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Symposium L: Liquid-Crystal Materials--Beyond Displays

* Invited paper
 

8:00 AM *L1.1
Nanophase Segregation Based on Helical Nanofilament Formation.Noel A. Clark, Physics, University of Colorado, Boulder, Colorado.

We studied mixtures of the achiral bent-core mesogen NOBOW, 1,3-phenylene bis(4-(4-9-alkoxyphenyliminonetyl)benzoate) and various other molecular species including the small, rodlike liquid crystals, using using high resolution synchrotron x-ray diffraction, freeze fracture transmission electron microscopy, and differential scanning calorimetry. NOBOW mixes in the isotropic state at high temperatures but phase separates at lower temperatures when NOBOW transforms into the B4 liquid crywtal pphase and forms chiral helical nanofilaments. In pure NOBOW, the nanofilaments are close packed but at moderate 8CB concentrations, they are separated by nanosized gaps filled by 8CB. At higher concentrations of 8CB, macroscopic phase separation occurs.


8:30 AM *L1.2
Using Fiber-Tip Based Localized Surface Plasma Resonance to Study Surface Driven Orientation Changes in Liquid Crystal Based Sensors.Robert Lindquist^1,2, Yongbin Lin², Yang Zou^1,2 and Yuanyao Mo²; ¹Electrical and Computer Engineering, University of Alabama in Huntsville, Huntsville, Alabama; ²Nano and Micro Devices Center, The University of Alabama in Huntsville, Huntsville, Alabama.

Over the past decade, surface induce ordering of liquid crystal(LC) films have been investigated to report binding events in a wide variety of chemical and biological applications. The research has shown that the ordering of the LC film is very sensitive to the nanoscale structure and the chemical functionality of the surface. Despite the ease at which the orientational changes can be seen using the transmission of a sample between crossed polarizers, the details of the ordering within 10s of nanometers of the surface are still not well understood. Although several experimental studies including second harmonic generation and localized surface plasmon resonance(LSPR) have provided valuable insight, this measurements have been too complicated or too weak to gain wide acceptance. In this effort, we have developed a simplified sensing platform that integrates a LSPR structure on a fiber tip with liquid crystals to investigate the details of ordering at the nanoscale and to potentially improve the sensitivity of LC-based sensors. Periodic arrays of gold (Au) nano-dots with subwavelength periodicity are formed on the tips of silica optical fibers. The structure is fabricated using electron beam lithography (EBL) and reactive ion etching (RIE). The spectral position of the maximum loss in the transmission spectra due to the excitation of localized surface plasmon resonance (LSPR) is linearly depended on the refractive index of the medium surrounding the sensor fiber tips. Using tips of optical fibers as a plasmonic sensing platform has several advantages over conventional planar substrate. First of all, unlike their planar substrate counterpart, the optical alignment for the fiber tip sensor is easy and does not require precision alignment tools. Secondly, the fiber tip sensor can be designed and engineered for remote sensing. Third, each tip can be functionalized to report a different analyte and thus enabling a highly compact multiplexing platform. Integrating a stabilized film LC with the fiber tip LSPR structure provides a simplified platform to characterize the ordering at the surface and to enhance the sensitivity of detection. The LC orientation changes in which the transmission minimum is tracked from the LSPR structure coated with a homogeneously film LC to a surfactant driven homeotropic alignment was 20 nanometers. We will report on several remarkable features of the optical fiber-based LSPR including a sensitivity as high as conventional planar substrate-based LSPR biosensors (~200nm/RIU) which is a six-fold improvement over previously reported LSPR fiber systems. Experimental results will be presented using the LC-LSRP sensor in gas sensing such as detection of DMMP, protein binding reporting using biotin-BSA as the model system, and characterization of ordering changes in aqueous environment.


9:00 AM *L1.3
Using Liquid Crystal Anchoring to Distinguish Single-stranded and Double-stranded DNA.Daniel K. Schwartz, Andrew Price and Stephanie Malone; Department of Chemical & Biological Engineering, University of Colorado, Boulder, Colorado.

The ability to distinguish double-stranded DNA (dsDNA) from single-stranded DNA (ssDNA) is the fundamental requirement for technologies that rely on DNA hybridization such as DNA microarray diagnostic devices. We have developed two approaches where a liquid crystal (LC) exhibits fundamentally different anchoring properties at interfaces decorated with ssDNA and dsDNA respectively. One involves a dynamic change of the LC polar tilt angle at the LC/aqueous interface in the presence of a monolayer of cationic surfactant. The other involves a distinctive azimuthal LC orientation when the LC is in direct contact with extended dsDNA. Because these methods respond directly to the dsDNA structure, instead of to a label, they are insensitive to target DNA that adsorbs non-specifically to the interface of interest, eliminating the most significant source of error in current DNA hybridization assays.


9:30 AM L1.4
Detection and Quantification of DNA on Solid Surfaces by Using Liquid Crystals.Chih-Hsin Chen, Siok Lian Lai and Kun-Lin Yang; Chemical and Biomolecular Engineering, National University of Singapore, Singapore, Singapore.

Determining DNA concentration is often accomplished by using laboratory-based instrumentation such as UV-vis or fluorescence spectrometer and it requires at least 1 μL of DNA solution. In this presentation, we report a label-free, liquid crystal (LC) based analytical method which is suitable for estimating DNA concentration by using less than 1 μL of DNA solution. The detection principle of this method is based on the disruption of the orientations of LCs by surface immobilized DNA. Because LCs are birefringent materials, disruption of their orientations by the immobilized DNA leads to distinct optical signals visible to the naked eye. There are two different protocols to estimate DNA concentration. The first one is a sequential dilution protocol. Following this method, the DNA concentration can be estimated from the number of bright LC spot in a small array comprises of diluents of different dilution ratios. The second method is by flowing DNA solutions into microfluidic channels. This way, the DNA concentration can be determined quantitatively from the length of the bright LC region in the microfluidic channels. The lowest detection limit of this method is approximately 0.8 μg/mL, and only 10 nL of DNA solution (or 8 pg of DNA) is required. To detect DNA with a specific sequence, we compared LC images before and after DNA hybridization. Because LCs give different colors when they are supported on surfaces decorated with single-stranded DNA (ssDNA) or double-stranded DNA, complementary DNA targets can be distinguished from non-complementary ones by using the optical textures of LCs. We will also present strategies such as incorporating biotin-labeled DNA and streptavidin to improve the detection limit of this method. This LC based analytical method for DNA detection is simple to apply and has the potential to be integrated with lab-on-chip devices for point-of-care diagnosis.


9:45 AM L1.5
Theory of Depletion Induced Phase Transition from Chiral Smectic A Twisted Ribbons to Semi-infinite Flat Membranes.C. Nadir Kaplan¹, Hao Tu², Robert A. Pelcovits² and Robert B. Meyer¹; ¹The Martin Fisher School of Physics, Brandeis University, Waltham, Massachusetts; ²Department of Physics, Brown University, Providence, Rhode Island.

We consider a theoretical model for the chiral smectic A twisted ribbons observed in assemblies of fd viruses condensed by depletion forces. The depletion interaction is modeled by an edge energy assumed to be proportional to the depletant polymer in solution. Our model is based on the Helfrich energy for surface bending and the de Gennes model of chiral smectic A liquid crystals with twist penetration at the edge. We consider two variants of this model, one with the conventional Helfrich Gaussian curvature term, and a second with saddle-splay energy. A mean field analysis of both models yields a first-order phase transition between ribbons and semi-infinite flat membranes as the edge energy is varied. The phase transition line and tilt angle profile are found to be nearly identical for the two models; the pitch of the ribbon, however, does show some differences. Our model yields good qualitative agreement with experimental observations if the sign of the Gaussian curvature or saddle-splay modulus is chosen to favor negative Gaussian curvature. C.N. Kaplan, H. Tu, R.A. Pelcovits, and R.B. Meyer, arXiv:1005.4355 (2010).


 

10:30 AM *L2.1
Columnar Liquid Crystals with High Carrier Mobility and Their Application to Printable Electronics. Masanori Ozaki¹, Yasuo Miyake^1,2, Tetsuro Hori¹, Naoyuki Yamasaki¹, Hiroyuki Yoshida¹, Akihiko Fujii¹ and Yo Shimizu²; ¹Dept. of Electronic Eng., Osaka University, Suita, Osaka, Japan; ²Research Inst. for Ubiquitous Energy Devices, AIST, Ikeda, Osaka, Japan.

Liquid crystal is one of the promising materials as an organic semiconductor because of the potentially high carrier mobility comparable to that of a-Si (0.1 cm2/Vs) and its self-assembling nature as attractive properties to “Printable Electronics”. In this presentation, we report alkylphthalocyanine homologue exhibiting ambipolar characteristics with high drift mobility in both columnar mesogenic and crystalline phases, which is a solution processable material, and its high quality thin film for the electronic devices such as a transistor and solar cell can be obtained using a spin coating technique. The carrier drift mobilities estimated by a time-of-flight technique in the columnar phase reached c.a. 0.2 cm2/Vs (hole) and c.a. 0.3 cm2/Vs (electron). The higher mobility in excess of 1 cm2/Vs could be observed in the crystalline phase. These values of carrier mobility are independent of the applied field and increased with decreasing temperature. We also report highly efficient thin film solar cells based on a bulk heterojunction of this material and C60 derivative.


11:00 AM *L2.2
Smart Energy Glass: Switchable Windows with Solar Energy Collection.Casper van Oosten¹ and Michael Debije²; ¹Peer+ B.V., Eindhoven, Netherlands; ²SFD group, Eindhoven University of Technology, Eindhoven, Netherlands.

In the modern built environment photovoltaics are difficult to integrate for their aesthetic appeal and the flexible geometries required. At the same time, there is a great pressure to work towards energy neutral buildings, as energy use in buildings accounts for about 40% of our energy use. Windows offer an opportunity for integration of PV as they are pre-fabricated building elements that have a similar, shiny appearance as photovoltaics. Simply pasting silicon PV onto glass, possibly with a gap between, would greatly obstruct the view to the outside and is therefore not attractive. Smart Energy Glass is a liquid crystal based technology that allows control over the incoming light while generating photovoltaic energy with the excess light. The transmittance of the window can simply be tuned with an electric field applied to the window, thus allowing light into the building when needed. All electronics are invisibly integrated into the window frame to allow for unobstructed views outside. The window is easily installed and savings of up to 10% of the buildings energy use can be achieved. Here we will explain the concept of Smart Energy Glass and demonstrate its functionality.


