Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session J28: Liquid Crystals I |
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Sponsoring Units: DCMP Chair: Peter Collins, Swarthmore College Room: 336 |
Tuesday, March 19, 2013 2:30PM - 2:42PM |
J28.00001: 2D Brownian motion of inclusions in low pressure environment on freely suspended liquid crystal film Zhiyuan Qi, Cheol Park, Joseph Maclennan, Matthew Glaser, Noel Clark The homogeneous freely suspended fluid SmA liquid crystal film of several nanometer thickness provides a very good system for studying 2D hydrodynamics. Using microscope and high-speed camera, we track the motion of inclusions of about 2-20$\mu$m in diameter that doing Brownian motion on the film. We report 2D Brownian motion experiment of drops in different air pressure environment. We found that at ambient pressure, the Hughes, Pailthorpe, and White (HPW) theory can perfectly predict the diffusion coefficient of those inclusions, while under low pressure when the mean free path of the air molecules is comparable with the size of inclusions, the HPW theory fails. We propose a model, based on freely diffused air molecules with Maxwell distribution, to explain the elevated diffusion coefficient in low pressure. [Preview Abstract] |
Tuesday, March 19, 2013 2:42PM - 2:54PM |
J28.00002: Between soap bubbles and vesicles: The dynamics of freely floating smectic bubbles Ralf Stannarius, Kathrin May, Kirsten Harth, Torsten Trittel The dynamics of droplets and bubbles, particularly on microscopic scales, are of considerable importance in biological, environmental, and technical contexts. We introduce freely floating bubbles of smectic liquid crystals and report their unique dynamic properties. Smectic bubbles can be used as simple models for dynamic studies of fluid membranes. In equilibrium, they form minimal surfaces like soap films. However, shape transformations of closed smectic membranes that change the surface area involve the formation and motion of molecular layer dislocations. These processes are slow compared to the capillary wave dynamics, therefore the effective surface tension is zero like in vesicles. Freely floating smectic bubbles are prepared from collapsing catenoid films and their dynamics is studied with optical high-speed imaging [1]. Experiments are performed under normal gravity and in microgravity during parabolic flights.\\[4pt] [1] K. May et al. {\em EPL} {\bf 100} 16003 (2012). [Preview Abstract] |
Tuesday, March 19, 2013 2:54PM - 3:06PM |
J28.00003: Critical Behavior of A Non-polar Smectic Liquid Crystal via Optical Birefringence Measurements Mehmet Can Cetinkaya, Selen Erkan, Sevtap Yildiz, Haluk Ozbek We present high sensitivity and high temperature resolution experimental data on the temperature dependence of the optical birefringence in the nematic and smectic A phases of nonpolar monolayer smectogen 4-butyloxyphenyl-4'-decyloxybenzoate liquid crystal by using a rotating-analyzer technique. We have used the birefringence data to probe the temperature behavior of the nematic order parameter S(T) in the vicinity of both the nematic-isotropic (N-I) and the nematic-smectic A (N-SmA) transitions. The critical behavior of S(T) at the N-I transition has been discussed in detail by comparing our results with the latest reports in literature and we have then concluded that the isotropic internal field assumption by Vuks model is adequate to extract the critical behavior of S(T) from the birefringence data [1-3]. We have tested the validity of the scaling relation $\lambda =$1-$\alpha $ between the critical exponent $\lambda $ describing the limiting behavior of the nematic order parameter and the specific heat capacity exponent $\alpha $. We have shown that the temperature derivative of the nematic order parameter S(T) near the N-SmA transition has the same power law behavior as the specific heat capacity [4,5]. [Preview Abstract] |
Tuesday, March 19, 2013 3:06PM - 3:18PM |
