Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session V21: Liquid Crystals II: Nano & Bio |
Hide Abstracts |
Sponsoring Units: DFD Chair: P. A. Heiney, University of Pennsylvania Room: Baltimore Convention Center 318 |
Thursday, March 16, 2006 11:15AM - 11:27AM |
V21.00001: A Phenomenological Model of the Effect of Magnetic Nanoparticles and Their Surface Coating on Smectic - A Liquid Crystal Order Luz J. Martinez-Miranda, Lynn K. Kurihara, Kevin McCarthey, Jason Harry, Alexis Noel We studied the interaction of a smectic-A liquid crystal with magnetic nanoparticles. The behavior of smectic-A liquid crystals with magnetic particles has not been very well characterized., especially where it concerns the effect of the particles' surface coating. The effect of this termination compound on the effect the nanoparticles have on liquid crystals, smectic or nematic, has not been systematically or consistently characterized. The surface coating is needed to ensure that the particles and the smectic liquid crystals do not phase separate. The surface coating in a nanoparticle is used in biological applications to identify a particular cell. We have found out that depending on the surface coating the interaction of the nanoparticles with the liquid crystal varies. This variation is related with how the surface coating aligns the liquid crystal and how it contributes to the concentration of the nanoparticles in the liquid crystal-nanoparticle mixture. This work was partially supported by NSF grant No. NSF-DMR-0080008. [Preview Abstract] |
Thursday, March 16, 2006 11:27AM - 11:39AM |
V21.00002: Carbon nanotube liquid crystal composites Reza Dodge, Shin-Woong Kang, Satyendra Kumar, Cheol Park, Mia Siochi The miscibility of carbon nanotubes (CNTs) in thermotropic liquid crystals is extremely low, yet they can have marked influence on the properties of their host medium. We mixed very small amounts of multi-walled CNTs in a number of cyanobiphenyl mesogens and measured the dielectric and electro-optical properties, and studied the optical textures of the composites. The homeotropic samples show a unique texture, under polarizing microscope, which indicates that the nanotubes behave as line singularities with the strength of +1. The distorted alignment around these singularities covers a limited range, which is comparable with the sample thickness. The results of experiments on composites with various concentrations of CNT will be presented. [Preview Abstract] |
Thursday, March 16, 2006 11:39AM - 11:51AM |
V21.00003: Organization of Magnetic Nanowires via Elastic Forces in a Periodic Multi-Domain Nematic Liquid Crystal Clayton Lapointe, Daniel Reich, Robert Leheny An anisotropic particle suspended in a thermotropic nematic liquid crystal imposes an elastic energy cost on the nematic that depends on the orientation of the particle relative to the nematic director. In a nematic with a spatially varying director field, such a particle can hence experience translational forces that depend on its orientation. We report experiments in which we exploit these forces to organize ferromagnetic Ni nanowires suspended in the nematic 4-pentyl-4-cyanobiphenyl (5CB). Using lithographic techniques to pattern the nematic anchoring conditions on substrates, we generate periodic multi-domain nematic environments for the wires. With their orientation controlled by a small external magnetic field, the wires sediment to preferred domains to minimize elastic energy. [Preview Abstract] |
Thursday, March 16, 2006 11:51AM - 12:03PM |
V21.00004: Liquid Crystal Alignment Induced by a Magnetic Field and the Associated Surface Memory Effect Rui Guo, Qingbing Wang, Satyendra Kumar, Yuri Reznikov Nematic liquid crystals, 4, 4'-n-pentylcyanobiphenyl (\textit {5CB}) and a commercial mixture, $E7,$ have been found to align in thin cells prepared by cooling from the isotropic phase in the presence of a strong magnetic field parallel to the ITO coated glass substrates. The field induced alignment is very stable and possesses surface memory effect [1]. Surprisingly, the azimuthal anchoring energy is as high as 10$^{-3}$erg/cm$^{2}$ and comparable to that obtained for rubbed polymer alignment layers. The surface memory effect is thermally stable and cannot be erased even after holding the cell more than 40K above the clearing point for up to two hours.$^{ }$We believe that the magnetic field directed rearrangement of the LC molecules adsorbed [2] at the substrate is responsible for the observed behavior. ------ [1]. N. A. Clark, Phys. Rev. Lett. \textbf{55}, 292 (1985). [2]. Y. shi, B. Cull, and S. Kumar, Phys. Rev. Lett. \textbf {71}, 2773 (1993). [Preview Abstract] |