11:30 AM L2.3
Low-dimensional Ion Conductors Obtained through Self-organization of Ionic Molecules.Masafumi Yoshio¹, Takahiro Ichikawa¹, Hiroyuki Ohno² and Takashi Kato¹; ¹Dept. of Chemistry and Biotechnology, School of Engineering, The University of Tokyo, Tokyo, Japan; ²Dept. of Biotechnology, Tokyo University of Agriculture and Technology, Tokyo, Japan.

Self-assembly of liquid crystals can be used to obtain functional materials that can transport electron, ions, and mass in low dimensions [1]. Herein, we report on liquid-crystalline low-dimensional ion conductors obtained through self-organization of ionic molecules. Columnar and bicontinuous cubic liquid-crystalline ion conductors are formed by nanosegregation of molecules having ionic and non-ionic block structures. Anisotropic 1D ionic conduction has been achieved for the aligned columnar liquid crystals. The bicontinuous cubic liquid crystals having 3D interconnected ionic nanochannels function as alignment free ion conductors. Moreover, nanostructured solid polymer conductors have been successfully obtained by UV irradiation of polymerizable nanostructured ionic liquid crystals. The mixing of ionic liquids and functionalized mesogenic molecules that can interact with the ionic moieties also leads to the formation of nanophase-segregated liquid-crystalline assemblies. [1] Reviews: T. Kato et al., Chem. Commun., 2009, 729; Struct. Bond., 2008, 128, 151; Angew.Chem. Int. Ed. 2006, 45, 38; Science 2002, 295, 2414.


11:45 AM L2.4
Charge Carrier Transport Properties of Biphenyl Liquid Crystals with a Dimer Structure.Jiang Wu, Takayuki Usui and Jun-ichi Hanna; Tokyo Institute of Technology, Tokyo, Japan.

Since the discovery of electronic conduction in discotic and smectic liquid crystals in the 1990s, the electronic conduction has been reported in various classes of liquid crystals including triphenylenes, porphyrins, naphthalenes, oligothiophenes, benzothiazoles, and biphenyls. Their charge carrier transport properties are characterized by high mobility over 10^-3 cm²/Vs typically and up to 1 cm²/Vs. However, there is no guiding principle of how to design liquid crystalline molecules for organic semiconductors having a high mobility. In order to have a better understanding design of liquid crystalline molecules as organic semiconductors. We started our research from synthesizing a series of biphenyls with a dimer structure in which two mesogenic moieties are linked via a flexible spacer, such as 1,8-bis[4-(4’-butylbiphenyl)]octane (4BP8BP4) and 1,8-bis[4-(4’-octylbiphenyl)]octane (8BP8BP8) and characterized their phase transition behaviors and charge transport properties in terms of Time of Flight(TOF) technique. We found that these biphenyl dimers exhibited smectic B (SmB_hex) phase at higher temperatures and higher mobility, i.e., 5~6 ×10^-3 cm²/Vs in Sm B_hex phase that is 5~6 times higher than that of its corresponding monomer, 4-octyl-4’-butylbiphenyl (8BP4), and the mobility also does not depend on temperature which is quite different from that of 8BP4. We discuss the present result in a framework of disorder in the liquid crystal phase and show how promising these liquid crystals are as a new type of organic semiconductors.




 

1:30 PM *L3.1
Ultrafast Switching Liquid Crystals for Photonic Devices and Microscopic Lasers.Harry J. Coles, Stephen M. Morris, Timothy D. Wilkinson, Flynn Castles and Philip J. Hands; Electrical Engineering Div B, CMMPE, University of Cambridge, Cambridge, United Kingdom.

We report on novel liquid crystals with extremely large flexoelectric coefficients used in a range of ultra-fast photonic modes, namely 1) the uniform lying helix, that leads to in-plain switching, birefringence based phase devices with 100 µs switching times at low fields, i.e.2-5 V/µm, and analogue or grey scale capability, 2) the uniform standing helix, using planar surface alignment and in-plane fields, with sub ms response times and optical contrasts in excess of 5000:1 with a perfect optically isotropic or black “off state”, 3) the wide temperature range blue phases that lead to field controlled reflective color, 4) chiral nematic optical reflectors, electric field tunable, over a wide wavelength range and 5) high slope efficiency, wide wavelength range tunable narrow linewidth microscopic liquid crystal lasers.The latter has led to a prototype miniature tunable wide wavelength laser system for use in medical applications and holographic projection. Typical output powers of 5mW per micro-laser spot were achieved and simultaneous Red-Green-Blue lasing has been demonstrated in 100 x 100 arrays of such micro-lasers on a 10mm x 10mm substrate. The output of the laser arrays can be combined in the far field to give a "white light" laser source or, using a single wavelength array, to greatly enhance the total output power available.Such 2D laser arrays then have applications in combinatorial spectroscopy.


2:00 PM *L3.2
Broadband Nonlinear Electro-optical Responses of Nematic Liquid Crystals for Ultrafast Optical Switching and Image Processing Applications.Iam-Choon Khoo, Electrical Engineering, Penn State University, University Park, Pennsylvania.

A critical review of liquid crystal nonlinear optical responses to short laser pulses in the sub-microsecond to nanoseconds time scale is presented, along with recently observed self-action all-optical switching that has implications in high performance transmission control and intensity dependent spatial frequency filtering operation. The underlying mechanisms that mediate these processes are optically induced order parameter modulations generated by coupled thermal/density fluctuations, in addition to trans-cis isomerism that create local disorder. Owing to the ultra-broadband birefringence of nematic and their unique physical characteristics, these switching processes can be realized in the visible through near infrared into the far infrared spectral regions. Current and future efforts to utilize these ultrafast optical nonlinearities for image-plane optical image processing will also be discussed. Ref. I. C. Khoo, “Nonlinear Optics of Liquid Crystalline Materials,” Physics Report 471, pp. 221-267 [2009]; D. N. Christodoulides, I. C. Khoo, G. J. Salamo, G. I. Stegeman, and E. W. Van Stryland, "Nonlinear refraction and absorption: mechanisms and magnitudes," Adv. Opt. Photon. 2, 60-200 (2010); I. C. Khoo, “Liquid Crystals” 2nd Edition (Wiley Inter-Science, NJ 2007). See also I. C. Khoo and S. T. Wu, “Optics and Nonlinear Optics of Liquid Crystals,” [World Scientific, Singapore 1993]; I. C. Khoo, A. Diaz, J. Liou, M. V. Stinger, J. Huang and Y. Ma, “Liquid Crystals Tunable Optical Metamaterials,” IEEE J. Selected Topics in Quantum Electronics, Special Issue Vol. 16, pp. 410-417 (2010); . G. Pawlik, M. Jarema, W. Walasik, A. C. Mitus and I. C. Khoo, ‘Field induced inhomogeneous index distribution of a nano-dispersed nematic liquid crystal near the Freedericksz transition:Monte carlo studies,” J. Opt. Soc. Am. B 27, no. 3 pp. 567-576, (2010).


2:30 PM L3.3
Interactions between Cholesteric Templated Polymers and Liquid Crystals.Michael E. McConney, Jennifer Hurtubise, Vincent P. Tondiglia, Lalgudi V. Natarajan, Timothy J. White and Timothy J. Bunning; Materials and Manufacturing Directorate, Wright Patterson Air Force Base, Dayton, Ohio.

Cholesteric liquid crystals are attractive for their ease of forming Bragg reflections in the visible spectrum. Typical chiral nematics are formed by adding a chiral dopant to a nematic liquid crystal. While this is a convenient way to form cholesterics and control the pitch, mixture based approaches have many limitations to designing liquid crystals systems. Recently, porous structured materials have become quite popular in altering the phase behavior and dynamics of liquid crystal mixtures, especially polymer stabilization. Here, we present investigations of the interplay between cholesteric templated polymers and liquid crystals. These investigations are leveraged on a technique involving creating a polymer scaffold in the presence of a cholesteric and then removing the cholesteric to fill the chiral polymer with any LC mixture. Our investigations specifically focus on the polymer-liquid crystal interaction and the interplay between LC phases and the polymer structure.


2:45 PM L3.4
Broadband Coverage Optical Sensor with Liquid Crystalline Materials and Pyroelectrics.Jingwen W. Zhang, Xiudong Sun and Hua Zhao; Physics, Harbin Institute of Technology, Harbin, Heilongjiang, China.

Development of sensors with broadband electromagnetic (EM) coverage is of great significance. In military applications, threat warning is key to increasing the survivability of military platforms.[1] The increasing complexity and compactness of modern missiles and other rocket-propelled threats guidance systems operate in multiple-modes, either sequentially or simultaneously, which necessitates tactical threat warning systems to operate over greater spectral (wavelength) and temporal (frequency) ranges to provide truly comprehensive situational awareness.[2] To meet these imminent needs, research activities in development of sensors with a broadband EM coverage are growing rapidly. We report a novel sensor concept that covers a broad EM waveband, ranging from UV light through visible, IR, THz waveband with supertwisted liquid crystal and perovskite material, empowered by a special coating technique based on the recent development in nanotechnologies, By utilizing thin layer of supertwisted liquid crystal and a perovskite material with excellent pyroelectric effect, coupled with coated carbon layer with excellent absorption in the frequency range of interest, the intensity of an incident EM radiation can be converted to a corresponding intensity variation of a reflected near-IR beam via optical modulation of the liquid crystal film. In other words, combining three major functional materials: broadband absorber, pyroelectric agent, and highly sensitive optical modulating liquid crystal cell, a highly sensitive broadband EM coverage sensor was developed. As the result, the spatial intensity distribution of an incident EM radiation can thus be perceived directly by a low-cost semiconductor sensor. Because of extreme low voltage operation (0.06 V) of a specifically designed supertwisted liquid crystal cell, the sensitivity of the proposed sensor is two orders higher than traditional pyroelectrics alone sensor. With flexible design of wave collecting arrangement, the broadband coverage sensor is suitable for viewing EM-giving objects with extreme large field-of-view. [1] D. Adamy, "EW 101 - A First Course in Electronic Warfare", Artech House, Massachusetts (2001) [2] J. S. Accetta, and D. Shumaker, "The Infrared and Electro-Optical Systems Handbook", Vol. 5:“Passive Electro-optical systems,” edited by S. B. Campana, Vol. 7: “Countermeasure Systems”, edited by D. Pollock, SPIE Optical Engineering Press, Washington (1993)


 

3:30 PM *L4.1
Shape Memory Liquid Crystalline Elastomers.Patrick T. Mather^1,2, Kelly A. Burke^3,2, Amir H. Torbati^1,2 and Ellen E. Benn¹; ¹Biomedical and Chemical Engineering, Syracuse University, Syracuse, New York; ²Syracuse Biomaterials Institute, Syracuse University, Syracuse, New York; ³Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio.

