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Sample records for liquid crystals phase

  1. Liquid crystal phase shifters for space applications

    NASA Astrophysics Data System (ADS)

    Woehrle, Christopher D.

    Space communication satellites have historically relied heavily on high gain gimbal dish antennas for performing communications. Reflector dish antennas lack flexibility in anti-jamming capabilities, and they tend to have a high risk associated to them given the need for mechanical mechanisms to beam steer. In recent years, a great amount of investment has been made into phased array antenna technologies. Phased arrays offer increased signal flexibility at reduced financial cost and in system risk. The problem with traditional phased arrays is the significant program cost and overall complexity added to the satellite by integrating antenna elements that require many dedicated components to properly perform adaptive beam steering. Several unique methods have been proposed to address the issues that plague traditional phase shifters slated for space applications. Proposed approaches range from complex mechanical switches (MEMS) and ferroelectric devices to more robust molecular changes. Nematic liquid crystals offer adaptive beam steering capabilities that traditional phased arrays have; however, with the added benefit of reduced system cost, complexity, and increased resilience to space environmental factors. The objective of the work presented is to investigate the feasibility of using nematic liquid crystals as a means of phase shifting individual phased array elements slated for space applications. Significant attention is paid to the survivability and performance of liquid crystal and associated materials in the space environment. Performance regarding thermal extremes and interactions with charged particles are the primary factors addressed.

  2. Polarization-modulated smectic liquid crystal phases.

    PubMed

    Coleman, D A; Fernsler, J; Chattham, N; Nakata, M; Takanishi, Y; Körblova, E; Link, D R; Shao, R-F; Jang, W G; Maclennan, J E; Mondainn-Monval, O; Boyer, C; Weissflog, W; Pelzl, G; Chien, L-C; Zasadzinski, J; Watanabe, J; Walba, D M; Takezoe, H; Clark, N A

    2003-08-29

    Any polar-ordered material with a spatially uniform polarization field is internally frustrated: The symmetry-required local preference for polarization is to be nonuniform, i.e., to be locally bouquet-like or "splayed." However, it is impossible to achieve splay of a preferred sign everywhere in space unless appropriate defects are introduced into the field. Typically, in materials like ferroelectric crystals or liquid crystals, such defects are not thermally stable, so that the local preference is globally frustrated and the polarization field remains uniform. Here, we report a class of fluid polar smectic liquid crystals in which local splay prevails in the form of periodic supermolecular-scale polarization modulation stripes coupled to layer undulation waves. The polar domains are locally chiral, and organized into patterns of alternating handedness and polarity. The fluid-layer undulations enable an extraordinary menagerie of filament and planar structures that identify such phases.

  3. A phase-field-crystal model for liquid crystals.

    PubMed

    Löwen, Hartmut

    2010-09-15

    On the basis of static and dynamical density functional theory, a phase-field-crystal model is derived which involves both the translational density and the orientational degree of ordering as well as a local director field. The model exhibits stable isotropic, nematic, smectic A, columnar, plastic-crystalline and orientationally ordered crystalline phases. As far as the dynamics is concerned, the translational density is a conserved order parameter while the orientational ordering is non-conserved. The derived phase-field-crystal model can serve for use in efficient numerical investigations of various nonequilibrium situations in liquid crystals.

  4. Liquid Crystals: The Phase of the Future.

    ERIC Educational Resources Information Center

    Ondris-Crawford, Renate; And Others

    1992-01-01

    Liquid crystal displays are currently utilized to convey information via graphic displays. Presents experiments and explanations that employ the concept of liquid crystals to learn concepts related to the various states of matter, electric and magnetic forces, refraction of light, and optics. Discusses applications of liquid crystal technology.…

  5. Wide Angle Liquid Crystal Optical Phased Array

    NASA Technical Reports Server (NTRS)

    Wang, Xing-Hua; Wang, Bin; Bos, Philip J.; Anderson, James E.; Pouch, John J.; Miranda, Felix A.; McManamon, Paul F.

    2004-01-01

    Accurate modeling of a high resolution, liquid crystal (LC) based, optical phased array (OPA) is shown. The simulation shows excellent agreement with a test 2-D LC OPA. The modeling method is extendable to cases where the array element size is close to the wavelength of light. The fringing fields of such a device are first studied, and subsequently reduced. This results in a device that demonstrates plus or minus 7.4 degrees of continuous beam steering at a wavelength of 1550 nm, and a diffraction efficiency (DE) higher than 72%.

  6. Room-Temperature Liquid Crystal Blue Phases

    NASA Astrophysics Data System (ADS)

    Taushanoff, Stefanie; van Le, Khoa; Twieg, Robert; Jakli, Antal

    2009-03-01

    The ``blue phases'' of a highly chiral liquid crystal are defect-studded structures of double-twist cylinders that are laced together. The three phases, BPI*, BPII* and BPIII* differ only in the packing of the double-twist cylinders. Until recently, blue phases were of limited practical use because they appeared for only a very narrow temperature range. Mixtures that show BPI* and BPII* phases for wide temperature ranges at or around room temperature are now available [1]. Relatively wide temperature BPIII (the blue fog) phase so far was available only at very high temperatures [2]. Here we present mixtures with room-temperature wide range BPIII* phase and compare the ability of chiral dopants to form the different blue phases in a base nematic mixture. PDLC films cast with blue-phase material are also examined.[3pt] [1] H. Coles and M. Pivnenko, Nature 2005 436-18 997-1000 [0pt] [2] C. V. Yelamaggad, I. S. Shashikala, G. Liao, D.S. Shankar Rao, S. K. Prasad , Q. Li A. Jakli, Chem. Mater Comm, 2006, 18, 6100-6102

  7. Blue-phase liquid crystal droplets

    PubMed Central

    Martínez-González, José A.; Zhou, Ye; Rahimi, Mohammad; Bukusoglu, Emre; Abbott, Nicholas L.; de Pablo, Juan J.

    2015-01-01

    Blue phases of liquid crystals represent unique ordered states of matter in which arrays of defects are organized into striking patterns. Most studies of blue phases to date have focused on bulk properties. In this work, we present a systematic study of blue phases confined into spherical droplets. It is found that, in addition to the so-called blue phases I and II, several new morphologies arise under confinement, with a complexity that increases with the chirality of the medium and with a nature that can be altered by surface anchoring. Through a combination of simulations and experiments, it is also found that one can control the wavelength at which blue-phase droplets absorb light by manipulating either their size or the strength of the anchoring, thereby providing a liquid–state analog of nanoparticles, where dimensions are used to control absorbance or emission. The results presented in this work also suggest that there are conditions where confinement increases the range of stability of blue phases, thereby providing intriguing prospects for applications. PMID:26460039

  8. Quantum Liquid Crystal Phases in Strongly Correlated Fermionic Systems

    ERIC Educational Resources Information Center

    Sun, Kai

    2009-01-01

    This thesis is devoted to the investigation of the quantum liquid crystal phases in strongly correlated electronic systems. Such phases are characterized by their partially broken spatial symmetries and are observed in various strongly correlated systems as being summarized in Chapter 1. Although quantum liquid crystal phases often involve…

  9. Defects and order in liquid crystal phases

    NASA Astrophysics Data System (ADS)

    Jain, Shilpa

    This thesis investigates the partial destruction of ordering in liquid crystalline systems due to the influence of defects and thermal fluctuations. The systems under consideration are hexagonal columnar crystals with crystalline order perpendicular to the columns, and two-dimensional smectics with order perpendicular to the layers. We first study the possibility of reentrant melting of a hexagonal columnar crystal of flexible charged polymers at high enough densities. The Lindemann criterion is employed in determining the melting point. Lattice fluctuations are calculated in the Debye model, and an analogy with the Abrikosov vortex lattice in superconductors is exploited in estimating both the elastic constants of the hexagonal lattice, and the appropriate Lindemann constant. We also discuss the unusual functional integral describing the statistical mechanics of a single polymer in an Einstein cage model using the path-integral formulation. A crossover as a function of an external field along the column axis is discussed as well. Next, we study defects in a columnar crystal in the form of vacancy/interstitial loops or strings of vacancies and interstitials bounded by column "heads" and "tails". These defect strings are oriented by the columnar lattice and can change size and shape by movement of the ends and forming kinks along the length. Hence an analysis in terms of directed living polymers is appropriate to study their size and shape distribution, volume fraction, etc. If the entropy of transverse fluctuations overcomes the string line tension in the crystalline phase, a string proliferation transition occurs, leading to a "supersolid" phase with infinitely long vacancy or interstitial strings. We estimate the wandering entropy and examine the behaviour in the transition regime. We also calculate numerically the line tension of various species of vacancies and interstitials in a triangular lattice for power-law potentials as well as for a modified Bessel

  10. Suppression of phase transitions in a confined rodlike liquid crystal.

    PubMed

    Grigoriadis, Christos; Duran, Hatice; Steinhart, Martin; Kappl, Michael; Butt, Hans-Jürgen; Floudas, George

    2011-11-22

    The nematic-to-isotropic, crystal-to-nematic, and supercooled liquid-to-glass temperatures are studied in the liquid crystal 4-pentyl-4'-cyanobiphenyl (5CB) confined in self-ordered nanoporous alumina. The nematic-to-isotropic and the crystal-to-nematic transition temperatures are reduced linearly with the inverse pore diameter. The finding that the crystalline phase is completely suppressed in pores having diameters of 35 nm and below yields an estimate of the critical nucleus size. The liquid-to-glass temperature is reduced in confinement as anticipated by the model of rotational diffusion within a cavity. These results provide the pertinent phase diagram for a confined liquid crystal and are of technological relevance for the design of liquid crystal-based devices with tunable optical, thermal, and dielectric properties.

  11. Interplay Between Two Phase Transitions: Crystallization and Liquid-Liquid Phase Separation in a Polyolefin Blend

    NASA Astrophysics Data System (ADS)

    Han, Charles C.; Zhang, Xiaohua

    2006-03-01

    The correlation between liquid-liquid phase separation (LLPS) and crystallization at several compositions in statistical copolymer blends of poly (ethylene-co-hexene) (PEH) and poly (ethylene-co-butene) (PEB) has been examined by optical microscopy (OM), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). The overwhelming change in the crystallization kinetics due to the density fluctuation caused by the spontaneous spinodal LLPS is observed. This coupling mechanism suggests a new mechanism in the nucleation-crystallization process. All evidences are pointing to a cross-over mechanism from the spinodal fluctuations (of liquid-liquid phase separation) to the nucleation and than crystallization. The detailed experimental evidences and a suggested physical model will be presented.

  12. Electro-optic phase modulation by polymer dispersed liquid crystals

    NASA Astrophysics Data System (ADS)

    Vicari, L.

    1997-05-01

    We present a mathematical model to describe the optical phase shift induced by polymer dispersed liquid crystals (PDLCs) on light impinging transversely on the sample. PDLCs are dispersions of liquid crystal microdroplets in a polymeric binder. Droplets appear as optically uniaxial spheres randomly oriented so that the material is optically isotropic. The application of an external electric field results in a reorientation of the liquid crystal and therefore in an electrically controllable optical uniaxicity of the material. The model is discussed by comparison with experimental data and with previous theory [F. Basile, F. Bloisi, L. Vicari, and F. Simoni, Phys. Rev. E 48, 432 (1993)].

  13. Phase behavior and dynamics of a cholesteric liquid crystal

    SciTech Connect

    Roy, D.; Fragiadakis, D.; Roland, C. M.; Dabrowski, R.; Dziaduszek, J.; Urban, S.

    2014-02-21

    The synthesis, equation of state, phase diagram, and dielectric relaxation properties are reported for a new liquid crystal, 4{sup ′}-butyl-4-(2-methylbutoxy)azoxybenzene (4ABO5*), which exhibits a cholesteric phase at ambient temperature. The steepness of the intermolecular potential was characterized from the thermodynamic potential parameter, Γ = 4.3 ± 0.1 and the dynamic scaling exponent, γ = 3.5 ± 0.2. The difference between them is similar to that seen previously for nematic and smectic liquid crystals, with the near equivalence of Γ and γ consistent with the near constancy of the relaxation time of 4ABO5* at the cholesteric to isotropic phase transition (i.e., the clearing line). Thus, chirality does not cause deviations from the general relationship between thermodynamics and dynamics in the ordered phase of liquid crystals. The ionic conductivity of 4ABO5* shows strong coupling to the reorientational dynamics.

  14. Stimuli-Responsive Cubosomes Formed from Blue Phase Liquid Crystals.

    PubMed

    Bukusoglu, Emre; Wang, Xiaoguang; Martinez-Gonzalez, Jose A; de Pablo, Juan J; Abbott, Nicholas L

    2015-11-18

    Cubosomes formed from blue phase liquid crystals (BPs) dispersed in aqueous media exhibit optical responses to biological amphiphiles. In this study, the formation of aqueous dispersions of BPs is reported, and the effects of confinement and lipids on the phase behavior, optical appearance, and morphology of BP droplets are characterized.

  15. Liquid-Crystal Phase Transition Probed by Fluorescent Molecules

    NASA Astrophysics Data System (ADS)

    Hattori, Toshiaki; Hanai, Nobuhiko; Inouye, Hideyuki; Nakatsuka, Hiroki

    2001-08-01

    Phase transition of four liquid crystal materials have been studied by measuring the decay times of time-resolved intensity of fluorescence from two kind of dyes, malachite green and cryptocyanine, doped in these materials. It was found that the observed fluorescence lifetimes observed depend strongly on the doped molecules and that they change depending on the phase transition of the liquid-crystal materials. These results show that the fluorescence lifetime measurements are effective molecular probes for estimating the microscopic dynamics in these materials.

  16. A polarization independent liquid crystal phase modulation adopting surface pinning effect of polymer dispersed liquid crystals

    NASA Astrophysics Data System (ADS)

    Lin, Yi-Hsin; Tsou, Yu-Shih

    2011-12-01

    A polarization-independent liquid crystal (LC) phase modulation using the surface pinning effect of polymer dispersed liquid crystals (SP-PDLC) is demonstrated. In the bulk region of the SP-PDLC, the orientations of LC directors are randomly dispersed; thus, any polarization of incident light experiences the same averaged refractive index. In the regions near glass substrates, the LC droplets are pinned. The orientations of top and bottom droplets are orthogonal. Two eigen-polarizations of an incident light experience the same phase shift. As a result, the SP-PDLC is polarization independent. Polarizer-free microlens arrays of SP-PDLC are also demonstrated. The SP-PDLC has potential for application in spatial light modulators, laser beam steering, and electrically tunable microprisms.

  17. In-situ isothermal phase transitions in photochromic liquid crystals

    NASA Astrophysics Data System (ADS)

    Watson, Samantha J.; Gleeson, Helen F.; D'Emanuele, Antony; Serak, Svetlana V.; Grozhik, Vladimir A.

    1998-06-01

    This study examines the optical response and physical properties of the homologous series 4-n-butyl-4'-n-alkoxyazobenzene. The members of this series all exhibit liquid crystalline phase behavior, and have also been used as dopants in 4-cyano-4'- n'pentylbiphenyl (5CB), a room temperature nematic liquid crystal. The guest-host system and the azobenzene series have been characterized using optical microscopy and UV-vis spectrophotometry. Illumination of these systems with light of a suitable wavelength induces a trans-cis isomerization of the azo- dye molecules which results in a reorientation of the liquid crystal director, often to such an extent that the liquid crystal phase is disrupted, causing an in situ isothermal phase transition. The response of the liquid crystal system to a linearly polarized beam of exciting radiation is examined with the use of a probe He:Ne laser. Changes in light transmission are then detected with a photodiode. Responses are discussed in terms of homologue, cell thickness and temperature.

  18. Intrinsic response of polymer liquid crystals in photochemical phase transition

    SciTech Connect

    Ikeda, Tomiki; Sasaki, Takeo; Kim, Haengboo )

    1991-01-24

    Time-resolved measurements were performed on the photochemically induced isothermal phase transition of polymer liquid crystals (PLC) with mesogenic side chains of phenyl benzoate (PAPB3) and cyanobiphenyl (PACB3) under conditions wherein the photochemical reaction of the doped photoresponsive molecule (4-butyl-4-{prime}-methoxyazobenzene, BMAB) was completed within {approximately} 10 ns, and the subsequent phase transition of the matrix PLC from nematic (N) to isotropic (I) state was followed by time-resolved measurements of the birefringence of the system. Formation of a sufficient amount of the cis isomer of BMAB with a single pulse of a laser lowered the N-I phase transition temperature of the mixture, inducing the N-I phase transition of PLCs isothermally in a time range of {approximately} 200 ms. This time range is comparable to that of low molecular weight liquid crystals, indicating that suppression in mobility of mesogens in PLCs does not affect significantly the thermodynamically controlled process.

  19. Common path point diffraction interferometer using liquid crystal phase shifting

    NASA Technical Reports Server (NTRS)

    Mercer, Carolyn R. (Inventor)

    1997-01-01

    A common path point diffraction interferometer uses dyed, parallel nematic liquid crystals which surround an optically transparent microsphere. Coherent, collimated and polarized light is focused on the microsphere at a diameter larger than that of the microsphere. A portion of the focused light passes through the microsphere to form a spherical wavefront reference beam and the rest of the light is attenuated by the dyed liquid crystals to form an object beam. The two beams form an interferogram which is imaged by a lens onto an electronic array sensor and into a computer which determines the wavefront of the object beam. The computer phase shifts the interferogram by stepping up an AC voltage applied across the liquid crystals without affecting the reference beam.

  20. Electrically tunable holographic polymer templated blue phase liquid crystal grating

    NASA Astrophysics Data System (ADS)

    He, Zheng-Hong; Chen, Chao-Ping; Zhu, Ji-Liang; Yuan, Ya-Chao; Li, Yan; Hu, Wei; Li, Xiao; Li, Hong-Jing; Lu, Jian-Gang; Su, Yi-Kai

    2015-06-01

    In this paper, we demonstrate an alternative approach to fabricating an electrically tunable holographic polymer templated blue phase liquid crystal grating. This grating is obtained by preforming a polymer template comprised of periodic fringes, and then refilling it with a blue phase liquid crystal. Compared with conventional holographic polymer dispersed liquid crystal gratings, our grating can remarkably reduce its switching voltage from 200 V to 43 V while maintaining a sub-millisecond response time. The holographic polymer templated blue phase liquid crystal (HPTBPLC) grating is free from electrode patterning, thus leading to a lower cost and more flexible applications. Project supported by the National Basic Research Program of China (Grant No. 2013CB328804), the National Natural Science Foundation of China (Grant No. 61307028), the Funds from the Science and Technology Commission of Shanghai Municipality (Grant Nos. 11JC1405300, 13ZR1420000, and 14ZR1422300), and the Fundamental Research Funds for the Central Universities, China (Grant No. XDJK 2011C047).

  1. Crystal growth in a three-phase system: diffusion and liquid-liquid phase separation in lysozyme crystal growth.

    PubMed

    Heijna, M C R; van Enckevort, W J P; Vlieg, E

    2007-07-01

    In the phase diagram of the protein hen egg-white lysozyme, a region is present in which the lysozyme solution demixes and forms two liquid phases. In situ observations by optical microscopy show that the dense liquid droplets dissolve when crystals grow in this system. During this process the demixed liquid region retracts from the crystal surface. The spatial distribution of the dense phase droplets present special boundary conditions for Fick's second law for diffusion. In combination with the cylindrical symmetry provided by the kinetically roughened crystals, this system allows for a full numerical analysis. Using experimental data for setting the boundary conditions, a quasi-steady-state solution for the time-dependent concentration profile was shown to be valid. Comparison of kinetically rough growth in a phase separated system and in a nonseparated system shows that the growth kinetics for a three-phase system differs from a two-phase system, in that crystals grow more slowly but the duration of growth is prolonged.

  2. Stretchable liquid-crystal blue-phase gels.

    PubMed

    Castles, F; Morris, S M; Hung, J M C; Qasim, M M; Wright, A D; Nosheen, S; Choi, S S; Outram, B I; Elston, S J; Burgess, C; Hill, L; Wilkinson, T D; Coles, H J

    2014-08-01

    Liquid-crystalline polymers are materials of considerable scientific interest and technological value. An important subset of these materials exhibit rubber-like elasticity, combining the optical properties of liquid crystals with the mechanical properties of rubber. Moreover, they exhibit behaviour not seen in either type of material independently, and many of their properties depend crucially on the particular mesophase employed. Such stretchable liquid-crystalline polymers have previously been demonstrated in the nematic, chiral-nematic, and smectic mesophases. Here, we report the fabrication of a stretchable gel of blue phase I, which forms a self-assembled, three-dimensional photonic crystal that remains electro-optically switchable under a moderate applied voltage, and whose optical properties can be manipulated by an applied strain. We also find that, unlike its undistorted counterpart, a mechanically deformed blue phase exhibits a Pockels electro-optic effect, which sets out new theoretical challenges and possibilities for low-voltage electro-optic devices.

  3. Synthesis and liquid crystal phase transitions of zirconium phosphate disks

    NASA Astrophysics Data System (ADS)

    Shuai, Min

    Solvent-mediated self-assembly of nanoparticles is an effective and efficient way for the bottom-up organization of functional structures. The primary object of this work is to build up a model system for the study of suspensions of disk-shaped nanoparticles, and use it for the study of self-assembly and discotic liquid crystal phase transitions of discotic particles. The work was introduced by the control over the size and polydispersity of zirconium phosphate (ZrP) disks through synthesis. Systematic experiments revealed that regular-shaped alpha-zirconium phosphate crystalline disks with a size-to-thickness ratio from 1 to 50 and size polydispersity as low as 0.2 can be obtained through hydrothermal treatment in 3 M to 15 M phosphoric acid solutions. Transmission and scanning electron micrographs revealed that the growth of the disks is mediated by oriented attachment, which happened continuously throughout the hydrothermal treatment between various sized disks. Ostwald ripening is effective in improving the regularity of the shape of the disks, especially under prolonged hydrothermal treatment. Under the microwave assisted hydrothermal conditions, the rate of attachment on the flat surfaces of the disks is accelerated, which leads to the formation of the column-shaped crystals. With the ability to adjust the size, aspect ratio, and polydispersity of ZrP disks, the study on self-assembly behavior and the discotic liquid crystal phases was enabled. Firstly, liquid crystal phases of aqueous suspensions of ZrP disks were investigated. Iridescent smectic phase and the critical points of phase transitions were found. Moreover, monolayer ZrP nanosheets with extremely high aspect ratio, which were achieved by exfoliating the ZrP crystals, were also used in this study. The high aspect ratio of nanosheets produces a laminar phase at low nanosheet concentration. Chiral liquid crystal phases were demonstrated when increased the concentration of the nanosheets. The

  4. Micellar hexagonal phases in lyotropic liquid crystals

    NASA Astrophysics Data System (ADS)

    Amaral, L. Q.; Gulik, A.; Itri, R.; Mariani, P.

    1992-09-01

    The hexagonal cell parameter a of the system sodium dodecyl lauryl sulfate and water as a function of volume concentration cv in phase Hα shows the functional behavior expected for micelles of finite length: a~c-1/3v. The interpretation of x-ray data based on finite micelles leads to an alternative description of the hexagonal phase Hα: spherocylindrical micelles of constant radius with length that may grow along the range of the Hα phase. Results are compared with recent statistical-mechanical calculations for the isotropic I-Hα transition. The absence of diffraction in the direction perpendicular to the hexagonal plane is ascribed to polydispersity of micellar length, which also is a necessary condition for the occurrence of direct I-Hα transitions.

  5. Three-dimensional colloidal crystals in liquid crystalline blue phases

    PubMed Central

    Ravnik, Miha; Alexander, Gareth P.; Yeomans, Julia M.; Žumer, Slobodan

    2011-01-01

    Applications for photonic crystals and metamaterials put stringent requirements on the characteristics of advanced optical materials, demanding tunability, high Q factors, applicability in visible range, and large-scale self-assembly. Exploiting the interplay between structural and optical properties, colloidal lattices embedded in liquid crystals (LCs) are promising candidates for such materials. Recently, stable two-dimensional colloidal configurations were demonstrated in nematic LCs. However, the question as to whether stable 3D colloidal structures can exist in an LC had remained unanswered. We show, by means of computer modeling, that colloidal particles can self-assemble into stable, 3D, periodic structures in blue phase LCs. The assembly is based on blue phases providing a 3D template of trapping sites for colloidal particles. The particle configuration is determined by the orientational order of the LC molecules: Specifically, face-centered cubic colloidal crystals form in type-I blue phases, whereas body-centered crystals form in type-II blue phases. For typical particle diameters (approximately 100 nm) the effective binding energy can reach up to a few 100 kBT, implying robustness against mechanical stress and temperature fluctuations. Moreover, the colloidal particles substantially increase the thermal stability range of the blue phases, for a factor of two and more. The LC-supported colloidal structure is one or two orders of magnitude stronger bound than, e.g., water-based colloidal crystals. PMID:21368186

  6. Structure, Hydrodynamics, and Phase Transition of Freely Suspended Liquid Crystals

    NASA Technical Reports Server (NTRS)

    Clark, Noel A.

    2000-01-01

    Smectic liquid crystals are phases of rod shaped molecules organized into one dimensionally (1D) periodic arrays of layers, each layer being between one and two molecular lengths thick. In the least ordered smectic phases, the smectics A and C, each layer is a two dimensional (2D) liquid. Additionally there are a variety of more ordered smectic phases having hexatic short range translational order or 2D crystalline quasi long range translational order within the layers. The inherent fluid-layer structure and low vapor pressure of smectic liquid crystals enable the long term stabilization of freely suspended, single component, layered fluid films as thin as 30A, a single molecular layer. The layering forces the films to be an integral number of smectic layers thick, quantizing their thickness in layer units and forcing a film of a particular number of layers to be physically homogeneous with respect to its layer structure over its entire area. Optical reflectivity enables the precise determination of the number of layers. These ultrathin freely suspended liquid crystal films are structures of fundamental interest in condensed matter and fluid physics. They are the thinnest known stable condensed phase fluid structures and have the largest surface-to-volume ratio of any stable fluid preparation, making them ideal for the study of the effects of reduced dimensionality on phase behavior and on fluctuation and interface phenomena. Their low vapor pressure and quantized thickness enable the effective use of microgravity to extend the study of basic capillary phenomena to ultrathin fluid films. Freely suspended films have been a wellspring of new liquid crystal physics. They have been used to provide unique experimental conditions for the study of condensed phase transitions in two dimensions. They are the only system in which the hexatic has been unambiguously identified as a phase of matter, and the only physical system in which fluctuations of a 2D XY system and

  7. Liquid Crystal Inquiries.

    ERIC Educational Resources Information Center

    Marroum, Renata-Maria

    1996-01-01

    Discusses the properties and classification of liquid crystals. Presents a simple experiment that illustrates the structure of liquid crystals and the differences between the various phases liquid crystals can assume. (JRH)

  8. Reversible Nanoparticle Cubic Lattices in Blue Phase Liquid Crystals.

    PubMed

    Gharbi, Mohamed Amine; Manet, Sabine; Lhermitte, Julien; Brown, Sarah; Milette, Jonathan; Toader, Violeta; Sutton, Mark; Reven, Linda

    2016-03-22

    Blue phases (BPs), a distinct class of liquid crystals (LCs) with 3D periodic ordering of double twist cylinders involving orthogonal helical director twists, have been theoretically studied as potential templates for tunable colloidal crystals. Here, we report the spontaneous formation of thermally reversible, cubic crystal nanoparticle (NP) assemblies in BPs. Gold NPs, functionalized to be highly miscible in cyanobiphenyl-based LCs, were dispersed in BP mixtures and characterized by polarized optical microscopy and synchrotron small-angle X-ray scattering (SAXS). The NPs assemble by selectively migrating to periodic strong trapping sites in the BP disclination lines. The NP lattice, remarkably robust given the small particle size (4.5 nm diameter), is commensurate with that of the BP matrix. At the BP I to BP II phase transition, the NP lattice reversibly switches between two different cubic structures. The simultaneous presence of two different symmetries in a single material presents an interesting opportunity to develop novel dynamic optical materials.

  9. Transparent nematic phase in a liquid-crystal-based microemulsion.

    PubMed

    Yamamoto, J; Tanaka, H

    2001-01-18

    Complex fluids are usually produced by mixing together several distinct components, the interactions between which can give rise to unusual optical and rheological properties of the system as a whole. For example, the properties of microemulsions (composed of water, oil and surfactants) are determined by the microscopic structural organization of the fluid that occurs owing to phase separation of the component elements. Here we investigate the effect of introducing an additional organizing factor into such a fluid system, by replacing the oil component of a conventional water-in-oil microemulsion with an intrinsically anisotropic fluid--a nematic liquid crystal. As with the conventional case, the fluid phase-separates into an emulsion of water microdroplets (stabilized by the surfactant as inverse micelles) dispersed in the 'oil' phase. But the properties are further influenced by a significant directional coupling between the liquid-crystal molecules and the surfactant tails that emerge (essentially radially) from the micelles. The result is a modified bulk-liquid crystal that is an ordered nematic at the mesoscopic level, but which does not exhibit the strong light scattering generally associated with bulk nematic order: the bulk material here is essentially isotropic and thus transparent.

  10. Phase-Shifting Liquid Crystal Interferometers for Microgravity Fluid Physics

    NASA Technical Reports Server (NTRS)

    Griffin, DeVon W.; Marshall, Keneth L.