Thursday, March 16, 2006 12:03PM - 12:15PM |
V21.00005: The Study of the Fluorescent Spectrum of Cd-Se Quantum Dots in Liquid Crystal Cell Yu-sung Lin, Wen-chi Hung, Wood-hi Cheng, I-min Jiang, Ming-shan Tsai We report the analysis of the fluorescent spectrum of Cd-Se quantum dots in liquid crystal matrices. The cell is filled with the commercial liquid crystal (E7) in homogeneous alignment. We can vary the director field orientation of liquid crystals by applying electrical fields. With a light source of a xenon lamp to excite the Cd-Se quantum dots, the effect on the fluorescent spectrum due to liquid crystal environment is then explored. The shift of fluorescent spectrum affected by the concentration of Cd-Se quantum dots is also discussed in the report. Then the Cd-Se quantum dots are excited by use of a monochromatic Nd-YAG laser, which is a polarized light source. We explore the effects of polarization on fluorescent spectrum of Cd-Se quantum dots also. [Preview Abstract] |
Thursday, March 16, 2006 12:15PM - 12:27PM |
V21.00006: Transmissive Fabry-Perot Spectrum of Liquid Crystal Device for measuring the Surface Plasmon Effect of Silver nano-Particle Wen-chi Hung, Yu-sung Lin, Ming-shan Tsai, I-min Jiang, Wood-hi Cheng A Fabry-Perot scheme for measuring the surface plasmon effect of Ag nano-particles has been presented. As an optical spectrum ananlyzer, the resolution of the Fabry-Perot etalon.is determined by the morphology of reflectors and resonated cavity of the etalon. Ag nano-particles of size 50 nm are deposited on the surfaces of two reflectors. The cavity is filled with liquid crystals which are homogeneous alignment. Because the surface plasmon effect (SPE) of metal nano particles is sensitive to the polarization of incident light (P-wave or S-wave), we apply various polarization lights to explore the spectra of Fabry-Perot etalon filled with liquid crystal to study the SPE of metal nano-particles. In the transmissive spectra, we find the wavelength shift at the peak (603 nm) is about 8 nm when the probed light is changed from P-wave to S-wave. Comparing the measurements of the etalon without filled with the liquid crystal; we discuss the correlation of the wavelength shift and SPE of Ag nano-particles in the liquid crystal etalon device. [Preview Abstract] |
Thursday, March 16, 2006 12:27PM - 12:39PM |
V21.00007: Investigating mixtures of rotor molecules and liquid crystals by dielectric spectroscopy and optical microscopy Debra Krause, Charles T. Rogers, Jose E. Nunez, Miguel Garcia-Garibay Rotor molecules are fundamental in nanotechnology. These molecules are synthesized with one part of the molecule designed to freely rotate while other parts are attached to a surface or within a crystalline super-structure. One class of rotor molecules have fluorobenzene rotors surrounded by bulky triphenyl groups. Studies of these electric dipole rotors in a crystalline state have shown that steric interactions between neighboring molecules can result in large energy barriers (up to 21 kcal/mol) that inhibit motion of the rotor. In an effort to free the rotor but maintain degrees of order in position and orientation, we mix these molecules with liquid crystals, particularly those based on benzylidene-(4-phenylazo-phenyl)-amine. The rotor molecules can dissolve in these liquid crystals into solutions of up to 20 percent by mass. To characterize the environment of the rotor, we study the mixtures using dielectric spectroscopy and optical microscopy. [Preview Abstract] |
Thursday, March 16, 2006 12:39PM - 12:51PM |