Shape memory polymers (SMPs) represent a class of smart materials that offers unique thermomechanical functionality useful for mechanical devices, long-stroke actuators, and sensors. In their most basic form, SMPs are covalently or physically crosskinked polymers that feature a processing-dictated permanent shape and later-defined temporary (or “fixed”) shape. While most shape memory polymers are rigid in their “fixed” state, smectic liquid crystalline elastomers enable fixing of temporary shapes while preserving material compliance. In this study, main-chain smectic-C liquid crystalline elastomers were synthesized using a variety of synthetic methodologies. Linear viscoelastic measurements were conducted over a wide temperature range to reveal a low modulus (E’ less than 100 MPa above 0 °C) that decreases in a stepwise fashion upon heating due to a sequence of mesogen glass transition followed by isotropization transition. In some compositions, these transitions were superimposed. The LCEs described herein have excellent one-way shape memory properties, with fixing and recovery generally exceeding 95 %. Those LCEs featuring a mesogen glass transition temperature slightly above room temperature allowed the LCE to function in a temporary shape at room temperature and to later recover the permanent shape by heating. The unusual combination of softness and shape memory capability was exploited for reversible embossing, where a shape memory cycle was localized at the surface of the LCE to give a temporary topography that could later be erased upon heating. This talk will reveal structure property relationships that enable control of shape memory properties closely related to liquid crystalline phase behavior.


4:00 PM L4.2
Photolocking of Complex Liquid Crystal Order Towards New Functionalities and Applications.Dirk J. Broer, Cees Bastiaansen and Albert Schenning; Chemical Engineering & Chemistry, Eindhoven University of Technology, Eindhoven, Netherlands.

In-situ photopolymerization of liquid crystalline (LC) monomers has proven to be a valuable technique for the formation of well-ordered polymer networks. Their anisotropic properties lead to a variety of applications in optics, electronics and mechanics. The use of light to initiate polymerization enables lithographic approaches to pattern the polymers. The LC behave enables formation of complex morphologies on a molecular level, especially if combined with surface boundary conditions, chirality and polymerization- induced diffusion. The combination of top-down lithography with bottom-up self-organization accommodates a wealth of applications that even are not fully explored yet. Polymerization initiated by means of a dichroic photoinitiator provides an additional degree of freedom for controlling the structure of LC networks formed. The photoinitiator adapts the director profile of the LC monomer. As a result planar oriented areas aligned orthogonal to the light beam polymerize faster than the parallel ones. Similarly, planar aligned areas with their orientation parallel to the electrical field vector of the light polymerize faster than the planar aligned areas oriented perpendicular to that. Based on this principle complex lithographic structures are build, not only forming structures in the plane of the polymerizing film but also in the third dimension along its cross-section. The LC networks have proven their utility by improving the optics in flat panel liquid crystal displays leading to higher contrast and viewing angle. Presently, based on similar or closely related materials new functions are being developed, e.g. as responsive mechanical elements in microfluidic systems. Control over complex director profile of an LC network provides a means to create morphing mechanical elements. The driving force is the change of the order parameter of the LC network, which upon decreasing order provides contraction along the director and expansion perpendicular to it. Various triggers have been studied among which temperature, light, pH and chemicals. By inkjet printing materials responding to different triggers can be integrated in a device configuration. By polymerization of smectic monomers containing hydrogen bridges anisotropic nanogels are being formed with well controlled pores. The pores have a layer-like shape, open or close as a response to pH changes and have a size of around 1 nm with a periodicity of 3 nm measured in the direction perpendicular to the layers.


4:15 PM L4.3
Modeling Dynamic Mechanical Response and Microstructural Evolution in Nematic Elastomers.Robin L. Selinger¹, Badel Mbanga^1,2, Jonathan Selinger¹ and Fangfu Ye³; ¹Liquid Crystal Institute, Kent State University, Kent, Ohio; ²Polymer Science and Engineering, Univ of Massachusetts, Amherst, Amherst, Massachusetts; ³Physics Dept., Univ of Illinois, Urbana, Urbana, Illinois.

When a nematic elastomer is deformed, its mechanical response depends on the evolution of microstructure--the underlying nematic director field--under strain. We model this process using a 3-d finite element elastodynamics approach. First we explore the elastic instability that arises when a monodomain elastomer is stretched perpendicular to the director axis. Our simulations show a semi-soft elastic response along with the nucleation and growth of domain stripes with alternating director rotation [1], like that observed in classic experiments by Kundler and Finkelman [2]. Next, we study the mechanical properties of polydomain elastomer films and their transition to monodomain under applied uniaxial strain. We show that the nature of the transition is governed by the thermomechanical history of the sample. In particular, polydomain samples crosslinked in the nematic phase (N-PNE) show a pronounced "crosslink memory" effect, in which the local preferred nematic director orientation is imprinted in the polymer network upon crosslinking. By contrast, the cross-link memory effect is at least an order of magnitude smaller in samples crosslinked in the isotropic phase (I-PNE). Our simulation results are in good qualitative agreement with observed differences in the stress-strain behaviors of N-PNE and I-PNE materials, as seen in experiments by Urayama [3]. This model allows us to explore the fundamental physics governing dynamic mechanical response of nematic elastomers and also provides a potentially useful computational tool for engineering device applications. [1] B. Mbanga et al, arXiv:0912.3293v1 [2] I. Kundler and H. Finkelmann, Macromol. Rapid Commun. 16, 679 (1995), and [3] K. Urayama et al, Macromolecules 42, 4084 (2009).


4:30 PM L4.4
Molecular Basis for Necking Instability in Polydomain Main-chain Smectic Elastomers.Huipeng Chen¹, Ziniu Yu¹, Daniel M. Lentz² and Ronald C. Hedden¹; ¹Chemical Eng., Texas Tech Univ., Lubbock, Texas; ²Materials Science and Engineering, Pennsylvania State Univ., University Park, Pennsylvania.

Liquid crystalline elastomers are rubber-like soft materials that have attracted attention as soft actuators. Recent efforts focused on identifying the molecular factors governing the mechanical response of smectic, polydomain main-chain LC elastomers. During elongation at a constant strain rate, yielding and neck formation are observed. The transition from polydomain to globally oriented morphology occurs in a spatially localized fashion within a narrow boundary region. In order to elucidate the molecular basis for necking, we have characterized the influence of temperature, strain rate, and thermal history on domain size and mechanical response (Young's modulus, yield stress, drawing stress). Unlike conventional elastomers, the smectic main-chain elastomers soften dramatically as temperature increases. Young's modulus, yield stress, and drawing stress each decrease markedly as temperature increases. The yield stress and drawing stress also generally increase as strain rate increases at constant temperature. In addition, the transition region becomes narrower and the neck becomes well-defined at lower temperatures and higher strain rates. Thermomechanical softening may promote neck formation at high rates of deformation. Thermal history profoundly affects the average domain size and mechanical response of smectic polydomain elastomers. Annealing near the clearing temperature followed by slow cooling produces larger average domain size than quick cooling, as determined by X-ray diffraction lineshape analysis. Annealed samples with larger domains exhibit a very high yield stress and drastically lower elongation at break compared to quick-cooled samples with smaller domain size. The mechanical response of the elastomer is affected by an energetic penalty for disordering of chain-folded microdomains, such that elastomers with larger, more stable microdomains resist deformation.


 

8:30 AM *L5.1
Dynamic Cholesteric Liquid Crystals Using Spatially Polymer Templated Structures.Timothy Bunning¹, Timothy White¹, Michael McConney¹, Jennifer Hurtubise¹, Nelson Tabiryan², Svetlana Serak², Lalgudi Natarajan³ and Vincent Tondiglia³; ¹Air Force Research laboratory, Wright-Patterson AFB, Ohio; ²BEAM, Inc., Winter Park, Florida; ³SAIC, Inc., Dayton, Ohio.

Cholesteric liquid crystals (CLCs) are well-known to have circularly polarized reflection, which makes them highly promising in a myriad of photonic-based applications. We present recent findings in the examination of phototunable azobenzene-based cholesteric liquid crystals and hyper-reflective CLC films. The inherent reflectivity of the CLC phase can be manipulated by light exposure, due to the photosensitive nature of azobenezene chiral or liquid crystalline materials utilized. The helical nature that defines CLCs inherently limits their reflection to 50% of unpolarized light. By manipulating the extent of a polymer network through a fraction of the cell thickness, cells which possess local R and L handedness are obtained. Thus from one cell, reflection of both handedness light is obtained. Morever, we extend this concept to demonstrate that one of the reflection notchs position is tunable. Single cells which can have greater than 95% reflectivity are obatined. We present our current work to develop dynamic hyper-reflective CLCs using spatial polymer templating techniques.


9:00 AM *L5.2
Phototropic Liquid Crystals.Bahman Taheri¹, Tamas Kosa¹, Ludmila Sukhomlinova¹, Antonio Munoz¹, Linli Su¹, Timothy White² and Timothy Bunning²; ¹AlphaMicron Inc., Kent, Ohio; ²AFRL, WPAFB, Ohio.

Liquid crystals are categorized into thermotropic, lyotropic or polymeric based on the method by which the liquid crystallinity is induced. Here, we introduce the phototropic liquid crystal effect in which liquid crystallinity is observed as a direct result of incident light beam. Much like the lyotropic and thermotropic liquid crystals, this class demonstrates a phase transition from isotropic to nematic, cholesteric, or smectic phases. However, in this class, an incident light induces the liquid crystalline phase. To achieve this, we have synthesized a novel class of photoinduced dichroic dyes which when added to some conventional liquid crystals can induce a phototropic effect. In particular, under appropriate light illumination, a mixture containing this class of dyes can exhibit a transition from order parameter of 0 (isotropic) to an order parameter observed in conventional liquid crystal. This in contrast to the conventional azo dyes typically added to liquid crystals. In particular, in those systems the light illumination disrupts the order whereas here we induce order. Furthermore, this is achieved without spatial phase separation between the constituents. In other words, the system as a whole exhibits this effect. We present our observations and results and demonstrate that this system can result in introduction of nematic, smectic and cholesteric phase transitions from isotropic system. We also explore some potential application of this effect for light actuated photonic devices.


9:30 AM L5.3
Polymer Stabilization of Phototunable Cholesteric Liquid Crystals.Lalgudi V. Natarajan¹, Timothy J. White², Quan Li³ and Timothy J. Bunning²; ¹Electro-optics Division, Science Applications International Corporation, Dayton, Ohio; ²Materials and Manufacturing Directorate, AFRL, Wright-Patterson Air Force Base, Ohio; ³Chemical Physics Department, Kent State University, Kent, Ohio.