    2002-01-01

    The initial focus of this project was to eliminate both of these problems in the Liquid Crystal Point-Diffraction Interferometer (LCPDI). Progress toward that goal will be described, along with the demonstration of a phase shifting Liquid Crystal Shearing Interferometer (LCSI) that was developed as part of this work. The latest LCPDI, other than a lens to focus the light from a test section onto a diffracting microsphere within the interferometer and a collimated laser for illumination, the pink region contained within the glass plates on the rod-mounted platform is the complete interferometer. The total width is approximately 1.5 inches with 0.25 inches on each side for bonding the electrical leads. It is 1 inch high and there are only four diffracting microspheres within the interferometer. As a result, it is very easy to align, achieving the first goal. The liquid crystal electro-optical response time is a function of layer thickness, with thinner devices switching faster due to a reduction in long-range viscoelastic forces between the LC molecules. The LCPDI has a liquid crystal layer thickness of 10 microns, which is controlled by plastic or glass microspheres embedded in epoxy 'pads' at the corners of the device. The diffracting spheres are composed of polystyrene/divinyl benzene polymer with an initial diameter of 15 microns. The spheres deform slightly when the interferometer is assembled to conform to the spacing produced by the microsphere-filled epoxy spacer pads. While the speed of this interferometer has not yet been tested, previous LCPDIs fabricated at the Laboratory for Laser Energetics switched at a rate of approximately 3.3 Hz, a factor of 10 slower than desired. We anticipate better performance when the speed of these interferometers is tested since they are approximately three times thinner. Phase shifting in these devices is a function of the AC voltage level applied to the liquid crystal. As the voltage increases, the dye in the liquid crystal

  11. Induced smectic phases of stoichiometric liquid crystal mixtures.

    PubMed

    Sugisawa, Shin-Ya; Tabe, Yuka

    2016-03-28

    We revealed the detailed structures of induced smectic liquid crystal (LC) phases composed of a binary mixture of charge-transfer (CT) LC substances. Although neither of the constituents had highly ordered smectic phases, the mixture exhibited smectic-E (SmE) or smectic-B (SmB) phases when mixed at ratios of 1 : 1 and 2 : 3, respectively. The results of polarized optical microscopy, differential scanning calorimetry, X-ray diffraction, and infrared spectroscopy indicated that the induced smectic phases were stabilized by an exquisite balance between the CT interactions, dipolar interactions, and excluded volume effects. We proposed a possible model for the molecular arrangements in the SmE and SmB phases, which consistently explained the experimental results including the stoichiometric ratios.

  12. High-efficiency and fast-response tunable phase grating using a blue phase liquid crystal.

    PubMed

    Yan, Jin; Li, Yan; Wu, Shin-Tson

    2011-04-15

    We demonstrate a tunable phase grating using a polymer-stabilized blue phase liquid crystal. Because of the electric-field-induced rectangularlike phase profile, a high diffraction efficiency of 40% is achieved. Moreover, this device shows submillisecond response time. The proposed tunable phase grating holds great potential for photonics and display applications. PMID:21499371

  13. Amphitropic liquid crystal phases from polyhydroxy sugar surfactants: Fundamental studies

    NASA Astrophysics Data System (ADS)

    Abou Zied, Osama K.; Hashim, Rauzah; Timimi, B. A.

    2015-03-01

    The self-assembly phenomena on a special class of poly-hydroxy sugar surfactant have been studied extensively. This class of material is classified as amphitropic liquid crystals since they exhibit both thermotropic and lyotropic liquid crystalline properties. Hence the potential applications of these non-ionic surfactants are more versatile than those from the conventional lyotropic liquid crystals including those from thermotropic phases, but the latters are yet to be realized. Unfortunately, due to the lack of interest (or even awareness), fundamental studies in thermotropic glycolipids are scanty to support application development, and any tangible progress is often mired by the complexity of the sugar stereochemistry. However, some applications may be pursued from these materials by taking the advantage of the sugar chirality and the tilted structure of the lipid organization which implies ferroelectric behavior. Here, we present our studies on the stereochemical diversity of the sugar units in glycosides that form the thermotropic/lyotropic phases. The structure to property relationship compares different chain designs and other popular polyhydroxy compounds, such as monooleins and alkylpolyglucosides. Different structural properties of these glycosides are discussed with respect to their self-assembly organization and potential applications, such as delivery systems and membrane mimetic study.

  14. Optical continuous phase-only correlator using liquid crystal television

    NASA Astrophysics Data System (ADS)

    Sheng, Yunlong; Paul-Hus, Gilles

    1993-11-01

    We use a commercially available liquid crystal television (LCTV) for encoding real-time on- axis continuous phase-only filter (POF) in a Vander Lugt type optical correlator. We show by theory and experiments that filter coded on the LCTV with phase mismatching and coupled amplitude modulation maintains a term that is the true POF with a diffraction efficiency to about 70%, plus a zero order spot. The correlation output is a superposition of the POF correlation peak with an image of the input. The filter, referred as to the phase dominant filter, behaves like the POF with advantages of on-axis correlation: high light efficiency and utilization of all the available space bandwidth product of the LCTV. Optical experimental results are shown.

  15. Asymmetric dynamic phase holographic grating in nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Ren, Chang-Yu; Shi, Hong-Xin; Ai, Yan-Bao; Yin, Xiang-Bao; Wang, Feng; Ding, Hong-Wei

    2016-09-01

    A new scheme for recording a dynamic phase grating with an asymmetric profile in C60-doped homeotropically aligned nematic liquid crystal (NLC) was presented. An oblique incidence beam was used to record the thin asymmetric dynamic phase holographic grating. The diffraction efficiency we achieved is more than 40%, exceeding the theoretical limit for symmetric profile gratings. Both facts can be explained by assuming that a grating with an asymmetric saw-tooth profile is formed in the NLC. Finally, physical mechanism and mathematical model for characterizing the asymmetric phase holographic grating were presented, based on the photo-refractive-like (PR-like) effect. Project supported by the Science and Technology Programs of the Educational Committee of Heilongjiang Province, China (Grant No. 12541730) and the National Natural Science Foundation of China (Grant No. 61405057).

  16. Theory of bent-core liquid-crystal phases and phase transitions

    NASA Astrophysics Data System (ADS)

    Lubensky, T. C.; Radzihovsky, Leo

    2002-09-01

    We study phases and phase transitions that can take place in the recently discovered bow-shaped or bent-core liquid-crystal molecules. We show that to completely characterize phases exhibited by such bent-core molecules a third-rank tensor Tijk order parameter is necessary in addition to the vector and the nematic (second-rank) tensor order parameters. We present an exhaustive list of possible liquid phases, characterizing them by their space-symmetry group and order parameters, and catalog the universality classes of the corresponding phase transitions that we expect to take place in such bent-core molecular liquid crystals. In addition to the conventional liquid-crystal phases such as the nematic phase, we predict the existence of other liquid phases, including the spontaneously chiral nematic (NT+2)* and chiral polar (VT+2)* phases, the orientationally ordered but optically isotropic tetrahedratic T phase, and a nematic NT phase with D2d symmetry that is neither uniaxial nor biaxial. Interestingly, the isotropic-tetrahedratic transition is continuous in mean-field theory, but is likely driven first order by thermal fluctuations. We conclude with a discussion of smectic analogs of these phases and their experimental signatures.

  17. Theory of bent-core liquid-crystal phases and phase transitions.

    PubMed

    Lubensky, T C; Radzihovsky, Leo

    2002-09-01

    We study phases and phase transitions that can take place in the recently discovered bow-shaped or bent-core liquid-crystal molecules. We show that to completely characterize phases exhibited by such bent-core molecules a third-rank tensor T(ijk) order parameter is necessary in addition to the vector and the nematic (second-rank) tensor order parameters. We present an exhaustive list of possible liquid phases, characterizing them by their space-symmetry group and order parameters, and catalog the universality classes of the corresponding phase transitions that we expect to take place in such bent-core molecular liquid crystals. In addition to the conventional liquid-crystal phases such as the nematic phase, we predict the existence of other liquid phases, including the spontaneously chiral nematic (N(T)+2)(*) and chiral polar (V(T)+2)(*) phases, the orientationally ordered but optically isotropic tetrahedratic T phase, and a nematic N(T) phase with D(2d) symmetry that is neither uniaxial nor biaxial. Interestingly, the isotropic-tetrahedratic transition is continuous in mean-field theory, but is likely driven first order by thermal fluctuations. We conclude with a discussion of smectic analogs of these phases and their experimental signatures. PMID:12366133

  18. Induced smectic phases in phase diagrams of binary nematic liquid crystal mixtures.

    PubMed

    Huang, Tsang-Min; McCreary, Kathleen; Garg, Shila; Kyu, Thein

    2011-03-28

    To elucidate induced smectic A and smectic B phases in binary nematic liquid crystal mixtures, a generalized thermodynamic model has been developed in the framework of a combined Flory-Huggins free energy for isotropic mixing, Maier-Saupe free energy for orientational ordering, McMillan free energy for smectic ordering, Chandrasekhar-Clark free energy for hexagonal ordering, and phase field free energy for crystal solidification. Although nematic constituents have no smectic phase, the complexation between these constituent liquid crystal molecules in their mixture resulted in a more stable ordered phase such as smectic A or B phases. Various phase transitions of crystal-smectic, smectic-nematic, and nematic-isotropic phases have been determined by minimizing the above combined free energies with respect to each order parameter of these mesophases. By changing the strengths of anisotropic interaction and hexagonal interaction parameters, the present model captures the induced smectic A or smectic B phases of the binary nematic mixtures. Of particular importance is the fact that the calculated phase diagrams show remarkable agreement with the experimental phase diagrams of binary nematic liquid crystal mixtures involving induced smectic A or induced smectic B phase.

  19. A polarization-independent liquid crystal phase modulation using polymer-network liquid crystal with orthogonal alignment layers

    NASA Astrophysics Data System (ADS)

    Chen, Ming-Syuan; Lin, Wei-Chih; Tsou, Yu-Shih; Lin, Yi-Hsin

    2012-10-01

    A polarization-independent liquid crystal (LC) phase modulation using polymer-network liquid crystals with orthogonal alignments layers (T-PNLC) is demonstrated. T-PNLC consists of three layers. LC directors in the two layers near glass substrates are orthogonal to each other. In the middle layer, LC directors are perpendicular to the glass substrate. The advantages of such T-PNLC include polarizer-free, larger phase shift (~0.4π rad) than the residual phase type (<0.05π rad), and low operating voltage (< 30Vrms). It does not require bias voltage for avoiding scattering because the refractive index of liquid crystals matches that of polymers. The phase shift of T-PNLC is affected by the cell gap and the curing voltages. The potential applications are laser beam steering, spatial light modulators and electrically tunable micro-lens arrays.

  20. Stabilizing blue phase liquid crystals with linearly polarized UV light

    NASA Astrophysics Data System (ADS)

    Xu, Daming; Yuan, Jiamin; Schadt, Martin; Yan, Jing; Wu, Shin-Tson

    2015-03-01

    Polymer-stabilized blue-phase liquid crystal (PS-BPLC) has become an increasingly important technology trend for information display and photonic applications. BPLC exhibits several attractive features, such as reasonably wide temperature range, submillisecond gray-to-gray response time, no need for alignment layer, optically isotropic voltageoff state, and large cell gap tolerance when an in-plane switching (IPS) cell is employed. However, some bottlenecks such as high operation voltage, relatively low transmittance, and noticeable hysteresis and prolonged response time at high field region for IPS mode, still remain to be overcome before widespread application of BPLC can be realized. To reduce operation voltage, both new BPLC materials and new device structures have been investigated. In this paper, we demonstrate the stabilization a photopolymer-embedded blue phase liquid crystal precursor using a linearly polarized UV light for first time. When the UV polarization axis is perpendicular to the stripe electrodes of an IPS cell, anisotropic polymer networks are formed through the linear photo-polymerization process and the electrostriction effect is suppressed. As a result, the measured hysteresis is dramatically reduced from 6.95% to 0.36% and the response time shortened by ~2X compared to unpolarized UV exposure. To induce larger anisotropy in polymer networks for mitigating the electrostriction effect, high-intensity linearly polarized UV exposure is preferred. It is foreseeable this method will guide future BPLC device and material development as well as manufacturing process. The dawn of BPLCD is near.

  1. Phase-Shifting Liquid Crystal Point-Diffraction Interferometry

    NASA Technical Reports Server (NTRS)

    Griffin, DeVon W.; Marshall, Kenneth L.; Mercer, Carolyn R.

    2000-01-01

    , the limited spatial resolution and the methods required for data reduction suggest that a more useful instrument needs to be developed. The category of interferometers known as common path interferometers can eliminate much of the vibration sensitivity associated with traditional interferometry as described above. In these devices, division of the amplitude of the wavefront following the test section produces the reference beam. Examples of these instruments include shearing and point diffraction interferometers. In the latter case, shown schematically, a lens focuses light passing through the test section onto a small diffracting object. Such objects are typically either a circle of material on a high quality glass plate or a small sphere in a glass cell. The size of the focused spot is several times larger than the object so that the light not intercepted by the diffracting object forms the test beam while the diffracted light generates a spherical reference beam. While this configuration is mechanically stable, phase shifting one beam with respect to the other is difficult due to the common path. Phase shifting enables extremely accurate measurements of the phase of the interferogram using only gray scale intensity measurements and is the de facto standard of industry. Mercer and Creath 2 demonstrated phase shifting in a point diffraction interferometer using a spherical spacer in a liquid crystal cell as the diffracting object. By changing the voltage across the cell, they were able to shift the phase of the undiffracted beam relative to the reference beam generated by diffraction from the sphere. While they applied this technology to fluid measurements, the device shifted phase so slowly that it was not useful for studying transient phenomena. We have identified several technical problems that precluded operation of the device at video frame rates and intend to solve them to produce a phase-shifting liquid crystal point-diffraction interferometer operating at

  2. Thick polymer-stabilized liquid crystal films for microwave phase control

    NASA Astrophysics Data System (ADS)

    Fujikake, Hideo; Kuki, Takao; Nomoto, Toshihiro; Tsuchiya, Yuzuru; Utsumi, Yozo

    2001-05-01

    This article describes the use of thick polymer-stabilized liquid crystal films in a new design for microwave variable phase shifters. A fine μm-order sized polymer network was formed in a 100-μm-thick liquid crystal film, using a photopolymerization-induced phase-separation method to stabilize the molecular alignment of the liquid crystal. Measurement of the electro-optic properties of the liquid crystal film revealed that the relaxation response time of the liquid crystal alignment was drastically decreased by doping the polymer at a concentration of several wt %. A new variable phase shifter composed of a microstrip transmission line (length: 193 mm, width: 200 μm) was also fabricated by using the liquid crystal film as the dielectric material. This device exhibited a microwave phase shift of -80° at a frequency of 20 GHz, when a drive voltage of 70Vrms was applied vertically to the liquid crystal film.

  3. The Nematic Phases of Bent-Core Liquid Crystals

    PubMed Central

    Gleeson, Helen F; Kaur, Sarabjot; Görtz, Verena; Belaissaoui, Abdel; Cowling, Stephen; Goodby, John W

    2014-01-01

    Over the last ten years, the nematic phases of liquid crystals formed from bent-core structures have provoked considerable research because of their remarkable properties. This Minireview summarises some recent measurements of the physical properties of these systems, as well as describing some new data. We concentrate on oxadiazole-based materials as exemplars of this class of nematogens, but also describe some other bent-core systems. The influence of molecular structure on the stability of the nematic phase is described, together with progress in reducing the nematic transition temperatures by modifications to the molecular structure. The physical properties of bent-core nematic materials have proven difficult to study, but patterns are emerging regarding their optical and dielectric properties. Recent breakthroughs in understanding the elastic and flexoelectric behaviour are summarised. Finally, some exemplars of unusual electric field behaviour are described. PMID:24700653

  4. Liquid-Liquid Phase Separation in Supersaturated Lysozyme Solutions and Associated Precipitate Formation/Crystallization

    NASA Technical Reports Server (NTRS)

    Muschol, Martin; Rosenberger, Franz

    1997-01-01

    Using cloud point determinations, the phase boundaries (binodals) for metastable liquid-liquid (L-L) separation in supersaturated hen egg white lysozyme solutions with 3%, 5%, and 7% (wlv) NaCl at pH= 4.5 and protein concentrations c between 40 and 400 mg/ml were determined. The critical temperature for the binodal increased approximately linearly with salt concentration. The coexisting liquid phases both remained supersaturated but differed widely in protein concentration. No salt repartitioning was observed between the initial and the two separated liquid phases. After the L-L separation, due to the presence of the high protein concentration phase, crystallization occurred much more rapidly than in the initial solution. At high initial protein concentrations, a metastable gel phase formed at temperatures above the liquid binodal. Both crystal nucleation and gel formation were accelerated in samples that had been cycled through the binodal. Solutions in the gel and L-L regions yielded various types of precipitates. Based on theoretical considerations, previous observations with other proteins, and our experimental results with lysozyme, a generic phase diagram for globular proteins is put forth. A limited region in the (T,c) plane favorable for the growth of protein single crystals is delineated.

  5. Surface order at surfactant-laden interfaces between isotropic liquid crystals and liquid phases with different polarity

    NASA Astrophysics Data System (ADS)

    Feng, Xunda; Bahr, Christian

    2011-03-01

    We present an ellipsometry study of the interface between thermotropic liquid crystals and liquid phases consisting of various binary mixtures of water and glycerol. The liquid-crystal samples contain a small constant amount of a surfactant which induces a homeotropic anchoring at the interface. We determine the smectic or nematic order at the interface in the temperature range above the liquid-crystal-isotropic transition while the water to glycerol ratio is varied, corresponding to a systematic modification of the polarity of the liquid phase. The surface-induced order becomes less pronounced with increasing glycerol concentration in the liquid phase. The observed behavior is compared with previous studies in which the surfactant concentration in the liquid-crystal bulk phase was varied. The results indicate that in both cases the magnitude of the surfactant coverage at the interface is the key quantity which determines the liquid-crystal surface order at the interface.

  6. Phase diagrams of orientational transitions in absorbing nematic liquid crystals

    SciTech Connect

    Zolot’ko, A. S. Ochkin, V. N.; Smayev, M. P.; Shvetsov, S. A.

    2015-05-15

    A theory of orientational transitions in nematic liquid crystals (NLCs), which employs the expansion of optical torques acting on the NLC director with respect to the rotation angle, has been developed for NLCs with additives of conformationally active compounds under the action of optical and low-frequency electric and magnetic fields. Phase diagrams of NLCs are constructed as a function of the intensity and polarization of the light field, the strength of low-frequency electric field, and a parameter that characterizes the feedback between the rotation of the NLC director and optical torque. Conditions for the occurrence of first- and second-order transitions are determined. The proposed theory agrees with available experimental data.

  7. Liquid crystal gratings from nematic to blue phase

    NASA Astrophysics Data System (ADS)

    Lu, Yan-qing; Hu, Wei; Lin, Xiao-wen; Srivastava, Abhishek; Chigrinov, Vladimir G.

    2012-10-01

    Some of our recent progress on liquid crystal (LC) gratings, from nematic to blue phase, is reviewed in this invited talk. The first kind of grating is fabricated by periodically adjusting the LC directors to form alternate micro phase retarders and polarization rotators in a cell placed between crossed polarizers. The second one is demonstrated by means of photoalignment technique with alternate orthogonal homogeneously-aligned domains. To improve the response time of the gratings, several approaches are also proposed by using dual-frequency addressed nematic LC, ferroelectric LC and blue phase LC, which shows great performance including high transmittance, polarization independency and submillisecond response. At last, to obtain other controllable LC microstructures rather than simple 1D/2D gratings, we develop a micro-lithography system with a digital micro-mirror device as dynamic mask forms. It may instantly generate arbitrary micro-images on photoalignment layers and further guides the LC molecule orientations. Besides normal phase gratings, more complex patterns such as quasicrystal structures are demonstrated. Some new applications such as tunable multiport optical switching and vector beam generations are expected.

  8. A phase-stepped point diffraction interferometer using liquid crystals

    NASA Technical Reports Server (NTRS)

    Mercer, Carolyn R.; Creath, Katherine; Rashidnia, Nasser

    1995-01-01

    A new instrument, the liquid crystal point diffraction interferometer (LCPDI), has been developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point diffraction interferometer (PDI) and adds to it phase stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wavefronts with high data density and with automated data reduction. The design of the LCPDI is briefly discussed. An algorithm is presented for eliminating phase measurement error caused by object beam intensity variation from frame-to-frame. The LCPDI is demonstrated by measuring the temperature distribution across a heated chamber filled with silicone oil. The measured results are compared to independently measured results and show excellent agreement with them. It is expected that this instrument will have application in the fluid sciences as a diagnostic tool, particularly in space based applications where autonomy, robustness, and compactness are desirable qualities. It should also be useful for the testing of optical elements, provided a master is available for comparison.

  9. Phase separations in mixtures of a liquid crystal and a nanocolloidal particle.

    PubMed

    Matsuyama, Akihiko

    2009-11-28

    We present a mean field theory to describe phase separations in mixtures of a liquid crystal and a nanocolloidal particle. By taking into account a nematic, a smectic A ordering of the liquid crystal, and a crystalline ordering of the nanoparticle, we calculate the phase diagrams on the temperature-concentration plane. We predict various phase separations, such as a smectic A-crystal phase separation and a smectic A-isotropic-crystal triple point, etc., depending on the interactions between the liquid crystal and the colloidal surface. Inside binodal curves, we find new unstable and metastable regions, which are important in the phase ordering dynamics. We also find a crystalline ordering of the nanoparticles dispersed in a smectic A phase and a nematic phase. The cooperative phenomena between liquid-crystalline ordering and crystalline ordering induce a variety of phase diagrams.

  10. Non-Fermi liquid phase in metallic Skyrmion crystals

    NASA Astrophysics Data System (ADS)

    Watanabe, Haruki; Parameswaran, Siddharth; Raghu, Srinivas; Vishwanath, Ashvin

    2014-03-01

    Motivated by reports of a non-Fermi liquid state in MnSi, we examine the effect of coupling phonons of an incommensurate skyrmion crystal (SkX) to conduction electrons. We find that non-Fermi liquid behavior emerges in both two and three dimensions over the entire phase, due to an anomalous electron-phonon coupling that is linked to the net skyrmion density. A small parameter, the spiral wave vector in lattice units, allows us to exercise analytic control and ignore Landau damping of phonons over a wide energy range. At the lowest energy scales the problem is similar to electrons coupled to a gauge field. The best prospects for realizing these effects is in short period skyrmion lattice systems such as MnGe or epitaxial MnSi films. We also compare our results with the unusual T 3 / 2 scaling of temperature dependent resistivity seen in high pressure experiments on MnSi. We acknowledge support from the NSF via Grant DMR-0645691, the DOE Office of Basic Energy Sciences via contract DE-AC02-76SF00515, and the Simons, Templeton, and Alfred P. Sloan Foundations.

  11. The Influence of Disorder on Thermotropic Nematic Liquid Crystals Phase Behavior

    PubMed Central

    Popa-Nita, Vlad; Gerlič, Ivan; Kralj, Samo

    2009-01-01

    We review the theoretical research on the influence of disorder on structure and phase behavior of condensed matter system exhibiting continuous symmetry breaking focusing on liquid crystal phase transitions. We discuss the main properties of liquid crystals as adequate systems in which several open questions with respect to the impact of disorder on universal phase and structural behavior could be explored. Main advantages of liquid crystalline materials and different experimental realizations of random field-type disorder imposed on liquid crystal phases are described. PMID:19865529

  12. A polarization-independent liquid crystal phase modulation using polymer-network liquid crystals in a 90° twisted cell

    NASA Astrophysics Data System (ADS)

    Lin, Yi-Hsin; Chen, Ming-Syuan; Lin, Wei-Chih; Tsou, Yu-Shih

    2012-07-01

    A polarization-independent liquid crystal phase modulation using polymer-network liquid crystals in a 90° twisted cell (T-PNLC) is demonstrated. T-PNLC consists of three layers. Liquid crystal (LC) directors in the two layers near glass substrates are orthogonal to each other and those two layers modulate two eigen-polarizations of an incident light. As a result, two eigen-polarizations of an incident light experience the same phase shift. In the middle layer, LC directors are perpendicular to the glass substrate and contribute no phase shift. The phase shift of T-PNLC is electrically tunable and polarization-independent. T-PNLC does not require any bias voltage for operation. The phase shift is 0.28 π rad for the voltage of 30 Vrms. By measuring and analyzing the optical phase shift of T-PNLC at the oblique incidence of transverse magnetic wave, the pretilt angle of LC directors and the effective thickness of three layers are obtained and discussed. The potential applications are spatial light modulators, laser beam steering, and micro-lens arrays.

  13. Phase-Shifting Liquid Crystal Point-Diffraction Interferometry

    NASA Technical Reports Server (NTRS)

    Griffin, DeVon W.; Marshall, Kenneth L.; Mercer, Carolyn R.

    2000-01-01

    , the limited spatial resolution and the methods required for data reduction suggest that a more useful instrument needs to be developed. The category of interferometers known as common path interferometers can eliminate much of the vibration sensitivity associated with traditional interferometry as described above. In these devices, division of the amplitude of the wavefront following the test section produces the reference beam. Examples of these instruments include shearing and point diffraction interferometers. In the latter case, shown schematically, a lens focuses light passing through the test section onto a small diffracting object. Such objects are typically either a circle of material on a high quality glass plate or a small sphere in a glass cell. The size of the focused spot is several times larger than the object so that the light not intercepted by the diffracting object forms the test beam while the diffracted light generates a spherical reference beam. While this configuration is mechanically stable, phase shifting one beam with respect to the other is difficult due to the common path. Phase shifting enables extremely accurate measurements of the phase of the interferogram using only gray scale intensity measurements and is the de facto standard of industry. Mercer and Creath 2 demonstrated phase shifting in a point diffraction interferometer using a spherical spacer in a liquid crystal cell as the diffracting object. By changing the voltage across the cell, they were able to shift the phase of the undiffracted beam relative to the reference beam generated by diffraction from the sphere. While they applied this technology to fluid measurements, the device shifted phase so slowly that it was not useful for studying transient phenomena. We have identified several technical problems that precluded operation of the device at video frame rates and intend to solve them to produce a phase-shifting liquid crystal point-diffraction interferometer operating at

  14. Liquid crystal phases of two-dimensional dipolar gases and Berezinskii-Kosterlitz-Thouless melting.

    PubMed

    Wu, Zhigang; Block, Jens K; Bruun, Georg M

    2016-01-01

    Liquid crystals are phases of matter intermediate between crystals and liquids. Whereas classical liquid crystals have been known for a long time and are used in electro-optical displays, much less is known about their quantum counterparts. There is growing evidence that quantum liquid crystals play a central role in many electron systems including high temperature superconductors, but a quantitative understanding is lacking due to disorder and other complications. Here, we analyse the quantum phase diagram of a two-dimensional dipolar gas, which exhibits stripe, nematic and supersolid phases. We calculate the stiffness constants determining the stability of the nematic and stripe phases, and the melting of the stripes set by the proliferation of topological defects is analysed microscopically. Our results for the critical temperatures of these phases demonstrate that a controlled study of the interplay between quantum liquid and superfluid phases is within experimental reach for the first time, using dipolar gases. PMID:26750156

  15. Liquid crystal phases of two-dimensional dipolar gases and Berezinskii-Kosterlitz-Thouless melting

    PubMed Central

    Wu, Zhigang; Block, Jens K.; Bruun, Georg M.

    2016-01-01

    Liquid crystals are phases of matter intermediate between crystals and liquids. Whereas classical liquid crystals have been known for a long time and are used in electro-optical displays, much less is known about their quantum counterparts. There is growing evidence that quantum liquid crystals play a central role in many electron systems including high temperature superconductors, but a quantitative understanding is lacking due to disorder and other complications. Here, we analyse the quantum phase diagram of a two-dimensional dipolar gas, which exhibits stripe, nematic and supersolid phases. We calculate the stiffness constants determining the stability of the nematic and stripe phases, and the melting of the stripes set by the proliferation of topological defects is analysed microscopically. Our results for the critical temperatures of these phases demonstrate that a controlled study of the interplay between quantum liquid and superfluid phases is within experimental reach for the first time, using dipolar gases. PMID:26750156

  16. Phase equilibria of binary liquid crystal mixtures involving induced ordered phases

    NASA Astrophysics Data System (ADS)

    Huang, Tsang-Min

    A phenomenological model for elucidating phase diagrams of hexagonal columnar/nematic liquid crystal mixtures has been developed on the basis of the combination of the Flory-Huggins (FH) free energy of isotropic mixing, Maier-Saupe (MS) free energy for nematic ordering, and Chandrasekhar-Clark free energy for hexagonal ordering. Self-consistent calculations show the theory is capable of predicting the various phase diagrams, covering nematic, hexagonal columnar, and isotropic phases. The model has been tested with the eutectic phase diagram of hexagonal columnar liquid crystal, 2, 3, 6, 7, 10, 11-hexapentyloxy triphenylene (HPTP)/reactive nematic mesogens, 4-(3-acryloyloxypropyloxy)-benzoic acid 2-methyl-1, 4-phenylene ester (RM257) mixtures determined by using DSC, polarized optical microscope (POM), and wide-angle X-ray diffraction (WAXD). The self-consistent calculation displays isotropic (I), nematic (N), hexagonal columnar (Colh), N + I, and Colh + I, and Colh + N coexistence regions. These phase regions has been confirmed by thermal quenching various compositions from the isotropic melt to different phase regions. Guided by the established phase diagram of HPTP/RM257 mixtures, photo-polymerization of the mixture has been carried out in different phase regions. The as-cured HPTP/p-(RM257) composites fabricated at isotropic phase (130 °C) remains single isotropic phase under optical microscope, whereas the SEM and TEM results show the bead-like microstructure with sub-micrometer scale. Polymerization-induced mesophase transition experiments have been carried out at isotropic temperatures slightly above the clearing point of the mixtures. Of particular interest is the development of liquid crystalline spherulites. Moreover, the fixation of the morphology is observed when the photopolymerization is carried out in the N, N + I, and N + Colh region. A generalized thermodynamic model for describing smectic A and smectic B ordering has been developed based on

  17. Determination of the liquid crystals phase transition temperatures using optical rotation effect

    NASA Astrophysics Data System (ADS)

    Niu, Xiao-ling; Liu, Wei-guo; Liu, Peng; Cai, Chang-long

    2011-11-01

    Using optical rotation effect, a sensitive, simple optical analytical system is developed for determining the phase transition temperatures of liquid crystals (LCs). When a monochromatic polarized light passes through LCs sample and analyzer, the light intensity changes with temperature. Especially, during the phase transition process, the intensity varies greatly due to optical rotation effect. The variation of light intensity versus variation of temperature curve shows the phase transition temperatures of LCs clearly. The phase transition temperatures of three cholesteric liquid crystals (ChLCs) and a nematic liquid crystals (NLCs) were detected by this method, and compared with those of the differential scanning calorimetry (DSC) and polarized light microscope (PLM) methods.