J28.00004: Statistical mechanics of bend flexoelectricity and the twist-bend phase in bent-core liquid crystals Shaikh Shamid, Subas Dhakal, Jonathan Selinger We develop a Landau theory for bend flexoelectricity in a liquid crystals of bent-core molecules. In the nematic phase of the model, the bend flexoelectric coefficient increases as we reduce the temperature, and it diverges at the nematic to polar phase transition. At this critical point, there is a second order transition from high-temperature uniform nematic phase to low-temperature nonuniform polar phase composed of twist-bend or splay-bend deformations. To test the predictions of Landau theory, we perform Monte Carlo simulations to find the behavior as a function of temperature, applied electric field and interaction parameters, and to determine the orientational distribution of the mesogenic molecules. [Preview Abstract] |
Tuesday, March 19, 2013 3:18PM - 3:30PM |
J28.00005: Imaging helical nano-filament and modulated smectic phases of bent shaped liquid crystals by cryo-TEM Cuiyu Zhang, Hans Sawade, Wolfgang Weissflog, Antal Jakli Recently we showed that cryo-TEM can be used to visualize smectic layers of thermotropic liquid crystals. Here we describe cryo-TEM studies of the nanofilaments (B4 phase) and the modulated smectic layers (B7 phase ) of various bent shaped liquid crystal compounds. In the B4 phase a periodic array of about 15 nm wide bands of parallel stripes, separated by a distance equal to the layer spacing, appear with a periodicity of about 120 nm corresponding to the half pitch of the nanofilaments. As cryo-TEM shows only layers that are parallel to the electron beam, these results indicate grains of straight layers twisted along the filament axis compose the nano-filaments. In the B7 phase cryo-TEM not only can visualize the smectic layers, but also the periodic modulation indicating defects with less dense molecular packing. In addition we observe a labyrinth structure with curvature radii in the 150 nm ranges. These results yield information complementary to freeze fracture TEM and X-ray observations. [Preview Abstract] |
Tuesday, March 19, 2013 3:30PM - 3:42PM |
J28.00006: Wide temperature range and hysteresis free blue phase liquid crystals doped with bent-core compound Jie Xiang, Oleg Twieg, Oleg Lavrentovich We explore an approach to widen the temperature range of the liquid crystalline blue phases based on mixtures of calamitic (rod-like) and bent-core mesogens. The calamitic component has a relatively low value of the bend elastic constant that is further reduced by adding the bent-core component. The mixtures exhibit the blue phase state in a wide temperature range, about 5$^{\circ}$C in the regime of heating and 40$^{\circ}$C (including the room temperature) upon cooling. We present a phenomenological model to illustrate the link between the temperature range of the blue phase and the bend elastic constant that is based on Kleman's model of double twist in liquid crystals. We also study the electro-optic properties of the mixtures. The electrooptic switching is reversible in the upper temperature range of the blue phase, but once the temperature decreases below a certain level, the electrooptic switching shows a hysteresis associated with phase separation of the components. The work was supported by NSF grant DMR 11212878. [Preview Abstract] |
Tuesday, March 19, 2013 3:42PM - 3:54PM |
J28.00007: Piezoelectric properties of polymers containing bent-shape liquid crystal molecules N. Diorio, M. Varga, A. Carif, J.E. Puskas, K. Fodor-Csorba, S. Sprunt, J.T. Gleeson, A. Jakli Recently, bent-core liquid crystal elastomers have shown to exhibit large values of flexoelectricity as many as 3 orders of magnitude larger than liquid crystal elastomers containing rod-shaped molecules. These unusual high responses are attributed to have piezoelectric origin. Motivated by this, in this study, two bent-core liquid crystals were used to make various types of materials; low molecular weight bent-core nematic fluid, side chain bent-core liquid crystal polymer, low molecular liquid crystal dispersed in a polyisobutylene-based thermoplastic elastomer, and side-chain bent-core elastomers. Liquid crystal elastomers combine elasticity and flexibility inherent to rubbers and the optical and electrical properties of liquid crystals, and are promising materials for applications such as electro-optics, flexible electronics and actuator technologies for biomedical applications. Most conventional liquid crystal elastomers have rod-shaped liquid crystal molecules chemically attached to a crosslinked polymer network. Converse piezoelectric responses were measured by a Mirau interferometer and the direct piezoelectric signals were studied by home-made device where the stress is provided by an audio speaker. The results will be analyzed in terms of ferroelectric clusters of the materials in the nematic phase and will be compared with other piezoelectric materials. [Preview Abstract] |