We have recently demonstrated phototuning of more than 2000 nm in an azobenzene-based cholesteric liquid crystal (CLC) composed of a nematic liquid crystal and a high helical-twisting power chiral bis(azo) molecule. Phototuning range and rate were dependent on azo dopant concentration, light intensity, and cell thickness. The time for restoration of the original spectral properties in the absence of light source was long, lasting for several hours. Polymer stabilization of the CLC reduced the relaxation time to less than an hour. In this work, we present the results of a systematic study of the effect of polymer stabilization on the kinetics of phototuning and dark relaxation of the bis(azo) based CLC. The impact of polymer concentration, cross linker concentration, curing power, and cell thickness on the optical performance of these photoresponsive CLCs will be discussed.


9:45 AM L5.4
Switching Light Using Light: Photoresponsive Liquid Crystal Fiber Devices.Vincent Hsiao, Applied Materials &Optoelectronic Engineering, National Chi Nan University, Nantou, Taiwan.

In the conference we would like to present our recent results on all-optical switching fiber devices using photoresponsive liquid crystal (LC). The photoresponsive LC is a guest/host system where azobenzene LC (azo-LC) is taken as guest while chiral-nematic LC is taken as host. The photoresponsive LC could be infiltrated into the photonic crystal fiber (PCF) or overlaid onto the side polished fiber (SPF). Those two devices have shown potential to used as an optically controllable fiber attenuator. An optically controllable fiber-knot resonator and an optically tunable SPF grating will also be demonstrated.


10:00 AM L5.5
Resonant Surface Plasmon Polariton Diffraction with Hybrid Photorefractive Liquid Crystal Cells.Stephen B. Abbott¹, David C. Smith¹, Keith R. Daly², Giampaolo D'Alessandro² and Malgosia Kaczmarek¹; ¹School of Physics and Astronomy, University of Southampton, Southampton, United Kingdom; ²School of Mathematics, University of Southampton, Southampton, United Kingdom.

The development of plasmonic based devices, such as optical analogues of electrical circuits and ultra-high bandwidth intra-chip interconnects, has attracted a lot of interest both from the scientific community as well as from industry with considerable investment in plasmonics from large high-tech companies including: Intel, Panasonic and Samsung. However, practical applications are limited by the short propagation length characteristic of high plasmonic content Surface Plasmon Polaritons (SPP) modes and a lack of available strong SPP-SPP non-linear systems. We demonstrate that hybrid photorefractive liquid crystal cells, with high photorefractive gain, e.g. 2000cm^-1, low cost and ease of fabrication, have considerable potential for solving both these problems and lead to a whole new class of SPP devices to be developed. The system we propose is based upon the hybrid photorefractive liquid crystal cells [1], with the addition of an Au layer to support SPP modes. The liquid crystals refractive index is controlled indirectly by light via a photoconducting layer. For uniform illumination of the cell with E7 liquid crystals, we have demonstrated strong interaction of SPPs with an effective refractive index change of 1.58 to 1.63. Theoretically we model the liquid crystal using an approximation to the commonly used Q-tensor method [2]. This is combined with a standard multilayer transfer matrix model for the optical propagation. We utilise it to model SPP diffraction from a spatially modulated liquid crystal grating coupler. Predicted efficiencies are as high as 16%. We will present experimental measurements of diffraction efficiencies from our un-optimised samples and indicate how it should be possible to achieve efficiencies close to those theoretically predicted. Extension of this work could lead to SPP signal gain and allow a variety of optically reconfigurable elements, including superlenses and photonic crystals, to be developed. [1] M. Kaczmarek, A. Dyadyusha, S. Slussarenko, and I. C. Khoo. The role of surface charge field in two-beam coupling in liquid crystal cells with photoconducting polymer layers. J. Appl. Phys., 96:2616-2623, 2004. [2] K. R. Daly, G. D’Alessandro and M. Kaczmarek. A fast and efficient non-stiff Q-tensor based algorithm for liquid crystal alignment. Submitted to SIAM Journal on Applied Mathematics. 2010.


 

10:30 AM *L6.1
The Prospect of Light-powered Polymer Engines and Photo-controlled Adaptive Membranes Based on Azobenzene Liquid Crystal Elastomers.Nelson Tabiryan¹, Svetlana Serak¹, Rafael Vergara¹, Timothy J. White², Richard Vaia² and Timothy J. Bunning²; ¹BEAM Engineering for Advanced Measurements Co., Winter Park, Florida; ²Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio.

A low power light, including sunlight, makes an azobenzene liquid crystal elastomer (azo LCE) film fold in half, unfold itself, to curl and twist, and even start high frequency oscillations in precisely controlled and reversible manner. We review our development of such materials and present the results describing their photo-deformation and photo-actuation at different conditions, including in vacuum. Evaluations are favorable for the prospect of developing polymer engines with high efficiency transformation of light energy into mechanical energy. Photo-controlled adaptive optics is another application that appears highly practical. We demonstrate laser beam steering using azo LCE films in the form of cantilevers, and light-controlled transmission of an optical system using photo-deformable azo LCE membranes. New material developments lay ground for relatively straightforward fabrication of good quality azo LCE films with well controlled properties. Functionalization of those films by modulating the liquid crystal orientation on the elastomer surface and/or in its bulk, and modifying their electrical properties (piezo-electric azobenzene structures) will further widen the realm of their applications. Reference S. Serak, N. Tabiryan, R. Vergara, T.J. White, R.A. Vaia, and T.J. Bunning, Liquid crystalline polymer cantilever oscillators fueled by light, Soft Matter, 6, 779-783, 2010.


11:00 AM L6.2
Shape Memory Behavior in Photoresponsive Azobenzene Liquid Crystal Polymer Networks.Kyungmin Lee^1,2, Timothy J. Bunning¹ and Timothy J. White¹; ¹Materials and Manufacturing Directorate, Wright-Patterson Air Force Research Lab, Wrigh-Patterson AFB, Ohio; ²Azimuth Corp., Dayton, Ohio.

Shape memory polymers have seen widespread interest for a variety of applications as adaptive materials. Recently, we have found that both polydomain and monodomain glassy azobenzene liquid crystal polymer networks (azo-LCNs) are unique and interesting shape memory materials. Towards this end, this presentation will demonstrate the capability of shape memory and photoresponse of these azo-LCNs. Monodomain and polydomain azo-LCNs with temporary fixed shapes are caused to oscillate or bend bidirectionally with light exposure.


11:15 AM L6.3
Polarized Light Induced Deformation of Azobenzene Liquid Crystal Elastomers.William S. Oates¹, Hongbo Wang¹, Tim White² and Kyung Min Lee²; ¹Florida State University, Tallahassee, Florida; ²Wright Patterson Air Force Research Laboratory, Wright Patterson Air Force Base, Ohio.

The photomechanics of azobenzene liquid crystal elastomers is studied using multi-physics modeling and comparisons with photobending experiments. Model development includes coupling between the electro-magnetics of light, nonlinear mechanics of the host elastomer, and the underlying liquid crystal domain structure evolution. Photomechanical polarized light coupling and the effect of different rates governing light propagation, liquid crystal photoisomerization, and nonlinear deformation are discussed. These relations are incorporated into a nonlinear finite element phase field model that includes time-dependent electro-magnetics, nonlinear mechanics, and a phase field description of the liquid crystal domain structure evolution. The effect of trans-cis-trans photoisomerization is discussed in comparison to the conventional trans-cis photoisomerization that is often used to induce bending mode deformation. Several numerical examples are given and compared with photobending experiments.


11:30 AM L6.4
New, Low Temperature, Reversible Photo-responsive Liquid Crystal Polymer.Michael T. Petr¹, Johannes Soulages², Bat-ami Katzman¹, Gareth McKinley² and Paula Hammond¹; ¹Chemical Engineering, MIT, Cambridge, Massachusetts; ²Mechanical Engineering, MIT, Cambridge, Massachusetts.

A new photo-responsive liquid crystal polymer (LCP), whose shear modulus responds significantly, quickly, and reversibly at room temperature and below, has been developed. The LCP is made of a calamitic azobenzene mesogen attached side-on to poly(vinylmethylsiloxane). During oscillatory shear rheometric measurement of the material’s modulus at temperatures between 5°C and 40°C, UV light was successively shined on the material and then turned off, and, with it, the modulus dropped 30-40% in less than a minute and then returned to its original value in less than a minute. This drop in modulus is due to isomerization of the azobenzene portion of the LC from trans to cis, which disrupts the nematic phase, as characterized by in-situ UV irradiated Polarized Light Microscopy (PLM) in which the nematic phase is colored and then goes almost completely black in less than a minute. This quick response is more favorable than typical LCPs because the low Tg siloxane backbone does not inhibit the trans to cis isomerization of the LC or the rearrangement of the LCs once the isomerization has taken place.


 

1:30 PM *L7.1
Templated Lyotropic Liquid Crystals for Biological Applications. Bradley S. Forney, Jason Clapper and Allan Guymon; Chemical and Biochemical Engineering, University of Iowa, Iowa City, Iowa.

A promising method of synthesizing functional polymers to accommodate a growing number of advanced biological and industrial applications utilizes the highly-ordered domains of self-assembling lyotropic liquid crystals (LLCs) to direct polymer structure on the nanometer scale. Of particular significance is the potential to improve and tailor properties dependent on local order by controlling polymer nanostructure. Unfortunately, it is often difficult to control polymer structure during polymerization. Thermodynamically driven phase separation often occurs as monomer is converted to polymer and frequently yields polymers with poorly defined nanostructures. For this work photopolymerization kinetics are utilized to identify phase separation events occurring during photopolymerization. Discontinuities are found in the polymerization rate of anisotropic polymers at several double bond conversions that are not present in the rate profiles of isotropic controls. Polymer morphology was subsequently characterized at particular conversions using small angle X-ray scattering. Changes in polymer nanostructure occur at double bond conversions that coincide with the observed rate discontinuities. These results demonstrate that photopolymerization kinetics can be used as a probe to monitor the evolution of polymer nanostructure during polymerization and optimize the conditions governing the control of polymer morphology to enhance properties dependent on nanostructure. The ability to understand and direct the polymer nanostructure has also lead to advances in biomaterials property control. For example, research utilizing LLC nanostructured hydrogels to create alternative vascular pathways has shown great promise for treatment in central retinal vein occlusion (CRVO), a common ophthalmic condition that can lead to moderate to severe vision loss. Specific optimization of the overall swell and degradation rate of the synthesized biomaterials was obtained solely through LLC ordering of the polymer network, providing an alternative to chemical manipulation to produce desired properties. Animal trials show that the induced nanostructure in stents implanted through the retina to the choroid and sclera results in much different bioresponse and biodegradation. Nanostructured biodegradable systems also enhance cellular interaction and appear with preliminary results indicating appropriate anastamoses between the retina and adjacent tissue.


