Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session P9: Liquid Crystals: Smectics, Nano-mixtures |
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Sponsoring Units: DFD Chair: Luz J. Martinez-Miranda, University of Maryland Room: D220 |
Wednesday, March 23, 2011 8:00AM - 8:12AM |
P9.00001: Achiral structure of B4 phase in a Bent-Core Liquid Crystal Dong Chen, Michael-Scott Heberling, Joseph Maclennan, Matthew Glaser, Noel Clark, Hideo Takezoe Bent-core smectic layers have a tendency to exhibit spontaneous saddle-splay curvature, driven by the intra-layer structural mismatch. In the chiral B4 phase, the tendency for twist in the orientation of neighboring molecules coupled with the saddle-splay curvature lead to the formation of helical nanofilaments with either clockwise or anticlockwise twist. In addition to the helical nanofilament structure, we observe another microscopic structure in P12OPIMB, which is achiral, with no helical twist. This coffee-bean-like microstructure is dominated by saddle-splay curvature, like the dark conglomerate phase, but appears to have three dimensional order. The origin of these structures will be discussed. [Preview Abstract] |
Wednesday, March 23, 2011 8:12AM - 8:24AM |
P9.00002: Two ferroelectric phases in a bent-core liquid crystal C. Zhang, N. Diorio, B.K. Sadashiva, A. J\'akli We report electro-optical, polarization current, dielectric and SAXS studies on novel bent-core materials that contain four ester groups; three in one arm and only one in the other. These materials differ from each other only by the number of carbons (n) in the alkyloxy chain terminating the one ester containing arm: in Ar 35 n=14, while in Ar 39 n=18. The phase sequences of Ar 35 and 39 are very similar to each other. Both have two mesophases, M1 and M2, with M1 in the 115$^{\circ}$C-140$^{\circ}$C temperature range, and M2 in between about 100$^{\circ}$C and 115$^{\circ}$C. Polarization current measurements indicate polarization current and optical switching in the M$_{1}$ phase with spontaneous polarization and switching time in the Ps$\sim $2.5-3mC/m$^{2}$ and $\tau \quad \sim $200$\mu $s range, respectively. While in Ar 35 the M2 phase cannot be switched, in the AR 39 we could detect polarization switching with a polarization value of about 5-6 mC/m$^{2}$ and switching time over a millisecond. Dielectric and X-ray scattering studies were employed to reveal the fine structure of the M$_{1}$ and M$_{2}$ phases. [Preview Abstract] |
Wednesday, March 23, 2011 8:24AM - 8:36AM |
P9.00003: Surface Induced Reduction of Twisting Power in Liquid Crystal Films LiDong Pan, Cheng-Cher Huang Null transmission ellipsometry was employed to study the temperature evolution of the helical structure in smectic liquid crystal films. Free standing films with thickness ranging from 31 to more than 400 layers were prepared and studied. The experimental results show a reduced twisting power in thin films. A simple model was constructed to explain the results. Surface effect was found to be the reason for this phenomenon. Our findings are consistent with the studies of helically ordered magnetic films. [Preview Abstract] |
Wednesday, March 23, 2011 8:36AM - 8:48AM |
P9.00004: Evolution of the isotropic to smectic-$A$ phase transition in liquid crystal and acetone binary mixtures Krishna Sigdel, Germano Iannacchione The first-order transition from the isotropic ($I$) to smectic- $A$(Sm$A$) phase in the liquid crystal 4-cyano-4'-decylbiphenyl (10CB) doped with the polar solvent acetone (ace) has been studied as a function of solvent concentration by high- resolution ac-calorimetry. Heating and cooling scans were performed for miscible 10CB+ace samples having acetone mole fractions from $x_{ace}$ = $0.05 (1$~wt.