  18. Phase and Topological Behavior of Lyotropic Chromonic Liquid Crystals in Double Emulsions

    NASA Astrophysics Data System (ADS)

    Davidson, Zoey S.; Jeong, Joonwoo; Tu, Fuquan; Lohr, Matt; Lee, Daeyeon; Collings, Peter J.; Lubensky, Tom C.; Yodh, A. G.

    2013-03-01

    Lyotropic chromonic liquid crystals, assembled by non-covalent interactions, have fascinating temperature- and concentration-dependent phase behavior. Using water-oil-water double emulsions, we are able control the inner droplet chromonic phase concentration by osmosis through the oil phase. We then study the configurations of the chromonic liquid crystal phases in droplets by varying the oil types, oil soluble surfactants, and inner droplet diameter. We employ polarization microscopy to observe resulting nematic and columnar phases of Sunset Yellow FCF, and we deduce the liquid crystal configuration of both phases within the droplets. Simulations based on Jones matrices confirm droplet appearance, and preliminary observations of chromonic liquid crystal shells in oil-water-oil double emulsions are reported. Supported by UPenn MRSEC DMR 11-20901 and NSF DMR 12-05463

  19. Modified phase-field-crystal model for solid-liquid phase transitions

    NASA Astrophysics Data System (ADS)

    Guo, Can; Wang, Jincheng; Wang, Zhijun; Li, Junjie; Guo, Yaolin; Tang, Sai

    2015-07-01

    A modified phase-field-crystal (PFC) model is proposed to describe solid-liquid phase transitions by reconstructing the correlation function. The effects of fitting parameters of our modified PFC model on the bcc-liquid phase diagram, numerical stability, and solid-liquid interface properties during planar interface growth are examined carefully. The results indicate that the increase of the correlation function peak width at k =km will enhance the stability of the ordered phase, while the increase of peak height at k =0 will narrow the two-phase coexistence region. The third-order term in the free-energy function and the short wave-length of the correlation function have significant influences on the numerical stability of the PFC model. During planar interface growth, the increase of peak width at k =km will decrease the interface width and the velocity coefficient C , but increase the anisotropy of C and the interface free energy. Finally, the feasibility of the modified phase-field-crystal model is demonstrated with a numerical example of three-dimensional dendritic growth of a body-centered-cubic structure.

  20. Modified phase-field-crystal model for solid-liquid phase transitions.

    PubMed

    Guo, Can; Wang, Jincheng; Wang, Zhijun; Li, Junjie; Guo, Yaolin; Tang, Sai

    2015-07-01

    A modified phase-field-crystal (PFC) model is proposed to describe solid-liquid phase transitions by reconstructing the correlation function. The effects of fitting parameters of our modified PFC model on the bcc-liquid phase diagram, numerical stability, and solid-liquid interface properties during planar interface growth are examined carefully. The results indicate that the increase of the correlation function peak width at k=k(m) will enhance the stability of the ordered phase, while the increase of peak height at k=0 will narrow the two-phase coexistence region. The third-order term in the free-energy function and the short wave-length of the correlation function have significant influences on the numerical stability of the PFC model. During planar interface growth, the increase of peak width at k=k(m) will decrease the interface width and the velocity coefficient C, but increase the anisotropy of C and the interface free energy. Finally, the feasibility of the modified phase-field-crystal model is demonstrated with a numerical example of three-dimensional dendritic growth of a body-centered-cubic structure. PMID:26274309

  1. Influence of phase delay profile on diffraction efficiency of liquid crystal optical phased array

    NASA Astrophysics Data System (ADS)

    Xu, Lin; Zhang, Jian; Wu, Li Ying

    2009-06-01

    The hardware structure and driving voltage of liquid crystal optical phased array (LCOPA) devices determine the produced phase delay characteristics. The phase delay profile influences directly the device's diffraction efficiency. In this paper, a sawtooth-shaped phase delay model of LCOPA was proposed to analyze quantitatively the influence factors of diffraction efficiency employing Fourier optics theory. Analysis results show that flyback region size is the main factor that affects diffraction efficiency. The influence extent varies with different maximum-phase-delays and grating periods. There exists an optimized curve between maximum-phase-delay and flyback region, and between maximum-phase-delay and grating period, individually. The smaller the grating period is or the larger the flyback region is, the more evident the optimization effect becomes, and the maximum increase ratio is up to 16%. Some feasible experiments were done to test theoretical analysis, and the experimental results agreed with the analysis results.

  2. Novel approach to study liquid crystal phase transitions using Legendre moments

    NASA Astrophysics Data System (ADS)

    Sreehari Sastry, S.; Mallika, K.; Gowri Sankara Rao, B.; Tiong Ha, Sie; Lakshminarayana, S.

    2012-08-01

    A novel approach is proposed to investigate the phase transitions of cholesteric liquid crystals using the Legendre moments. The textures of cholesteric liquid crystals (cholesteryl butyrate, cholesteryl n-valerate, cholesteryl decanoate, and cholesteryl myristate) are captured as a function of temperature using high-resolution camera attached to the arthroscopic mode of polarizing optical microscope with hot stage. A recurrence formula is used to compute the Legendre moments of the liquid crystal textures based on the Legendre polynomial using MATLAB software. The abrupt change in the values of Legendre moments as a function of temperature gives the phase transitions of liquid crystals. The investigated transition temperatures of cholesteric liquid crystals are compared with other techniques.

  3. Stability of liquid crystalline phases in the phase-field-crystal model.

    PubMed

    Achim, Cristian V; Wittkowski, Raphael; Löwen, Hartmut

    2011-06-01

    The phase-field-crystal model for liquid crystals is solved numerically in two spatial dimensions. This model is formulated with three position-dependent order parameters, namely the reduced translational density, the local nematic order parameter, and the mean local direction of the orientations. The equilibrium free-energy functional involves local powers of the order parameters up to fourth order, gradients of the order parameters up to fourth order, and different couplings between the order parameters. The stable phases of the equilibrium free-energy functional are calculated for various coupling parameters. Among the stable liquid crystalline states are the isotropic, nematic, columnar, smectic-A, and plastic crystalline phases. The plastic crystals can have triangular, square, and honeycomb lattices and exhibit orientational patterns with a complex topology involving a sublattice with topological defects. Phase diagrams were obtained by numerical minimization of the free-energy functional. Their main features are qualitatively in line with much simpler one-mode approximations for the order parameters.

  4. Electrically tunable refractive index in the dark conglomerate phase of a bent-core liquid crystal

    NASA Astrophysics Data System (ADS)

    Nagaraj, M.; Görtz, V.; Goodby, J. W.; Gleeson, H. F.

    2014-01-01

    Here we report an electrically tunable refractive index observed in an isotropic liquid crystal phase known as the dark conglomerate (DC) phase. This unusual change in the refractive index which has not been reported before in the DC phase of other bent-core liquid crystals occurs because of a series of electric-field-driven transformations that take place in the DC phase of the studied bent-core liquid crystal. These transformations give rise to a decrease in the refractive index of the system, when an electric field is applied across the device, and no change in the birefringence is seen during such behavior. The electro-optic phenomenon is described in detail and the possibility of exploiting this for a number of liquid crystal based device applications is discussed.

  5. Morphology and crystal phase evolution of GeO 2 in liquid phase deposition process

    NASA Astrophysics Data System (ADS)

    Jing, Chengbin; Sun, Wei; Wang, Wei; Li, Yi; Chu, Junhao

    2012-01-01

    Morphology and crystal phase evolution of GeO 2 in liquid phase deposition (LPD) process is investigated. Rod-like solid phases precipitate out of solution ahead of truncated cube-like phases. SEM, XRD and TEM analyses reveal that the two sorts of solid phases are tetragonal GeO 2 and hexagonal GeO 2, respectively. The tetragonal GeO 2 phases start to experience a re-dissolving process as soon as the hexagonal phases come into being. The prior precipitation of the rod-like phase arises from a relatively low solute saturation of tetragonal GeO 2. Fast growth of a tetragonal GeO 2 phase along [111] direction leads to development of a rod-like shape. The re-dissolving phenomenon does not agree with the classic growth kinetics of crystals but is strongly favored by our calculations based on thermodynamics. The GeO 2 solutes are released in a fluctuant way by germanate ions, which promotes the occurrence of the re-dissolution phenomenon. The current researches open a door for room-temperature LPD growth of not only the hexagonal GeO 2 particles and film but also the one-dimensional tetragonal GeO 2 product.

  6. Liquid-crystal phase grating based on in-plane switching.

    PubMed

    Fujieda, I

    2001-12-01

    A simple phase grating is constructed by insertion of a liquid-crystal layer between two glass plates, upon one of which a pair of transparent interdigitated electrodes is formed. With a bias application, liquid-crystal molecules align themselves along the electric field lines, which are substantially parallel to the glass plates. By controlling the degree of this in-plane switching for the liquid-crystal molecules, one can generate various phase-shift distributions for the light passing through the device. The grating characteristics are altered accordingly. Versatile design and ease of fabrication are potential advantages of this device for some future applications. PMID:18364930

  7. Dual-period tunable phase grating using polymer stabilized blue phase liquid crystal.

    PubMed

    Yan, Jing; Xing, Yufei; Li, Qing

    2015-10-01

    Dual-period tunable phase grating using polymer stabilized blue phase liquid crystal is demonstrated by controlling its driving scheme. High efficiencies of 35.3% for the small-period phase grating and 28.7% for the large-period phase grating have been achieved because of the rectangular-like phase profile which shows good agreement with the simulation results. The diffraction angle can be alternatively tuned, as well as the diffraction efficiency. Moreover, this device also possesses polarization independency and fast response with a rise time of 826 μs and a decay time of 1.143 ms which shows great potential for diffractive optics. PMID:26421571

  8. Semiconductor nanorod liquid crystals

    SciTech Connect

    Li, Liang-shi; Walda, Joost; Manna, Liberato; Alivisatos, A. Paul

    2002-01-28

    Rodlike molecules form liquid crystalline phases with orientational order and positional disorder. The great majority of materials in which liquid crystalline phases have been observed are comprised of organic molecules or polymers, even though there has been continuing and growing interest in inorganic liquid crystals. Recent advances in the control of the sizes and shapes of inorganic nanocrystals allow for the formation of a broad class of new inorganic liquid crystals. Here we show the formation of liquid crystalline phases of CdSe semiconductor nanorods. These new liquid crystalline phases may have great importance for both application and fundamental study.

  9. Improving liquid-crystal-based biosensing in aqueous phases.

    PubMed

    Iglesias, Wilder; Abbott, Nicholas L; Mann, Elizabeth K; Jákli, Antal

    2012-12-01

    Liquid crystal (LC)-based biological sensors permit the study of aqueous biological samples without the need for the labeling of biological species with fluorescent dyes (which can be laborious and change the properties of the biological sample under study). To date, studies of LC-based biosensors have explored only a narrow range of the liquid crystal/alignment layer combinations essential to their operation. Here, we report a study of the role of LC elastic constants and the surface anchoring energy in determining the sensitivity of LC-based biosensors. By investigating a mixture of rod-shape and bent-shape mesogens, and three different alignment layers, we were able to widen the useful detection range of a LC-based sensor by providing an almost-linear mapping of effective birefringence with anionic surfactant concentrations between 0.05 mM and 1 mM (model target analyte). These studies pave the way for optimization of LC-based biosensors and reveal the importance of the choice of both the LC material and the alignment layer in determining sensor properties. PMID:23157269

  10. IMPROVING LIQUID CRYSTAL-BASED BIOSENSING IN AQUEOUS PHASES

    PubMed Central

    Iglesias, Wilder; Abbott, Nicholas L.; Mann, Elizabeth K.; Jákli, Antal

    2012-01-01

    Liquid crystal (LC)-based biological sensors permit the study of aqueous biological samples without the need for the labeling of biological species with fluorescent dyes (which can be laborious and change the properties of the biological sample under study). To date, studies of LC-based biosensors have explored only a narrow range of the liquid crystal/alignment layer combinations essential to their operation. Here we report a study of the role of LC elastic constants and the surface anchoring energy in determining the sensitivity of LC-based biosensors. By investigating a mixture of rod-shape and bent-shape mesogens, and three different alignment layers, we were able to widen the useful detection range of a LC-based sensor by providing an almost linear mapping of effective birefringence with concentration between 0.05 and 1mM of an anionic surfactant (model target analyte). These studies pave the way for optimization of LC-based biosensors and reveal the importance of the choice of both the LC material and the alignment layer in determining sensor properties. PMID:23157269

  11. Diffraction based phase compensation method for phase-only liquid crystal on silicon devices in operation.

    PubMed

    Zhang, Zichen; Yang, Haining; Robertson, Brian; Redmond, Maura; Pivnenko, Mike; Collings, Neil; Crossland, William A; Chu, Daping

    2012-06-10

    A method to measure the optical response across the surface of a phase-only liquid crystal on silicon device using binary phase gratings is described together with a procedure to compensate its spatial optical phase variation. As a result, the residual power between zero and the minima of the first diffraction order for a binary grating can be reduced by more than 10 dB, from -15.98 dB to -26.29 dB. This phase compensation method is also shown to be useful in nonbinary cases. A reduction in the worst crosstalk by 5.32 dB can be achieved when quantized blazed gratings are used. PMID:22695663

  12. Liquid Crystal Phase Behaviour of Attractive Disc-Like Particles

    PubMed Central

    Wu, Liang; Jackson, George; Müller, Erich A.

    2013-01-01

    We employ a generalized van der Waals-Onsager perturbation theory to construct a free energy functional capable of describing the thermodynamic properties and orientational order of the isotropic and nematic phases of attractive disc particles. The model mesogen is a hard (purely repulsive) cylindrical disc particle decorated with an anisotropic square-well attractive potential placed at the centre of mass. Even for isotropic attractive interactions, the resulting overall inter-particle potential is anisotropic, due to the orientation-dependent excluded volume of the underlying hard core. An algebraic equation of state for attractive disc particles is developed by adopting the Onsager trial function to characterize the orientational order in the nematic phase. The theory is then used to represent the fluid-phase behaviour (vapour-liquid, isotropic-nematic, and nematic-nematic) of the oblate attractive particles for varying values of the molecular aspect ratio and parameters of the attractive potential. When compared to the phase diagram of their athermal analogues, it is seen that the addition of an attractive interaction facilitates the formation of orientationally-ordered phases. Most interestingly, for certain aspect ratios, a coexistence between two anisotropic nematic phases is exhibited by the attractive disc-like fluids. PMID:23965962

  13. Amphiphilic Liquid Crystal Exhibiting the Smectic A to Smectic C Phase Transition without Layer Contraction

    NASA Astrophysics Data System (ADS)

    Ishida, Norihiro; Takanishi, Yoichi; Yamamoto, Jun; Yoshizawa, Atsushi

    2011-02-01

    We prepared an amphiphilic liquid crystal composed of a semiperfluorinated alkyl chain and a 2,3-difluoro-1,4-diphenylbenzene core, and investigated its physical properties using polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction analysis. The compound was found to exhibit the smectic A to smectic C phase transition without layer contraction. The compound doped with a ferroelectric liquid crystal exhibited a fast electro-optical switching with a response time of 10 µs in the chiral smectic A phase in spite of the absence of a chiral smectic C phase. The phase transition behavior is interpreted using the de Vries cone model.

  14. Control algorithms of liquid crystal phased arrays used as adaptive optic correctors

    NASA Astrophysics Data System (ADS)

    Dayton, David; Gonglewski, John; Browne, Stephen

    2006-08-01

    Multi-segment liquid crystal phased arrays have been demonstrated as adaptive optics elements for correction of atmospheric turbulence. High speed dual-frequency nematic liquid crystal has sufficient bandwidth to keep up with moderate atmospheric Greenwood frequencies. However the segmented piston correction only spatial nature of the devices requires novel approaches to control algorithms especially when used with Shack-Hartmann wave front sensors. In this presentation we explore approaches and their effects on closed loop Strehl ratios. A Zernike modal based approach has produced the best results. The presentation will contain results from experiments with a Meadowlark optics liquid crystal device.

  15. Phase diagrams of mixtures of a polymer and a cholesteric liquid crystal under an external field.

    PubMed

    Matsuyama, Akihiko

    2014-11-14

    We present a mean field theory to describe phase behaviors in mixtures of a polymer and a cholesteric liquid crystal under an external magnetic or electric field. Taking into account a chiral coupling between a polymer and a liquid crystal under the external field, we examine twist-untwist phase transitions and phase separations in the mixtures. It is found that a cholesteric-nematic phase transition can be induced by not only the external field but also concentration and temperature. Depending on the strength of the external field, we predict cholesteric-paranematic (Ch+pN), nematic-paranematic (N+pN), cholesteric-nematic (Ch+N) phase separations, etc., on the temperature-concentration plane. We also discuss mixtures of a non-chiral nematic liquid crystal and a chiral dopant. PMID:25399158

  16. Phase diagrams of mixtures of a polymer and a cholesteric liquid crystal under an external field

    SciTech Connect

    Matsuyama, Akihiko

    2014-11-14

    We present a mean field theory to describe phase behaviors in mixtures of a polymer and a cholesteric liquid crystal under an external magnetic or electric field. Taking into account a chiral coupling between a polymer and a liquid crystal under the external field, we examine twist-untwist phase transitions and phase separations in the mixtures. It is found that a cholesteric-nematic phase transition can be induced by not only the external field but also concentration and temperature. Depending on the strength of the external field, we predict cholesteric-paranematic (Ch+pN), nematic-paranematic (N+pN), cholesteric-nematic (Ch+N) phase separations, etc., on the temperature-concentration plane. We also discuss mixtures of a non-chiral nematic liquid crystal and a chiral dopant.

  17. Temperature tuning of lasing emission from dye-doped liquid crystal at intermediate twisted phase

    NASA Astrophysics Data System (ADS)

    Liao, Kuan-Cheng; Lin, Ja-Hon; Jian, Li-Hao; Chen, Yao-Hui; Wu, Jin-Jei

    2015-07-01

    Temperature tuning of lasing emission from dye-doped cholesteric liquid crystal (CLC) at intermediate twisted phase has been demonstrated in this work. With heavily doping of 42.5% chiral molecules into the nematic liquid crystals, the shifts of photonic bandgap versus temperature is obviously as thermal controlling of the sample below the certain value. By the differential scanning calorimetr measuremet, we demonstrate the phase transition from the CLC to the smectic phase when the temperature is lowered to be about 15°C. Between CLC and smectic phase, the liquid crystal mixtures are operated at intermediate twisted phase that can be used the temperature related refractive mirror. After pump by the Q-switched Nd:YAG laser, the lasing emission from this dye doped LC mixtures has been demonstrated whose emission wavelength can be tuned from 566 to 637 nm with 1.4°C variation.

  18. Liquid Crystals

    NASA Technical Reports Server (NTRS)

    1990-01-01

    Thermochromic liquid crystals, or TLCs, are a type of liquid crystals that react to changes in temperature by changing color. The Hallcrest/NASA collaboration involved development of a new way to visualize boundary layer transition in flight and in wind tunnel testing of aircraft wing and body surfaces. TLCs offered a new and potentially better method of visualizing the boundary layer transition in flight. Hallcrest provided a liquid crystal formulation technique that afforded great control over the sensitivity of the liquid crystals to varying conditions. Method is of great use to industry, government and universities for aerodynamic and hydrodynamic testing. Company's principal line is temperature indicating devices for industrial use, such as non-destructive testing and flaw detection in electric/electronic systems, medical application, such as diagnostic systems, for retail sale, such as room, refrigerator, baby bath and aquarium thermometers, and for advertising and promotion specials. Additionally, Hallcrest manufactures TLC mixtures for cosmetic applications, and liquid crystal battery tester for Duracell batteries.

  19. Large-scale and highly oriented liquid crystal phase in suspensions of polystyrene-block-poly(L-lactide) single crystals.

    PubMed

    Jiang, Chunbo; Wang, Zongbao; Huang, Haiying; He, Tianbai

    2011-04-19

    A large number of lozenge-shaped and sandwiched polystyrene-block-poly(L-lactide) (PS-b-PLLA) single crystals were prepared by the self-seeding technique. The single crystals were nearly monodispersed in both thickness and diameter. They are well-dispersed because of the steric stabilization offered by tethered PS in p-xylene, which is a good solvent for PS. The suspensions were observed to separate into a transparent upper phase and a turbid lower phase. The lower phase showed uniform iridescent stripes extending over the whole tube between crossed polarizers. The birefringence demonstrates the liquid crystal order, and the uniform stripes reveal that the phase is a well-oriented single domain. The phase-transition concentration is rather low. Polarizing light microscopy (PLM) images show Schlieren texture and thread-like texture. Small-angle X-ray scattering (SAXS) results showed that the single crystals in the liquid crystal phase oriented horizontally with a vertical repeat distance of about 70 nm. Additionally, the possible structure of the liquid crystal phase is being discussed. The novel disclike colloidal particle might be useful for anisotropic photonic materials. PMID:21405072

  20. A binary phase field crystal study for liquid phase heteroepitaxial growth

    NASA Astrophysics Data System (ADS)

    Lu, Yanli; Peng, Yingying; Chen, Zheng

    2016-09-01

    The liquid phase heteroepitaxial growth on predefined crystalline substrate is studied with binary phase field crystal (PFC) model. The purpose of this paper focuses on changes of the morphology of epitaxial films, influences of substrate vicinal angles on epitaxial growth, characteristics of islands growth on both sides of the substrate as well. It is found that the morphology of epitaxial films undergoes the following transitions: layer-by-layer growth, islands formation, mismatch dislocations nucleation and climb towards the film-substrate interface. Meanwhile, the density of steps and islands has obviously direct ratio relations with the vicinal angles. Also, preferential regions are found when islands grow on both sides of the substrate. For thinner substrate, the arrangement of islands is more orderly and the appearance of preferential growth is more obvious than that of thicker substrate. Also, the existing of preferential regions is much more valid for small substrate vicinal angles in contrast for big substrate vicinal angles.

  1. Liquid Crystal Optofluidics

    SciTech Connect

    Vasdekis, Andreas E.; Cuennet, J. G.; Psaltis, D.

    2012-10-11

    By employing anisotropic fluids and namely liquid crystals, fluid flow becomes an additional degree of freedom in designing optofluidic devices. In this paper, we demonstrate optofluidic liquid crystal devices based on the direct flow of nematic liquid crystals in microfluidic channels. Contrary to previous reports, in the present embodiment we employ the effective phase delay acquired by light travelling through flowing liquid crystal, without analysing the polarisation state of the transmitted light. With this method, we demonstrate the variation in the diffraction pattern of an array of microfluidic channels acting as a grating. We also discuss our recent activities in integrating mechanical oscillators for on-chip peristaltic pumping.

  2. Large Microwave Birefringence Liquid-Crystal Characterization for Phase-Shifter Applications

    NASA Astrophysics Data System (ADS)

    Dubois, Frédéric; Krasinski, Freddy; Splingart, Bertrand; Tentillier, Nicolas; Legrand, Christian; Spadlo, Anna; Dabrowski, Roman

    2008-05-01

    This work is concerned with the improvement of a microwave liquid-crystal phase shifter using a large birefringence nematic liquid crystal. This material is a eutectic mixture of isothiocyanatotolane molecules. Microwave dielectric properties are reported and compared to the data obtained with the 5CB cyanobiphenyl material in the 26-40 GHz frequency range using a rectangular waveguide. The phase-shifter design consists of a central cavity, where a liquid crystal is inserted, and two coplanar strip lines accesses. Its dimensions were calculated by electromagnetic simulation, using measured dielectric permittivities of the liquid crystal. The measurements were performed with a commercial Wiltron 3680 K probe test fixture. Phase-shift variations with and without bias voltage versus frequency are presented. As expected, the large-birefringence nematic liquid crystal exhibits a higher microwave dielectric anisotropy (Δɛ' = 1.06 against 0.34) and the tunability of the phase shifter strongly increases (1.8 deg·cm-1·GHz-1 against 0.8 deg·cm-1·GHz-1).

  3. Phase grating wavefront curvature sensor based on liquid crystal spatial light modulator

    NASA Astrophysics Data System (ADS)

    Chen, Bo; Li, Xiaoyang; Yang, Xu

    2015-08-01

    The phase grating wavefront curvature sensor based on liquid crystal spatial light modulator is introduced. A close-loop phase retrieval method based on Eigen functions of Laplacian is proposed, and its accuracy and efficiency are analyzed through numerical experiments of atmospheric phase retrieval. The results show that the close-loop phase retrieval method has a high accuracy. Moreover, it is stable regardless of modal cross coupling.

  4. Optically addressed and submillisecond response phase only liquid crystal spatial light modulator

    NASA Astrophysics Data System (ADS)

    Zhao, Xiangjie; Duan, Jiazhu; Zhang, Dayong; Luo, Yongquan

    2014-10-01

    Liquid crystal based phase only spatial light modulator has attracted many research interests since last decades because of its superior advantage. Until now the liquid crystal spatial light modulator has been applied in many fields, but the response speed of nematic LC limited its further application. In this paper, an optically addressed phase only LC spatial light modulator was proposed based on polymer network liquid crystal. Morphology effect on the light scattering of PNLC was studied, which was mainly consisted of fiber and fiber bundles. The morphology nearly determined the light scattering and electro-optical property. Due to the high threshold voltage, to address the PNLC phase modulator was also concerned. Optical addressing method was proposed, in which BSO crystal was selected to replace one of the glass substrate. The response speed of PNLC was so fast that the reorientation of liquid crystal director will follow the change of effective voltage applied on LC layer, which was related with the voltage signal and especially with electron transport of photo-induced carriers due to diffusion and drift. The on state dynamic response of phase change was investigated. Based on this device, beam steering was also achieved by loading 488nm laser strip on the optical addressed phase only spatial light modulator.

  5. Non-equilibrium phase transitions in a liquid crystal

    NASA Astrophysics Data System (ADS)

    Dan, K.; Roy, M.; Datta, A.

    2015-09-01

    The present manuscript describes kinetic behaviour of the glass transition and non-equilibrium features of the "Nematic-Isotropic" (N-I) phase transition of a well known liquid crystalline material N-(4-methoxybenzylidene)-4-butylaniline from the effects of heating rate and initial temperature on the transitions, through differential scanning calorimetry (DSC), Fourier transform infrared and fluorescence spectroscopy. Around the vicinity of the glass transition temperature (Tg), while only a change in the baseline of the ΔCp vs T curve is observed for heating rate (β) > 5 K min-1, consistent with a glass transition, a clear peak for β ≤ 5 K min-1 and the rapid reduction in the ΔCp value from the former to the latter rate correspond to an order-disorder transition and a transition from ergodic to non-ergodic behaviour. The ln β vs 1000/T curve for the glass transition shows convex Arrhenius behaviour that can be explained very well by a purely entropic activation barrier [Dan et al., Eur. Phys. Lett. 108, 36007 (2014)]. Fourier transform infrared spectroscopy indicates sudden freezing of the out-of-plane distortion vibrations of the benzene rings around the glass transition temperature and a considerable red shift indicating enhanced coplanarity of the benzene rings and, consequently, enhancement in the molecular ordering compared to room temperature. We further provide a direct experimental evidence of the non-equilibrium nature of the N-I transition through the dependence of this transition temperature (TNI) and associated enthalpy change (ΔH) on the initial temperature (at fixed β-values) for the DSC scans. A plausible qualitative explanation based on Mesquita's extension of Landau-deGennes theory [O. N. de Mesquita, Braz. J. Phys. 28, 257 (1998)] has been put forward. The change in the molecular ordering from nematic to isotropic phase has been investigated through fluorescence anisotropy measurements where the order parameter, quantified by the

  6. Non-equilibrium phase transitions in a liquid crystal.

    PubMed

    Dan, K; Roy, M; Datta, A

    2015-09-01

    The present manuscript describes kinetic behaviour of the glass transition and non-equilibrium features of the "Nematic-Isotropic" (N-I) phase transition of a well known liquid crystalline material N-(4-methoxybenzylidene)-4-butylaniline from the effects of heating rate and initial temperature on the transitions, through differential scanning calorimetry (DSC), Fourier transform infrared and fluorescence spectroscopy. Around the vicinity of the glass transition temperature (Tg), while only a change in the baseline of the ΔCp vs T curve is observed for heating rate (β) > 5 K min(-1), consistent with a glass transition, a clear peak for β ≤ 5 K min(-1) and the rapid reduction in the ΔCp value from the former to the latter rate correspond to an order-disorder transition and a transition from ergodic to non-ergodic behaviour. The ln β vs 1000/T curve for the glass transition shows convex Arrhenius behaviour that can be explained very well by a purely entropic activation barrier [Dan et al., Eur. Phys. Lett. 108, 36007 (2014)]. Fourier transform infrared spectroscopy indicates sudden freezing of the out-of-plane distortion vibrations of the benzene rings around the glass transition temperature and a considerable red shift indicating enhanced coplanarity of the benzene rings and, consequently, enhancement in the molecular ordering compared to room temperature. We further provide a direct experimental evidence of the non-equilibrium nature of the N-I transition through the dependence of this transition temperature (TNI) and associated enthalpy change (ΔH) on the initial temperature (at fixed β-values) for the DSC scans. A plausible qualitative explanation based on Mesquita's extension of Landau-deGennes theory [O. N. de Mesquita, Braz. J. Phys. 28, 257 (1998)] has been put forward. The change in the molecular ordering from nematic to isotropic phase has been investigated through fluorescence anisotropy measurements where the order parameter, quantified by the

  7. Field-induced phase transitions in chiral smectic liquid crystals studied by the constant current method

    NASA Astrophysics Data System (ADS)

    H, Dhaouadi; R, Zgueb; O, Riahi; F, Trabelsi; T, Othman

    2016-05-01

    In ferroelectric liquid crystals, phase transitions can be induced by an electric field. The current constant method allows these transition to be quickly localized and thus the (E,T) phase diagram of the studied product can be obtained. In this work, we make a slight modification to the measurement principles based on this method. This modification allows the characteristic parameters of ferroelectric liquid crystal to be quantitatively measured. The use of a current square signal highlights a phenomenon of ferroelectric hysteresis with remnant polarization at null field, which points out an effect of memory in this compound.