2:00 PM L7.2
Biotic-abiotic Interfaces Based on Liquid Crystals.Nicholas L. Abbott, Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin.

Cells actively control the spatial and temporal organization of their membranes as a strategy to manipulate their functional properties. In contrast, the interfaces of relatively few synthetic materials permit spatial and temporal control over the organization of biomolecules. In this presentation, we will report the emergence of principles for active control of biomolecules assembled at interfaces between thermotropic liquid crystals and aqueous phases. Specifically, experiments will be described that demonstrate that the ordering of the liquid crystal can be used to direct the organization of the biomolecules. Phospholipids will be used as a first example. We will demonstrate that nematic elasticity can induce lateral organizations of phospholipids are not observed in the absence of the liquid crystalline order. Extension of these principles to manipulation of mesoscopic objects at interfaces will also be described. Because weak fields can be used to manipulate liquid crystals with high spatial (micrometer) and temporal (millisecond) resolution, these results define approaches for the realization of materials that will permit active control of the interfacial organization of biomolecules and thus their functionality. The utility of such materials will also be discussed.


2:15 PM L7.3
Cholesteric Focal Conic Domains and Circularly Polarized Iridescence of the Beetle Chrysina Gloriosa.Vivek Sharma¹, Matija Crne², Jung O. Park³ and Mohan Srinivasarao³; ¹Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts; ²Proctor and Gamble, Damstadt, Germany; ³Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia.

The exoskeleton of jewel beetles provides a remarkable example of a structurally stable matrix with selective reflectivity relying on a cholesteric liquid crystal, thus providing an attractive pathway for making multifunctional materials with controlled optical properties. Specifically, the exoskeleton of iridescent metallic green beetle, Chrysina gloriosa, is decorated by hexagonal cells (~10 micron) that selectively reflect left circularly polarized light. In bright field microscopy, each cell contains a bright yellow core, placed in a greenish cell with yellowish border, but the core disappears in dark field, and the size/color of the yellow core depends on the cone of the angle of incident light (size of aperture). Further, we find that the fraction of hexagons that coexist with pentagons and heptagons decreases or local entropy increases with an increase in curvature. Using confocal microscopy, we observe that the individual cells consist of nearly concentric, nested arcs that lie on surface of a shallow cone. We infer that the patterns are structurally and optically analogous to the focal conic domains formed spontaneously on the free surface of a cholesteric liquid crystal. The microstructure provides the basis for the morphogenesis as well as key insights for emulating the intricate optical response the exoskeleton of scarab beetles.


2:30 PM L7.4
Origin of Iridescence in Nanocrystalline Cellulose for Encryption and Enhanced Color.Mark Andrews¹, Yu Ping Zhang², Melodie Carluer¹, Vamsy Chodavarapu², Andrew Kirk² and Gilles Picard³; ¹Chemistry, McGill University, Montreal, Quebec, Canada; ²Electrical Engineering, McGill University, Montreal, Quebec, Canada; ³Physics, College Ahuntsic, Montreal, Quebec, Canada.

There is much interest in color travel phenomena related to iridescence. Our study examines optical and electro-optical properties at the origin of iridescence in colloidal fluid suspensions and dried phases of nanocrystalline cellulose. We establish ways in which surface charge, surface hydrophobicity/hydrophilicity, and surface sterics affect the hydrodynamic evolution of the liquid crystal cholesteric phase order in a variety of NCC fluids. Transition from Bernal-Fankuchen tactoid-like texture to anisotropic texture occurs under hydrodynamic flow. Vivid iridescence is observed. We report on the electric field response of NCC solutions for the first time, as well as some implications of NCCs for encryption.


2:45 PM L7.5
The Effect of Chirality on the Self-assembly of Attractive Rod-like Particles.Thomas Gibaud¹, Mark Zakhary¹, Edward Barry¹, Andy Ward¹, Rudolf Oldenbourg² and Zvonimir Dogic¹; ¹Brandeis University, Waltham, Massachusetts; ²mbl, Woods Hole, Massachusetts.

Filamentous bacteriophages such as the fd virus have long been used as a model systems to investigate the liquid crystal behavior of suspensions of rod-like particles. Here we explore the effect of attraction induce by a non-absorbing depleting polymers on the phase behavior of filamentous viruses. Attraction induces the formation of equilibrium viruses’ mono-layers that behave like classical membranes composed of amphiphilic molecules [1,2]. These membranes are composed of a one micron thick fluid-like monolayer of aligned rods (Fig. a,b). Chirality, however, favors twist between adjacent viruses, which is incompatible with a flat (translationally invariant) 2D surface. Near the membrane’s edge this constraint is removed and weakly chiral rods form a thin locally twisted layer. Strong chirality frustrates assembly of 2D membranes altogether, and instead drives the formation of other chiral structures such as twisted ribbons (Fig. c,d). With the help of various microscopy techniques (DIC, fluorescence, Polscope [3]) and laser tweezers experiments we explore the role of the chirality through the use of different viruses to interpret the formation and the stability of the membrane and the twisted ribbon phases. [1] E. Barry and Z. Dogic. accepted by PNAS (2010) [2] E. Barry, Z. Dogic, R. B. Meyer, R. A. Pelcovits and R. Oldenbourg J. of Phys. Chem. B 113, 3910-3913 (2009). [3] R. Oldenbourg, R. 1996. Nature 381: 811-812


 

3:30 PM *L8.1
Submillisecond-response Infrared Phase Modulators Based on Polymer Network Liquid Crystals. Jie Sun, Haiqing Xianyu and Shin-tson Wu; College of Optics and Photonics, University of Central Florida, Orlando, Florida.

Infrared liquid crystal (LC) spatial light modulators are useful for electronic beam steering using optical phased array and adaptive optics for wavefront correction. However, the response time of a nematic spatial light modulator is usually in 10-ms range if a large phase change (say, 2π) is required. This response time is too slow for tracking fast moving objects, such as atmospheric fluctuations. In order to achieve submillisecond response time, polymer network liquid crystal (PNLC) is emerging as a promising approach. However, two major challenges associated with PNLC are light scattering and a relatively high operating voltage. In this paper, we demonstrated a scattering-free, submillisecond response time, and 2π phase change PNLC modulator at λ=1064 nm. Fast response time results from strong surface anchoring energy induced by the polymer networks and sub-micron domain sizes. However, the trade-off is higher operating voltage. To reduce operating voltage, we have developed a high birefringence and large dielectric anisotropy nematic LC mixture by doping our fluorinated cyano terphenyl LC compounds into Merck E48 host. In our experiment, we achieved ~94 μs decay time at 50°C with an operating voltage of ~120V. Computer simulation results agree well with the experiments. Possible approaches to further reduce the operating voltage will be discussed.


4:00 PM L8.2
Optical Switching Devices Based on Carbon Nanotubes or Conducting Polymer Electrodes.Frederick Roussel¹, Roch Chan Yu King² and Mourad Boussoualem¹; ¹Univ Lille Nord de France, Villeuneuve d'Ascq, France; ²USAO, Chickasha, Oklahoma.

Flat-panel liquid crystal-based material displays (LCD) are an integral part of everyday electronic devices from smartphones to TVs. These display devices make use of transparent electrodes mostly fabricated from glass panels coated with a thin layer of conducting indium tin oxide (ITO). Owing to their exceptional optical, electrical and mechanical properties, intrinsic conducting polymers (ICP) and carbon nanotubes (CNT) are potential candidates for the replacement of ITO. In this paper, we report on our latest developments on the fabrication and the characterization of (flexible) optical switching devices driven by ICP or CNT electrodes. R Chan Yu King, F. Roussel, Appl. Phys. A, 86, 159 (2007)


4:15 PM L8.3
Broadening of a Polymer Stabilized Negative Dielectric Anisotropy Cholesteric Reflection Notch Using a DC Field.Lalgudi V. Natarajan¹, Vincent P. Tondiglia¹, Madeline Duning², Christopher Bailey², Timothy J. White² and Timothy J. Bunning²; ¹Electro-optics Division, Science Applications International Corporation, Dayton, Ohio; ²Materials and Manufacturing Directorate, AFRL, Wright-Patterson Air Force Base, Ohio.

A weakly polymer stabilized cholesteric liquid crystal containing a negative dielectric anisotropy nematic was subjected to a low DC field. Broadening of the notch bandwidth was observed up to three times the original value. The cholesteric mixture consisted of the chiral dopant S811, the negative dielectric LC ZLI-2079, 5% LC diacrylate monomer RM257 and 0.05% of UV initiator Irgacure 369. Monomer concentrations were varied from 2 to 10 percent by weight with the largest broadening observed at concentrations of 5 percent. The curing was done by illuminating with a flood lit laser line at 364nm or an EXFO UV lamp with a 365nm filter. The broadening effect is proportional to the strength of the applied DC field and relaxes to the original bandwidth when the DC field is removed. Fields greater than a critical value (> 3V/micron) cause a blue shift of the broadened band. The response times for broadening were of the order of 1.5 secs whereas relaxation times were ~0.8 sec.


 

L9.1
Photomechanical Response of Azobenzene Liquid Crystal Polymer Networks as a Function of Temperature.Kyungmin Lee^1,2, Yanira Torres^1,2,3, Hilmar Koerner¹, Richard Vaia¹, Timothy J. Bunning¹ and Timothy J. White¹; ¹Materials and Manufacturing Directorate, Wright-Patterson Air Force Research Lab, Wrigh-Patterson AFB, Ohio; ²Azimuth Corp, Dayton, Ohio; ³Mechanical Engineering, Florida State University, Tallahassee, Florida.

Azobenzene liquid crystal polymer networks (azo-LCN) are capable of tranducing light energy into mechanical work. Recently, we have correlated the relationship between the photomechanical and thermomechanical response of both monodomain and polydomain orientations. This presentation will correlate the photomechanical response of these materials to their thermomechanical properties as a function of chemistry-type, crosslinker, and thickness among other variables.


L9.2
Photoinduced Broadening of Cholesteric Liquid Crystal Reflectors.Alexander Freer^1,2, Timothy J. White¹, Nelson V. Tabiryan³ and Timothy J. Bunning¹; ¹Air Force Research Labs, Dayton, Ohio; ²Azimuth Corporation, Dayton, Ohio; ³BEAM Engineering for Advanced Measurements, Winter Park, Florida.