\%) to $0.36 (10\%)$ over a wide temperature range from $310$ to $327 K$. Two distinct first-order phase transition features are observed in the mixture whereas there is only one transition ($I$-Sm$A$) in the pure 10CB for that particular temperature range. Both calorimetric features reproduce on repeated heating and cooling scans and evolve with increasing $x_{ace}$ with the high temperature feature relatively stable in temperature but reduced in size while the low temperature feature shifts dramatically to lower temperature and exhibits increased dispersion. Polarizing optical microscopy supports the identification of a smectic phase below the high-temperature heat capacity signature indicating that the low-temperature feature represents an injected smectic-smectic phase transition. These effects may be the consequence of screening the intermolecular potential of the liquid crystals by the solvent that stabilizes a weak smectic phase intermediate of the isotropic and pure smectic-$A$. [Preview Abstract] |
Wednesday, March 23, 2011 8:48AM - 9:00AM |
P9.00005: The Power of Poincar\'e: Elucidating the Hidden Symmetries in Focal Conic Domains Elisabetta A. Matsumoto, Gareth P. Alexander, Bryan Gin-ge Chen, Randall D. Kamien Focal conic domains are typically the ``smoking gun'' by which smectic liquid crystalline phases are identified. The geometry of the equally spaced smectic layers is highly generic but, at the same time, difficult to work with. We develop an approach to the study of focal sets in smectics which exploits a hidden Poincar\'e symmetry revealed only by viewing the smectic layers as projections from one-higher dimension. We use this perspective to shed light upon the concentric cyclides of Dupin and several classic focal conic textures which exhibit a more widespread level of geometric organization as in Friedel's law of corresponding cones, the networks and trellises expounded by Bouligand, or Apollonian packings. [Preview Abstract] |
Wednesday, March 23, 2011 9:00AM - 9:12AM |
P9.00006: Phase behavior of platelets at different aspect ratios Andres Mejia, Ya-wen Chang, Dazhi Sun, Agustin Diaz, Abraham Clearfield, Hung-Jue Sun, Zhengdong Cheng Suspensions of $\alpha$ -ZrP monolayer plates have recently been found to exhibit an isotropic to nematic (I-N) and nematic to smectic (N-S) phase transition. In the past, computer simulations have been developed to study the phase diagrams of platelets. In order to experimentally investigate the phase transitions and rheological behaviors of these particles, it is necessary to be able to manipulate their size, thickness and reduce their size distribution. We demonstrate here the strong dependency of the I-N transition on the aspect ratio (diameter/thickness) via the control of pristine $\alpha$ -ZrP platelets. We confirmed that the I-N transition volume fraction decrease monotonically with the aspect ratio as shown in previous simulations by J.A.C. Veerman and D. Frenkel. Furthermore, we found additional isotropic and gel phases by increasing the polydispersity of platelet sizes. [Preview Abstract] |
Wednesday, March 23, 2011 9:12AM - 9:24AM |
P9.00007: Liquid Crystal-ZnO Nanoparticle Potential Photovoltaics: Role of LC Order and ZnO Particle Size and Concentration Luz J. Martinez-Miranda, Janelle Branch, Robert Thompson, Jefferson W. Taylor, Lourdes Salamanca-Riba We investigate the role order plays in the transfer of charges in ZnO nanoparticle - 8CB liquid crystal system for photovoltaic applications as well as the role the nominally 5x7nm$^{2}$ ZnO nanoparticles play in improving that order. Our results for the 5nm nanoparticles show an improvement in the alignment of the liquid crystal with increasing weight percentage of ZnO nanoparticles, up to a concentration of 30{\%} wt for the 5nm particles accompanied by an increase by three orders of magnitude in the current generated.\footnote{L. J. Mart\'{\i}nez-Miranda, Kaitlin M. Traister, Iriselies Mel\'{e}ndez-Rodr\'{\i}guez, and Lourdes Salamanca-Riba, Appl. Phys. Letts, \underline {97,} in press (2010).} Our results for the 5 x 7 nm$^{2}$ sample show that the current is larger than the current obtained for the 5 nm samples. The photocurrent can be expressed as the conductivity as a function dependent in the order in the sample times the portion of the electric field that is absorbed and transformed into the current. [Preview Abstract] |
Wednesday, March 23, 2011 9:24AM - 9:36AM |