V21.00008: Flexible plastic cells fabricated using phase separation of liquid crystal from its mixture in a prepolymer Qingbing Wang, Rui Guo, Satyendra Kumar During phase separation of liquid crystal (LC) from its mixture in a prepolymer, in a cell, the prepolymer accumulates near the spacers. After the phase separation is complete, UV irradiation is used to crosslink the polymer thereby fixing the position of the spacers and bonding them to the substrates. We employ this method to create polymer-embedded spacers to improve cell gap uniformity for LC displays using plastic substrates. Spacers remain adhered to their initial positions thus preventing them from movement or aggregation during temporary cell deformation. Scanning electron microscopy was employed to evaluate the internal polymer morphologies formed under different polymerization conditions. Electro-optical performances and the flexibility of plastic LC cells were determined and the details will be presented. [Preview Abstract] |
Thursday, March 16, 2006 12:51PM - 1:03PM |
V21.00009: Adding Mono- and Multivalent Ions to Lyotropic Chromonic Liquid Crystals Luana Tortora, Heung-Shik Park, Kelly Antion, Chris Woolwerton, Daniele Finotello, Oleg Lavrentovich Lyotropic Chromonic Liquid Crystals (LCLCs) are a distinct class of liquid crystals formed in aqueous solutions by molecules with rigid polyaromatic cores and ionic groups at the periphery [1-4]. The phase diagrams of these materials should depend on entropic factors (as in the Onsager model) and electrostatic interactions. Using optical polarizing microscopy, we studied the effects of mono- and multivalent ions on the phase diagrams of Blue 27 [3] and Sunset Yellow [2]. The monovalent ions change the temperatures of phase transitions, as described in [4], while the effect of multivalent ions is more dramatic and, in addition to the changed temperatures of phase transitions by tens of degrees, it often involves condensation of LCLC aggregates into domains with birefringence much higher than that in a normal nematic phase. Work supported by OBR B-7844. [1]J. Lydon, \textit{Current Opin. Colloid {\&} Interface Sci.} \textbf{3}, 458 (1998);\textbf{8}, 480-489 (2004); [2]V. R. Horowitz, L. A. Janowitz, A. L. Modic, P. J. Heiney, and P. J. Collings, 2005, \textit{Phys. Rew. E} \textbf{72}, 041710; [3]Yu. A. Nastishin, H. Liu, T. Schneider, T., V. Nazarenko, R. Vasyuta, S. V. Shiyanovskii, and O. D. Lavrentovich, 2005, \textit{Phys. Rev. E} \textbf{72}, 041711; [4]A.F. Kostko, B. H. Cipriano, O. A. Pinchuk, L. Ziserman, M. A. Anisimov, D. Danino, and S. R. Raghavan. J. Phys. Chem. B \textbf{109}, 19126-19133 (2005) [Preview Abstract] |
Thursday, March 16, 2006 1:03PM - 1:15PM |
V21.00010: Building Shape Surfactants: Creating rod-coil complexes using genetically engineered viruses Phil Huang, Seth Fraden Complex self-assembled structures (micelles, lamellar phases) are often found in dispersions of amphiphilic molecules like surfactants. We genetically engineered M13 bacteriophage, a long filamentous particle that forms liquid crystalline phases, and coupled a 15 base pair oligonucleotide to one end of the virus. A plasmid DNA fragment was then ligated to the oligonucleotide to form a rod-coil particle. Based on the above complex conjugate, we are attempting to create supramolecular liquid crystalline structures. [Preview Abstract] |
Thursday, March 16, 2006 1:15PM - 1:27PM |
V21.00011: Stretching the limits of membrane charge density using Dendrimer Lipids - New Highly Transfecting Hexagonal Phases for Gene Delivery Kai Ewert, Alexandra Zidovska, Heather M. Evans, Cyrus R. Safinya Newly designed multivalent lipids ranging in head group charge from 4+ to 16+ have been synthesized and investigated as DNA delivery vectors. These dendritic lipids (DLs) allow a controlled study of the relationship between membrane charge density ($\sigma )$ and transfection efficiency (TE). An earlier report from our group described that TE of different cationic lipids of charge 1+ to 5+ follows a common, bell shaped curve as a function of membrane charge density [1]. To further probe this universal behavior, the dendritic lipids with higher valence were designed in order to reach higher values of $\sigma $. Structural studies using x-ray diffraction reveal new phases, where cylindrical micelles of DLs form a hexagonal lattice which holds together a continuous DNA network, described as H$_{I}^{C}$ [2]. The new hexagonal phase is highly transfecting in the regime where the TE of lamellar complexes follows a decrease in the bell curve. Small angle x-ray scattering studies have revealed a rich phase diagram of micelles made from DL/DOPC mixtures. Funding provided by NIH GM-59288 and NSF DMR-0503347. [1] A. Ahmad et al., \textit{J. Gene Med., }2005, V7:739-748. [2] K. Ewert et al., \textit{J. Am. Chem. Soc., (submitted).} [Preview Abstract] |