  8. Experimental investigation of modulation characteristic of liquid-crystal phase modulator

    NASA Astrophysics Data System (ADS)

    Antonov, Yuri G.; Grigoriev, Slava V.; Moskaletz, Dmitry O.; Tokarev, Dmitry S.

    2004-02-01

    In this paper a liquid-crystal phase modulator (LCPM) is investigated, the volt-phase chracteristics being important parameter of this modulator. This LCPM is the most impotent element in acousto-optic scheme of quasi-matched filter, which allows controlling of impulse response. Method of measurement of volt-phase characteristic of LCFM is described. Experimental results that were obtained are considered.

  9. Micellar-shape anisometry near isotropic-liquid-crystal phase transitions

    NASA Astrophysics Data System (ADS)

    Itri, R.; Amaral, L. Q.

    1993-04-01

    Micellar phases of the sodium dodecyl (lauryl) sulfate (SLS)-water-decanol system have been studied by x-ray scattering in the isotropic (I) phase, with emphasis on the I-->hexagonal (Hα) and I-->nematic-cylindrical (Nc) lyotropic liquid-crystal phase transitions. Analysis of the scattering curves is made through modeling of the product P(q)S(q), where P(q) is the micellar form factor and S(q) is the intermicellar interference function, calculated from screened Coulombic repulsion in a mean spherical approximation. Results show that micelles grow more by decanol addition near the I-->Nc transition (anisometry ν~=3) than by increased amphiphile concentration in the binary system near the I-->Hα phase transition (ν~=2.4). These results compare well with recent theories for isotropic-liquid-crystal phase transitions.

  10. Paraelectric-antiferroelectric phase transition in achiral liquid crystals

    NASA Astrophysics Data System (ADS)

    Pociecha, Damian; Gorecka, Ewa; Čepič, Mojca; Vaupotič, Nataša; Gomola, Kinga; Mieczkowski, Jozef

    2005-12-01

    Critical freezing of molecular rotation in an achiral smectic phase, which leads to polar ordering through the second order paraelectric-antiferroelectric (Sm-A→Sm-APA) phase transition is studied theoretically and experimentally. Strong softening of the polar mode in the Sm-A phase and highly intensive dielectric mode in the Sm-APA phase are observed due to weak antiferroelectric interactions in the system. In the Sm-APA phase the dielectric response behaves critically upon biasing by a dc electric field. Such a behavior is found general for the antiferroelectric smectic phase with significant quadrupolar interlayer coupling.

  11. Near infrared light-driven liquid crystal phase transition enabled by hydrophobic mesogen grafted plasmonic gold nanorods.

    PubMed

    Gutierrez-Cuevas, Karla G; Wang, Ling; Xue, Chenming; Singh, Gautam; Kumar, Satyendra; Urbas, Augustine; Li, Quan

    2015-06-18

    Light-driven phase transition in liquid crystals is a fascinating endeavour from both scientific and technological points of view. Here we demonstrate the proof-of-principle that the photothermal effect of organo-soluble plasmonic gold nanorods can introduce the phase transition of thermotropic liquid crystals upon near infrared laser irradiation. Interestingly, the reverse process occurs when the laser is switched off.

  12. Phase transitional behaviors of bent-cored liquid crystal in electric field

    NASA Astrophysics Data System (ADS)

    Peng, Huan-Gao; Zhou, Zicong; Merlitz, Holger; Wu, Chen-Xu

    2016-06-01

    Monte Carlo (MC) simulations based on lattice model were performed to study the phase diagram (anisotropy, uniaxiality and biaxiality) of liquid crystals formed by bent-cored molecules with a strong transverse dipole moment deviating from their angular bisector. It is shown that the asymmetric strong dipolar interaction enhances biaxiality slightly but encourages uniaxiality greatly and as a result suppresses the system's isotropic order, which is different from a system free from external field in that dipole moment increases biaxiality by suppressing the uniaxial and the isotropic orders simultaneously. It is also found that an external electric field encourages the biaxiality slightly but considerably enhances the uniaxiality of bent-cored liquid crystal.

  13. Dielectric spectroscopy of isotropic liquids and liquid crystal phases with dispersed graphene oxide

    PubMed Central

    Al-Zangana, Shakhawan; Iliut, Maria; Boran, Gökçen; Turner, Michael; Vijayaraghavan, Aravind; Dierking, Ingo

    2016-01-01

    Graphene oxide (GO) flakes of different sizes were prepared and dispersed in isotropic and nematic (anisotropic) fluid media. The dielectric relaxation behaviour of GO-dispersions was examined for a wide temperature (25–60 oC) and frequency range (100 Hz–2 MHz). The mixtures containing GO flakes exhibited varying dielectric relaxation processes, depending on the size of the flakes and the elastic properties of the dispersant fluid. Relaxation frequencies of the GO doped isotropic media, such as isopropanol IPA, were observed to be much lower than the GO doped thermotropic nematic medium 5CB. It is anticipated that the slow relaxation frequencies (~10 kHz) could be resulting from the relaxation modes of the GO flakes while the fast relaxation frequencies (~100 kHz) could indicate strongly slowed down molecular modes of the nematogenic molecules, which are anchored to the GO flakes via dispersion interactions. The relaxation frequencies decreased as the size of the GO flakes in the isotropic solvent was increased. Polarizing microscopy showed that GO flakes with a mean diameter of 10 μm, dispersed in water, formed a lyotropic nematic liquid crystal phase. This lyotropic nematic exhibited the slowest dielectric relaxation process, with relaxation frequencies in the order of 2 kHz, as compared to the GO-isotropic suspension and the GO-doped 5CB. PMID:27555475

  14. Dielectric spectroscopy of isotropic liquids and liquid crystal phases with dispersed graphene oxide

    NASA Astrophysics Data System (ADS)

    Al-Zangana, Shakhawan; Iliut, Maria; Boran, Gökçen; Turner, Michael; Vijayaraghavan, Aravind; Dierking, Ingo

    2016-08-01

    Graphene oxide (GO) flakes of different sizes were prepared and dispersed in isotropic and nematic (anisotropic) fluid media. The dielectric relaxation behaviour of GO-dispersions was examined for a wide temperature (25–60 oC) and frequency range (100 Hz–2 MHz). The mixtures containing GO flakes exhibited varying dielectric relaxation processes, depending on the size of the flakes and the elastic properties of the dispersant fluid. Relaxation frequencies of the GO doped isotropic media, such as isopropanol IPA, were observed to be much lower than the GO doped thermotropic nematic medium 5CB. It is anticipated that the slow relaxation frequencies (~10 kHz) could be resulting from the relaxation modes of the GO flakes while the fast relaxation frequencies (~100 kHz) could indicate strongly slowed down molecular modes of the nematogenic molecules, which are anchored to the GO flakes via dispersion interactions. The relaxation frequencies decreased as the size of the GO flakes in the isotropic solvent was increased. Polarizing microscopy showed that GO flakes with a mean diameter of 10 μm, dispersed in water, formed a lyotropic nematic liquid crystal phase. This lyotropic nematic exhibited the slowest dielectric relaxation process, with relaxation frequencies in the order of 2 kHz, as compared to the GO-isotropic suspension and the GO-doped 5CB.

  15. Dielectric spectroscopy of isotropic liquids and liquid crystal phases with dispersed graphene oxide.

    PubMed

    Al-Zangana, Shakhawan; Iliut, Maria; Boran, Gökçen; Turner, Michael; Vijayaraghavan, Aravind; Dierking, Ingo

    2016-01-01

    Graphene oxide (GO) flakes of different sizes were prepared and dispersed in isotropic and nematic (anisotropic) fluid media. The dielectric relaxation behaviour of GO-dispersions was examined for a wide temperature (25-60 (o)C) and frequency range (100 Hz-2 MHz). The mixtures containing GO flakes exhibited varying dielectric relaxation processes, depending on the size of the flakes and the elastic properties of the dispersant fluid. Relaxation frequencies of the GO doped isotropic media, such as isopropanol IPA, were observed to be much lower than the GO doped thermotropic nematic medium 5CB. It is anticipated that the slow relaxation frequencies (~10 kHz) could be resulting from the relaxation modes of the GO flakes while the fast relaxation frequencies (~100 kHz) could indicate strongly slowed down molecular modes of the nematogenic molecules, which are anchored to the GO flakes via dispersion interactions. The relaxation frequencies decreased as the size of the GO flakes in the isotropic solvent was increased. Polarizing microscopy showed that GO flakes with a mean diameter of 10 μm, dispersed in water, formed a lyotropic nematic liquid crystal phase. This lyotropic nematic exhibited the slowest dielectric relaxation process, with relaxation frequencies in the order of 2 kHz, as compared to the GO-isotropic suspension and the GO-doped 5CB. PMID:27555475

  16. Photo-stimulated phase and anchoring transitions of chiral azo-dye doped nematic liquid crystals.

    PubMed

    Kundu, Sudarshan; Kang, Shin-Woong

    2013-12-16

    We report concurring phase and anchoring transitions of chiral azo-dye doped nematic liquid crystals. The transitions are induced by photo-stimulation and stable against light and thermal treatments. Photochromic trans- to cis-isomerization of azo-dye induces an augmented dipole moment and strong dipole-dipole interaction of the cis-isomers, resulting in the formation of nano-sized dye-aggregates. Consequent phase separation of the aggregates of a chiral azo-dye induces phase transition from a chiral to nonchiral nematic phase. In addition, the deposition of dye-aggregates at the surfaces brings about anchoring transition of LC molecules. The stability and irreversibility of the transition, together with no need of pretreatments for LC alignment, provide fascinating opportunity for liquid crystal device applications.

  17. Effects of solute characteristics and concentration on a lyotropic liquid crystal: solute-induced phase change.

    PubMed

    Ibrahim, H G; Sallam, E S; Takieddin, M; Habboub, M

    1993-05-01

    We investigated the effects of increased concentrations of the solutes, salicylic acid, benzoic acid, and o-, m-, and p-methoxy benzoic acids, on the anisotropic properties of a liquid crystal solvent. The lamellar liquid crystal was composed of 37% polyoxyethylene (20) isohexadecyl ether in aqueous buffer of pH 1. Phase change, transition temperature, refractive index, and specific resistance of the mesophase were studied in the presence of solutes. Transfer rates of the solutes from the bulk mesophase into aqueous buffer across a lipoidal barrier were used to determine their apparent permeability coefficients. The results indicate that a phase change occurred in the liquid crystal from a lamellar to a hexagonal structure, in the case of salicylic, benzoic, and m-methoxy benzoic acids. However, o- and p-methoxy benzoic acids showed no effect on the packing arrangement of the liquid crystal in the concentration range studied. The occurrence of the phase change was both solute and concentration dependent. Relative values of apparent permeability coefficients of solutes reflected the extent of solute-solvent interactions in the systems.

  18. Phase Transition and Dynamics in Imidazolium-Based Ionic Liquid Crystals through a Metastable Highly Ordered Smectic Phase.

    PubMed

    Nozaki, Yoko; Yamaguchi, Keito; Tomida, Kenji; Taniguchi, Natsumi; Hara, Hironori; Takikawa, Yoshinori; Sadakane, Koichiro; Nakamura, Kenji; Konishi, Takashi; Fukao, Koji

    2016-06-16

    The phase transition behavior and dynamics of ionic liquid crystals, 1-methyl-3-alkylimidazolium tetrafluoroborate with various alkyl chain lengths, were investigated by X-ray scattering, differential scanning calorimetry, optical microscopy, and dielectric relaxation spectroscopy to elucidate the mechanism of their structural and phase changes. A metastable phase was found to appear via a supercooled smectic phase on cooling. In the metastable phase, disorder in the smectic phase is partially frozen; thus, the phase has order higher than that of the smectic phase but lower than that of the crystalline phase. During the subsequent heating process, the frozen disorder activates, and a crystalline phase appears in the supercooled smectic phase before entering the smectic phase. The relationship between the phase behavior and the dynamics of charge carriers such as ions is also discussed.

  19. The inherent dynamics of isotropic- and nematic-phase liquid crystals.

    PubMed

    Frechette, Layne; Stratt, Richard M

    2016-06-21

    The geodesic (shortest) pathways through the potential energy landscape of a liquid can be thought of as defining what its dynamics would be if thermal noise were removed, revealing what we have called the "inherent dynamics" of the liquid. We show how these inherent paths can be located for a model liquid crystal former, showing, in the process, how the molecular mechanisms of translation and reorientation compare in the isotropic and nematic phases of these systems. These mechanisms turn out to favor the preservation of local orientational order even under macroscopically isotropic conditions (a finding consistent with the experimental observation of pseudonematic domains in these cases), but disfavor the maintenance of macroscopic orientational order, even in the nematic phase. While the most efficient nematic pathways that maintain nematic order are indeed shorter than those that do not, it is apparently difficult for the system to locate these paths, suggesting that molecular motion in liquid-crystal formers is dynamically frustrated, and reinforcing the sense that there are strong analogies between liquid crystals and supercooled liquids.

  20. The inherent dynamics of isotropic- and nematic-phase liquid crystals

    NASA Astrophysics Data System (ADS)

    Frechette, Layne; Stratt, Richard M.

    2016-06-01

    The geodesic (shortest) pathways through the potential energy landscape of a liquid can be thought of as defining what its dynamics would be if thermal noise were removed, revealing what we have called the "inherent dynamics" of the liquid. We show how these inherent paths can be located for a model liquid crystal former, showing, in the process, how the molecular mechanisms of translation and reorientation compare in the isotropic and nematic phases of these systems. These mechanisms turn out to favor the preservation of local orientational order even under macroscopically isotropic conditions (a finding consistent with the experimental observation of pseudonematic domains in these cases), but disfavor the maintenance of macroscopic orientational order, even in the nematic phase. While the most efficient nematic pathways that maintain nematic order are indeed shorter than those that do not, it is apparently difficult for the system to locate these paths, suggesting that molecular motion in liquid-crystal formers is dynamically frustrated, and reinforcing the sense that there are strong analogies between liquid crystals and supercooled liquids.

  1. Liquid-Phase Quartz Crystal Microbalance for Photovoltaics Research (Presentation)

    SciTech Connect

    Perkins, C. L.; Li, X.

    2008-05-01

    The construction of a new QCM-based flow reactor has been completed. Initial results include: (1) stable oscillation achieved with crystals sputter coated at 200 C with 500 nm ZnO; (2) sub-Hz noise level means << monolayer sensitivity; (3) Operation at elevated temperature possible after installation of membrane contactors; (4) determination of ZnO etch rates using dilute ethanolic NH{sub 4}Cl; (5) demonstration of use of an etchant as a probe of oxide-molecule interactions; (6) and use in flow rate-dependent CdS chemical deposition.

  2. Hydration-Responsive Folding and Unfolding in Graphene Oxide Liquid Crystal Phases

    PubMed Central

    Guo, Fei; Kim, Franklin; Han, Tae Hee; Shenoy, Vivek B.; Huang, Jiaxing; Hurt, Robert H.

    2011-01-01

    Graphene oxide is promising as a plate-like giant molecular building block for the assembly of new carbon materials. Its water dispersibility, liquid crystallinity, and ease of reduction offer advantages over other carbon precursors if its fundamental assembly rules can be identified. This article shows that graphene oxide sheets of known lateral dimension form nematic liquid crystal phases with transition points in agreement with the Onsager hard-plate theory. The liquid crystal phases can be systematic ordered into defined supramolecular patterns using surface anchoring, complex fluid flow, and micro-confinement. Graphene oxide is seen to exhibit homeotropic surface anchoring at interfaces driven by excluded volume entropy and by adsorption enthalpy associated with its partially hydrophobic basal planes. Surprisingly, some of the surface-ordered graphene oxide phases dry into graphene oxide solids that undergo a dramatic anisotropic swelling upon rehydration to recover their initial size and shape. This behavior is shown to be a unique hydration-responsive folding and unfolding transition. During drying, surface tension forces acting parallel to the layer planes cause a buckling instability that stores elastic energy in accordion-folded structures in the dry solid. Subsequent water infiltration reduces interlayer frictional forces and triggers release of the stored elastic energy in the form of dramatic unidirectional expansion. We explain the folding/unfolding phenomena by quantitative nanomechanics, and introduce the potential of liquid crystal-derived graphene oxide phases as new stimuli-response materials. PMID:21877716

  3. Fast, large and controllable phase modulation using dual frequency liquid crystals

    NASA Astrophysics Data System (ADS)

    Kirby, Andrew K.; Love, Gordon D.

    2004-04-01

    We report on a method for high speed, large stroke phase modulation using dual frequency control of liquid crystals. Our system uses an all-electronic feedback system in order to simplify the control. We show half wave phase modulations of ~120Hz with the operating point varying over nearly the full dynamic range of the device, and demonstrate larger phase shifts (2.5 waves) at a frequency of 37Hz. For large phase shifts, the speeds are an order of magnitude faster than existing techniques.

  4. Optical phase conjugation in azo-dye doped chiral liquid crystal

    SciTech Connect

    Karpinski, Pawel; Miniewicz, Andrzej

    2012-10-15

    We report on optical phase conjugation phenomenon observed in chiral nematic liquid crystal showing band gap type Bragg reflection. The phase conjugate to the signal beam is observable only in the small temperature interval when the Bragg condition is fulfilled and only for circularly polarized light. The optical phase conjugation signals were observed at low cw laser light intensities (<100 mW/cm{sup 2}, {lambda} = 532 nm). Estimated value of third order optical susceptibility {chi}{sup (3)} = 2.8 Multiplication-Sign 10{sup -17} m{sup 2}/V{sup 2} is attributed to enhancement due to photoisomerisation of azo-dye (disperse red 1) inducing molecular reorientation process of liquid crystal molecules.

  5. Liquid Crystal Phases of Molecular Bananas: Polarity and Chirality as Broken Symmetries

    NASA Astrophysics Data System (ADS)

    Clark, Noel

    2006-03-01

    The study of the interplay of chirality and polarity has been a particularly rich theme of soft matter science since Meyer's seminal discovery that tilted smectics of chiral molecules are macroscopically polar. This event, and the subsequent realization of polar domains and high-speed electro-optic switching in chiral smectics, engaged the liquid crystal community in a worldwide pursuit of novel smectics for applications, featured by the synthesis of more than 50,000 new liquid crystal compounds, and by a consequent broad diversification of the palette of liquid crystal phases and possibilities for supermolecular ordering. A current important activity in this scenario is the study of polar order in synthetically achiral molecules, for example, in molecular bananas, which, as their shape suggests, might be expected to organize in a polar way. Indeed they do, but beyond this, almost everything learned about them has been surprising, including their persistent tendency to exhibit chirality as a spontaneously broken symmetry. I will discuss some of these new phases and phenomena, including the discovery of fluid conglomerates (Pasteur's experiment in a fluid), triclinic fluid order, chiral twist grain boundary phases of achiral molecules, chirality flipping and field-induced deracemization, ferroelectric and antiferroelectric phases with supermolecular- scale polarization modulation, and chiral thermotropic sponge phases.

  6. Balance of optical, structural, and electrical properties of textured liquid phase crystallized Si solar cells

    NASA Astrophysics Data System (ADS)

    Preidel, V.; Amkreutz, D.; Haschke, J.; Wollgarten, M.; Rech, B.; Becker, C.

    2015-06-01

    Liquid phase crystallized Si thin-film solar cells on nanoimprint textured glass substrates exhibiting two characteristic, but distinct different surface structures are presented. The impact of the substrate texture on light absorption, the structural Si material properties, and the resulting solar cell performance is analyzed. A pronounced periodic substrate texture with a vertical feature size of about 1 μm enables excellent light scattering and light trapping. However, it also gives rise to an enhanced Si crystal defect formation deteriorating the solar cell performance. In contrast, a random pattern with a low surface roughness of 45 nm allows for the growth of Si thin films being comparable to Si layers on planar reference substrates. Amorphous Si/crystalline Si heterojunction solar cells fabricated on the low-roughness texture exhibit a maximum open circuit voltage of 616 mV and internal quantum efficiency peak values exceeding 90%, resulting in an efficiency potential of 13.2%. This demonstrates that high quality crystalline Si thin films can be realized on nanoimprint patterned glass substrates by liquid phase crystallization inspiring the implementation of tailor-made nanophotonic light harvesting concepts into future liquid phase crystallized Si thin film solar cells on glass.

  7. Balance of optical, structural, and electrical properties of textured liquid phase crystallized Si solar cells

    SciTech Connect

    Preidel, V. Amkreutz, D.; Haschke, J.; Wollgarten, M.; Rech, B.; Becker, C.

    2015-06-14

    Liquid phase crystallized Si thin-film solar cells on nanoimprint textured glass substrates exhibiting two characteristic, but distinct different surface structures are presented. The impact of the substrate texture on light absorption, the structural Si material properties, and the resulting solar cell performance is analyzed. A pronounced periodic substrate texture with a vertical feature size of about 1 μm enables excellent light scattering and light trapping. However, it also gives rise to an enhanced Si crystal defect formation deteriorating the solar cell performance. In contrast, a random pattern with a low surface roughness of 45 nm allows for the growth of Si thin films being comparable to Si layers on planar reference substrates. Amorphous Si/crystalline Si heterojunction solar cells fabricated on the low-roughness texture exhibit a maximum open circuit voltage of 616 mV and internal quantum efficiency peak values exceeding 90%, resulting in an efficiency potential of 13.2%. This demonstrates that high quality crystalline Si thin films can be realized on nanoimprint patterned glass substrates by liquid phase crystallization inspiring the implementation of tailor-made nanophotonic light harvesting concepts into future liquid phase crystallized Si thin film solar cells on glass.

  8. Formation of binary phase gratings in photopolymer-liquid crystal composites by a surface-controlled anisotropic phase separation

    SciTech Connect

    Park, Jae-Hong; Khoo, Iam Choon; Yu, Chang-Jae; Jung, Min-Sik; Lee, Sin-Doo

    2005-01-10

    We report on formation of binary phase gratings in photopolymer-liquid crystal (PLC) composites using a surface-controlled phase separation method. The binary nature of the PLC phase gratings is produced by employing a single step photo-ablation through an amplitude photomask which precisely controls the interfacial interactions between the LC and the photopolymer on the alignment layer. A subsequent illumination of the ultraviolet light onto the whole PLC promotes an anisotropic phase separation resulting in the formation of distinct binary patterns for the PLC structure. The electrically tunable diffraction properties of the binary phase gratings are presented.

  9. Subdiffusive dynamics of a liquid crystal in the isotropic phase

    NASA Astrophysics Data System (ADS)

    De Gaetani, Luca; Prampolini, Giacomo; Tani, Alessandro

    2008-05-01

    The isotropic phase dynamics of a system of 4-n-hexyl-4'-cyano-biphenyl (6CB) molecules has been studied by molecular dynamics computer simulations. We have explored the range of 275-330K keeping the system isotropic, although supercooled under its nematic transition temperature. The weak rototranslational coupling allowed us to separately evaluate translational (TDOF) and orientational degrees of freedom (ODOF). Evidences of subdiffusive dynamics, more apparent at the lowest temperatures, are found in translational and orientational dynamics. Mean square displacement as well as self-intermediate center of mass and rotational scattering functions show a plateau, also visible in the orientational correlation function. According to the mode coupling theory (MCT), this plateau is the signature of the β-relaxation regime. Three-time intermediate scattering functions reveal that the plateau is related to a homogeneous dynamics, more extended in time for the orientational degrees of freedom (up to 1ns). The time-temperature superposition principle and the factorization property predicted by the idealized version of MCT hold, again for both kinds of dynamics. The temperature dependence of diffusion coefficient and orientational relaxation time is well described by a power law. Critical temperatures Tc are 244±6 and 258±6K, respectively, the latter is some 10K below the corresponding experimental values. The different values of Tc we obtained indicate that ODOF freezes earlier than TDOF. This appears due to the strongly anisotropic environment that surrounds a 6CB molecule, even in the isotropic phase. The lifetime of these "cages," estimated by time dependent conditional probability functions, is strongly temperature dependent, ranging from some hundreds of picoseconds at 320K to a few nanoseconds at 275K.

  10. Low symmetry tetrahedral nematic liquid crystal phases: Ambidextrous chirality and ambidextrous helicity.

    PubMed

    Pleiner, Harald; Brand, Helmut R

    2014-02-01

    We discuss the symmetry properties as well as the dynamic behavior of various non-polar nematic liquid crystal phases with tetrahedral order. We concentrate on systems that show biaxial nematic order coexisting with octupolar (tetrahedral) order. Non-polar examples are phases with D2 and S4 symmetries, which can be characterized as biaxial nematics lacking inversion symmetry. It is this combination that allows for new features in the statics and dynamics of these phases. The D2-symmetric phase is chiral, even for achiral molecules, and shows ambidextrous chirality in all three preferred directions. The achiral S4-symmetric phase allows for ambidextrous helicity, similar to the higher-symmetric D2d-symmetric phase. Such phases are candidates for nematic phases made from banana-shaped molecules.

  11. Discovery of a Novel Smectic-C Liquid Crystal Phase with Six Layer Periodicity

    SciTech Connect

    Wang, S.; Pindak, R.; Pan, L.D.; Liu, Z.Q; Nguyen, H.T.; Huang, C.C.

    2010-01-13

    We report the discovery of a new smectic-C* liquid-crystal phase with six-layer periodicity by resonant x-ray diffraction. Upon cooling, the new phase appears between the SmC{sub {alpha}}* phase having a helical structure and the SmC{sub d4}* phase with four-layer periodicity. This SmC{sub d6}* phase was identified in two mixtures which have an unusual reversed SmC{sub d4}*-SmC* phase sequence. The SmC{sub d6}* phase shows a distorted clock structure. Three theoretical models have predicted the existence of a six-layer phase. However, our experimental findings are not consistent with the theories.

  12. Discovery of a novel smectic-C{*} liquid-crystal phase with six-layer periodicity.

    PubMed

    Wang, Shun; Pan, Lidong; Pindak, R; Liu, Z Q; Nguyen, H T; Huang, C C

    2010-01-15

    We report the discovery of a new smectic-C{*} liquid-crystal phase with six-layer periodicity by resonant x-ray diffraction. Upon cooling, the new phase appears between the SmC{alpha}{*} phase having a helical structure and the SmC{d4}{*} phase with four-layer periodicity. This SmC{d6}{*} phase was identified in two mixtures which have an unusual reversed SmC{d4}{*}-SmC{*} phase sequence. The SmC{d6}{*} phase shows a distorted clock structure. Three theoretical models have predicted the existence of a six-layer phase. However, our experimental findings are not consistent with the theories.

  13. Phase behavior of chromonic liquid crystal mixtures of Sunset Yellow and Disodium Cromoglycate

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Akihiro; Smith, Gregory; Yi, Youngwoo; Xu, Charles; Biffi, Silvia; Serra, Francesca; Bellini, Tommaso; Clark, Noel

    2014-03-01

    Chromonic liquid crystals (CLCs) are formed when planar molecules dissolved in water stack into rod-like aggregates that can order as liquid crystals. Isotropic, nematic, and M-phases can be observed depending on the degree of molecular orientational and positional order by variation of the CLC concentration. We focused on mixtures of two well-known CLCs, Sunset Yellow, a food dye, and disodium cromoglycate (DSCG), an asthma medication. In order to study the phase behaviors of these mixtures, we observed their textures in glass cells and capillaries using polarized light microscopy. We report here a ternary phase diagram describing the complete phase behavior of the CLC mixtures. We observed a variety of phase behaviors depending on species ratio and concentration. In the isotropic phase, no clear phase separation of the two dyes was observed, while separation did occur in many nematic and M-phase combinations. We will also describe phase observations made using a light spectroscopy and bulk centrifugal partitioning. Grant support: NSF DMR 1207606 and NSF MRSEC DMR-0820579.