P9.00008: Interaction of a Bi-molecular Liquid Crystal Film With Functionalized Nanoparticles Jefferson W. Taylor, Luz J. Martinez-Miranda, Lynn K. Kurihara We investigate the properties of a nominally bi-molecular film of liquid crystal mixed with a magnetic nanoparticle (CoFe) that was functionalized with an organic compound (MHDA or APTS) with the atomic force microscope (AFM). We seek to investigate if the functionalization compound has an effect on the ordering of the liquid crystal in the vicinity of the nanoparticle. Studies in bulk liquid crystals have shown that the functionalization compound influences how the liquid crystal will reorganize.\footnote{L. J. Mart\'{\i}nez-Miranda, and Lynn Kurihara, \textit{J. Appl. Phys, 105, }p. 084305 (2009).} The results of this investigation are compared to the results of work done on phospholipids in close contact with uncovered silica nanoparticles.\footnote{Yuri Roiter, Maryna Ornatska, Aravind R. Rammohan, Jitendra Balakrishnan, David R. Heine, and Sergiy Minko, \textit{Langmuir}, $25$, 6287-6299 (2009).} There seems to be a relation between the way that the two functionalizations behave in the bulk 8CB. The two functionalizations studied behave differently for particles larger than 22 nm, and apparently for the smaller particles. [Preview Abstract] |
Wednesday, March 23, 2011 9:36AM - 9:48AM |
P9.00009: Directed assembly of CdSe/ZnS quantum dots in cholesteric liquid crystal matrix Andrea Rodarte, Linda S. Hirst, Sayantani Ghosh Controlled self assembly of quantum dots (QDs) over macroscopic scales is important to realizing the potential for new applications such as photovoltaic devices and sensors. Here, we suspend CdSe/ZnS core/shell QDs in a cholesteric liquid crystal (LC) and investigate the dispersion and collective emission of the QDs when loaded into a Grandjean-Cano wedge cell. We use polarized optical microscopy and scanning photoluminescence microscopy to generate spatial and spectral maps of the QD-liquid crystal samples. We find that the LC forms Grandjean steps approximately 200um in width and the spectral effects of the QD emission correlate to the stripe formation. We also find that the cholesteric LC modulates the spectral emission of the QDs, creating a wavelength gradient dependant on the orientation of the collection polarizer with the director axis of the liquid crystal molecules. [Preview Abstract] |
Wednesday, March 23, 2011 9:48AM - 10:00AM |
P9.00010: ABSTRACT WITHDRAWN |
Wednesday, March 23, 2011 10:00AM - 10:12AM |
P9.00011: Diffusion-controlled Aggregation of Bucky Balls on Freely Suspended Smectic Liquid Crystal Films Zoom Nguyen, Tatyana Malinina, Cheol Park, Joseph Maclennan, Matthew Glaser, Noel Clark Bucky balls (BB) have the tendency to clump together, making it hard to have them suspended in a solvent. We find that in highly viscous bulk 8CB, a smectic liquid crystal at room temperature, the aggregation happens more slowly. As the result, a freely suspended film made from the 8CB-BB mixture contains mostly small BB clumps. The diffusion coefficients of the clumps in thin films are much bigger than in the bulk, however, accelerating the aggregation process. We measure, via video microscopy, the decrease of the clumps' diffusion coefficients over time, indicating that their sizes increase towards a terminal size determined from the rate of diffusion. The terminal-sized clumps still diffuse around and stick to each other when they meet, forming the classic fractal pattern. [Preview Abstract] |
Wednesday, March 23, 2011 10:12AM - 10:24AM |
P9.00012: Investigation of the lyotropic liquid crystal phase of Graphene Oxide solution Yue Shi, Rizwan Mahmood, Dong Chen, Noel Clark Graphite Oxide spontaneously exfoliates into single-layer Graphene Oxide flakes in water. As the concentration becomes higher, Graphene Oxide solution shows a phase transition from the isotropic to the lyotropic liquid crystal phase. In the liquid crystal phase, the Graphene Oxide flakes can be ordered spontaneously by flow and shearing forces. We will report the investigation of the liquid crystal phase of the Graphene Oxide solution. In addition, the light scattering studies give dynamic information of the Graphene Oxide solution. Both the translational and rotational diffusion properties are investigated corresponding to different phases formed by Graphene Oxide at different concentrations. [Preview Abstract] |