Cholesteric liquid crystals have been examined as dynamic optical materials owing to their selective reflection that can be formulated across the visible and infrared spectrum. Previously, it has been shown that the reflection of CLCs can be broadened by polymer stabilization to form dynamic mirrors. This work uses light induced changes in an azo-based CLC to optically broaden the reflection of a CLC from 100 nm to as much as 1700 nm. The broadening is caused by the attenuation of UV light throughout the thick and highly absorbing CLC cells. This presentation will summarize the role of thickness, chiral dopant, and light intensity on the photobroadening. Additionally, a novel all-optical technique to ‘trap’ the broadened CLC at a given bandwidth will be discussed.


L9.3
Cholesteric Pitch Broadening Relationships for Negative Dielectric Anisotropy Materials.Anastasia Voevodin¹, Lalgudi Natarajan², Vincent Tondiglia², Madeline Duning¹, Christopher Bailey¹, Timothy White¹ and Timothy Bunning¹; ¹Air Force Research laboratory, Wright-Patterson AFB, Ohio; ²SAIC, Dayton, Ohio.

Previously, negative dielectric anisotropy cholesteric liquid crystals that have been polymer stabilized using UV radiation were shown to broaden their selective reflection notch bandwidth under the application of DC field. This work compares changes in this broadening as a function of the magnitude of the birefringence, cell thickness, polymer content, and field strength. Cholesteric notches of much narrower bandwidth were formed using small birefringence LC materials. Initial results indicate that the ratio of the original notch bandwidth to the final, DC-field broadened notch bandwidth is the same (approximately 3 times broadening) regardless of starting birefringence. In all cases, this broadening occurred with very small field strengths, typically < 4V/micron.


L9.4
Surface Initiated Polymer Stabilized Liquid Crystals.Jennifer Hurtubise, Michael E. McConney, Vincent P. Tondiglia, Lalgudi V. Natarajan, Timothy J. White and Timothy J. Bunning; Materials and Manufacturing Directorate, Wright Patterson Air Force Base, Dayton, Ohio.

Polymer stabilization of cholesteric liquid crystals enables the realization of novel dynamic optical effects in standard, commercially available materials. Typically, these materials reflect only right- or left- handed circularly polarized light. We have recently demonstrated that surface initiated polymer stabilization can yield a so-called hyper-reflective CLC, one in which a single LC cell reflects both left-handed and right-handed circularly polarized light. At this point, little is known about the interaction between the CLC host and the surface-tethered polymer network. Towards this end, systematic examinations of three fundamentally different monomer formulations have been examined. Specifically, the role of the chiral LC diacrylate, LC monoacrylate, and LC diacrylate monomers on the retention of a narrow bandwidth notch is examined. It is shown herein that the notch bandwidth and spectral position are strongly influenced by the monomer formulation. Comparison of transmission spectra before and after polymerization shows that the achiral crosslinker is strongly correlated to the broadening of the notch after polymerization.


L9.5
Electric and Dielectric Properties of a Lithium Salt-doped Photoaddressable Liquid Crystal. Alexandre Allart¹, Frederick Roussel¹ and Patrick Judeinstein²; ¹Univ Lille Nord de France, Villeuneuve d'Ascq, France; ²Univ Paris-Sud, Orsay, France.

Solid polymer electrolytes are of major scientific interest from fundamental standpoint and have numerous potential technological applications, such as high-capacity lithium rechargeable batteries, fuel cells, sensors, and electrochromic device. One way to obtain these intriguing materials is to dissolve alkali salts into media based on poly(ethylene oxide) (PEO), now considered as one of the most efficient materials. Several authors have pointed out that some geometric factors of these (macro)molecules, such as the proximity of polar and non-polar moieties, the control of the PEO chain length, or the partial ordering of the PEO segment, could help to increase the ionic conductivity. Following these assumptions, the present study describes the ability to tune the ionic conductivity of light-sensitive PEO liquid crystal doped with lithium salt by using ultraviolet radiation. P. Judeinstein, F. Roussel, Adv. Mater. 17, 723 (2005)


L9.6
Carbon Nanotubes Induced Changes in the Phase Diagram of 5CB Liquid Crystal.Michael B. McIntyre¹, Erin Gombos¹, Georgi Georgiev^1,2 and Peggy Cebe²; ¹Natural Sicences, Assumption College, Worcester, Massachusetts; ²Physics and Astronomy, Tufts University, Medford, Massachusetts.

Multiwall Carbon Nanotubes (MWCNTs) form a liquid crystalline (LC) state in their lyotropic form, enabling their mixing and coupling their nematic director with LCs. An important aspect of this LC/MWCNT interaction for applications other than display technology is looking at the ways the MWCNTs affect the physical properties of the LCs, in particular 4-cyano-4-n-pentylbiphenyl (5CB). For the first time, we study the effect of MWCNTs on the nematic to crystal phase transition and the crystalline phase of 5CB. Through Polarized Microscopy, Ellipsometry and DSC we are able to observe a change in crystalline order and an increase in nematic to crystal phase transition temperature with increasing CNTs concentration due to the crystal nucleation activity by the CNTs. The trend reverses above 3.0% CNTs. The crystal structure shifts from being spherullitic when CNTs are not present to a fibrillar. The effects of CNTs on the crystal phase of LCs have not been studied and it promises to create new crystal forms for the purposes of optical transmission and other applications. Acknowledgements: the authors thank Assumption College for a Faculty Development Grant and financial support for summer and winter student research.


L9.7
Studies of the Interactions Between Carbon Nanotubes and Liquid Crystals. Erin A. Gombos¹, Michael B. McIntyre¹, Georgi Georgiev^1,2 and Peggy Cebe²; ¹Natural Sicences, Assumption College, Worcester, Massachusetts; ²Physics and Astronomy, Tufts University, Medford, Massachusetts.

In carbon nanotube - liquid crystal (CNT-LC) dispersions the CNTs become aligned by coupling to the LC’s nematic director. We investigate the interactions between the host LC and CNTs, which is useful for applications beyond display technology. Using FTIR and Raman scattering we have found that the modes corresponding to the aromatic ring are affected the most in the presence of CNTs which points to pi-pi stacking of 5CB’s biphenyl rigid core to the rings on the CNTs’ surface. Our spectroscopic results also point to more complicated interactions of the CN group and the CH3 side chain of 5CB to the CNTs. Differential scanning calorimetry results show CNTs affect the LC phase transitions both in peak temperature and shape. This can be explained with the proposed interactions as revealed by spectroscopy. Acknowledgements: the authors thank Assumption College for a Faculty Development Grant and financial support for summer and winter student research.


L9.8
Abstract Withdrawn


L9.9
Rewritable Photopatterning of a Bisanthracene-functionalized Mesogenic Compound by Photodimerization and Thermal Back-reaction of the Anthracene Moiety.Hideyuki Kihara¹, Masashi Motohashi², Kazunari Matsumura² and Masaru Yoshida¹; ¹Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan; ²Materials Science and Engineering, Shibaura Institute of Technology, Koto-ku, Tokyo, Japan.

A new method for photopatterning of a bisanthracene-functionalized mesogenic compound was developed. We synthesized a liquid-crystalline monomer with two anthracene moieties on each end of the molecule. The monomer showed crystalline or liquid-crystalline phase at room temperature. UV-irradiation of the monomer in its molten state caused photodimerization of the anthracene moieties and consequently resulted in the formation of a linear polymer. Unlike the monomer, the polymer obtained exhibited amorphous phase at room temperature. The reason why the polymer showed amorphous phase is probably because the steric bulkiness of the anthracene photodimer disturbs exhibiting the ordered phase. When the monomer were irradiated with UV light through a photomask, the irradiated areas changed to amorphous phase, in contrast, the non-irradiated areas remained the ordered phase. This phenomenon resulted in a clear contrast and visual images under polarized light. In addition, the images could be erased by heating the whole samples at elevated temperature, because the amorphous phase areas reverted to the ordered phase due to reproduction of the mesogenic monomer resulting from the thermal back-reaction of the anthracene photodimer. Photopatterning was performed for the erased sample again and the process was found to be reversible.


L9.10
Effect of Interdigitation on Phase Changes in Side-chain Liquid Crystalline Polymers Bearing Cholesterol.Suk-kyun Ahn¹ and Rajeswari M. Kasi^1,2; ¹Institute of Materials Science Polymer Program, University of Connecticut, Storrs, Connecticut; ²Department of Chemistry, University of Connecticut, Storrs, Connecticut.

Herein, we describe structure-property relations of side-chain liquid crystalline polymers (SCLCPs) where varied flexible methylene spacer (n=4, 5, 9, 10 and 15) decouples motion between polynorbornene main-chains and cholesteryl side-chains. Upon change of the length of flexible methylene spacer, the SCLCPs exhibit different smectic A (SmA) polymorphism from non-interdigitated bilayers (n=4, 5), partially interdigitated mixed layers (n=9, 10) and highly interdigitated single layers (n=15) as determined by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Interestingly, the cholesteric phases exclusively appear in the partially interdigitated mixed layers along with SmA layers upon annealing the sample for extended period of time. The presence of cholesteric phases and their selective light reflection properties are characterized by polarized optical microscopy (POM), transmission electron microscopy (TEM), and UV-VIS. The characteristic oily-streak textures of cholesteric phases are observed by POM, and the helical pitch of cholesteric layers are determined by TEM and UV-VIS. Finally, we propose a simulated model to describe how the extent of interdigitation induces cholesteric phase from SmA phase within particular temperature ranges.


L9.11
Synthesis, Mesomorphism, and Optoelectronic Properties of Highly Fluorescent Room-temperature Liquid Crystal Molecule.Seong-Jun Yoon¹, Jong Won Chung¹, Jong H. Kim¹, Kil Suk Kim², Fabrice Mathevet³, Andre-Jean Attias³, Dongho Kim² and Soo Young Park¹; ¹Department of Materials Science and Engineering, Seoul National University, Seoul, Korea, Republic of; ²Department of Chemistry, Yonsei University, Seoul, Korea, Republic of; ³Laboratory of Polymers Chemistry, Pierre and Marie Curie University, Paris, France.

