monomer mixture. In the nematic phase, in addition to the usual two hydrodynamic director modes, the results reveal a single non-hydrodynamic process that is associated with fluctuations in orientational order in the plane perpendicular to the primary (uniaxial) ordering direction. On the other hand, data from the N$_{TB}$ phase demonstrate a pair of non-hydrodynamic modes and a single hydrodynamic mode. The non-hydrodynamic modes are strongly temperature-dependent, slowing down as the transition is approached from the N$_{TB}$ side. Our results may be explained by a Landau-deGennes expansion of free energy for the N to N$_{TB}$ transition in terms of a helical polarization field, which is nonzero in the N$_{TB}$ state and is coupled to the heliconical director that characterizes the N$_{TB}$ state. The short pitch of the structure allows a ``coarse-graining'' of the free energy that accounts for the observed fluctuation mode structure and properties at optical wavevectors. In the model, the helical axis is the effective director, and the helical planes become smectic-like layers. We estimate an effective compression constant, B $=$ 4000 Pa, for the N$_{TB}$ ``layer'' structure. [Preview Abstract] |
Thursday, March 17, 2016 8:36AM - 8:48AM |
R37.00004: Layer Thinning in Freely-Suspended Thin Liquid Films of a Symmetric Liquid Crystal Dimer Shokir Pardaev, Zeinab Parsouzi, James Gleeson, Antal Jakli, Samuel Sprunt We report optical reflectivity and dynamic light scattering (DLS) studies on freely suspended smectic films of a symmetric liquid crystal dimer, which exhibits the phase sequence isotropic---nematic---twist-bend nematic---smectic in cooling. In sufficiently thin films the reflectivity $R$ is expected to scale as the square of the number of smectic layers ($N^{\mathrm{2}})$ while the frequency $f$ of underdamped layer fluctuations scales as $N^{\mathrm{-1/2}}$. On heating thin films drawn in the smectic phase, we observe a sequence of layer thinning transitions, with $R$ and $f$ following the expected scaling relations, provided the stepwise melting involves double rather than single layers. We will describe a model to explain the unusual layer thinning process.$\backslash $pardWe thank M. G. Tamba and G. Mehl for providing the liquid crystal compound: NSF grant DMR-1307674. [Preview Abstract] |
Thursday, March 17, 2016 8:48AM - 9:00AM |
R37.00005: ABSTRACT WITHDRAWN |
Thursday, March 17, 2016 9:00AM - 9:12AM |
R37.00006: Giant Magnetic Field-induced Phase Transitions in Dimeric Liquid Crystals. Seyyed Muhammad Salili, Miroslaw Salamonczyk, Maria-Gabriela Tamba, Samuel Sprunt, Georg Mehl, Antal Jakli, James Gleeson Liquid crystals are responsive to external fields such as electric, magnetic fields. The first experimental observation of dependence of isotropic to nematic phase transition on the applied magnetic field was done using a strong magnetic field on bent-core nematogens and the phase transition temperature exhibited an upshift of 0.7 C at B$=$30 T [1]. We report on measurements of giant magnetic field-induced isotropic-nematic transition of chainsticks (nunchuks) type dimeric liquid crystals. Upon using the B$=$25 T split-helix resistive solenoid magnet at NHMFL, we have observed up to 18 C upshift of the isotropic to nematic phase transition temperature at B$=$22T. We discuss the results within the context of differential thermodynamic potential and the two basic mean-field theories. To our knowledge, this is the first observation of such huge shifts in the phase transitions of thermotropic liquid ctystals. [1] T. Ostapenko et al, Phys. Rev. Lett. 101, 247801 (2008). [Preview Abstract] |
Thursday, March 17, 2016 9:12AM - 9:24AM |
R37.00007: Smectic Phase Formed by DNA Dimers Miroslaw Salamonczyk, James Gleeson, Antal Jakli, Samuel Sprunt, Jan Dhont, Emmanuel Stiakakis h $-abstract-$\backslash $pard The rapidly expanding bio market is driving the development and characterization of new multifunctional materials. In particular, nucleic acids are under intense study for gene therapy, drug delivery and other bio-safe applications [1,2,3]. DNA is well-known to form a cholesteric nematic liquid crystal in its native form; however, much recent research has focused on self-assembly and mesomorphic behavior in concentrated solutions of short DNA helices [4]. Our work focuses on DNA dimers, consisting of 48 base-pair double-stranded helices connected by a 5 to 20 base flexible single strand, and suspended in a natural buffer. Depending on temperature, concentration and length of the flexible spacer, polarizing optical microscopy and small angle x-ray scattering reveal cholesteric nematic and, remarkably, smectic liquid crystalline phases. A model for smectic phase formation in this system will be presented.1] J.-L. Lim et al., Int. J. of. Pharm. 490 (2015) 2652] D.-H. Kim et al., Nature Biotech. 23 (2005) 2223] K. Liu et al., Chem. Eur. J. 21 (2015) 48984] M. Nakata et al., Science 318 (2007) 1276$\backslash $pard-/abstract-$\backslash $\tex [Preview Abstract] |