Tuesday, March 19, 2013 3:54PM - 4:06PM |
J28.00008: SAXS studies of short-range order in the nematic phase of reduced symmetry mesogens S. Chakraborty, N. Diorio, C. Zhang, R. Breckon, R. Twieg, J. Gleeson, A. Jakli, S. Sprunt Recently, we proposed a model based on persistent, nano-scale smectic-C-like domains (``smectic clusters'') to explain the features present in the small angle x-ray diffraction patterns from certain bent-core nematic liquid crystals (which do not possess an underlying smectic phase). We report on new results from a wider range of nematics formed by reduced-symmetry molecules -- including laterally-branched (``Y''-shaped) mesogens and ``H'' shaped dimers -- that also lack a low temperature smectic phase. We find that our model, extended to incorporate the notion of staggered molecular arrangements, is successful in reproducing the SAXS patterns and reveals variation in the temperature-dependence of cluster size among different systems. Supported by NSF DMR-0964765. [Preview Abstract] |
Tuesday, March 19, 2013 4:06PM - 4:18PM |
J28.00009: Local orientation and temperature effects of a liquid crystal in contact with a nanoparticle Jefferson Ward Taylor, Lynn K. Kurihara, Luz J. Martinez-Miranda We have studied the effects on the orientation of the liquid crystal in the immediate vicinity of a nanoparticle. We have observed a ``halo'' surrounding the nanoparticle, when studying the effects of the nanoparticle on the liquid crystal with the AFM. We believe this halo has an effect on the ordering of the liquid crystal in the immediate vicinity of the nanoparticle. We have also observed a short range order peak in the X-ray scattering signal, which is also associated with the effects on the liquid crystal in the immediate vicinity of the nanoparticle. The value of the coherence length of this peak is close to the value of the molecular spacing or very close of the liquid crystal in the X-ray scattering experiment for all nanocomposites studied. This coherence length does not change as a function of temperature, when the temperature is changed and goes through the SmA-nematic transition temperature. The peak and its coherence length persist into the nematic phase. [Preview Abstract] |
Tuesday, March 19, 2013 4:18PM - 4:30PM |
J28.00010: Electro-optical Characteristics of Carbon Nanotupe Doped Polar Smectic Liquid Crystal Ilknur Koseoglu, Mehmet Can Cetinkaya, Haluk Ozbek, Sevtap Yildiz We present the results of electro-optical characteristics of the liquid crystal octyl-cyanobiphenyl (8CB) doped with well-dispersed multiwall carbon nanotubes (MWCNT) under an AC driving voltage. 8CB-MWCNT composites were prepared by following the procedures in literature [1-4]. Polarized optical microscopy (POM) has been performed to check the homogenous dispersion of 8CB-MWCNT composite. We compare threshold voltages and switching behavior of pure 8CB and 8CB doped with MWCNTs which have surfaces of untreated and treated with carboxyl functional group. Threshold voltages have been determined from optical transmittance-driving voltage curves at various temperatures. While the pure 8CB switches from a bright state through some intensity oscillations to the dark state, a drastic change has been observed in the transmittance curves for 8CB-MWCNT composites, namely hysteretic behavior has been detected. For 8CB-MWCNT composites we have observed that the first cycle for the transmittance-voltage curves shows the highest amount of loop area, which gradually decreases through the following cycles, then reaching saturation. Notice that the number cycle at which the saturation is reached depend on temperature [5]. [Preview Abstract] |
Tuesday, March 19, 2013 4:30PM - 4:42PM |