  14. Nematic and blue phase liquid crystals for temperature stabilization and active optical tuning of silicon photonic devices (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Ptasinski, Joanna N.; Khoo, Iam Choon; Fainman, Yeshaiahu

    2015-10-01

    We describe the underlying theories and experimental demonstrations of passive temperature stabilization of silicon photonic devices clad in nematic liquid crystal mixtures, and active optical tuning of silicon photonic resonant structures combined with dye-doped nematic and blue phase liquid crystals. We show how modifications to the resonator device geometry allow for not only enhanced tuning of the resonator response, but also aid in achieving complete athermal operations of silicon photonic circuits. [Ref.: I.C. Khoo, "DC-field-assisted grating formation and nonlinear diffractions in methyl-red dye-doped blue phase liquid crystals," Opt. Lett. 40, 60-63 (2015); J. Ptasinski, I.C. Khoo, and Y. Fainman, "Enhanced optical tuning of modified-geometry resonators clad in blue phase liquid crystals," Opt. Lett. 39, 5435-5438 (2014); J. Ptasinski, I.C. Khoo, and Y. Fainman, "Passive Temperature Stabilization of Silicon Photonic Devices Using Liquid Crystals," Materials 7(3), 2229-2241 (2014)].

  15. Application of a quartz-crystal microbalance for detection of phase transitions in liquid crystals and lipid multibilayers

    SciTech Connect

    Okahata, Yoshio; Ebato, Hiroshi )

    1989-10-01

    Resonance frequency increased abruptly at the phase transition temperature (T{sub c}) from solid to liquid crystalline state of liquid crystals (LCs) or lipid multibilayer films cast on a quartz-crystal microbalance (QCM) electrode when the ambient temperature increased gradually. The large frequency enhancement at the T{sub c} was observed in the case of smectic LC-coated QCM compared with those of nematic and cholesteric LC-coated QCM. Although the frequency enhancement at the T{sub c} of the LC-coated QCM was observed independent of media such as water and air phases, the frequency of the lipid multibilayer-coated QCM increased abruptly at the T{sub c} only in a water phase, but not in an air phase. Frequency enhancements at T{sub c} can be explained by slipping between layered structures of smectic LC and lipid multibilayer in the fluid liquid crystalline state above the T{sub c}. In the case of lipid multibilayers, the penetration of water into interlayers (swelling) occurs at the T{sub c} and then the frequency increase is observed due to slipping between hydrated and fluid layers only in aqueous phases.

  16. Liquid crystal terahertz phase shifters with functional indium-tin-oxide nanostructures for biasing and alignment

    SciTech Connect

    Yang, Chan-Shan; Tang, Tsung-Ta; Pan, Ru-Pin; Yu, Peichen; Pan, Ci-Ling

    2014-04-07

    Indium Tin Oxide (ITO) nanowhiskers (NWhs) obliquely evaporated by electron-beam glancing-angle deposition can serve simultaneously as transparent electrodes and alignment layer for liquid crystal (LC) devices in the terahertz (THz) frequency range. To demonstrate, we constructed a THz LC phase shifter with ITO NWhs. Phase shift exceeding π/2 at 1.0 THz was achieved in a ∼517 μm-thick cell. The phase shifter exhibits high transmittance (∼78%). The driving voltage required for quarter-wave operation is as low as 5.66 V (rms), compatible with complementary metal-oxide-semiconductor (CMOS) and thin-film transistor (TFT) technologies.

  17. X-ray studies of tilted hexatic phases in thin liquid-crystal films

    SciTech Connect

    Sirota, E.B.; Pershan, P.S.; Sorensen, L.B.; Collett, J.

    1985-11-04

    X-ray-diffraction studies of the structures and phase transitions of the tilted hexatic phases (smectic F and smectic I) in thin liquid-crystal films of 4-n-heptyloxybenzylidene-4-n-heptylaniline (7O.7) are reported. The measured correlation lengths were strongly anisotropic in both phases. The smectic-I to smectic-F transition is first order as expected from the symmetry change. The smectic-F to smectic-G transition is first order with strong pretransition effects and becomes nearly second order as the film thickness is decreased.

  18. Chiral-induced self-assembly sphere phase liquid crystal with fast switching time

    SciTech Connect

    Zhu, Ji-Liang; Ni, Shui-Bin; Ping Chen, Chao; Lu, Jian-Gang Su, Yikai; Wu, Dong-Qing; Song, Xiao-Long; Chen, Chao-Yuan; Shieh, Han-Ping D.

    2014-03-03

    A fluid self-assembly sphere phase (SP) of liquid crystal induced by chiral dopant is observed in a narrow temperature range between isotropic and blue phase or between isotropic and chiral nematic phase. The SP consists of three-dimensional twist spheres (3-DTSs) and disclinations among 3-DTSs. The temperature range of the SP has been broadened to more than 85 °C by stabilizing the disclinations with amorphous polymer chains. The electro-optical switching time of the polymer-stabilized SP is demonstrated in sub-millisecond with a low switching electric field of 4.4 V μm{sup −1}, which is of promising applications in displays, 3-D tunable photonic crystals, and phase modulators.

  19. Liquid Crystal Devices.

    ERIC Educational Resources Information Center

    Bradshaw, Madeline J.

    1983-01-01

    The nature of liquid crystals and several important liquid crystal devices are described. Ideas for practical experiments to illustrate the properties of liquid crystals and their operation in devices are also described. (Author/JN)

  20. Assessment of a Single-Shot Pixelated Phase-Shifting Interferometer Utilizing a Liquid Crystal Spatial Light Modulator

    SciTech Connect

    Baker, K L; Stappaerts, E A

    2005-10-01

    This article introduces a novel phase shifting pixelated interferometer based on a liquid crystal spatial light modulator and simulates the expected performance. The phase shifted frames are captured simultaneously which reduces the problems arising from vibrations and air turbulence. The liquid crystal spatial light modulator is very flexible and can be configured to provide a large number of phase shift levels and geometries to reduce the measurement error.

  1. Liquid-crystal solid interface structure at the antiferroelectric-ferroelectric phase transition

    NASA Astrophysics Data System (ADS)

    Coleman, D.; Bardon, S.; Radzihovsky, L.; Danner, G.; Clark, N. A.

    2002-12-01

    Total internal reflection is used to probe the molecular organization at the surface of a tilted chiral smectic liquid crystal at temperatures in the vicinity of the bulk antiferroelectric-ferroelectric phase transition. Data are interpreted using an exact analytical solution of a real model for ferroelectric order at the surface. In the mixture T3, ferroelectric surface order is expelled with the bulk ferroelectric-antiferroelectric transition. The conditions for ferroelectric order at the surface of an antiferroelectric bulk are presented.

  2. Surface modes in "photonic cholesteric liquid crystal-phase plate-metal" structure.

    PubMed

    Vetrov, S Ya; Pyatnov, M V; Timofeev, I V

    2014-05-01

    The light transmission spectrum has been calculated for a "cholesteric liquid crystal-phase plate-metal" structure. It is shown that the system can have an isolated waveguide surface mode with characteristics efficiently controllable by external fields acting on the cholesteric. The degree of localization of surface modes and the transmission coefficients have been found to differ considerably for the light of different polarizations. PMID:24784092

  3. Effect of Enantiomeric Excess on the Phase Behavior of Antiferroelectric Liquid Crystals

    SciTech Connect

    L Pan; B McCoy; S Wang; Z Liu; S Wang; R Pindak; C Huang

    2011-12-31

    Null transmission ellipsometry and resonant x-ray diffraction are employed to study the effect of enantiomeric excess (EE) on the phase behavior of antiferroelectric liquid crystal 10OTBBB1M7. Phase sequence, layer spacing, and pitch of the helical structures of the smectic-C*{sub {alpha}} and smectic-C* phases are studied as a function of temperature and EE. Upon reducing EE, a liquid-gas-type critical point of the smectic-C*{sub {alpha}} to smectic-C* transition is observed, as well as the disappearance of the smectic-C*{sub d4} and the smectic-C*{sub d3} phases. Results are analyzed in a mean-field model.

  4. Pattern phase transitions of self-propelled particles: gases, crystals, liquids, and mills

    NASA Astrophysics Data System (ADS)

    Cheng, Zhao; Chen, Zhiyong; Vicsek, Tamás; Chen, Duxin; Zhang, Hai-Tao

    2016-10-01

    To understand the collective behaviors of biological swarms, flocks, and colonies, we investigated the non-equilibrium dynamic patterns of self-propelled particle systems using statistical mechanics methods and H-stability analysis of Hamiltonian systems. By varying the individual vision range, we observed phase transitions between four phases, i.e., gas, crystal, liquid, and mill-liquid coexistence patterns. In addition, by varying the inter-particle force, we detected three distinct milling sub-phases, i.e., ring, annulus, and disk. Based on the coherent analysis for collective motions, one may predict the stability and adjust the morphology of the phases of self-propelled particles, which has promising potential applications in natural self-propelled particles and artificial multi-agent systems.

  5. Pattern Polymerization-Induced Phase Separation in a Polymer-Dispersed Liquid Crystal System

    NASA Astrophysics Data System (ADS)

    Kyu, Thein

    2002-03-01

    Liquid crystal (LC)/polymer composite films have gained attention increasingly due to their applications in flat panel displays and shutters. Photopolymerization is a preferred method to produce LC/polymer composite films from mixtures of reactive monomers and LCs. On the basis of the combined Flory-Huggins free energy for isotropic mixing and Maier-Saupe free energy for nematic ordering along with the elastic free energy of the network, phase diagrams have been established by solving self-consistently. A theoretical simulation has been modeled by incorporating the kinetics of crosslinking reaction into the time-dependent Ginzburg-Landau (TDGL-model C) equations to elucidate the emergence of nematic domains during photopolymerization induced phase separation in electrically switchable holographic polymer-dispersed liquid crystals (H-PDLC). The simulated morphological patterns in the concentration and orientation order parameter fields show discrete layers of liquid crystal droplets alternating periodically with polymer network-rich layers. Furthermore, we recognized the potential for producing electrically tunable microlens from PDLC systems through pattern-photopolymerization-induced phase separation by means of the interference of two horizontal waves and two vertical waves. Our simulation revealed that the emerged LC microlens are of the order of a few hundred nanometers. These LC microlens are not only uniformed in size, but also form in regular arrays, reminiscence of the compound eyes found in flies, ants, and wasps. Supported by ALCOM, NSF DMR 99-03519, and OBR.

  6. Liquid-crystal phase diagrams of binary mixtures of hard spherocylinders.

    PubMed

    Cinacchi, Giorgio; Mederos, Luis; Velasco, Enrique

    2004-08-22

    We have built the liquid crystal phase diagram of several binary mixtures of freely rotating hard spherocylinders employing a second-order virial density functional theory with Parsons scaling, suitably generalized to deal with mixtures and smectic phases. The components have the same diameter and aspect ratio of moderate value, typical of many mesogens. Attention has been paid to smectic-smectic demixing and the types of arrangement that rods can adopt in layered phases. Results are shown to depend on the aspect ratio of the individual components and on the ratio of their lengths. Smectic phases are seen not to easily mix together at sufficiently high pressures. Layered phases where the longer rods are the majority component have a smectic-A structure. In the opposite case, a smectic-A(2) phase is obtained where the shorter particles populate the layers and the longer ones prefer to stay parallel to the latter in the interlayer region.

  7. Phases and properties of nanocomposites of hydrogen-bonded liquid crystals and carbon nanotubes.

    PubMed

    Petrov, M; Katranchev, B; Rafailov, P M; Naradikian, H; Dettlaff-Weglikowska, U; Keskinova, E; Spassov, T

    2013-10-01

    We investigated a series of nanocomposites, built of the hydrogen-bonded liquid crystal (LC) p-n-heptyloxybenzoic acid (7OBA) and single-walled carbon nanotubes (SWCNTs) by optical microtexture analysis and other complementary methods. The surface orientation strength of the LC cell and the bulk interaction of the dimeric LC molecules with the SWCNTs turn out to mainly govern the type (symmetry), thermal stability, and chirality of the LC states induced in these nanocomposites. As a result, a cascade of phase transitions and phases not typical for pristine 7OBA were observed and additionally confirmed by temperature-dependent Raman spectroscopy and differential scanning calorimetry. The most effective SWCNT concentrations in the LC matrix, ensuring both the necessary conformability between these materials and induction of liquid crystal phases with unique optical and electro-optical properties, were found to be in the range of 0.01-0.007 wt%. Reversal of smectic phases into reentrant nematic states as well as induction of chirality in all LC phases were observed in the SWCNT-7OBA nanocomposite, even though pure 7OBA is typically achiral. However, our most intriguing result is the detection below the reentrant nematic of a triclinic smectic-C(G) phase, which is chiral and biaxial, and exhibits bulk ferroelectricity. PMID:24229197

  8. Berry Phase of Light under Bragg Reflection by Chiral Liquid-Crystal Media.

    PubMed

    Barboza, Raouf; Bortolozzo, Umberto; Clerc, Marcel G; Residori, Stefania

    2016-07-29

    A Berry phase is revealed for circularly polarized light when it is Bragg reflected by a chiral liquid-crystal medium of the same handedness. By using a chiral nematic layer we demonstrate that if the input plane of the layer is rotated with respect to a fixed reference frame, a geometric phase effect occurs for the circularly polarized light reflected by the periodic helical structure of the medium. Theory and numerical simulations are supported by an experimental observation, disclosing novel applications in the field of optical manipulation and fundamental optical phenomena. PMID:27517773

  9. Thick strings, the liquid crystal blue phase, and cosmological large-scale structure

    NASA Technical Reports Server (NTRS)

    Luo, Xiaochun; Schramm, David N.

    1992-01-01

    A phenomenological model based on the liquid crystal blue phase is proposed as a model for a late-time cosmological phase transition. Topological defects, in particular thick strings and/or domain walls, are presented as seeds for structure formation. It is shown that the observed large-scale structure, including quasi-periodic wall structure, can be well fitted in the model without violating the microwave background isotropy bound or the limits from induced gravitational waves and the millisecond pulsar timing. Furthermore, such late-time transitions can produce objects such as quasars at high redshifts. The model appears to work with either cold or hot dark matter.

  10. Continuous Beam Steering From A Segmented Liquid Crystal Optical Phased Array

    NASA Technical Reports Server (NTRS)

    Pouch, John; Nguyen, Hung; Miranda, Felix; Titus, Charles M.; Bos, Philip J.

    2002-01-01

    Optical communications to and from deep space probes will require beams possessing divergence on the order of a microradian, and must be steered with sub-microradian precision. Segmented liquid crystal spatial phase modulators, a type of optical phased array, are considered for this ultra-high resolution beam steering. It is shown here that in an ideal device of this type, there are ultimately no restrictions on the angular resolution. Computer simulations are used to obtain that result, and to analyze the influence of beam truncation and substrate flatness on the performance of this type of device.

  11. Continuous Beam Steering From a Segmented Liquid Crystal Optical Phased Array

    NASA Technical Reports Server (NTRS)

    Titus, Charles M.; Pouch, John; Nguyen, Hung; Miranda, Felix; Bos, Philip J.

    2002-01-01

    Optical communications to and from deep space probes will require beams possessing divergence on the order of a microradian, and must be steered with sub-microradian precision. Segmented liquid crystal spatial phase modulators, a type of optical phased array, are considered for this ultra-high resolution beam steering. It is shown here that in an ideal device of this type, there are ultimately no restrictions on the angular resolution. Computer simulations are used to obtain that result, and to analyze the influence of beam truncation and substrate flatness on the performance of this type of device.

  12. Berry Phase of Light under Bragg Reflection by Chiral Liquid-Crystal Media

    NASA Astrophysics Data System (ADS)

    Barboza, Raouf; Bortolozzo, Umberto; Clerc, Marcel G.; Residori, Stefania

    2016-07-01

    A Berry phase is revealed for circularly polarized light when it is Bragg reflected by a chiral liquid-crystal medium of the same handedness. By using a chiral nematic layer we demonstrate that if the input plane of the layer is rotated with respect to a fixed reference frame, a geometric phase effect occurs for the circularly polarized light reflected by the periodic helical structure of the medium. Theory and numerical simulations are supported by an experimental observation, disclosing novel applications in the field of optical manipulation and fundamental optical phenomena.

  13. Flexoelectricity and Piezoelectricity: The Reason for the Rich Variety of Phases in Antiferroelectric Smectic Liquid Crystals

    SciTech Connect

    Cepic, Mojca; Zeks, Bostjan

    2001-08-20

    The free energy of antiferroelectric smectic liquid crystals which takes into account polar order explicitly is presented. Steric, van der Waals, piezoelectric, and flexoelectric interactions to the nearest layers, and dipolar electrostatic interactions to the nearest and to the next-nearest layers, induce indirect tilt interactions with chiral and achiral properties, which extend to the third- and to the fourth-nearest layers. Although the strength of microscopic interactions changes monotonically with decreasing temperature, the effective interlayer interactions change nonmonotonically and give rise to a nonmonotonic change of the modulation period through various phases. Increased chirality changes the phase sequence.

  14. Polymer-stabilized blue-phase liquid crystal grating cured with interfered visible light.

    PubMed

    Yuan, Yachao; Li, Yan; Chen, Chao Ping; Liu, Shuxin; Rong, Na; Li, Weihuan; Li, Xiao; Zhou, Pengcheng; Lu, Jiangang; Liu, Ruili; Su, Yikai

    2015-07-27

    In this paper, we demonstrate a holographic polymer-stabilized blue-phase liquid crystal grating fabricated using a visible laser. As blue phase is stabilized by the interfered light, polymer-concentration gradient is achieved simultaneously. With the application of a uniform vertical electric field, periodic index distribution is obtained due to polymer-concentration gradient. The grating exhibits several attractive features such as polarization-independency, a broad temperature range, sub-millisecond response, simple fabrication, and low cost, thus holding great potential for photonics applications. PMID:26367659

  15. Metastable liquid-liquid phase transition in a single-component system with only one crystal phase and no density anomaly

    NASA Astrophysics Data System (ADS)

    Franzese, G.; Malescio, G.; Skibinsky, A.; Buldyrev, S. V.; Stanley, H. E.

    2002-11-01

    We investigate the phase behavior of a single-component system in three dimensions with spherically-symmetric, pairwise-additive, soft-core interactions with an attractive well at a long distance, a repulsive soft-core shoulder at an intermediate distance, and a hard-core repulsion at a short distance, similar to potentials used to describe liquid systems such as colloids, protein solutions, or liquid metals. We showed [Nature (London) 409, 692 (2001)] that, even with no evidence of the density anomaly, the phase diagram has two first-order fluid-fluid phase transitions, one ending in a gas-low-density-liquid (LDL) critical point, and the other in a gas-high-density-liquid (HDL) critical point, with a LDL-HDL phase transition at low temperatures. Here we use integral equation calculations to explore the three-parameter space of the soft-core potential and perform molecular dynamics simulations in the interesting region of parameters. For the equilibrium phase diagram, we analyze the structure of the crystal phase and find that, within the considered range of densities, the structure is independent of the density. Then, we analyze in detail the fluid metastable phases and, by explicit thermodynamic calculation in the supercooled phase, we show the absence of the density anomaly. We suggest that this absence is related to the presence of only one stable crystal structure.

  16. Smectic-A and Hexatic-B Liquid Crystal Phases of Sanidic Alkyl-Substituted Dibenzo[fg,op]naphthacenes.

    PubMed

    Repasky, Paul J; Agra-Kooijman, Deña M; Kumar, Satyendra; Hartley, C Scott

    2016-03-17

    Despite longstanding interest in liquid crystalline compounds with simple rod- or disc-like shapes (calamitics or discotics), very few examples of the analogous board-shaped, or "sanidic", liquid crystals exist. A new series of alkyl-substituted dibenzo[fg,op]naphthacenes have been prepared by planarization of o-phenylene precursors through dehydrohalogenation. Their photophysical properties have been studied in dichloromethane. Liquid crystal phase behavior was characterized by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. All of the compounds exhibit monotropic liquid crystal phases on cooling from the isotropic phase. The compounds with shorter alkyl (pentyl and heptyl) chains exhibit the uniaxial smectic-A phase analogous to that of simple calamitic mesogens. The compounds with longer alkyl (nonyl, undecyl, and tridecyl) chains exhibit a new smectic liquid crystal phase featuring short-range positional order with an apparent rectangular lattice in the smectic layers, that is, an orthogonal biaxial hexatic-B. The molecular arrangement in this phase likely corresponds to a distorted herringbone packing of the board-shaped structures. Further, the compound with nonyl chains exhibits an underlying smectic-B phase. DFT calculations show that the cores of the mesogens are twisted into C2-symmetric saddle-shaped geometries because of steric interactions along their rims. The liquid crystal phases and their structures are discussed in the context of the compounds' board-like shapes and intercore interactions.

  17. Fatty-acid monolayers at the nematic/water interface: phases and liquid-crystal alignment.

    PubMed

    Price, Andrew D; Schwartz, Daniel K

    2007-02-01

    The two-dimensional (2D) phases of fatty-acid monolayers (hexadecanoic, octadecanoic, eicosanoic, and docosanoic acids) have been studied at the interface of a nematic liquid crystal (LC) and water. When observed between crossed polarizers, the LC responds to monolayer structure owing to mesoscopic alignment of the LC by the adsorbed molecules. Similar to Langmuir monolayers at the air/water interface, the adsorbed monolayer at the nematic/water interface displays distinct thermodynamic phases. Observed are a 2D gas, isotropic liquid, and two condensed mesophases, each with a characteristic anchoring of the LC zenithal tilt and azimuth. By varying the monolayer temperature and surface concentration we observe reversible first-order phase transitions from vapor to liquid and from liquid to condensed. A temperature-dependent transition between two condensed phases appears to be a reversible swiveling transition in the tilt azimuth of the monolayer. Similar to monolayers at the air/water interface, the temperature of the gas/liquid/condensed triple-point temperature increased by about 10 degrees C for a two methylene group increase in chain length. However, the absolute value of the triple-point temperatures are depressed by about 40 degrees C compared to those of analogous monolayers at the air/water interface. We also observe a direct influence by the LC layer on the mesoscopic and macroscopic structure of the monolayer by analyzing the shapes and internal textures of gas domains in coexistence with a 2D liquid. An effective anisotropic line tension arises from elastic forces owing to deformation of the nematic director across phase boundaries. This results in the deformation of the domain from circular to elongated, with a distinct singularity. The LC elastic energy also gives rise to transition zones displaying mesoscopic realignment of the director tilt or azimuth between adjacent regions with a sudden change in anchoring.

  18. Polarization-independent and submillisecond response phase modulators using a 90° twisted dual-frequency liquid crystal

    NASA Astrophysics Data System (ADS)

    Huang, Yuhua; Wen, Chien-Hui; Wu, Shin-Tson

    2006-07-01

    A polarization-independent phase modulator using a 90° twisted dual-frequency liquid crystal (DFLC) is demonstrated. In addition to being polarization independent, such a phase modulator exhibits many other advantages such as being scattering-free and having large phase change, low operating voltage, and submillisecond response time. Using a 15μm transmissive DFLC cell, the phase shift achieves 1π at λ =633nm and the applied voltage is lower than 25Vrms. Potential applications of such a phase modulator for laser beam steering, tunable-focus lenses, and switchable two-dimensional/three-dimensional liquid crystal displays are foreseeable.

  19. A Biaxial Banana Liquid Crystal Phase with Short-range Layer Ordering

    NASA Astrophysics Data System (ADS)

    Shen, Yongqiang; Gong, Tao; Chen, Dong; Shao, Renfan; Zhu, Chenhui; Glaser, Matthew; Maclennan, Joseph; Walba, David; Clark, Noel

    2012-02-01

    W623, a single-tail, bent-core molecule with a polar termination on one end and a siloxane-terminated tail on the other, exhibits a ferroelectric, orthorhombic, fluid smectic liquid crystal phase, the SmAPF. Powder x-ray diffraction (XRD) measurements reveal an exotic structural transition on cooling from the SmAPF to a SmX phase, in which resolution-limited fluid smectic layering reflections give way to four much broader peaks, indicating short-range layer ordering. This behavior points to the kind of internal frustration that gives rise to our recently discovered helical nanofilament phases. We have performed two-dimensional XRD on aligned samples and discovered that one of the four peaks is from the in-plane order. Freeze-fracture transmission electron microscope (FFTEM) measurements confirm that there is two-dimensional short-range order in the SmX phase, with one periodicity in the layer plane and another normal to the layers. The in-plane periodicity can be measured directly from the packing of fibrils to be about 8 nm, consistent with the in-plane x-ray reflection peak. We will present depolarized transmission light microscopy, high-resolution XRD, and FFTEM studies of pure W623, and of mixtures of W623 with the calamitic liquid crystal 8CB.

  20. Photocontrolled phase transitions and reflection behaviors of smectic liquid crystals by a chiral azobenzene.

    PubMed

    Guan, Jingjing; Zhang, Mingzhi; Li, Birong; Yang, Huai; Wang, Guojie

    2012-12-01

    The photocontrolled phase transitions and reflection behaviors of a smectic liquid crystal, 4-octyl-4'-cyanobiphenyl (8CB), tuned by a chiral azobenzene, are systematically investigated. For the smectic 8CB doped with the chiral azobenzene (1R)-(-)-4-n-hexyl-4'-menthylazobenzene (ABE), the initial smectic phase can be switched to cholesteric and then to isotropic upon UV irradiation due to the trans-to-cis photoisomerization of ABE; however, no reflection band is observed. For the smectic 8CB doped with ABE and the chiral agent (S)-(-)-1,1'-binaphthyl-2,2'-diol (BN), a reflection band located in the short-wavelength infrared region is observed, which disappears after further UV irradiation. For the smectic 8CB doped with ABE and a chiral agent with higher helical twisting power, (S)-2,2'-methylendioxy-1,1'-binaphthalene (DBN), a phototunable system with cholesteric pitch short enough to reflect visible light is demonstrated. With a given concentration of the chiral dopant DBN, a reversible reflection color transition is realized tuned by the isomerization of azobenzene. The reverse phase transition from isotropic to cholesteric and then to smectic can be recovered upon visible irradiation. The photocontrolled phase transitions in smectic liquid crystals and the corresponding changes in reflection band switched by photoisomerization of azobenzene may provide impetus for their practical application in optical memories, displays, and switches.

  1. Equilibrium Liquid Crystal Phase Diagrams and Detection of Kinetic Arrest in Cellulose Nanocrystal Suspensions

    NASA Astrophysics Data System (ADS)

    Honorato Rios, Camila; Kuhnhold, Anja; Bruckner, Johanna; Dannert, Rick; Schilling, Tanja; Lagerwall, Jan

    2016-05-01

    The cholesteric liquid crystal self-assembly of water-suspended cellulose nanocrystal (CNC) into a helical arrangement was observed already more than 20 years ago and the phenomenon was used to produce iridescent solid films by evaporating the solvent or via sol-gel processing. Yet it remains challenging to produce optically uniform films and to control the pitch reproducibly, reflecting the complexity of the three-stage drying process that is followed in preparing the films. An equilibrium liquid crystal phase formation stage is followed by a non-equilibrium kinetic arrest, which in turn is followed by structural collapse as the remaining solvent is evaporated. Here we focus on the first of these stages, combining a set of systematic rheology and polarizing optics experiments with computer simulations to establish a detailed phase diagram of aqueous CNC suspensions with two different values of the surface charge, up to the concentration where kinetic arrest sets in. We also study the effect of varying ionic strength of the solvent. Within the cholesteric phase regime, we measure the equilibrium helical pitch as a function of the same parameters. We report a hitherto unnoticed change in character of the isotropic-cholesteric transition at increasing ionic strength, with a continuous weakening of the first-order character up to the point where phase coexistence is difficult to detect macroscopically due to substantial critical fluctuations.

  2. Effect of dipolar interactions on the phase behavior of the Gay-Berne liquid crystal model

    NASA Astrophysics Data System (ADS)

    Houssa, Mohammed; Rull, Luis F.; McGrother, Simon C.

    1998-12-01

    A computer simulation study of the phase behavior of the dipolar Gay-Berne liquid crystal model is presented. The phase transitions are determined with isothermal-isobaric (NPT) Monte Carlo simulations, utilizing the reaction field method. The electrostatic forces are found to have a considerable effect on the nature of the observed phases, but the density at which the isotropic fluid becomes unstable with respect to partially ordered phases is seen to be remarkably insensitive to the strength of the dipole. We pay particular attention to the structure of the mesophases, combining information from several singlet and pair distribution functions to build up an accurate picture of the molecular arrangement of the systems.

  3. Induced smectic phase in mixtures of hyperbranched polyester and liquid crystal mesogens.

    PubMed

    Kim, Namil; Huang, Tsang-Min; Kyu, Thein; Nosaka, Mami; Kudo, Hiroto; Nishikubo, Tadatomi

    2008-10-23

    The phase diagram of a mixture consisting of hyperbranched polyester (HBPEAc-COOH) and eutectic nematic liquid crystals (E7) has been established experimentally by means of differential scanning calorimetry and polarized optical microscopy subjected to prolonged annealing. The observed phase diagram is an upper azeotrope, exhibiting the coexistence of nematic + isotropic phase in the vicinity of 90 approximately 110 degrees C above the clearing temperature of neat E7 (60 degrees C). With decreasing temperature, a focal-conic fan shaped texture develops in the composition range of 63 approximately 93 wt % of the annealed E7/HBPEAc-COOH blends, suggestive of induced smectic phase in the mixture. Wide angle X-ray diffraction (WAXD) technique revealed the existence of higher order mesophase(s).