Thursday, March 17, 2016 9:24AM - 9:36AM |
R37.00008: Lipid decorated liquid crystal pressure sensors Tetiana Lopatkina, Piotr Popov, Lawrence Honaker, Antal Jakli, Elizabeth Mann Surfactants usually promote the alignment of liquid crystal (LC) director parallel to the surfactant chains, and thus on average normal to the substrate (homeotropic), whereas water promotes tangential (planar) alignment. A water-LC interface is therefore very sensitive to the presence of surfactants, such as lipids: this is the principle of LC-based chemical and biological sensing introduced by Abbott et al[1].Using a modified configuration[2], we found that at higher than 10 micro molar lipid concentration, the uniformly dark texture seen for homeotropic alignment between left-, and right-handed circular polarizers becomes unstable and slowly brightens again. This texture shows extreme sensitivity to external air pressure variations offering its use for sensitive pressure sensors. Our analysis indicates an osmotic pressure induced bending of the suspended films explaining both the birefringence and pressure sensitivity. In the talk we will discuss the experimental details of these effects. [1] J. M. Brake, M. K. Daschner, Y.-Y. Luk, and N. L. Abbott, Science (80-. ). 302, 2094 (2003). [2] P. Popov, E. K. Mann, and A. Jakli, Phys. Rev. Appl. 1, 034003 (2014). [Preview Abstract] |
Thursday, March 17, 2016 9:36AM - 9:48AM |
R37.00009: 2D and 3D Histioid Disclination Networks in Liquid Crystals Miao Jiang, Yubing Guo, Oleg Lavrentovich, Qi-Huo Wei Topological defects and disclination lines are of both fundamental interest and practical importance. In this paper, we will show that periodic/non-periodic 2D/3D networks of disclination lines can be created in nematic liquid crystal cells by setting well-designed alignment patterns at the top and bottom substrate surfaces. The desired complex patterns of liquid crystal molecular alignments at the substrates are obtained using a projection photoalignment technique based on plasmonic metamasks. The designs of alignment patterns and their resulting disclination line networks will be presented. These designable topological networks represent a new kind of artificial materials which could be of useful for directing colloidal and molecular assembly. [Preview Abstract] |
Thursday, March 17, 2016 9:48AM - 10:00AM |
R37.00010: Photophysics of guest-host liquid crystal systems containing naphthopyran derivatives Mariacristina Rumi, Tamas Kosa, Ludmila Sukhomlinova, Bahman Taheri, Timothy White, Timothy Bunning Photoinduced order-increase changes can be observed in guest-host liquid crystal systems containing certain phototropic species, such as naphthopyrans. We are investigating the dynamics of the naphthopyran photoinduced interconversion reaction and the related liquid crystal order increase process as a function of excitation conditions and temperature. The thermal relaxation from different photostationary states is also been monitored. The guest-host system behavior is compared with that of the same guest species in isotropic media and other photoresponsive materials in liquid crystalline media, to determine if the naphthopyran interconversion reaction is affected by the anisotropy of the environment surrounding the guest molecules. This will provide a better understanding of the mutual influence of the guest and host molecules on the properties of the photoresponsive mixed systems. [Preview Abstract] |
Thursday, March 17, 2016 10:00AM - 10:12AM |
R37.00011: Plasmonic Photopatterning of Complex Molecular Orientations in Liquid Crystals Yubing Guo, Miao Jiang, Chenhui Peng, Kai Sun, Oleg Yaroshchuk, Oleg Lavrentovich, Qi-Huo Wei Aligning liquid crystal (LC) molecules in spatially non-uniform patterns are highly demanded for applications such as programmable origami and liquid crystal enabled nonlinear electrokinetics. We developed a high resolution projection photoalignment technique for patterning arbitrary LC alignment fields. The photoalignment is based on carefully engineered metasurfaces, or dubbed as plasmonic metamasks (PMMs). When illuminated by light, the PMMs generate patterns of both light intensity and polarization. By projecting the light transmitted through the PMMs onto liquid crystal cells coated with photosensitive materials, alignment patterns predesigned in polarization patterns of the PMMs can be imposed in liquid crystals. This technique makes the liquid crystal alignment a repeatable and scalable process similar to conventional photolithography, promising various applications. [Preview Abstract] |
Thursday, March 17, 2016 10:12AM - 10:24AM |