J28.00011: Effect of quantum dots on the isotropic to nematic and nematic to smectic-A phase transitions in nano composites Parvathalu Kalakonda, Germano S. Iannacchione Modulated Differential Scanning Calorimetry (MDSC) is used to investigate the weakly first-order isotropic to nematic ($I$-$N$) and the continuous nemat to smectic-$A$ ($N$-Sm$A$) phase transitions of the liquid crystal octylcyanobiphenyl (8CB) doped with well-dispersed quantum dots (QdS) as a function of Qd concentrations. Thermal scans were performed for all samples having Qd (CdS) weight percent from $\phi_{w}$ = 0.3 to 3 wt$\% $ first on cooling and then heating under near-equilibrium conditions. The I-N transitions heat capacity peak first glows then decreases in magnitude with increasing $\phi_{w}$ leaving a maximum at $\phi_{w}$ = 0.3$\% $. The N-SmA heat capacity peak remains bulk-like for all samples. Both transitions temperatures shift lower monotonically by 3 K for $\phi_{w}$ = 0.3$\% $. The enthalpy of both transitions evolve in a nontrival way, generally decreasing with increasing $\phi_{w}$. These results are discussed in terms of the predominate disordering effects of the Qds. [Preview Abstract] |
Tuesday, March 19, 2013 4:42PM - 4:54PM |
J28.00012: Towards an optical nano-laboratory in a liquid crystal defect Paul Ackerman, Ivan Smalyukh, Jao van de Lagemaat Probing photonic effects due to nanoscale interactions between colloids such as quantum dots and rods and anisotropic plasmonic metal nanoparticles is of great interest for applications in third-generation solar cells, optical metamaterials, and nanoantennas. Liquid crystal (LC) structures and defects stabilized by chirality, confinement, and/or presence of colloidal microparticles can enable trapping and well-defined alignment of anisotropic semiconductor, plasmonic, and other nanoparticles with respect to the far-field director and each other. Minimization of the free energy due to LC defects provides a rich environment for precisely controlled experiments with individual and small groups of nanoparticles in the LC. This presentation will discuss characterization of trapping and alignment of various nanoparticles by LC defects and also photonic experiments performed on a single-particle level for metal and semiconductor quantum nanoparticles entrapped by these defects. This work was supported by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the US Department of Energy under Contract No. DE-AC36-08GO28308 with the National Renewable Energy Laboratory (J.v.d.L. and J.S.E.). [Preview Abstract] |
Tuesday, March 19, 2013 4:54PM - 5:06PM |
J28.00013: Interaction of discotics and nanoparticles Luz J. Martinez-Miranda, Eduardo A. Soto-Bustamante We mixed a discotic, and 5 nm nanoparticles of ZnO up to a percentage weight of 30 -- 35{\%}, by heating them together, past the isotropic transition temperature. At that point, we mixed them together, and allowed them to cool to room temperature. We then prepared a sample for Xray study, by taking a small amount of the crystallites formed and placing them in a glass slide. We prepared a sample of the pure discotic to compare to the mixture. We found that the addition of the nanoparticle results in an enhancement of the axis in the direction parallel to the glass slide, with an intensity approximately six times that of the discotic alone and a correlation length approximately 1.3 times better. The role of the nanoparticle isvery similar to the alignment role of a flat surface observed on discotics. [Preview Abstract] |
Tuesday, March 19, 2013 5:06PM - 5:18PM |
J28.00014: High resolution synchrotron X-ray studies of lyotropic liquid crystal phases of monolayer Zirconium Phosphate nanosheet Yue Shi, Yongqiang Shen, Noel Clark, Min Shuai, Zhengdong cheng Aqueous suspensions of monolayer zirconium phosphate nanosheets (ZrP-NS) form various lyotropic liquid crystal phases. An interesting stripe pattern can be observed in a range of nanosheet concentrations when the suspensions were confined between flat surfaces. The stripe patterns were stable while slow evaporation of the solvent and were well-preserved even when the suspensions dried out. A high resolution synchrotron X-ray study gives detailed investigations of ZrPNS lyotropic phases at different concentrations. [Preview Abstract] |
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