  4. Ferroelectric order in liquid crystal phases of polar disk-shaped ellipsoids.

    PubMed

    Bose, Tushar Kanti; Saha, Jayashree

    2014-05-01

    The demonstration of a spontaneous macroscopic ferroelectric order in liquid phases in the absence of any long range positional order is considered an outstanding problem of both fundamental and technological interest. Recently, we reported that a system of polar achiral disklike ellipsoids can spontaneously exhibit a long searched ferroelectric nematic phase and a ferroelectric columnar phase with strong axial polarization. The major role is played by the dipolar interactions. The model system of interest consists of attractive-repulsive Gay-Berne oblate ellipsoids embedded with two parallel point dipoles positioned symmetrically on the equatorial plane of the ellipsoids. In the present work, we investigate in detail the profound effects of changing the separation between the two symmetrically placed dipoles and the strength of the dipoles upon the existence of different ferroelectric discotic liquid crystal phases via extensive off-lattice N-P-T Monte Carlo simulations. Ferroelectric biaxial phases are exhibited in addition to the uniaxial ferroelectric fluids where the phase biaxiality results from the dipolar interactions. The structures of all the ferroelectric configurations of interest are presented in detail. Simple phase diagrams are determined which include different polar and apolar discotic fluids generated by the system.

  5. Ferroelectric order in liquid crystal phases of polar disk-shaped ellipsoids

    NASA Astrophysics Data System (ADS)

    Bose, Tushar Kanti; Saha, Jayashree

    2014-05-01

    The demonstration of a spontaneous macroscopic ferroelectric order in liquid phases in the absence of any long range positional order is considered an outstanding problem of both fundamental and technological interest. Recently, we reported that a system of polar achiral disklike ellipsoids can spontaneously exhibit a long searched ferroelectric nematic phase and a ferroelectric columnar phase with strong axial polarization. The major role is played by the dipolar interactions. The model system of interest consists of attractive-repulsive Gay-Berne oblate ellipsoids embedded with two parallel point dipoles positioned symmetrically on the equatorial plane of the ellipsoids. In the present work, we investigate in detail the profound effects of changing the separation between the two symmetrically placed dipoles and the strength of the dipoles upon the existence of different ferroelectric discotic liquid crystal phases via extensive off-lattice N-P-T Monte Carlo simulations. Ferroelectric biaxial phases are exhibited in addition to the uniaxial ferroelectric fluids where the phase biaxiality results from the dipolar interactions. The structures of all the ferroelectric configurations of interest are presented in detail. Simple phase diagrams are determined which include different polar and apolar discotic fluids generated by the system.

  6. Modification of the Electro-optical Properties of the B1 Liquid Crystal Phase using a Rod-like Liquid Crystal Dopant

    SciTech Connect

    J Kirchhoff; L Hirst

    2011-12-31

    It has recently been observed that on application of an alternating electric field, the B1 liquid-crystalline phase may be induced to form a switchable phase. This induced phase has been shown to have an almost thresholdless dielectric response. In this paper we examine this E-field-induced transition as a function of temperature both with and without a ferroelectric liquid-crystal dopant. Although the aim of this experiment was to enhance and stabilize the field-induced phase on addition of dopant, we find that the opposite is the case. The ferroelectric dopant actually increases the threshold E-fields required for transformation to the switching phase and at just 5 wt?% dopant a smectic-A phase is formed. Addition of the dopant also acts against the low-field switching and significantly speeds relaxation back to the B1 phase on field removal. In addition we find that the field-induced phase experiences a slower crystallization. We use polarized optical microscopy, differential scanning calorimetry, and x-ray scattering experiments to characterize the physical properties of the mixtures.

  7. Liquid phase crystallized silicon on glass: Technology, material quality and back contacted heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Haschke, Jan; Amkreutz, Daniel; Rech, Bernd

    2016-04-01

    Liquid phase crystallization has emerged as a novel approach to grow large grained polycrystalline silicon films on glass with high electronic quality. In recent years a lot of effort was conducted by different groups to determine and optimize suitable interlayer materials, enhance the crystallographic quality or to improve post crystallization treatments. In this paper, we give an overview on liquid phase crystallization and describe the necessary process steps and discuss their influence on the absorber properties. Available line sources are compared and different interlayer configurations are presented. Furthermore, we present one-dimensional numerical simulations of a rear junction device, considering silicon absorber thicknesses between 1 and 500 µm. We vary the front surface recombination velocity as well as doping density and minority carrier lifetime in the absorber. The simulations suggest that a higher absorber doping density is beneficial for layer thicknesses below 20 µm or when the minority carrier lifetime is short. Finally, we discuss possible routes for device optimization and propose a hybride cell structure to circumvent current limitations in device design.

  8. Generation of frustrated liquid crystal phases by mixing an achiral nematic-smectic-C mesogen with an antiferroelectric chiral smectic liquid crystal.

    PubMed

    Lagerwall, Jan P F; Giesselmann, Frank; Selbmann, Christine; Rauch, Sebastian; Heppke, Gerd

    2005-04-01

    By mixing the achiral liquid crystal HOAB, exhibiting a nematic (N)-smectic-C (SmC) mesophase sequence, with the chiral antiferroelectric liquid crystal (AFLC) (S,S)-M7BBM7, forming the antiferroelectric SmC(a)(*) phase, at least seven different mesophases have been induced which neither component forms on its own: a twist-grain-boundary (TGB(*)) phase, two or three blue phases, the untilted SmA(*) phase, as well as all three chiral smectic-C-type "subphases," SmC(alpha)(*), SmC(beta)(*), and SmC(gamma)(*). The nature of the induced phases and the transitions between them were determined by means of optical and electro-optical investigations, dielectric spectroscopy, and differential scanning calorimetry. The induced phases can to a large extent be understood as a result of frustration, TGB(*) at the border between nematic and smectic, the subphases between syn and anticlinic tilted smectic organization. X ray scattering experiments reveal that the smectic layer spacing as well as the degree of smectic order is relatively constant in the whole mixture composition range in which AFLC behavior prevails, whereas both these parameters rapidly decrease as the amount of HOAB is increased to such an extent that no other smectic-C-type phase than SmC/SmC(*) exists. By tailoring the composition we are able to produce liquid crystal mixtures exhibiting unusual phase sequences, e.g., with a direct isotropic-SmC(a)(*) transition or a temperature range of the SmC(beta)(*) subphase of about 50 K.

  9. Gelled Lyotropic Liquid Crystals.

    PubMed

    Xu, Yang; Laupheimer, Michaela; Preisig, Natalie; Sottmann, Thomas; Schmidt, Claudia; Stubenrauch, Cosima

    2015-08-11

    In our previous work we were able to prove that gelled bicontinuous microemulsions are a novel type of orthogonal self-assembled system. The study at hand aims at complementing our previous work by answering the question of whether gelled lyotropic liquid crystals are also orthogonal self-assembled systems. For this purpose we studied the same system, namely, water-n-decane/12-hydroxyoctadecanoic acid (12-HOA)-n-decyl tetraoxyethylene glycol ether (C10E4). The phase boundaries of the nongelled and the gelled lyotropic liquid crystals were determined visually and with (2)H NMR spectroscopy. Oscillating shear measurements revealed that the absolute values of the storage and loss moduli of the gelled liquid crystalline (LC) phases do not differ very much from those of the binary organogel. While both the phase behavior and the rheological properties of the LC phases support the hypothesis that gelled lyotropic liquid crystals are orthogonal self-assembled systems, freeze-fracture electron microscopy (FFEM) seems to indicate an influence of the gel network on the structure of the Lα phase and vice versa.

  10. Detection of an intermediate biaxial phase in the phase diagram of biaxial liquid crystals: Entropic sampling study

    NASA Astrophysics Data System (ADS)

    Kamala Latha, B.; Jose, Regina; Murthy, K. P. N.; Sastry, V. S. S.

    2014-05-01

    We investigate the phase sequence of biaxial liquid crystals, based on a general quadratic model Hamiltonian over the relevant parameter space, with a Monte Carlo simulation which constructs equilibrium ensembles of microstates, overcoming possible (free) energy barriers (combining entropic and frontier sampling techniques). The resulting phase diagram qualitatively differs from the universal phase diagram predicted earlier from mean-field theory (MFT), as well as the Monte Carlo simulations with the Metropolis algorithm. The direct isotropic-to-biaxial transition predicted by the MFT is replaced in certain regions of the space by the onset of an additional intermediate biaxial phase of very low order, leading to the sequence NB-NB1-I. This is due to inherent barriers to fluctuations of the components comprising the total energy, and may explain the difficulties in the experimental realization of these phases.

  11. Detection of an intermediate biaxial phase in the phase diagram of biaxial liquid crystals: entropic sampling study.

    PubMed

    Kamala Latha, B; Jose, Regina; Murthy, K P N; Sastry, V S S

    2014-05-01

    We investigate the phase sequence of biaxial liquid crystals, based on a general quadratic model Hamiltonian over the relevant parameter space, with a Monte Carlo simulation which constructs equilibrium ensembles of microstates, overcoming possible (free) energy barriers (combining entropic and frontier sampling techniques). The resulting phase diagram qualitatively differs from the universal phase diagram predicted earlier from mean-field theory (MFT), as well as the Monte Carlo simulations with the Metropolis algorithm. The direct isotropic-to-biaxial transition predicted by the MFT is replaced in certain regions of the space by the onset of an additional intermediate biaxial phase of very low order, leading to the sequence N(B)-N(B1)-I. This is due to inherent barriers to fluctuations of the components comprising the total energy, and may explain the difficulties in the experimental realization of these phases.

  12. Low voltage polymer-stabilized blue phase liquid crystal reflective display by doping ferroelectric nanoparticles.

    PubMed

    Xu, X W; Zhang, X W; Luo, D; Dai, H T

    2015-12-14

    Low driving voltage is achieved in full color reflective display based on polymer-stabilized blue phase liquid crystal (PS-PBLC), by doping a small amount of ferroelectric nanoparticles. Both reflectance spectra of PS-PBLC with and without BaTiO₃ ferroelectric nanoparticles are studied under different applied external voltages. Superior to PS-PBLC without ferroelectric nanoparticles, the vertical driving electric fields of PS-PBLC with 0.4 wt.% BaTiO₃ ferroelectric nanoparticles are dramatically reduced by more than 70% for red, green and blue cells. The proposed approach would accelerate the practical application of full color PS-BPLC reflective display.

  13. Gelator-doped liquid-crystal phase grating with multistable and dynamic modes

    SciTech Connect

    Lin, Hui-Chi Yang, Meng-Ru; Tsai, Sheng-Feng; Yan, Shih-Chiang

    2014-01-06

    We demonstrate a gelator-doped nematic liquid-crystal (LC) phase grating, which can be operated in both the multistable mode and the dynamic mode. Thermoreversible association and dissociation of the gelator molecules can vary and fix the multistable diffraction efficiencies of the gratings. A voltage (V) can also be applied to modulate dynamically the diffraction efficiencies of the grating, which behaves as a conventional LC grating. Experimental results show that the variations of the diffraction efficiencies in the multistable and dynamic modes are similar. The maximum diffraction efficiency is approximately 30% at V = 2 V.

  14. Data association multiple target tracking using a phase-mostly liquid crystal television

    NASA Technical Reports Server (NTRS)

    Tam, Eddy C.; Yu, Francis T. S.; Tanone, Aris; Gregory, Don A.; Juday, Richard D.

    1990-01-01

    This paper presents a technique of using data association target tracking in a motion sequence via an adaptive joint transform correlator. The massive data in the field of view can be reduced to a few correlation peaks. The average velocity of a target during the tracking cycle is then determined from the location of the correlation peak. A data association algorithm is used for the analysis of these correlation signals, with which multiple targets can be tracked. A phase-mostly liquid-crystal TV is used in the hybrid joint transform correlation system, and simultaneous tracking of three targets is demonstrated.

  15. Optical rotatory power of polymer-stabilized blue phase liquid crystals

    NASA Astrophysics Data System (ADS)

    Liu, Yifan; Lan, Yi-fen; Zhang, Hongxia; Zhu, Ruidong; Xu, Daming; Tsai, Cheng-Yeh; Lu, Jen-Kuei; Sugiura, Norio; Lin, Yu-Chieh; Wu, Shin-Tson

    2013-04-01

    Macroscopically, a polymer-stabilized blue phase liquid crystal (BPLC) is assumed to be an optically isotropic medium. Our experiment challenges this assumption. Our results indicate that the optical rotatory power (ORP) of some nano-scale double-twist cylinders in a BPLC composite causes the polarization axis of the transmitted light to rotate a small angle, which in turn leaks through the crossed polarizers. Rotating the analyzer in azimuthal direction to correct this ORP can greatly improve the contrast ratio. A modified De Vries equation based on a thin twisted-nematic layer is proposed to explain the observed phenomena.

  16. Liquid-crystal-solid interface structure at the antiferroelectric-ferroelectric phase transition.

    PubMed

    Coleman, D; Bardon, S; Radzihovsky, L; Danner, G; Clark, N A

    2002-12-01

    Total internal reflection is used to probe the molecular organization at the surface of a tilted chiral smectic liquid crystal at temperatures in the vicinity of the bulk antiferroelectric-ferroelectric phase transition. Data are interpreted using an exact analytical solution of a real model for ferroelectric order at the surface. In the mixture T3, ferroelectric surface order is expelled with the bulk ferroelectric-antiferroelectric transition. The conditions for ferroelectric order at the surface of an antiferroelectric bulk are presented. PMID:12513307

  17. Observation of blue phase in chiral nematic liquid crystal and its stabilization by silica nanoparticles

    NASA Astrophysics Data System (ADS)

    Singh, Arshdeep; Malik, Praveen; Jayoti, Divya

    2016-01-01

    In the present work, we report the blue phase (BP) in a binary mixture of cholesteryl nonanoate (CN) and N-(4-ethoxybenzylidene)-4-butylaniline (EBBA). The mixture exhibits BP over a temperature range of 2.3 K at optimum composition (50:50) of liquid crystals (LCs). The effect of silica nanoparticles (SNPs) doping on thermal stability of BPs has also been demonstrated and nearly 6 K wide BP temperature range was achieved at 0.5 wt.% of SNPs. A porous type texture was also observed during the BP formation process in the doped samples.

  18. Design characterization of an electronic steerable Ka-band antenna using liquid crystal phase shifters

    NASA Astrophysics Data System (ADS)

    Hoehn, A.; Hager, P. B.; Harder, J. T.

    Modern high data rate satellite communication systems increasingly utilize the Ka-band due to its ability to support higher bandwidth. Prior research work presented a copper-galvanically produced Ka-band horn array antenna and associated waveguide distribution network, mounted on a two axes mechanical steerable mechanism (LISAMS) for use aboard fast, low earth orbiting satellites. The current project, LISAES, investigates the feasibility of a similar horn array antenna, but fitted with liquid crystal phase shifters in the transmission path of each horn, which now allow steering of the antenna boresight through beam forming without the use of mechanically moving parts.

  19. Characterization of the phase behaviour of a novel polymerizable lyotropic ionic liquid crystal.

    PubMed

    Goujon, Nicolas; Forsyth, Maria; Dumée, Ludovic F; Bryant, Gary; Byrne, Nolene

    2015-09-21

    The development of new polymerizable lyotropic liquid crystals (LLCs) utilizing charged amphiphilic molecules such as those based on long chain imidazolium compounds, is a relatively new design direction for producing robust membranes with controllable nano-structures. Here we have developed a novel polymerizable ionic liquid based LLC, 1-hexadecyl-3-methylimidazolium acrylate (C16mimAcr), where the acrylate anion acts as the polymerizable moiety. The phase behaviour of the C16mimAcr upon the addition of water was characterized using small and wide angle X-ray scatterings, differential scanning calorimetry and polarized optical microscopy. We compare the phase behaviour of this new polymerizable LLC to that of the well known LLC chloride analogue, 1-hexadecyl-3-methylimidazolium chloride (C16mimCl). We find that the C16mimAcr system has a more complex phase behaviour compared to the C16mimCl system. Additional lyotropic liquid crystalline mesophases such as hexagonal phase (H1) and discontinuous cubic phase (I1) are observed at 20 °C for the acrylate system at 50 and 65 wt% water respectively. The appearance of the hexagonal phase (H1) and discontinuous cubic phase (I1) for the acrylate system is likely due to the strong hydrating nature of the acrylate anion, which increases the head group area. The formation of these additional mesophases seen for the acrylate system, especially the hexagonal phase (H1), coupled with the polymerization functionality offers great potential in the design of advanced membrane materials with selective and anisotropic transport properties.

  20. Characterization of the phase behaviour of a novel polymerizable lyotropic ionic liquid crystal.

    PubMed

    Goujon, Nicolas; Forsyth, Maria; Dumée, Ludovic F; Bryant, Gary; Byrne, Nolene

    2015-09-21

    The development of new polymerizable lyotropic liquid crystals (LLCs) utilizing charged amphiphilic molecules such as those based on long chain imidazolium compounds, is a relatively new design direction for producing robust membranes with controllable nano-structures. Here we have developed a novel polymerizable ionic liquid based LLC, 1-hexadecyl-3-methylimidazolium acrylate (C16mimAcr), where the acrylate anion acts as the polymerizable moiety. The phase behaviour of the C16mimAcr upon the addition of water was characterized using small and wide angle X-ray scatterings, differential scanning calorimetry and polarized optical microscopy. We compare the phase behaviour of this new polymerizable LLC to that of the well known LLC chloride analogue, 1-hexadecyl-3-methylimidazolium chloride (C16mimCl). We find that the C16mimAcr system has a more complex phase behaviour compared to the C16mimCl system. Additional lyotropic liquid crystalline mesophases such as hexagonal phase (H1) and discontinuous cubic phase (I1) are observed at 20 °C for the acrylate system at 50 and 65 wt% water respectively. The appearance of the hexagonal phase (H1) and discontinuous cubic phase (I1) for the acrylate system is likely due to the strong hydrating nature of the acrylate anion, which increases the head group area. The formation of these additional mesophases seen for the acrylate system, especially the hexagonal phase (H1), coupled with the polymerization functionality offers great potential in the design of advanced membrane materials with selective and anisotropic transport properties. PMID:26271610

  1. Preparation and Optical Properties of Spherical Inverse Opals by Liquid Phase Deposition Using Spherical Colloidal Crystals

    NASA Astrophysics Data System (ADS)

    Aoi, Y.; Tominaga, T.

    2013-03-01

    Titanium dioxide (TiO2) inverse opals in spherical shape were prepared by liquid phase deposition (LPD) using spherical colloidal crystals as templates. Spherical colloidal crystals were produced by ink-jet drying technique. Aqueous emulsion droplets that contain polystyrene latex particles were ejected into air and dried. Closely packed colloidal crystals with spherical shape were obtained. The obtained spherical colloidal crystals were used as templates for the LPD. The templates were dispersed in the deposition solution of the LPD, i.e. a mixed solution of ammonium hexafluorotitanate and boric acid and reacted for 4 h at 30 °C. After the LPD process, the interstitial spaces of the spherical colloidal crystals were completely filled with titanium oxide. Subsequent heat treatment resulted in removal of templates and spherical titanium dioxide inverse opals. The spherical shape of the template was retained. SEM observations indicated that the periodic ordered voids were surrounded by titanium dioxide. The optical reflectance spectra indicated that the optical properties of the spherical titanium dioxide inverse opals were due to Bragg diffractions from the ordered structure. Filling in the voids of the inverse opals with different solvents caused remarkable changes in the reflectance peak.

  2. Acousto-optic liquid-crystal analog beam former for phased-array antennas.

    PubMed

    Riza, N A

    1994-06-10

    A compact phased-array antenna acousto-optic beam former with element-level analog phase (0-2π) and amplitude control using nematic-liquid-crystal display-type technology is experimentally demonstrated. Measurements indicate > 6-bit phase control and 52.6 dB of amplitude-attenuation control. High-quality error calibration and antenna sidelobe-level control is possible with this low-control-power analog beam former. Optical system options using rf Bragg cells or wideband Bragg cells are discussed, with the rf design being the current preferred approach. Transmit-receive beam forming based on frequency upconversion-downconversion by electronic mixing is introduced for the rf Bragg-cell beam former, and comparisons with digital beam forming are highlighted. A millimeter-wave signal generation and control optical architecture is described.

  3. Influence of interface stabilisers and surrounding aqueous phases on nematic liquid crystal shells.

    PubMed

    Noh, JungHyun; Reguengo De Sousa, Kevin; Lagerwall, Jan P F

    2016-01-14

    We investigate the nematic-isotropic (N-I) transition in shells of the liquid crystal 5CB, surrounded by aqueous phases that conventionally are considered to be immiscible with 5CB. The aqueous phases contain either sodium dodecyl sulfate (SDS) or polyvinyl alcohol (PVA) as stabiliser, the former additionally promoting homeotropic director alignment. For all shell configurations we find a depression of the clearing point compared to pure 5CB, indicating that a non-negligible fraction of the constituents of the surrounding phases enter the shell, predominantly water. In hybrid-aligned shells, with planar outer and homeotropic inner boundary (or vice versa), the N-I transition splits into two steps, with a consequent three-step textural transformation. We explain this as a result of the order-enhancing effect of a monolayer of radially aligned SDS molecules adsorbed at the homeotropic interface. PMID:26512764

  4. Dimerlike smectic-{ital A} and -{ital C} phases in highly fluorinated thermotropic liquid crystals

    SciTech Connect

    Rieker, T.P.; Janulis, E.P. |

    1995-09-01

    X-ray scattering studies on a homologous series of thermotropic liquid crystals with one tail perfluorinated reveal that the smectic layer thickness depends only on the length of the fluorocarbon tail. Density measurements in combination with the x-ray results show that the average cross-sectional area per molecule, parallel to the smectic layers, depends only on the length of the hydrocarbon tail. These experimental results lead to a model in which steric interactions drive antiparallel alignment of nearest neighbors in the smectic-{ital A} and -{ital C} phases. These unique dimerlike phases have a layer spacing comparable to the length of the molecules, demonstrate registration of nearest neighbors along their lengths, and exhibit ferroelectric switching in the chiral smectic-{ital C} phase.

  5. Optically isotropic liquid-crystal phase of bent-core molecules with polar nanostructure

    NASA Astrophysics Data System (ADS)

    Liao, G.; Stojadinovic, S.; Pelzl, G.; Weissflog, W.; Sprunt, S.; Jákli, A.

    2005-08-01

    We found that the optically isotropic (IM) mesophase observed recently below the nematic phase of the bent-core liquid crystal 4-chlororesorcinol bis[4-(4-n-dodecyloxybenzoyloxy)benzoate] shows ferroelectric-type switching. Polarizing microscopic, electric current, dielectric, and dynamic light scattering studies lead us to propose that the IM phase is composed of interconnected orthoconic racemic smectic (Sm-CaPF) nanodomains with random layer orientations. Near the nematic phase, where the polarization can be saturated by electric fields, the system responds in a fashion analogous to the granular structure of a magnetic spin glass—in particular, we observed that the relaxation back to the nonpoled structure follows a similar, inverse logarithmic rule.

  6. The existence region and composition of a polymer-induced liquid precursor phase for DL-glutamic acid crystals.

    PubMed

    Jiang, Yuan; Gower, Laurie; Volkmer, Dirk; Cölfen, Helmut

    2012-01-14

    The existence region of a polymer-induced liquid precursor (PILP) phase for crystals of an organic compound (DL-glutamic acid, Glu) was determined for the first time in the phase diagram of the Glu-polyethyleneimine-water-ethanol system. The existence region and the amount of PILP phase relative to the thermodynamically stable crystal phase were very small. Other phases detected in the phase diagram were coacervates, homogenous mixtures, and crystals obtained via a clear solution. The PILP phase is rich in the polymeric additive, which helps to explain the long induction period of PILP before crystallization occurs. Volume measurements indicated that its amount is <1 vol%, showing that this precursor phase is only a minor component.

  7. Phase-field crystal modeling of equilibrium bcc-liquid interfaces

    NASA Astrophysics Data System (ADS)

    Wu, Kuo-An; Karma, Alain

    2007-11-01

    We investigate the equilibrium properties of bcc-liquid interfaces modeled with a continuum phase-field crystal (PFC) approach [K. R. Elder and M. Grant, Phys. Rev. E 70, 051605 (2004)]. A multiscale analysis of the PFC model is carried out which exploits the fact that the amplitudes of crystal density waves decay slowly into the liquid in the physically relevant limit where the freezing transition is weakly first order. This analysis yields a set of coupled equations for these amplitudes that is similar to the set of equations derived from Ginzburg-Landau (GL) theory [K.-A. Wu , Phys. Rev. B 73, 094101 (2006)]. The two sets only differ in the details of higher order nonlinear couplings between different density waves, which is determined by the form of the nonlinearity assumed in the PFC model and by the ansatz that all polygons with the same number of sides have equal weight in GL theory. Despite these differences, for parameters (liquid structure factor and solid density wave amplitude) of Fe determined from molecular dynamics (MD) simulations, the PFC and GL amplitude equations yield very similar predictions for the overall magnitude and anisotropy of the interfacial free-energy and density wave profiles. These predictions are compared with MD simulations as well as numerical solutions of the PFC model.

  8. Detecting, visualizing, and measuring gold nanoparticle chirality using helical pitch measurements in nematic liquid crystal phases.

    PubMed

    Sharma, Anshul; Mori, Taizo; Lee, Huey-Charn; Worden, Matthew; Bidwell, Eric; Hegmann, Torsten

    2014-12-23

    Chirality at the nanoscale, or more precisely, the chirality or chiroptical effects of chiral ligand-capped metal nanoparticles (NPs) is an intriguing and rapidly evolving field in nanomaterial research with promising applications in catalysis, metamaterials, and chiral sensing. The aim of this work was to seek out a system that not only allows the detection and understanding of NP chirality but also permits visualization of the extent of chirality transfer to a surrounding medium. The nematic liquid crystal phase is an ideal candidate, displaying characteristic defect texture changes upon doping with chiral additives. To test this, we synthesized chiral cholesterol-capped gold NPs and prepared well-dispersed mixtures in two nematic liquid crystal hosts. Induced circular dichroism spectropolarimetry and polarized light optical microscopy revealed that all three gold NPs induce chiral nematic phases, and that those synthesized in the presence of a chiral bias (disulfide) are more powerful chiral inducers than those where the NP was formed in the absence of a chiral bias (prepared by conjugation of a chiral silane to preformed NPs). Helical pitch data here visually show a clear dependence on the NP size and the number of chiral ligands bound to the NP surface, thereby supporting earlier experimental and theoretical data that smaller metal NPs made in the presence of a chiral bias are stronger chiral inducers.

  9. Optical diffractometry of highly anisotropic holographic gratings formed by liquid crystal and polymer phase separation.

    PubMed

    Kakiuchida, Hiroshi; Tazawa, Masato; Yoshimura, Kazuki; Ogiwara, Akifumi

    2012-12-01

    Optical diffractometry is proposed as a practical method of quantitatively analyzing the microscopic structural origins of a wide range of highly efficient and linearly polarized optical diffraction grating produced from holographic polymer-dispersed liquid crystal. The structure is organized by a spatially periodical distribution of submicrometer-scale liquid crystal (LC) droplets in a polymer matrix. Six independent Bragg diffraction spectra were obtained at two orthogonal polarization states at temperatures below, at, and above the nematic-to-isotropic phase transition point. These spectra were simultaneously analyzed by employing anisotropic diffraction theory under the restraint of a simple and widely useful structural model constructed on the basis of the previously reported microscopic observations. The refractive indices of spatially periodic LC- and polymer-rich phases were analyzed using Cauchy's equation as a function of optical wavelength. The present diffractometry was demonstrated for a variety of holographic structures, and the structural parameters were discussed such as the filling ratio of LC droplets to polymer matrix, the orientational order in the droplets, and the thermo-optic properties in the LC droplets. Furthermore, the higher order Bragg diffractions were measured and discussed. The proposed method was examined in consistency by comparisons with polarizing optical microscopy and scanning electron microscopy. PMID:23367963

  10. Salt effects on the phase behavior, structure, and rheology of chromonic liquid crystals.

    PubMed

    Kostko, Andrei F; Cipriano, Bani H; Pinchuk, Olga A; Ziserman, Lior; Anisimov, Mikhail A; Danino, Dganit; Raghavan, Srinivasa R

    2005-10-20

    Chromonic liquid crystals are formed by the addition of aromatic molecules such as disodium chromoglycate (cromolyn) to water. In this study, we investigate the addition of salts to the lyotropic nematic phase of cromolyn aqueous solutions. The addition of sodium and potassium salts shifts the isotropic-nematic phase boundary upward by more than 10 degrees C, so that samples that were isotropic at room temperature are transformed into nematic phases. Salt effects are predominantly dictated by the cation, not the anion, and appear to differ based on cation size. In contrast to small, hydrated cations like sodium, large, weakly hydrated cations such as tetraethylammonium and tetrabutylammonium shift the phase boundary downward, thus stabilizing the isotropic phase at the expense of the nematic one. The phase behavior results are highly correlated with viscosity measurements, with an upward shift in the phase boundary correlating with an increase in solution viscosity and vice versa. We also probe the microstructure in cromolyn-salt solutions, both indirectly by small-angle neutron scattering (SANS) and directly by cryo-transmission electron microscopy (cryo-TEM). The cryo-TEM images show the presence of rodlike aggregates that possibly undergo a higher order aggregation into bundles in the presence of salt.

  11. Observing in space and time the ephemeral nucleation of liquid-to-crystal phase transitions.

    PubMed

    Yoo, Byung-Kuk; Kwon, Oh-Hoon; Liu, Haihua; Tang, Jau; Zewail, Ahmed H

    2015-01-01

    The phase transition of crystalline ordering is a general phenomenon, but its evolution in space and time requires microscopic probes for visualization. Here we report direct imaging of the transformation of amorphous titanium dioxide nanofilm, from the liquid state, passing through the nucleation step and finally to the ordered crystal phase. Single-pulse transient diffraction profiles at different times provide the structural transformation and the specific degree of crystallinity (η) in the evolution process. It is found that the temporal behaviour of η exhibits unique 'two-step' dynamics, with a robust 'plateau' that extends over a microsecond; the rate constants vary by two orders of magnitude. Such behaviour reflects the presence of intermediate structure(s) that are the precursor of the ordered crystal state. Theoretically, we extend the well-known Johnson-Mehl-Avrami-Kolmogorov equation, which describes the isothermal process with a stretched-exponential function, but here over the range of times covering the melt-to-crystal transformation.