R37.00012: Flow Meter Based on Freely Suspended Smectic Liquid Crystal Films Adam Green, Zhiyuan Qi, Cheol Park, Matthew Glaser, Joseph Maclennan, Noel Clark We present the realization of a idealized 2D hydrodynamic system coupled to air-flow, and show that freely suspended films (FSF) of smectic liquid crystals can be used as a novel flow-meter. Freely-suspended films of liquid crystals are one of the closest physical realizations of an idealized 2D fluid. The velocity of air-flow above a film suspended above a channel can be inferred by studying the velocity profile of the smectic film. This velocity profile can be measured using digital video microscopy to track the inclusions present in the moving film. The velocity profile is then fitted to the coupled 2D solutions of an embedded fluid in air, and the velocity of the air can then be extracted. This flow meter serves as a demonstration of a robust test-bed for further exploration of 2D hydrodynamics. [Preview Abstract] |
Thursday, March 17, 2016 10:24AM - 10:36AM |
R37.00013: Optical fibers based on compositions of polymers and liquid crystals for gas detection. Petr Shibaev, Anthony Tantillo Optical fibers based on compositions of methacrylic and vinyl polymers mixed with low molar mass liquid crystals were prepared and studied as promising gas sensors. A range of concentrations producing anisotropic fibers that are mostly sensitive to the vapors of organic solvents was determined. The fibers were prepared by stretching gel-like compositions of polymers and liquid crystals. Mechanical properties of the compositions leading to the most stable fibers were studied. It was found that under certain conditions the fibers develop multilayered structure with anisotropic (mostly liquid crystalline) core. These fibers are very sensitive to changing gaseous atmosphere and to the presence of organic solvent vapors. The sensitivity of different types of fibers to a variety of organic solvents vapors was determined. Some fibers were crosslinked by using hydrogen bonding molecules. The behavior of these optical fibers with respect to the influence of organic vapors with and without hydrogen donor/acceptor moieties was also analyzed. It was shown that hydrogen bonding increases the mechanical strength of the fibers but does not affect substantially their sensitivity to gases. Optical calculations and model discussion accompany the presentation of experimental data. [Preview Abstract] |
Thursday, March 17, 2016 10:36AM - 10:48AM |
R37.00014: Reorientation and isotropisation of liquid crystals induced by gas diffusion. Anthony Tantillo, Petr Shibaev Reorientation and isotropisation of liquid crystals induced by organic solvent vapors was studied experimentally in relation to the use of liquid crystals as gas sensors. Reorientation and isotropisation were studied in the droplets deposited on the flat surface and on the tip of the hollow fibers. The anisotropy of gas diffusion was studied in the films and droplets of different sizes deposited on the surfaces with planar and homeotropic conditions. It was revealed that the diffusion coefficients differ approximately by a factor of two for liquid crystals in planar and homeotropic orientations. It was also shown that interference pattern created by passing light in liquid crystalline droplets deposited on the planar surface and on the tip of the hollow fiber can be used in detection of very small concentration of vapors. The model of diffusion is suggested and molecular dynamics simulations of the diffusion in liquid crystals with different molecular orientation are performed. The molecular dynamics simulations were performed on a time scale of about tens nanoseconds. In general they confirm the experimental results, but provide larger differences (by a factor 2 to 4) for diffusion coefficient in liquid crystals with planar and homeotropic orientation. [Preview Abstract] |
Thursday, March 17, 2016 10:48AM - 11:00AM |
R37.00015: Drying, phase separation, and deposition in droplets of sunset yellow chromonic liquid crystal Adam Gross, Zoey S. Davidson, Yongyang Huang, Tim Still, Chao Zhou, A.G. Yodh We investigate the drying process and the final deposition patterns of multi-phase sessile droplets containing aqueous lyotropic chromonic liquid crystal (LC). The experiments employ a variety of optical techniques including profilometry, polarization optical microscopy and optical coherence microscopy. An unusual hierarchical LC assembly is observed during drying; in particular, LC mesogens are first formed at the start of drying and then compartments of isotropic, nematic and columnar phases arise. Nonuniform evaporation creates concentration gradients in droplets such that LC phases emerge from the outer edge of the drop and advance to the center over the course of drying. Distinct outward flows associated with the ``coffee-ring effect’’ are seen initially, but the assembly of the mesogens creates viscosity, density, and surface tension gradients that effectively introduce new convective flows and complex LC phase boundaries within the drop. Finally, we show that the final deposit shape of chromonic materials changes with rate of evaporation. [Preview Abstract] |
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