Thursday, March 16, 2006 1:27PM - 1:39PM |
V21.00012: Hollow Rectangular Columnar Structure in Dendritic Supramolecular Assemblies Mihai Peterca, Paul Heiney, Marc Ilies, Andres Dulcey, Sami Nummelin, Virgil Percec Hollow columnar phases have recently attracted interest for their potential applications as channel mimics in membrane transport, as photonic band gap materials, and for selective encapsulation. The first dendritic structures that self-assemble into hollow rectangular phases have been synthesized and a method for their structural analysis by x- ray diffraction experiments has been developed. The structural analysis method developed allows the calculation of the pore separation, shape and size, creating new opportunities for separation processes of symmetric or asymmetric compounds. [Preview Abstract] |
Thursday, March 16, 2006 1:39PM - 1:51PM |
V21.00013: X-Ray Determination of the Structure and Phases of Liquid Crystals of Nanoscale Duplex DNA Michi Nakata, Giuliano Zanchetta, Christopher Jones, Brandon Chapman, Ronald Pindak, Tommaso Bellini, Noel Clark Polymeric DNA chains are known to exhibit chiral nematic and hexagonal columnar LC phases. Recently we found that even very short duplex B-DNA oligomers 6-basepairs (bp) to 16-bp in length also form nematic and columnar phases depending on the concentration of DNA. To investigate the structure of those phases, we used micro-beam x-ray diffraction (10 micron spot size), enabling the study of single LC domains. In the columnar phases of 8bp, 12bp and 16bp all shows reflection spots corresponding to 20$/AA$ which almost the same length scale of the width of DNA double helix. By selecting a proper orientation of the domains the diffraction pattern shows a hexagonal packing of columns of spacing which does not depend on the length of the basepair. On the other hand, there is no clear diffraction in the chiral nematic phase, which indicates that there is no significant highly ordered molecular aggregation. Those data indicate that short oligomers stack end- to end to form flexible rod-shaped DNA aggregates can then form LC phases. Work supported by NSF MRSEC Grant DMR 0213918 and NSF Grant 0072989. [Preview Abstract] |
Thursday, March 16, 2006 1:51PM - 2:03PM |
V21.00014: Probing the mechanical unzipping of DNA Nikos K. Voulgarakis, Alan R. Bishop, Kim O. Rasmussen Recent advances in single-molecule force spectroscopy have made a systematic study of local melting in DNA possible. This provide new insight into important biological processes as replication and transcription. In this work, we present an extensive study of the micromechanical unzipping of DNA in the framework of the Peyrard-Bishop-Dauxois (PBD) model. The force required to separate the doubled strand is derived through analysis of the force-extension curve, while an estimation of the nucleation bubble size of the unzipping process is obtained by the distribution of the rapture force. Our findings are in very good agreement with existing experimental results; for example the force-temperature phase diagram obtained by the PBD model agrees excellently with recent constant-force experimental measurements of the lambda-phage DNA. Fundamental differences between the in vivo and vitro DNA unzipping, as predicted by the PBD model, are also discussed. [Preview Abstract] |
Thursday, March 16, 2006 2:03PM - 2:15PM |
V21.00015: Asymmetrical binding of cationic peptides onto an oppositely-charged lipid-bilayer membrane: area expansion and membrane rupture Sattar Taheri-Araghi, Bae-Yeun Ha We study asymmetrical binding of cationic peptides onto a negatively charged lipid-bilayer membrane. The peptide not only interacts electrostatically with anionic lipids, rearranging their spatial distributions, but it can also insert hydrophobically into the membrane, expanding the area of its binding layer ({\i.e.}, the outer layer). We examine how peptide charges and peptide insertion (thus area expansion) are intertwined. Our results illustrate why high valences are required for selective toxicity of antimicrobial peptides, ({\i.e.}, they selectively rupture bacterial membranes while leaving host cells intact). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700