  12. Liquid crystalline phase as a probe for crystal engineering of lactose: carrier for pulmonary drug delivery.

    PubMed

    Patil, Sharvil S; Mahadik, Kakasaheb R; Paradkar, Anant R

    2015-02-20

    The current work was undertaken to assess suitability of liquid crystalline phase for engineering of lactose crystals and their utility as a carrier in dry powder inhalation formulations. Saturated lactose solution was poured in molten glyceryl monooleate which subsequently transformed into gel. The gel microstructure was analyzed by PPL microscopy and SAXS. Lactose particles recovered from gels after 48 h were analyzed for polymorphism using techniques such as FTIR, XRD, DSC and TGA. Particle size, morphology and aerosolisation properties of prepared lactose were analyzed using Anderson cascade impactor. In situ seeding followed by growth of lactose crystals took place in gels with cubic microstructure as revealed by PPL microscopy and SAXS. Elongated (size ∼ 71 μm) lactose particles with smooth surface containing mixture of α and β-lactose was recovered from gel, however percentage of α-lactose was more as compared to β-lactose. The aerosolisation parameters such as RD, ED, %FPF and % recovery of lactose recovered from gel (LPL) were found to be comparable to Respitose® ML001. Thus LC phase (cubic) can be used for engineering of lactose crystals so as to obtain particles with smooth surface, high elongation ratio and further they can be used as carrier in DPI formulations.

  13. Observing in space and time the ephemeral nucleation of liquid-to-crystal phase transitions

    PubMed Central

    Yoo, Byung-Kuk; Kwon, Oh-Hoon; Liu, Haihua; Tang, Jau; Zewail, Ahmed H.

    2015-01-01

    The phase transition of crystalline ordering is a general phenomenon, but its evolution in space and time requires microscopic probes for visualization. Here we report direct imaging of the transformation of amorphous titanium dioxide nanofilm, from the liquid state, passing through the nucleation step and finally to the ordered crystal phase. Single-pulse transient diffraction profiles at different times provide the structural transformation and the specific degree of crystallinity (η) in the evolution process. It is found that the temporal behaviour of η exhibits unique ‘two-step' dynamics, with a robust ‘plateau' that extends over a microsecond; the rate constants vary by two orders of magnitude. Such behaviour reflects the presence of intermediate structure(s) that are the precursor of the ordered crystal state. Theoretically, we extend the well-known Johnson–Mehl–Avrami–Kolmogorov equation, which describes the isothermal process with a stretched-exponential function, but here over the range of times covering the melt-to-crystal transformation. PMID:26478194

  14. Thermotropic liquid crystals from biomacromolecules

    PubMed Central

    Liu, Kai; Chen, Dong; Marcozzi, Alessio; Zheng, Lifei; Su, Juanjuan; Pesce, Diego; Zajaczkowski, Wojciech; Kolbe, Anke; Pisula, Wojciech; Müllen, Klaus; Clark, Noel A.; Herrmann, Andreas

    2014-01-01

    Complexation of biomacromolecules (e.g., nucleic acids, proteins, or viruses) with surfactants containing flexible alkyl tails, followed by dehydration, is shown to be a simple generic method for the production of thermotropic liquid crystals. The anhydrous smectic phases that result exhibit biomacromolecular sublayers intercalated between aliphatic hydrocarbon sublayers at or near room temperature. Both this and low transition temperatures to other phases enable the study and application of thermotropic liquid crystal phase behavior without thermal degradation of the biomolecular components. PMID:25512508

  15. Grating lobes analysis based on blazed grating theory for liquid crystal optical-phased array

    NASA Astrophysics Data System (ADS)

    Chen, Jian; Cui, Guolong; Kong, Lingjiang; Xiao, Feng; Liu, Xin; Zhang, Xiaoguang

    2013-09-01

    The grating lobes of the liquid crystal optical-phased array (LCOPA) based on blazed grating theory is studied. Using the Fraunhofer propagation principle, the analytical expressions of the far-field intensity distribution are derived. Subsequently, we can obtain both the locations and the intensities of the grating lobes. The derived analytical functions that provide an insight into single-slit diffraction and multislit interference effect on the grating lobes are discussed. Utilizing the conventional microwave-phased array technique, the intensities of the grating lobes and the main lobe are almost the same. Different from this, the derived analytical functions demonstrate that the intensities of the grating lobes are less than that of the main lobe. The computer simulations and experiments show that the proposed method can correctly estimate the locations and the intensities of the grating lobes for a LCOPA simultaneously.

  16. Low voltage transflective blue-phase liquid crystal display with a non-uniform etching substrate

    NASA Astrophysics Data System (ADS)

    Wang, Jian; Mao, Jiang-Lin; Fan, Hao-Xiang; Wang, Qiong-Hua

    2016-09-01

    A transflective polymer-stabilized blue-phase liquid crystal display (BP-LCD) with a non-uniform etching substrate is proposed. In-plane switching (IPS) electrodes on the bottom substrate are put on the different gaps, and the bottom substrate between the electrodes is etched into different depths in transmissive (T) and reflective (R) regions. This structure can balance the optical phase retardation in the two regions and is helpful to achieve well-matched voltag-dependent transmittance and reflectance curves. This transflective display has high optical efficiency, a wide viewing angle, and low operating voltage (approximately 6 V). Project supported by the National Natural Science Foundation of China (Grant Nos. 61535007 and 61320106015) and the National Basic Research Program of China (Grant No. 2013CB328802).

  17. A New Phase of Liquid Crystal with Quenched Disorder: The Columnar Elastic Glass

    NASA Astrophysics Data System (ADS)

    Toner, John; Saunders, Karl; Ettouhami, A. M.; Radzihovsky, Leo

    2002-03-01

    The properties of the columnar liquid crystal phase confined in random porous media, e.g. aerogel, are studied. It is found that the quenched disorder leads to a complete destruction of the long-ranged columnar translational order. Nevertheless, dislocations remain bound in the resulting phase, which therefore retains columnar topological and orientational order, and is referred to as a columnar elastic glass (CEG). The elasticity of the CEG is found to be anomalous, i.e. wavevector dependent, and is characterized by universal anomalous exponents, which are calculated using an ɛ = 7/2 - d expansion. The CEG also exhibits a negative universal Poisson ratio which is calculated. Furthemore, the recently predicted spontaneous vortex lattice in dirty ferromagnetic superconductors falls into the CEG universality class [1]. [1] Leo Radzihovsky, A. M. Ettouhami, Karl Saunders, John Toner, Phys. Rev. Lett.87, 27001 (2001).

  18. Laser-Directed Hierarchical Assembly of Liquid Crystal Defects and Control of Optical Phase Singularities

    SciTech Connect

    Ackerman, P. J.; Qi, Z. Y.; Lin, Y. H.; Twombly, C. W.; Laviada, M. J.; Lansac, Y.; Smalyukh, I. I.

    2012-06-07

    Topological defect lines are ubiquitous and important in a wide variety of fascinating phenomena and theories in many fields ranging from materials science to early-universe cosmology, and to engineering of laser beams. However, they are typically hard to control in a reliable manner. Here we describe facile erasable 'optical drawing' of self-assembled defect clusters in liquid crystals. These quadrupolar defect clusters, stabilized by the medium's chirality and the tendency to form twisted configurations, are shaped into arbitrary two-dimensional patterns, including reconfigurable phase gratings capable of generating and controlling optical phase singularities in laser beams. Our findings bridge the studies of defects in condensed matter physics and optics and may enable applications in data storage, singular optics, displays, electro-optic devices, diffraction gratings, as well as in both optically- and electrically-addressed pixel-free spatial light modulators.

  19. Waterlike features, liquid-crystal phase and self-assembly in Janus dumbbells

    NASA Astrophysics Data System (ADS)

    Bordin, José Rafael

    2016-10-01

    We explore the phase diagram of Janus nanoparticles using Molecular Dynamics simulations. Each monomer in the dimer has distinct characteristics. One type of monomer interacts by a Lennard Jones potential, while the other type interacts through a two length scale potential. Previous studies for the monomeric system using this specific two length scale potential do not indicate the presence of waterlike anomalies. However, our results show that the combination of two length scales potential and LJ potential in the Janus nanoparticle will lead to thermodynamic and dynamic anomalies. The self-assembly properties were also explored. We observe distinct kinds of self-assembled structures and a liquid-crystal phase. This result indicates that it is possible to create Janus nanoparticles with waterlike features using monomers without anomalous behavior. The anomalies and structures are explained with the two length scale potential characteristics.

  20. Laser-directed hierarchical assembly of liquid crystal defects and control of optical phase singularities

    PubMed Central

    Ackerman, Paul J.; Qi, Zhiyuan; Lin, Yiheng; Twombly, Christopher W.; Laviada, Mauricio J.; Lansac, Yves; Smalyukh, Ivan I.

    2012-01-01

    Topological defect lines are ubiquitous and important in a wide variety of fascinating phenomena and theories in many fields ranging from materials science to early-universe cosmology, and to engineering of laser beams. However, they are typically hard to control in a reliable manner. Here we describe facile erasable “optical drawing” of self-assembled defect clusters in liquid crystals. These quadrupolar defect clusters, stabilized by the medium's chirality and the tendency to form twisted configurations, are shaped into arbitrary two-dimensional patterns, including reconfigurable phase gratings capable of generating and controlling optical phase singularities in laser beams. Our findings bridge the studies of defects in condensed matter physics and optics and may enable applications in data storage, singular optics, displays, electro-optic devices, diffraction gratings, as well as in both optically- and electrically-addressed pixel-free spatial light modulators. PMID:22679553

  1. Light-melt adhesive based on dynamic carbon frameworks in a columnar liquid-crystal phase

    NASA Astrophysics Data System (ADS)

    Saito, Shohei; Nobusue, Shunpei; Tsuzaka, Eri; Yuan, Chunxue; Mori, Chigusa; Hara, Mitsuo; Seki, Takahiro; Camacho, Cristopher; Irle, Stephan; Yamaguchi, Shigehiro

    2016-07-01

    Liquid crystal (LC) provides a suitable platform to exploit structural motions of molecules in a condensed phase. Amplification of the structural changes enables a variety of technologies not only in LC displays but also in other applications. Until very recently, however, a practical use of LCs for removable adhesives has not been explored, although a spontaneous disorganization of LC materials can be easily triggered by light-induced isomerization of photoactive components. The difficulty of such application derives from the requirements for simultaneous implementation of sufficient bonding strength and its rapid disappearance by photoirradiation. Here we report a dynamic molecular LC material that meets these requirements. Columnar-stacked V-shaped carbon frameworks display sufficient bonding strength even during heating conditions, while its bonding ability is immediately lost by a light-induced self-melting function. The light-melt adhesive is reusable and its fluorescence colour reversibly changes during the cycle, visualizing the bonding/nonbonding phases of the adhesive.

  2. Organization of the polarization splay modulated smectic liquid crystal phase by topographic confinement

    PubMed Central

    Ki Yoon, Dong; Deb, Rajdeep; Chen, Dong; Körblova, Eva; Shao, Renfan; Ishikawa, Ken; Rao, Nandiraju V. S.; Walba, David M.; Smalyukh, Ivan I.; Clark, Noel A.

    2010-01-01

    Recently, the topographic patterning of surfaces by lithography and nanoimprinting has emerged as a new and powerful tool for producing single structural domains of liquid crystals and other soft materials. Here the use of surface topography is extended to the organization of liquid crystals of bent-core molecules, soft materials that, on the one hand, exhibit a rich, exciting, and intensely studied array of novel phases, but that, on the other hand, have proved very difficult to align. Among the most notorious in this regard are the polarization splay modulated (B7) phases, in which the symmetry-required preference for ferroelectric polarization to be locally bouquet-like or “splayed” is expressed. Filling space with splay of a single sign requires defects and in the B7 splay is accommodated in the form of periodic splay stripes spaced by defects and coupled to smectic layer undulations. Upon cooling from the isotropic phase this structure grows via a first order transition in the form of an exotic array of twisted filaments and focal conic defects that are influenced very little by classic alignment methods. By contrast, growth under conditions of confinement in rectangular topographic channels is found to produce completely new growth morphology, generating highly ordered periodic layering patterns. The resulting macroscopic order will be of great use in further exploration of the physical properties of bent-core phases and offers a route for application of difficult-to-align soft materials as are encountered in organic electronic and optical applications. PMID:21098307

  3. Improvement of decay time in nematic-liquid-crystal-loaded coplanar-waveguide-type microwave phase shifter by polymer stabilizing method

    NASA Astrophysics Data System (ADS)

    Nguyen, Thanh; Umeno, Shuhei; Higuchi, Hiroki; Kikuchi, Hirotsugu; Moritake, Hiroshi

    2014-01-01

    Polymer stabilization by UV light irradiation in nematic liquid crystals is proposed to improve the decay time of coplanar-waveguide-type microwave phase shifters. The effect of polymer concentration on the decay time of polymer-stabilized nematic liquid crystals is confirmed by a dielectric experiment on a liquid-crystal-sandwiched indium-tin-oxide (ITO) glass cell before loading into a coplanar-waveguide-type microwave phase shifter. The decay time, phase shift value, and insertion loss of microwave phase shifters with different polymer concentrations are measured. The decay time of polymer-stabilized nematic liquid crystals in the microwave phase shifter markedly decreases compared with that of pure nematic liquid crystals. It is confirmed that the use of polymer-stabilized nematic liquid crystals is effective to improve the response time of microwave phase shifters.

  4. Utilization of a liquid crystal spatial light modulator in a gray scale detour phase method for Fourier holograms.

    PubMed

    Makey, Ghaith; El-Daher, Moustafa Sayem; Al-Shufi, Kanj

    2012-11-10

    This paper introduces a new modification for the well-known binary detour phase method, which is largely used to represent Fourier holograms; the modification utilizes gray scale level control provided by a liquid crystal spatial light modulator to improve the traditional binary detour phase. Results are shown by both simulation and experiment.

  5. Shear viscosity of nematic liquid crystals in the vicinity of the smectic-A phase in alkyloxycyanobiphenyl mixtures.

    PubMed

    Jadzyn, J; Czechowski, G

    2001-11-01

    The paper presents a singular temperature behavior of the shear viscosity measured for freely flowing nematic liquid crystals in vicinity to smectic-A phase in n-octyloxycyanobiphenyl and n-hexyloxycyanobiphenyl mixtures--a system exhibiting the reentrant nematic phase.

  6. Atomistic DMD Simulations of Spontaneous Formation of Nematic and Smectic Phase in a Model Liquid Crystal

    NASA Astrophysics Data System (ADS)

    Linhananta, Apichart; Mackay, Ian

    2009-03-01

    We present atomistic discontinuous molecular dynamics (DMD) simulations of the bulk liquid crystal phases of the molecular fluid 8CB. The model is based on previous DMD models of protein folding (A. Linhananta, J. Boer and Ian MacKay, J. Chem. Phys., 2005, 122, 114901) in which all atoms including polar hydrogen, but not nonpolar hydrogen, are represented. Bonded pairs interact by infinite square well, while nonbonded atoms interact by hard-sphere square-well potentials. For the model 8CB, molecular parameters are scaled using AMBER and CHARMM force fields. The hard interaction potentials allow very rapid equilibration of ordered phases. Starting the DMD simulations from initial random states, without positional or orientation order, the 8CB systems spontaneously form ordered nematic and smectic phases. The simulations were performed in a 40 A X 40 A X 40 A box with 100 to 500 8CB molecules. At fixed temperature, as the density increases, the phase change from disorder to nematic to smectic. Finally a density-temperature phase diagram is presented.

  7. Characterization of submillisecond response optical addressing phase modulator based on low light scattering polymer network liquid crystal

    SciTech Connect

    Xiangjie, Zhao E-mail: zxjdouble@gmail.com; Cangli, Liu; Jiazhu, Duan; Dayong, Zhang; Yongquan, Luo

    2015-01-07

    Optically addressed conventional nematic liquid crystal spatial light modulator has attracted wide research interests. But the slow response speed limited its further application. In this paper, polymer network liquid crystal (PNLC) was proposed to replace the conventional nematic liquid crystal to enhance the response time to the order of submillisecond. The maximum light scattering of the employed PNLC was suppressed to be less than 2% at 1.064 μm by optimizing polymerization conditions and selecting large viscosity liquid crystal as solvent. The occurrence of phase ripple phenomenon due to electron diffusion and drift in photoconductor was found to deteriorate the phase modulation effect of the optical addressed PNLC phase modulator. The wavelength effect and AC voltage frequency effect on the on state dynamic response of phase change was investigated by experimental methods. These effects were interpreted by electron diffusion and drift theory based on the assumption that free electron was inhomogeneously distributed in accordance with the writing beam intensity distribution along the incident direction. The experimental results indicated that the phase ripple could be suppressed by optimizing the wavelength of the writing beam and the driving AC voltage frequency when varying the writing beam intensity to generate phase change in 2π range. The modulation transfer function was also measured.

  8. Experimental analysis of beam pointing system based on liquid crystal optical phase array

    NASA Astrophysics Data System (ADS)

    Shi, Yubin; Zhang, Jianmin; Zhang, Zhen

    2016-06-01

    In this paper, we propose and demonstrate an elementary non-mechanical beam aiming and steering system with a single liquid crystal optical phase array (LC-OPA) and charge-coupled device (CCD). With the conventional method of beam steering control, the LC-OPA device can realize one dimensional beam steering continuously. An improved beam steering strategy is applied to realize two dimensional beam steering with a single LC-OPA. The whole beam aiming and steering system, including an LC-OPA and a retroreflective target, is controlled by the monitor. We test the feasibility of beam steering strategy both in one dimension and in two dimension at first, then the whole system is build up based on the improved strategy. The experimental results show that the max experimental pointing error is 56 µrad, and the average pointing error of the system is 19 µrad.

  9. Multifocal axial confocal microscopic scanning with a phase-only liquid crystal spatial light modulator

    NASA Astrophysics Data System (ADS)

    Zou, Li Min; Pang, Ming Shu; Zhou, Meng Jiao; Wang, Bao Kai

    2015-02-01

    Aiming at the shortcomings of mechanical scanning methods, non-mechanical scanning method is proposed. A zoom illuminating lens which has multiple focal points is realized by introducing Liquid Crystal Spatial Light Modulator (LC-SLM) into the confocal illumination light path, and thus it produces the multifocal zoom lens axially. The axial optical sectioning in a conventional confocal microscope is achieved by beam scanning rather than mechanically moving the objective lens, which enhances the capacity of chromatography and improves the scanning speed with greater accuracy. To generate and shift the multiple axial focal points, the modulation phase bitmaps of LC-SLM is changed. Simulation results further show that multifocal axial confocal beam scanning replacing mechanical scanning can therefore be implemented.

  10. Drying, phase separation, and deposition in droplets of sunset yellow chromonic liquid crystal

    NASA Astrophysics Data System (ADS)

    Gross, Adam; Davidson, Zoey S.; Huang, Yongyang; Still, Tim; Zhou, Chao; Yodh, A. G.

    We investigate the drying process and the final deposition patterns of multi-phase sessile droplets containing aqueous lyotropic chromonic liquid crystal (LC). The experiments employ a variety of optical techniques including profilometry, polarization optical microscopy and optical coherence microscopy. An unusual hierarchical LC assembly is observed during drying; in particular, LC mesogens are first formed at the start of drying and then compartments of isotropic, nematic and columnar phases arise. Nonuniform evaporation creates concentration gradients in droplets such that LC phases emerge from the outer edge of the drop and advance to the center over the course of drying. Distinct outward flows associated with the ``coffee-ring effect'' are seen initially, but the assembly of the mesogens creates viscosity, density, and surface tension gradients that effectively introduce new convective flows and complex LC phase boundaries within the drop. Finally, we show that the final deposit shape of chromonic materials changes with rate of evaporation. We gratefully acknowledge financial support through NSF DMR12-05463, MRSEC DMR11-20901, NASA NNX08AO0G, and NSF DBI-1455613.

  11. Phase Behavior of Blends of Polymers and Smectic-A Liquid Crystals.

    PubMed

    Benmouna; Coqueret; Maschke; Benmouna

    1998-07-28

    The phase behavior of blends of polymers and smectic-A liquid crystals (LCs) is investigated using Flory-Huggins and Maier-Saupe-McMillan theories. Various examples are considered to depict the effects of the architecture and the size of the polymer together with the nature of anisotropic ordering forces on the phase diagram. The strength of these forces is characterized by a parameter alpha which is directly related to the temperature of the smectic-nematic transition. Three cases are considered depending on the value of alpha, and the corresponding phase diagrams are constructed. Substantial differences are observed in these diagrams, and the reasons for these differences are discussed. A comparative study is performed between mixtures of polymers and LCs, where the polymer is made of linear and crosslinked chains. The LC consists either of molecules with nematic ordering only or of molecules presenting both nematic and smectic-A ordering. Blends where polymer matrices are cross-linked networks are also examined. Remarkable properties are found in the nature of the phase diagrams for such mixtures. In general, it is observed that the ordering forces favor unmixing with a stronger effect for the higher smectic-A ordering. Spinodal curves are also reported for these mixtures. The effects of fluctuations near the transition temperatures are briefly discussed.

  12. The role of temperature on dielectric relaxation and conductivity mechanism of dark conglomerate liquid crystal phase

    NASA Astrophysics Data System (ADS)

    Yildiz, Alptekin; Canli, Nimet Yilmaz; Özdemir, Zeynep Güven; Ocak, Hale; Eran, Belkız Bilgin; Okutan, Mustafa

    2016-03-01

    In this study, dielectric properties and ac conductivity mechanism of the bent-core liquid crystal 3‧-{4-[4-(3,7-Dimethyloctyloxy)benzoyloxy]benzoyloxy}-4-{4-[4-[6-(1,1,3,3,5,5,5-heptamethyltrisiloxan-1yl)hex-1-yloxy]benzoyloxy]benzoyloxy}biphenyl (DBB) have been analyzed by impedance spectroscopy measurements at different temperatures. According to the polarizing microscopy results, DBB liquid crystal compound exhibits a dark conglomerate mesophase (DC[*] phase) which can be identified by the occurrence of a conglomerate of domains with opposite chirality. The chiral domains of this low-birefringent mesophase become more visible by rotating the polarizer. The variation of the real (ε‧) and imaginary (ε″) parts of dielectric constant with angular frequency and Cole-Cole curves of DBB have been analyzed. The fitting results for dispersion curves at different temperatures revealed that DBB system exhibits nearly Debye-type relaxation except for 125 °C. Moreover, it has been determined that while the relaxation frequencies shift to higher frequencies as the temperature increases from 25 °C to 125 °C, the peak intensities remarkably decrease with increasing temperature. According to Cole-Cole plot and phase angle versus frequency curve, it has been determined that DBB LC may have a possibility of utilizing as a super-capacitor at room temperature. Furthermore, it has been found that the conductivity mechanism of the DBB alters from Correlated Barrier Hoping (CBH) model to Quantum Tunneling Model (QMT) with in increasing temperature at high frequency region. In terms of CBH model, optical band gaps at 25 °C and 75 °C temperatures have also been calculated. Finally, activation energies for some selected angular frequencies have also been calculated.

  13. Chromonic liquid crystalline nematic phase exhibited in binary mixture of two liquid crystals

    SciTech Connect

    Govindaiah, T. N. Sreepad, H. R.; Sridhar, K. N.; Sridhara, G. R.; Nagaraja, N.

    2015-06-24

    A binary mixture of abietic acid and orthophosphoric acid (H{sub 3}PO{sub 4}) exhibits co-existence of biphasic region of Nematic+Isotropic (N+I), lyotropic Nematic (ND) and Smectic-G (SmG) phases. The mixture exhibits N+I, N and SmG phases at different concentrations and at different temperatures. Mixtures with all concentrations of abietic acid exhibit I→N+I→N→SmG phases sequentially when the specimen is cooled from its isotropic melt. These phases have been characterized by using differential scanning calorimetric, X-ray diffraction, and optical texture studies.

  14. Chromonic liquid crystalline nematic phase exhibited in binary mixture of two liquid crystals

    NASA Astrophysics Data System (ADS)

    Govindaiah, T. N.; Sreepad, H. R.; Sridhar, K. N.; Sridhara, G. R.; Nagaraja, N.

    2015-06-01

    A binary mixture of abietic acid and orthophosphoric acid (H3PO4) exhibits co-existence of biphasic region of Nematic+Isotropic (N+I), lyotropic Nematic (ND) and Smectic-G (SmG) phases. The mixture exhibits N+I, N and SmG phases at different concentrations and at different temperatures. Mixtures with all concentrations of abietic acid exhibit I→N+I→N→SmG phases sequentially when the specimen is cooled from its isotropic melt. These phases have been characterized by using differential scanning calorimetric, X-ray diffraction, and optical texture studies.

  15. Phase selection during crystallization of undercooled liquid eutectic lead-tin alloys

    NASA Technical Reports Server (NTRS)

    Fecht, H. J.

    1991-01-01

    During rapid solidification substantial amounts of undercooling are in general required for formation of metastable phases. Crystallization at varying levels of undercooling and melting of metastable phases were studied during slow cooling and heating of emulsified PB-Sn alloys. Besides the experimental demonstration of the reversibility of metastable phase equilibra, two different principal solidification paths have been identified and compared with the established metastable phase diagram and predictions from classical nucleation theory. The results suggest that the most probable solidification path is described by the 'step rule' resulting in the formation of metastable phases at low undercooling, whereas the stable eutectic phase mixture crystallizes without metastable phase formation at high undercooling.

  16. Stereochemical control of nonamphiphilic lyotropic liquid crystals: chiral nematic phase of assemblies separated by six nanometers of aqueous solvents.

    PubMed

    Yang, Sijie; Wang, Bing; Cui, Dawei; Kerwood, Deborah; Wilkens, Stephan; Han, Junjie; Luk, Yan-Yeung

    2013-06-13

    Unlike conventional thermotropic and lyotropic liquid crystals, nonamphiphilic lyotropic liquid crystals consist of hydrated assemblies of nonamphiphilic molecules that are aligned with a separation of about 6 nm between assemblies in an aqueous environment. This separation raises the question of how chirality, either from chiral mesogens or chiral dopants, would impact the phase as the assemblies that need to interact with each other are about 6 nm apart. Here, we report the synthesis of three stereoisomers of disodium chromonyl carboxylate, 5'DSCG-diviol, and the correlation between the molecular structure, bulk assembly, and liquid crystal formation. We observed that the chiral isomers (enantiomers 5'DSCG-(R,R)-diviol and 5'DSCG-(S,S)-diviol) formed liquid crystals while the achiral isomer 5'DSCG-meso-diviol did not. Circular dichroism indicated a chiral conformation with bisignate cotton effect. The nuclear Overhauser effect in proton NMR spectroscopy revealed conformations that are responsible for liquid crystal formation. Cryogenic transmission electron microscopy showed that chiral 5'DSCG-diviols form assemblies with crossings. Interestingly, only planar alignment of the chiral nematic phase was observed in liquid crystal cells with thin spacers. The homeotropic alignment that permitted a fingerprint texture was obtained only when the thickness of the liquid crystal cell was increase to above ~500 μm. These studies suggest that hydrated assemblies of chiral 5'DSCG-diviol can interact with each other across a 6 nm separation in an aqueous environment by having a twist angle of about 0.22° throughout the sample between the neighboring assemblies. PMID:23688325

  17. Phase diagrams for the blue phases of highly chiral liquid crystals

    NASA Astrophysics Data System (ADS)

    Bowling, Miriam B.; Collings, Peter J.; Booth, Christopher J.; Goodby, John W.

    1993-11-01

    Polarizing microscopy and optical-activity measurements are used to determine the phase diagram for the blue phases of chiral-racemic mixtures of terephthaloyloxy-bis-4-(2'-methylbutyl) benzoate. Contrary to an earlier report, it is the second blue phase (BP II) rather than the first blue phase (BP I) that is not stable relative to the other blue phases at high chirality. With this development, all phase diagrams for the blue phases reported to date have the same topology. Using similar data for two other highly chiral systems, it is found that a simple scaling of the temperature and chiral-fraction axes produces phase diagrams in quantitative agreement with the present results. Thus, in spite of differences in molecular structure, the number of chiral centers, and phase-transition temperatures, these three systems possess remarkably similar phase diagrams and lend evidence for a universal phase diagram for the blue phases.

  18. Density-functional theory and Monte Carlo simulations of the phase behavior of a simple model liquid crystal.

    PubMed

    Giura, Stefano; Schoen, Martin

    2014-08-01

    We consider the phase behavior of a simple model of a liquid crystal by means of modified mean-field density-functional theory (MMF DFT) and Monte Carlo simulations in the grand canonical ensemble (GCEMC). The pairwise additive interactions between liquid-crystal molecules are modeled via a Lennard-Jones potential in which the attractive contribution depends on the orientation of the molecules. We derive the form of this orientation dependence through an expansion in terms of rotational invariants. Our MMF DFT predicts two topologically different phase diagrams. At weak to intermediate coupling of the orientation dependent attraction, there is a discontinuous isotropic-nematic liquid-liquid phase transition in addition to the gas-isotropic liquid one. In the limit of strong coupling, the gas-isotropic liquid critical point is suppressed in favor of a fluid- (gas- or isotropic-) nematic phase transition which is always discontinuous. By considering three representative isotherms in parallel GCEMC simulations, we confirm the general topology of the phase diagram predicted by MMF DFT at intermediate coupling strength. From the combined MMF DFT-GCEMC approach, we conclude that the isotropic-nematic phase transition is very weakly first order, thus confirming earlier computer simulation results for the same model [see M. Greschek and M. Schoen, Phys. Rev. E 83, 011704 (2011)].