In the past decades, liquid crystals (LCs) have attracted much attention in both industrial and academic fields due to their unique molecular order and dynamics. Especially over the last decade, a great deal of attention has been paid on π-conjugated LC molecules aiming at their innovative applications in molecular electronics. Several examples of π-conjugated LC molecules with photo- and electroactive functions have been reported, although practical application has been limited because of their high LC temperature region. Herein, we have synthesized a new cyanostilbene-based liquid crystalline material, (2Z,2'Z)-2,2'-(1,4-phenylene)bis(3-(3,4,5-tris(dodecyloxy)phenyl)acrylonitrile), GDCS, which forms hexagonal columnar LC phase at room temperature. GDCS organizes to form the planar molecular disk consisting of two molecules, assisted by local dipole interaction of polar cyano group to give a rather unique phasmidic construction of LC structure. GDCS shows very intense green/yellow fluorescence in liquid/solid crystal state, due to the characteristic aggregation-induced enhanced emission (AIEE) process. AIEE and two-color luminescence behaviors are promoted by intra- and intermolecular actions, which are caused by the peculiar molecular structure including the dipolar cyanostilbene unit. It has been repeatedly found that the intramolecular planarization is responsible for AIEE phenomenon. The origin for the two-color luminescence behavior was elucidated to the intermolecular stacking alternation enabled by two different mode of local dipole coupling, which cause a substantial alternation of π-π overlap. These changes could be directly correlated with the subsequent intermolecular excitonic and excimeric coupling. To explore GDCS photoluminescence characteristics, we have comprehensively carried out temperature-dependent steady-state and time-resolved fluorescence measurement. In addition, we fabricated aligned LC microwires of GDCS by the micromolding in capillaries (MIMIC). We obtained an enhanced electrical conductivity (0.8×10^-5 Scm^-1/3.9×10^-5 Scm^-1) of the LC/crystal aligned microwires, because the MIMIC process induced almost perfect shear alignment of LC material. In this presentation, we will discuss the fundamental LC properties of GDCS, as well as the photo- and electroactive features.


L9.12
Enabling Mode Excitation Control in Holy Fiber with Liquid Crystal for Sensor Application.Jimmy Wang, Tsungyuan Wang, Hongjie Lu and Kunshain Wu; Department of Photonics, NSYSU, Kaohsiung, Taiwan.

The flexibility of controlling mode excitation pattern in fiber is one of important functionality for rapidly promoting new applications in all-fiber design. For instance, the utilization of higher order mode for dispersion compensation in communication and for physical property measurement in sensor has been demonstrated. However, it also clearly revealed the requirement of having a flexible and reliable mode-excitation device. In this study, we would like to investigate the mode excitation in holy fiber with implanting liquid crystal into the core. The fiber insertion loss, mode excitation pattern and mode power partition will be discussed as function of launching condition, holy fiber design, electrical field, and various liquid crystals. The application of liquid-crystal filled holy fiber on chemical sensor will be characterized.


L9.13
High Birefringent Calamitic Reactive Mesogens Based on Hydroquinone Core. Jiho Yun¹, Jung Shin Park¹, Jae-Won Ka¹, Jinsoo Kim¹, Taek Ahn² and Mi Hye Yi¹; ¹Information & Electronics Polymer Research Center, Korea Research Institute of Chemical Technology, Daejeon, Korea, Republic of; ²Department of Chemistry, Kyungsung University, Busan, Korea, Republic of.

High birefringent liquid crystalline materials have been attracting interest for the use in optical devices such as compensation films for wide viewing angle in LCD, liquid crystalline micro-lens array for 3D display, anti-reflection films in OLED, and polarizers. The birefringence (Δn) of liquid crystal is mainly determined by the conjugation length, molecular shape, and polarizability. We have been studying conjugation and polarizable substituents on benzoate and tolane (phenyl-acetylene-phenyl) groups to induce high Δn. Here, we'll report the synthesis of phase-transition temperature controlled tolane bridged novel calamitic liquid crystals based on hydroquinone core with polymerizable terminal groups and alignment properties of prepared calamitic mesogens on the rubbed polyimide substrate. From our experiments, high birefringence (> 0.35) of hydroquinone based liquid crystal films obtained through photo or thermal crosslinking of them. Systematic synthetic approaches to high birefringent materials and the detailed characterizations using polarized optical microscopy and opto-electrical measurement will be discussed.


L9.14
Molecular Engineering of Polymerisable Liquid Crystal Compounds Based on 2,7-Dithiophene-9,9-dialkylfluorene Core.Jinsoo Kim¹, Ji-min Park¹, Jung Shin Park¹, Hye Jung Suk¹, Taek Ahn², Jae-Won Ka¹ and Mi Hye Yi¹; ¹Information&Electronics Polymer Research Institute, Korea Research Institute of Chemical Technology, Daejeon, Korea, Republic of; ²Department of Chemistry, Kyungsung University, Busan, Korea, Republic of.

Reactive liquid crystal (LC) compounds with alignment layers could be converted to morphology controlled polymer films that can be applied in manufacturing the many kinds of optoelectronic devices.[1] Especially, there has been increasing interest in the fluorene based polymerisable LCs, because of their good thermal stability, charge transporting and luminescent properties. Potentially, these fluorene based LC polymer networks could be used as a key component in OFET, OLED, and OPV devices. In our study, we have successfully synthesized 2,7-dithiophene-9,9-dialkylfluorene cored polymerisable LC materials. In order to take advantage of the self organization properties of fluorene LC compounds in preparing LC films, wide LC phase region with room temperature is necessary.[2] We systematically approached this by the substitution as lateral or side alkyl chain into 2,7-dithiophene-9,9-dialkylfluorene cored LC material. In the paper, we will describe the synthesis of polymerisable fluorene LCs and the detailed phase transition behaviours depending on LC molecular structures. In addition, alignment control of fluorene based LCs with alignment layer and optical properties will be discussed. [1] O'Neill, M.; Kelly, S. M. Adv. Mater., 2003, 15(14), 1135. [2] Contoret, A. E. A.; Farrar, S.R.; O’Neill, M.; Nicholls, J. E.; Richards, G. J.; Kelly, S. M.; Hall, A. W. Chem. Mater., 2002, 14, 1477.


L9.15
Abstract Withdrawn


 

8:00 AM *L10.1
Optical Metamaterials and Liquid Crystallinity.Peter Palffy-Muhoray, Liquid Crystal Institute, Kent State University, Kent, Ohio.

Metamaterials consisting of nanoparticles offer rich possibilities for optical applications. Since the susceptibilities of nanoparticles are strongly shape & orientation dependent, systems of orientationally ordered anisometric particles - and particle clusters - can exhibit unique and unusual optical properties. In this talk, I will consider the optical response of metallic nanorods and nanorod clusters, as well as experimental methods for probing these. Methods of producing metallic nanorods and a variety of schemes for obtaining orientationally ordered bulk samples with high loading will be discussed. Although the relation between the individual particle susceptibility and the bulk optical response is an open question, intriguing possibilities are suggested by the close analogy with low molecular weight liquid crystals. Another interesting topic is the definition of liquid crystallinity in nanocolloids. Finally, the problem of describing and modeling liquid crystalline order and its dynamics in guest-host systems will be addressed.


8:30 AM *L10.2
Optical Structuring of Cholesteric Liquid Crystals for Singular Optics, All-optical, and Photonic Applications.Ivan I. Smalyukh, Physics, University of Colorado at Boulder, Boulder, Colorado; Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado.

This lecture will discuss the optical realignment of confined cholesteric liquid crystals by use of the laser beams with optical phase singularities. This realignment allows for formation of localized twisted structures - dubbed Torons - that can be utilized to form a broad range of multistable two-dimensional periodic photonic structures embedded into an untwisted confined cholesteric liquid crystal. The particle-like excitations contain three-dimensional twist of the liquid crystal director matched to the uniform background director field by topological point or line defects. Using both single-beam-steering and holographic generation approaches, the periodic crystal lattices of Torons are tailored by tuning their periodicity, reorienting their crystallographic axes, introducing defects, etc. Moreover, these lattices can be dynamically generated, modified, erased and then recreated, depending on the need of photonic applications. This robust control is performed by tightly-focused laser beams of power 10-100mW and by low-frequency electric fields at voltages ~10V applied to the cell electrodes. The lecture will show how these optically-generated structures can be used as optically-controlled diffraction gratings and for a variety of other applications in photonics, diffractive optics, and singular optics. This work was supported by the Renewable and Sustainable Energy Initiative and Innovation Initiative Seed Grant Programs of University of Colorado, International Institute for Complex Adaptive Matter, and by NSF grants DMR0645461, DMR0820579, and DMR0847782.


9:00 AM *L10.3
Harvesting Single Ferroelectric Domain Nanoparticles for Use in Liquid Crystal Systems.Carl Leibig^1,2, Gary Cook^1,2, Victor Y. Reshetnyak³, Sergey A. Basun^1,4, Ronald Ziolo⁵, Arturo Ponce⁵, Anatoly V. Glushchenko⁶ and Dean R. Evans¹; ¹Azimuth Corporation, Dayton, Ohio; ²AFRL, Dayton, Ohio; ³National Taras Shevchenko University of Kyiv, Kyiv, Ukraine; ⁴UTC, Dayton, Ohio; ⁵CIQA, Saltillo, Coahuila, Mexico; ⁶University of Colorado at Colorado Springs, Colorado Springs, Colorado.

The addition of low concentrations of nanoparticles fabricated from inorganic ferroelectric materials has a profound effect on the electrical and optical properties of liquid crystal systems. The field behavior and electro-optic response of the resulting composite medium is usually significantly different from that of the constituent ingredients and has attracted much scientific interest. In this paper we report on novel harvesting methods for ferroelectric nanoparticles and on the profound effects these have when included in liquid crystal media. We describe the introduction of mechanically generated nanoparticles in the forms of both gaseous aerosol and liquid phase dispersion into extreme electric field gradients. The latter process creates a translational force sufficient to overcome Brownian motion mixing of the aerosol and liquid dispersions. These techniques separate nanoparticles containing a single ferroelectric domain from those which may contain multiple ferroelectric domains. We compare these methods and present two-beam coupling results obtained from the use of harvested single ferroelectric domain nanoparticles in hybrid organic-inorganic photorefractive media. We further present new data from Freedericksz transition measurements which show that low concentrations of harvested single ferroelectric domain nanoparticles impart a programmable and permanent polarization to liquid crystal cells which can either significantly increase or reduce the Freedericksz transition voltage, depending on the sign of the applied DC field in respect to the voltage history of the cell. Acknowledgment: This work has been partially supported by EOARD Grant 078001


9:30 AM L10.4
Fiber Spinning from Liquid Crystalline Solutions of Carbon Nanotubes in Superacids.Anson Ma¹, Colin C. Young¹, Natnael Behabtu¹, A. Nicholas G. Parra-Vasquez², Dmitri Tsentalovich¹, Francesca Mirri¹ and Matteo Pasquali¹; ¹Rice University, Houston, Texas; ²Université Bordeaux 1, Bordeaux, France.