Wednesday, March 23, 2011 10:24AM - 10:36AM |
P9.00013: Defect dynamics in monodomain formation of a lyotropic chromonic liquid crystal under confinement Xuxia Yao, Alejandro Rey, Jung Park, Mohan Srinivasarao Lyotropic chromonic liquid crystals are a relatively new class of liquid crystals. We have studied the process of monodomain formation and the associated defect dynmaics of an anionic dye, Sunset Yellow FCF(SSY), under confinement in a flat capillary. SSY solutions were filled into a flat capillary by capillary action in isotropic phase and subsequently cooled to nematic state. Defect coarsening processes due to confinemnet include growth of small uniform domains, splitting of a center disclination line (+1) into two lines (+1/2), merging of uniform domains, and relaxation of defect curvature after pinch-off. Previously we studied the kinematics of a branch point involving a +1 and two +1/2 intersecting lines. Here we report on the collision of two such branch points and the subsequent emergence of two curved +1/2 lines that eventually coarsen into two paralell lines close to the edge of the capillary. A model that includes bending and tension line elasticity describes the branch point post collision and provides the means to asses viscoleatic moduli. [Preview Abstract] |
Wednesday, March 23, 2011 10:36AM - 10:48AM |
P9.00014: Thermotropic~Gold~Nanorod~Liquid Crystal Phases Paul Luchette, Peter Palffy-Muhoray Large scale, oriented arrays of gold~nanorods~(Au NR) are of interest for a variety of applications, such as negative index materials and hyperbolic dispersion lenses. We report a method for preparing~lyotropic, nematic~LC phases of Au NR by combining polymer coated Au NR with a low molecular weight ($<$ 3200) polymers~solvent. The solvent system was~prepared by reacting hydroxymethyl siloxane and styrene~via a hydrosilylation reaction. At appropriate ratios, these mixtures exhibit liquid crystalline phase behavior. ~Lyotropic LC phases of Au NR were observed for Au NR with aspect ratio above 4, diameter $\sim $15nm, using either linear or cyclic siloxane-styrene polymers as the solvent. Compared with other preparation methods such as lithography or evaporative deposition that produce static films, these self-assembled thermotropic LC phases of Au NR may be re-oriented in response to thermal or electric stimulus. [Preview Abstract] |
Wednesday, March 23, 2011 10:48AM - 11:00AM |
P9.00015: Organic-Inorganic Liquid Crystalline Composites Petr Shibaev Design of novel liquid crystalline composites consisting of organic liquid crystals, metal oxides (titanium oxide, zinc oxide, etc.) and ``interface'' layer covering inorganic materials is presented and discussed. The composites respond to light irradiation by changing orientation of liquid crystalline molecules, resulting in the changes of transmission and reflection properties of cells made of composite materials. The interaction of composite materials with light results from a complex chain of physico-chemical processes inside both the inorganic component and the ``interface'' layer. The processes that play the major role in the re-orientation of liquid crystalline molecules in the surface layer include: i. light-induced formation of electron-donor pairs inside metal oxides, ii. energy transfer of electron excitations to molecules inside the ``interface'' layer, iii. breaking of hydrogen bonds and conformational changes of molecules inside the ``interface'' layer. The experimental study of the processes resulting in re-orientation of liquid crystals by light is accompanied by theoretical calculations of conformational changes inside the ``interface'' layer and molecular re-orientation on the surface of inorganic materials. [Preview Abstract] |
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