Carbon nanotube (CNT) is perhaps one of the most studied nano-scale materials in the last century, given their fascinating physical and electrical properties. A key challenge, however, is being able to process CNTs into macroscopic articles whilst resembling their intrinsic properties as individual entities. In a recent paper (Davis et al., Nat Nano 4, 830-834, 2009), we have shown that single-walled CNTs dissolve spontaneously in chlorosulfonic acid and form liquid crystals (LC) when dispersed at high concentrations. The identification of a "solvent" for CNTs has opened up the great possibility of processing this - otherwise difficult to process - material, in a way similar to that by which high performance polymer fibers (e.g. Kevlar® and Zylon®) are produced. In this presentation, we will report our latest findings on the formation of LC for various types of CNTs in chlorosulfonic acid and how these solutions can be further processed into macroscopic fibers. Special attention will be given to solutions containing long CNTs (> 10 μm) with great potential of achieving unprecedented material properties. Not only do this type of LC solutions form strikingly beautiful Schlieren texture with domain size in the order of 100 - 200 μm, but they also demonstrate peculiar extensional flow behavior, such as beads-on-a-string filament structure, that has not been previously reported for ordinary CNT systems.


9:45 AM L10.5
Reversible Evaporation to Measure and Control the Phase Behavior of Nanorod and Nanosphere Mixtures.Rafael A. Cabanas, Ryan McDonough and Seth Fraden; Physics, Brandeis University, Waltham, Massachusetts.

To study the phase behavior of mixtures of liquid crystals of filamentous virus fd and spherical colloids we employ a microfluidic device, the PhaseChip, which precisely meters, mixes, and stores sub-nanoliter amounts of sample, solvent, and other reagents. Thousands of individual mixtures are stored on a chip in individual wells. Furthermore, each well is in contact with a reservoir through a membrane through which only water can pass, but not salt, polymer, or amphiphile. This enables the precise and reversible dehydration and rehydration of all the nanoparticles in the mixture. Movies of the PhaseChip in action: http://www.elsie.brandeis.edu/


10:30 AM *L10.6
Reconfigurable and Switchable Colloidal Dispersions of Metal Nanorods with Liquid Crystalline Order.Oleg D. Lavrentovich, Liquid Crystal Institute, Kent State University, Kent, Ohio.

In modern “transformation optics”, one explores metamaterials with properties that vary from point to point in space and time. Control of mutual orientation of anisotropic nanoparticles is of prime importance in designing the metamaterials. Typically, the metastructures are fabricated by a nanolithography approach that has limited applicability when complex three- dimensional arrangements or switching are required. We explore non-lithographic approaches to create three-dimensional reconfigurable and switchable metamaterials. As a starting point, we explore isotropic colloidal dispersions of metal nanorods. The carrier medium is either water or toluene. The nanorods are much smaller (length 50-70 nm, diameter 10-20 nm) than the wavelength of visible light. We describe two approaches to control orientation and concentration of nanorods. In the first approach, we use aggregates of lyotopic chromonic liquid crystals to cause anisometric interactions of gold nanorods and assemble them either side-by-side or end-to-end. The lyotropic chromonic aggregates represent cylindrical stacks of diameter 1-2 nm and length up to 10 nm that are highly charged and are capable to link the properly functionalized nanorods in anisometric fashion. The assembly is non-covalent and as a result, can be easily controlled or even reversed, say, by changing the pH of solution. In the second approach, we use the phenomenon of dielectrophoresis to create gradients of nanorods concentration and to align them. The dispersion is placed in a nonuniform electric field. The latter causes the nanorods to concentrate in the regions with the maximum field. The field-controlled placement of nanorods causes optical effects such as varying refractive index, optical anisotropy (birefringence), and reduced visibility of an object enclosed by the metamaterial. The research has been supported by AFOSR under MURI grant FA9550-06-1-0337 and NSF ARRA grant DMR-0906751.


11:00 AM *L10.7
Assemblies of Patterned and Shaped Colloidal Particles in Nematics.Slobodan Zumer^1,2,3, Miha Ravnik^4,1 and Jayasri Dontabhaktuni¹; ¹Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia; ²Jozef Stefan Institute, Ljubljana, Slovenia; ³Center of Excellence Namaste, Ljubljana, Slovenia; ⁴Rudolf Peierls Centre for Theoretical Physics, Oxford University, Oxford, United Kingdom.

Here we show how our experience with simple spherical colloidal particles in nematic liquid crystals that assemble in 1D, 2D and 3D structures [1,2] can be extended to particles with patterned surface anchoring and to faceted particles. The main binding mechanism of nematic colloidal structures is based on elastic interactions mediated by the topological defects that appear in a confined nematic order after insertion of particles. This effective interaction between colloidal particles that is intrinsically anisotropic leads to numerous organizations of colloidal particles not present in simple liquids. Our approach is based on phenomenological Landau - de Gennes approach and topological theory [2]. In such complex systems modeling is extremely helpful for predicting stable and metastable structures and for finding possible ways to controlled assembling of desired structures. The anisotropic features of particles add additional level of complexity. The effect of a patterned surface interaction is illustrated by spherical Janus particles exhibiting planar and homeotropic nematic anchoring on the two hemispheres [3]. Nematic ordering around such a particle is characterized by a boojum defect on the planar side and by half of a Saturn ring disclination on the homeotropic side leads to numerous assemblies with specific super structures. Further we examine assemblies based on faceted particles [4] where simple geometrical shapes of particles enable formation of well defined colloidal lattice structures. Predictions are contrasted with the latest experimental studies [3,4]. We expect that some of these assemblies will open new ways to complex structures for photonic and plasmonic applications and to possible formation of metamaterials. (1) I. Musevic, M. Skarabot, U. Tkalec, M. Ravnik, S. Zumer, Two-dimensional nematic colloidal crystals self-assembled by topological defects, Science 18, 954-958 (2006) (2) M. Ravnik and S. Zumer, Landau-de Gennes modelling of nematic liquid crystal colloid, Liq. Cryst. 36, 1201 (2009) (3) M. Conradi, M. Ravnik, M. Bele, M. Zorko, S. Zumer and I. Musevic, Janus nematic colloids, Soft Matter 5, 3905 (2009) (4) C. Lapointe, T. Mason, and I.I. Smalyukh, Shape-controlled colloidal interactions in nematic liquid crystals, Science 326, 1083-1086 (2009).


11:30 AM L10.8
Characterising Texture Formation of Faceted Particles Embedded in a Nematic Liquid Crystal Matrix. Paul Phillips and Alejandro Rey; McGill University, Montreal, Quebec, Canada.

Filled nematic liquid crystals with faceted particles are a new kind of soft matter with potential as functional material. The interaction between long range orientational order and geometric discontinuities in the embedded faceted particles gives rise to novel routes to defect and texture generation that can be the source of new functionalities. This work presents texture theory and simulation of filled nematic with faceted particles with the aim of elucidating new mechanism of defect formation. A two dimensional computational study is performed on the texturing of fiber-filled nematic liquid crystals using the Landau-de Gennes model describing the spatio-temporal evolution of the second moment of the orientation distribution function or quadrupolar tensor order parameter. The computation is performed on a consistent computational domain with a square particle embedded within the system. Interest is focused on the role of temperature and the size of the particle and their effect on the nucleation and evolution of defect structures. In the case of faceted particles the well known bulk defects are generated within the system due to the anchoring effect that the particles apply within the system. There is the additional case of surface defects which occur due to the discontinuity within the director field located at edge vertices. This brings an additional property to the system as there is interaction between the two types of defects. Simulations are seen where bulk defects are formed at initial time steps and become absorbed by the corner defects, leaving the system in a corner defect mode. In other simulations the system may remain in a bulk defect mode state. Another defect mode state observed is the generation of biaxial strings occurring between corners of the particles. These different mode types are investigated as a function of temperature and particle width, with the intention of classifying the behaviour with a phase diagram. The transition line between the different defect mode cases are investigated and there are clear results of critical dynamical slow down and metastable effects. The topology of the defect structures are considered at different evolutionary stages. The profile of the corner defects are considered prior and following the bulk defect absorption, complimented by a consideration of the director field. The topology of the bulk defects are considered as a function of temperature, considering the evolution toward the string defect mode.


11:45 AM L10.9
Temperature-induced Positional Ordering in Colloidal Liquid Crystals.Henrik Hemmen¹, Elisabeth Lindbo Hansen¹, Davi de Miranda Fonseca¹, Christophe Coutant^1,2, Mats Sigstad¹ and Jon Otto Fossum¹; ¹Department of Physics, Norwegian University of Science and Technology, Trondheim, Norway; ²UFR Structure et Propriétés de la Matière, Université de Rennes 1, Rennes, France.

Colloidal dispersions of platelet-shaped particles may self-organize into liquid crystalline phases at certain conditions. Due to the importance and ubiquity of clay minerals and their potential applications e.g. in composite materials, self-organization of clay particles in dispersions has been extensively studied in recent years. Nematic phases in natural clay suspensions were until recently [1] not observed since Langmuir’s study in 1938, which has been attributed to a competition between gellation and nematic ordering [2]. Here we report on studies of the polydisperse synthetic clay sodium-fluorohectorite (NaFh), which exhibits coexisting isotropic and nematic phases in aqueous dispersions. In regions of samples with a gel nature, we observe nematic ordering with characteristics that depend on the concentration of clay and ionic strength, as well as the type of confinement. No long-range positional order of the platelets is observed. We find that upon increasing the temperature from room temperature to approximately 40 °C, positional correlation sets in, as evidenced by peaks in small angle x-ray scattering (SAXS). In addition, the SAXS intensity at longer real-space length scales than the peak decays as the temperature is further increased. We take this as an indication of reorganization of the particles and/or nematic domains, reducing the positional correlations of the extended fractal gel network [3], but increasing correlations at length scales proportional to the typical particle thickness. Consequently, the observed behaviour shows indications of a gel-to-glass transition, and the results should be interesting contributions to the ongoing debate on the structure of gels of charged platelets [4]; attractive gels (house of cards), or repulsive gels/glasses. [1] L. J. Michot, I. Bihannic, S. Maddi, S. S. Funari, C. Baravian, P. Levitz, and P. Davidson, Proc. Natl. Acad. Sci. U.S.A. 103 (2006). [2] D. van der Beek and H. N. W. Lekkerkerker, Europhys. Lett. 61 (2003). [3] H. Tanaka, J. Meunier, and D. Bonn, Phys. Rev. E 69 (2004). [4] M. C. D. Mourad, D. V. Byelov, A. V. Petukhov and H. N. W. Lekkerkerker, J. Phys.: Condens. Matter 20 (2008).