  19. Liquid crystal alignment at macroscopically isotropic polymer surfaces: Effect of an isotropic-nematic phase transition

    NASA Astrophysics Data System (ADS)

    Aryasova, Natalie; Reznikov, Yuri

    2016-09-01

    We study the effect of an isotropic-nematic (I -N ) phase transition on the liquid crystal alignment at untreated polymer surfaces. We demonstrate that the pattern at the untreated substrate in the planar cell where the other substrate is uniformly rubbed strongly depends on the temperature gradient across the cell during the I -N phase transition, being macroscopically isotropic if the untreated substrate is cooled faster, but becoming almost homogeneous along the rubbing direction in the opposite temperature gradient. We interpret the observed effect using complementary models of heat transfer and nematic elasticity. Based on the heat transfer model we show that the asymmetric temperature conditions in our experiments provide unidirectional propagation of the I -N interface during the phase transition and determine the initial director orientation pattern at the test's untreated surface. Using the Frank-Oseen model of nematic elasticity, we represent the three-dimensional director field in the nematic cell as a two-dimensional (2D) pattern at the untreated surface and perform 2D numeric simulations. The simulations explain the experimental results: Different initial director orientations at the untreated surface evolve into different stationary patterns.

  20. The effect of liquid-liquid phase separation of glass on the properties and crystallization behavior

    NASA Technical Reports Server (NTRS)

    Li, J. Z.

    1985-01-01

    A theoretical discussion is given of the phase separation mechanism of amorphous materials. This includes nucleus growth, spinoidal decomposition, and nuclei agglomeration and coarsening. Various types of glass are analyzed.

  1. Isothermal solidification stage during transient liquid-phase bonding single-crystal superalloys

    NASA Astrophysics Data System (ADS)

    Sheng, Naicheng; Liu, Jide; Jin, Tao; Sun, Xiaofeng; Hu, Zhuangqi

    2014-04-01

    In this work, the isothermal solidification stage during transient liquid-phase bonding (TLP) single-crystal superalloys has been investigated. Experiments were performed to ascertain the bonding microstructures and the kinetics during the isothermal solidification. The results have shown that the isothermal solidification stage deviates from the standard parabolic TLP models. Lots of the borides with fine, short bar and acicular morphologies formed in the diffusion affected zone (DAZ) in the thick wall and thin wall substrate specimens at the isothermal solidification stage. Electron probe microanalysis results have shown that there exists B composition peak in the DAZ. Examination of the bonding kinetics presented that there are three stages in the isothermal solidification stage: initial stage, transient stage and final stage with different growth velocity of the isothermal solidification zone (ISZ). And the relationship of the width of the ISZ with the square root of the bonding time didn't satisfy the parabolic relationship. Based on the microstructures and kinetics observed, a film ISZ mechanism is proposed, and a model is constructed to illustrate the isothermal solidification stage during bonding single-crystal superalloys.

  2. Light-melt adhesive based on dynamic carbon frameworks in a columnar liquid-crystal phase.

    PubMed

    Saito, Shohei; Nobusue, Shunpei; Tsuzaka, Eri; Yuan, Chunxue; Mori, Chigusa; Hara, Mitsuo; Seki, Takahiro; Camacho, Cristopher; Irle, Stephan; Yamaguchi, Shigehiro

    2016-01-01

    Liquid crystal (LC) provides a suitable platform to exploit structural motions of molecules in a condensed phase. Amplification of the structural changes enables a variety of technologies not only in LC displays but also in other applications. Until very recently, however, a practical use of LCs for removable adhesives has not been explored, although a spontaneous disorganization of LC materials can be easily triggered by light-induced isomerization of photoactive components. The difficulty of such application derives from the requirements for simultaneous implementation of sufficient bonding strength and its rapid disappearance by photoirradiation. Here we report a dynamic molecular LC material that meets these requirements. Columnar-stacked V-shaped carbon frameworks display sufficient bonding strength even during heating conditions, while its bonding ability is immediately lost by a light-induced self-melting function. The light-melt adhesive is reusable and its fluorescence colour reversibly changes during the cycle, visualizing the bonding/nonbonding phases of the adhesive. PMID:27373592

  3. Frequency-shift vs phase-shift characterization of in-liquid quartz crystal microbalance applications

    SciTech Connect

    Montagut, Y. J.; Garcia, J. V.; Jimenez, Y.; Arnau, A.; March, C.; Montoya, A.

    2011-06-15

    The improvement of sensitivity in quartz crystal microbalance (QCM) applications has been addressed in the last decades by increasing the sensor fundamental frequency, following the increment of the frequency/mass sensitivity with the square of frequency predicted by Sauerbrey. However, this sensitivity improvement has not been completely transferred in terms of resolution. The decrease of frequency stability due to the increase of the phase noise, particularly in oscillators, made impossible to reach the expected resolution. A new concept of sensor characterization at constant frequency has been recently proposed. The validation of the new concept is presented in this work. An immunosensor application for the detection of a low molecular weight contaminant, the insecticide carbaryl, has been chosen for the validation. An, in principle, improved version of a balanced-bridge oscillator is validated for its use in liquids, and applied for the frequency shift characterization of the QCM immunosensor application. The classical frequency shift characterization is compared with the new phase-shift characterization concept and system proposed.

  4. Frequency-shift vs phase-shift characterization of in-liquid quartz crystal microbalance applications.

    PubMed

    Montagut, Y J; García, J V; Jiménez, Y; March, C; Montoya, A; Arnau, A

    2011-06-01

    The improvement of sensitivity in quartz crystal microbalance (QCM) applications has been addressed in the last decades by increasing the sensor fundamental frequency, following the increment of the frequency/mass sensitivity with the square of frequency predicted by Sauerbrey. However, this sensitivity improvement has not been completely transferred in terms of resolution. The decrease of frequency stability due to the increase of the phase noise, particularly in oscillators, made impossible to reach the expected resolution. A new concept of sensor characterization at constant frequency has been recently proposed. The validation of the new concept is presented in this work. An immunosensor application for the detection of a low molecular weight contaminant, the insecticide carbaryl, has been chosen for the validation. An, in principle, improved version of a balanced-bridge oscillator is validated for its use in liquids, and applied for the frequency shift characterization of the QCM immunosensor application. The classical frequency shift characterization is compared with the new phase-shift characterization concept and system proposed. PMID:21721715

  5. Frequency-shift vs phase-shift characterization of in-liquid quartz crystal microbalance applications

    NASA Astrophysics Data System (ADS)

    Montagut, Y. J.; García, J. V.; Jiménez, Y.; March, C.; Montoya, A.; Arnau, A.

    2011-06-01

    The improvement of sensitivity in quartz crystal microbalance (QCM) applications has been addressed in the last decades by increasing the sensor fundamental frequency, following the increment of the frequency/mass sensitivity with the square of frequency predicted by Sauerbrey. However, this sensitivity improvement has not been completely transferred in terms of resolution. The decrease of frequency stability due to the increase of the phase noise, particularly in oscillators, made impossible to reach the expected resolution. A new concept of sensor characterization at constant frequency has been recently proposed. The validation of the new concept is presented in this work. An immunosensor application for the detection of a low molecular weight contaminant, the insecticide carbaryl, has been chosen for the validation. An, in principle, improved version of a balanced-bridge oscillator is validated for its use in liquids, and applied for the frequency shift characterization of the QCM immunosensor application. The classical frequency shift characterization is compared with the new phase-shift characterization concept and system proposed.

  6. Light-melt adhesive based on dynamic carbon frameworks in a columnar liquid-crystal phase

    PubMed Central

    Saito, Shohei; Nobusue, Shunpei; Tsuzaka, Eri; Yuan, Chunxue; Mori, Chigusa; Hara, Mitsuo; Seki, Takahiro; Camacho, Cristopher; Irle, Stephan; Yamaguchi, Shigehiro

    2016-01-01

    Liquid crystal (LC) provides a suitable platform to exploit structural motions of molecules in a condensed phase. Amplification of the structural changes enables a variety of technologies not only in LC displays but also in other applications. Until very recently, however, a practical use of LCs for removable adhesives has not been explored, although a spontaneous disorganization of LC materials can be easily triggered by light-induced isomerization of photoactive components. The difficulty of such application derives from the requirements for simultaneous implementation of sufficient bonding strength and its rapid disappearance by photoirradiation. Here we report a dynamic molecular LC material that meets these requirements. Columnar-stacked V-shaped carbon frameworks display sufficient bonding strength even during heating conditions, while its bonding ability is immediately lost by a light-induced self-melting function. The light-melt adhesive is reusable and its fluorescence colour reversibly changes during the cycle, visualizing the bonding/nonbonding phases of the adhesive. PMID:27373592

  7. Aggregation Properties and Liquid Crystal Phase of a Dye Based on Naphthalenetetracarboxylic Acid

    NASA Astrophysics Data System (ADS)

    Tomasik, Michelle; Collings, Peter

    2007-03-01

    R003 is a dye produced for thin film optical components by Optiva, Inc.^1 made from the sulfonation of the dibenzimidazole derivative of naphthalenetetracarboxylic acid. Its molecular structure is very different from the aggregating food dye previously investigated in our laboratory^2 and R003 forms a liquid crystal phase at significantly lower concentrations. We have performed polarizing microscopy, absorption spectroscopy, and x-ray diffraction experiments in order to determine the phase diagram and aggregate structure. In addition, we have included both translational and orientational entropy in the theoretical analysis of the aggregation process, and have used a more realistic lineshape in analyzing the absorption data. Our results indicate that the ``bond energy'' for molecules in an aggregate is even larger than for the previously studied dye and that the aggregate structure has a cross-sectional area equal to two or three molecular areas rather than one.^1Lazarev, P., N. Ovchinnikova, M. Paukshto, SID Int. Symp. Digest of Tech. Papers, San Jose, California, June XXXII, 571 (2001).^2V. R. Horowitz, L. A. Janowitz, A. L. Modic, P. A. Heiney, and P. J. Collings, Phys. Rev. E 72, 041710 (2005).

  8. Studies of the underlying mechanisms for optical nonlinearities of blue phase liquid crystals (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Chen, Chun-Wei; Khoo, Iam Choon; Zhao, Shuo; Lin, Tsung-Hsien; Ho, Tsung-Jui

    2015-10-01

    We have investigated the mechanisms responsible for nonlinear optical processes occurring in azobenzene-doped blue phase liquid crystals (BPLC), which exhibit two thermodynamically stable BPs: BPI and BPII. In coherent two wave-mixing experiments, a slow (minutes) and a fast (few milliseconds) side diffractions are observed. The underlying mechanisms were disclosed by monitoring the dynamics of grating formation and relaxation as well as by some supplementary experiments. We found the photothermal indexing and dye/LC intermolecular torque leading to lattice distortion to be the dominant mechanisms for the observed nonlinear response in BPLC. Moreover, the response time of the nonlinear optical process varied with operating phase. The rise time of the thermal indexing process was in good agreement with our findings on the temperature dependence of BP refractive index: τ(ISO) > τ(BPI) > τ(BPII). The relaxation time of the torque-induced lattice distortion was analogue to its electrostriction counterpart: τ'(BPI) > τ'(BPII). In a separate experiment, lattice swelling with selective reflection of <110> direction changed from green to red was also observed. This was attributable to the isomerization-induced change in cholesteric pitch, which directly affects the lattice spacing. The phenomenon was confirmed by measuring the optical rotatory power of the BPLC.

  9. Liquid crystal-templated conducting organic polymers

    DOEpatents

    Stupp, Samuel I.; Hulvat, James F.

    2004-01-20

    A method of preparing a conductive polymeric film, includes providing a liquid crystal phase comprising a plurality of hydrophobic cores, the phase on a substrate, introducing a hydrophobic component to the phase, the component a conductive polymer precursor, and applying an electric potential across the liquid crystal phase, the potential sufficient to polymerize the said precursor.

  10. Numerical simulation and experimental study of transient liquid phase bonding of single crystal superalloys

    NASA Astrophysics Data System (ADS)

    Ghoneim, Adam

    The primary goals of the research in this dissertation are to perform a systematic study to identify and understand the fundamental cause of prolonged processing time during transient liquid phase bonding of difficult-to-bond single crystal Ni-base materials, and use the acquired knowledge to develop an effective way to reduce the isothermal solidification time without sacrificing the single crystalline nature of the base materials. To achieve these objectives, a multi-scale numerical modeling approach, that involves the use of a 2-D fully implicit moving-mesh Finite Element method and a Cellular Automata method, was developed to theoretically investigate the cause of long isothermal solidification times and determine a viable way to minimize the problem. Subsequently, the predictions of the theoretical models are experimentally validated. Contrary to previous suggestions, numerical calculations and experimental verifications have shown that enhanced intergranular diffusivity has a negligible effect on solidification time in cast superalloys and that another important factor must be responsible. In addition, it was found that the concept of competition between solute diffusivity and solubility as predicted by standard analytical TLP bonding models and reported in the literature as a possible cause of long solidification times is not suitable to explain salient experimental observations. In contrast, however, this study shows that the problem of long solidification times, which anomalously increase with temperature is fundamentally caused by departure from diffusion controlled parabolic migration of the liquid-solid interface with holding time during bonding due to a significant reduction in the solute concentration gradient in the base material. Theoretical analyses showed it is possible to minimize the solidification time and prevent formation of stray-grains in joints between single crystal substrates by using a composite powder mixture of brazing alloy and base

  11. Electrically tunable microlens arrays based on polarization-independent optical phase of nano liquid crystal droplets dispersed in polymer matrix.

    PubMed

    Yu, Ji Hoon; Chen, Hung-Shan; Chen, Po-Ju; Song, Ki Hoon; Noh, Seong Cheol; Lee, Jae Myeong; Ren, Hongwen; Lin, Yi-Hsin; Lee, Seung Hee

    2015-06-29

    Electrically tunable focusing microlens arrays based on polarization independent optical phase of nano liquid crystal droplets dispersed in polymer matrix are demonstrated. Such an optical medium is optically isotropic which is so-called an optically isotropic liquid crystals (OILC). We not only discuss the optical theory of OILC, but also demonstrate polarization independent optical phase modulation based on the OILC. The experimental results and analytical discussion show that the optical phase of OILC microlens arrays results from mainly orientational birefringence which is much larger than the electric-field-induced birefringence (or Kerr effect). The response time of OILC microlens arrays is fast~5.3ms and the tunable focal length ranges from 3.4 mm to 3.8 mm. The potential applications are light field imaging systems, 3D integrating imaging systems and devices for augment reality.

  12. Leaning-type polar smectic-C phase in a freely suspended bent-core liquid crystal film.

    PubMed

    Chattham, Nattaporn; Tamba, Maria-Gabriela; Stannarius, Ralf; Westphal, Eduard; Gallardo, Hugo; Prehm, Marko; Tschierske, Carsten; Takezoe, Hideo; Eremin, Alexey

    2015-03-01

    A rich variety of responsive behavior occurs in complex structured fluids due to their lower symmetries. On the other hand, fluid disorder tends to increase the symmetry of liquid crystal mesophases. Here, we report direct evidence for the existence of a mesophase with CS symmetry. The observations are based on optical studies of director inversion walls in freely suspended films in electric fields under obliquely incident light. This phase is distinguished by the polarization lying in the molecular tilt plane in freely suspended films. Such a low-symmetry polar fluid phase has been long predicted to occur in bent-core liquid crystals. The stability of this phase is attributed to the bent shape of the mesogens and dominating dispersion interactions.

  13. Electrically tunable microlens arrays based on polarization-independent optical phase of nano liquid crystal droplets dispersed in polymer matrix.

    PubMed

    Yu, Ji Hoon; Chen, Hung-Shan; Chen, Po-Ju; Song, Ki Hoon; Noh, Seong Cheol; Lee, Jae Myeong; Ren, Hongwen; Lin, Yi-Hsin; Lee, Seung Hee

    2015-06-29

    Electrically tunable focusing microlens arrays based on polarization independent optical phase of nano liquid crystal droplets dispersed in polymer matrix are demonstrated. Such an optical medium is optically isotropic which is so-called an optically isotropic liquid crystals (OILC). We not only discuss the optical theory of OILC, but also demonstrate polarization independent optical phase modulation based on the OILC. The experimental results and analytical discussion show that the optical phase of OILC microlens arrays results from mainly orientational birefringence which is much larger than the electric-field-induced birefringence (or Kerr effect). The response time of OILC microlens arrays is fast~5.3ms and the tunable focal length ranges from 3.4 mm to 3.8 mm. The potential applications are light field imaging systems, 3D integrating imaging systems and devices for augment reality. PMID:26191743

  14. Constant pressure and temperature molecular dynamics simulation of a fully hydrated liquid crystal phase dipalmitoylphosphatidylcholine bilayer.

    PubMed Central

    Tu, K; Tobias, D J; Klein, M L

    1995-01-01

    We report a constant pressure and temperature molecular dynamics simulation of a fully hydrated liquid crystal (L alpha) phase bilayer of dipalmitoylphosphatidylcholine at 50 degrees C and 28 water molecules/lipid. We have shown that the bilayer is stable throughout the 1550-ps simulation and have demonstrated convergence of the system dimensions. Several important aspects of the bilayer structure have been investigated and compared favorably with experimental results. For example, the average positions of specific carbon atoms along the bilayer normal agree well with neutron diffraction data, and the electron density profile is in accord with x-ray diffraction results. The hydrocarbon chain deuterium order parameters agree reasonably well with NMR results for the middles of the chains, but the simulation predicts too much order at the chain ends. In spite of the deviations in the order parameters, the hydrocarbon chain packing density appears to be essentially correct, inasmuch as the area/lipid and bilayer thickness are in agreement with the most refined experimental estimates. The deuterium order parameters for the glycerol and choline groups, as well as the phosphorus chemical shift anisotropy, are in qualitative agreement with those extracted from NMR measurements. PMID:8599662

  15. Soft-core particles freezing to form a quasicrystal and a crystal-liquid phase.

    PubMed

    Archer, A J; Rucklidge, A M; Knobloch, E

    2015-07-01

    Systems of soft-core particles interacting via a two-scale potential are studied. The potential is responsible for peaks in the structure factor of the liquid state at two different but comparable length scales and a similar bimodal structure is evident in the dispersion relation. Dynamical density functional theory in two dimensions is used to identify two unusual states of this system: a crystal-liquid state, in which the majority of the particles are located on lattice sites but a minority remains free and so behaves like a liquid, and a 12-fold quasicrystalline state. Both are present even for deeply quenched liquids and are found in a regime in which the liquid is unstable with respect to modulations on the smaller scale only. As a result, the system initially evolves towards a small-scale crystal state; this state is not a minimum of the free energy, however, and so the system subsequently attempts to reorganize to generate the lower-energy larger-scale crystals. This dynamical process generates a disordered state with quasicrystalline domains and takes place even when this large scale is linearly stable, i.e., it is a nonlinear process. With controlled initial conditions, a perfect quasicrystal can form. The results are corroborated using Brownian dynamics simulations. PMID:26274178

  16. Quantum Hall Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Radzihovsky, Leo

    2003-03-01

    Liquid-crystals, defined as states of matter intermediate in their properties between fully disordered isotropic liquids and fully ordered crystals are ubiquitous in nature. Recent transport measurements on two-dimensional electron systems in moderate magnetic fields suggest the existence of a spontaneously orientationally-ordered, compressible liquid state. I will discuss electronic liquid-crystals interpretation of these experiments, focusing on a recently proposed quantum Hall nematic state that is predicted to exhibit a novel, highly anisotropic q^3 density-director mode and other interesting phenomenology.

  17. Synthesis of 1,4-Bis(phenylethynyl)benzenes and Their Application as Blue Phase Liquid Crystal Composition

    PubMed Central

    Li, Ning; Li, Zhengqiang; Zhang, Xing; Hua, Ruimao

    2013-01-01

    A number of 1,4-bis(phenylethynyl)benzene derivatives (BPEBs) and their analogues with different numbers of side-substitute fluorine atoms on benzene rings, and alkyl chains, ethoxyl groups, fluorine atoms and trifluoromethyl groups as the end groups have been synthesized. The effects of the different substituents on their properties such as thermal behavior of melting point and clearing point, the temperature of nematic phase, optical anisotropy and dielectric anisotropy have been well investigated, and it has been found that some BPEBs have a wide range of the nematic phase temperature with high optical anisotropy (Δn) and acceptable dielectric anisotropy (Δɛ), which have been applied as the crucial compositions to constitute a liquid crystal mixture having the properties of Δɛ = 29.0 and Δn = 0.283 at 25 °C. With the addition of the chiral dopant to the obtained liquid crystal mixture, blue phase liquid crystal with a blue phase temperature range of 8 °C has been achieved. PMID:24287903

  18. Formation of smectic phases in binary liquid crystal mixtures with a huge length ratio.

    PubMed

    Kapernaum, Nadia; Knecht, Friederike; Hartley, C Scott; Roberts, Jeffrey C; Lemieux, Robert P; Giesselmann, Frank

    2012-01-01

    A system of two liquid-crystalline phenylpyrimidines differing strongly in molecular length was studied. The phase diagram of these two chemically similar mesogens, with a length ratio of 2, was investigated, and detailed X-ray diffraction and electrooptical measurements were performed. The phase diagram revealed a destabilization of the nematic phase, which is present in the pure short compound, while the smectic state was stabilized. The short compound forms smectic A and smectic C phases, whereas the longer compound forms a broad smectic C phase and a narrow higher-ordered smectic phase. Nevertheless, in the mixtures, the smectic C phase is destabilized and disappears rapidly, whereas smectic A is the only stable phase observed over a broad concentration range. In addition, the smectic translational order parameters as well as the tilt angles of the mixtures are reduced. The higher-ordered smectic phase of the longer mesogen was identified as a smectic F phase.

  19. Formation of smectic phases in binary liquid crystal mixtures with a huge length ratio

    PubMed Central

    Knecht, Friederike; Hartley, C Scott; Roberts, Jeffrey C; Lemieux, Robert P; Giesselmann, Frank

    2012-01-01

    Summary A system of two liquid-crystalline phenylpyrimidines differing strongly in molecular length was studied. The phase diagram of these two chemically similar mesogens, with a length ratio of 2, was investigated, and detailed X-ray diffraction and electrooptical measurements were performed. The phase diagram revealed a destabilization of the nematic phase, which is present in the pure short compound, while the smectic state was stabilized. The short compound forms smectic A and smectic C phases, whereas the longer compound forms a broad smectic C phase and a narrow higher-ordered smectic phase. Nevertheless, in the mixtures, the smectic C phase is destabilized and disappears rapidly, whereas smectic A is the only stable phase observed over a broad concentration range. In addition, the smectic translational order parameters as well as the tilt angles of the mixtures are reduced. The higher-ordered smectic phase of the longer mesogen was identified as a smectic F phase. PMID:23019439

  20. Optical studies on smectic phases in binary mixture of liquid crystals

    NASA Astrophysics Data System (ADS)

    Govindaiah, T. N.; Sreepad, H. R.; Nagaraja, N.; Sridhara, G. R.; Ravi, H. R.

    2015-06-01

    The binary mixture of two non-mesogenic compounds viz., Didodecyl dimethyl ammonium bromide (DDAB) and ethylene glycol (EG) exhibits different liquid crystalline phase's at large range of concentrations and temperature. The concentrations with lower / higher percentage of DDAB exhibit I-SmA-SmC*-SmE-K sequentially when the specimen is cooled from isotropic phase. Different liquid crystalline phases observed in the mixture were studied using DSC, X-ray, and Optical microscopic techniques. The temperature variations of optical anisotropy have also been discussed.

  1. Smectic-A and smectic-C phases and phase transitions in 8¯S5 liquid-crystal-aerosil gels

    NASA Astrophysics Data System (ADS)

    Freelon, B.; Ramazanoglu, M.; Chung, P. J.; Page, R. N.; Lo, Yuan-Tse; Valdivia, P.; Garland, C. W.; Birgeneau, R. J.

    2011-09-01

    High-resolution x-ray scattering studies of the nonpolar thermotropic liquid crystal 4-n-pentylphenylthiol-4'-n-octyloxybenzoate (8¯S5) in aerosil gel nanonetworks reveal that the aerosil-induced disorder significantly alters both the nematic to smectic-A and smectic-A to smectic-C phase transitions. The limiting 8¯S5 smectic-A correlation length follows a power-law dependence on the aerosil density in quantitative agreement with the limiting lengths measured previously in other smectic-A liquid crystal gels. The smectic-A to smectic-C liquid crystalline phase transition is altered fundamentally by the presence of the aerosil gel. The onset of the smectic-C phase remains relatively sharp but there is an extended coexistence region where smectic-A and smectic-C domains can exist.

  2. Critical behavior at the isotropic-to-nematic phase transition in a bent-core liquid crystal

    NASA Astrophysics Data System (ADS)

    Wiant, D.; Stojadinovic, S.; Neupane, K.; Sharma, S.; Fodor-Csorba, K.; Jákli, A.; Gleeson, J. T.; Sprunt, S.

    2006-03-01

    Magnetic birefringence and dynamic light scattering measurements of orientational order parameter fluctuations at the isotropic-nematic phase transition of a bent-core liquid crystal reveal a pretransitional temperature dependence consistent with the standard Landau-deGennes mean field theory. However, as follows: the transition in the bent-core compound is more weakly first order (TNI-T*≈0.4°C) , the leading Landau coefficient is ˜30 times lower, the viscosity associated with nematic order fluctuations is ˜10 times higher, and the density change is ˜10 times lower, than typically observed in calamitic (rod-shaped) liquid crystals. One consistent explanation for these anomalies is an optically isotropic phase composed of microscopic complexes or “clusters” of bent-core molecules.

  3. Acoustical and optical investigations of the size effect in nematic-isotropic phase transition in liquid crystal microemulsions

    NASA Astrophysics Data System (ADS)

    Maksimochkin, G. I.; Pasechnik, S. V.; Lukin, A. V.

    2015-07-01

    The absorption of ultrasound (at a frequency of 2.7 MHz) and the depolarized light transmission and scattering (at a wavelength of 630 nm) in liquid crystal (LC) emulsions have been studied during the nematic-isotropic (N-I) phase transition in LC droplets with radii ranging from 150 to 2300 nm. The obtained acoustical and optical data are used to determine the influence of the droplet size on characteristics of the N-I phase transition. It is shown that the acoustical and optical characteristics of LC emulsions have good prospects to be used for the investigation of phase transitions in submicron samples.

  4. Tailoring the interfaces between nematic liquid crystal emulsions and aqueous phases via layer-by-layer assembly.

    PubMed

    Tjipto, Elvira; Cadwell, Katie D; Quinn, John F; Johnston, Angus P R; Abbott, Nicholas L; Caruso, Frank

    2006-10-01

    We report the assembly of polyelectrolyte multilayer (PEM) films at the interfaces of thermotropic liquid crystal (LC) droplets dispersed in an aqueous phase. Exposure of PEM-coated droplets to surfactant slowed the bipolar-to-radial ordering transition of the LCs by 2 orders of magnitude relative to naked droplets. This shows that PEMs can be used to influence the interactions of analytes with the LC cores of the droplets, allowing tuning of the LC emulsion sensing properties.

  5. Closed-loop adaptive-optics system with a liquid-crystal television as a phase retarder

    NASA Astrophysics Data System (ADS)

    Dou, Rensheng; Giles, Michael K.

    1995-07-01

    We present a closed-loop adaptive-optics system that uses a liquid-crystal television (LCTV) as a phase retarder. The system consists of a LCTV inserted into one leg of a Mach-Zehnder interferometer so that one measures the wave-front function by analyzing the interferogram using a video CCD camera and a computer and corrects the wave-front distortion by placing the conjugate function on the LCTV. Experimental results are presented.

  6. Compact 4 cm aperture transmissive liquid crystal optical phased array for free-space optical communications

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Hua; Mahajan, Milind; Taber, Donald; Wen, Bing; Winker, Bruce

    2005-08-01

    There is a critical need for high bandwidth, high availability free-space optical communication links between the battlefield and the global information grid. Compact large aperture transceivers with low size, weight and power (SWaP) are needed to initiate and maintain communication links involving airborne platforms. The transceiver optical beam director typically contains fine and coarse steering stages. Existing beam director technology is based on electro-mechanical gimbaled mirrors with large SWaP that hinders deployment on many airborne platforms. To address the need for compact beam directors, we designed, fabricated, and tested an optical phased array (OPA) based on electro-optic dual frequency liquid crystal technology. This OPA has a transmissive architecture that enables a lower system SWaP, as compared to conventional reflective OPA. It has an 8 μm pixel pitch and steers over a 2.5° field of regard in one dimension at 1.55 μm. Two such OPAs can be stacked to steer in two dimensions. It has four independently addressable 1 cm x 4 cm regions arranged in a linear array to produce a continuous 4 cm x 4 cm aperture. The device incorporates novel addressing schemes to reduce the number of control channels by over an order of magnitude compared to conventional OPA addressing methods. It also utilizes proprietary low-loss transparent conductive TransconTM film for low optical absorption in the infrared. The OPA uses a custom multi-channel controller circuit operating at a 500 Hz frame rate. We present results on OPA design, fabrication, and optical performance on steering.

  7. Liquid crystal devices with continuous phase variation based on high-permittivity thin films

    NASA Astrophysics Data System (ADS)

    Willekens, Oliver; Neyts, Kristiaan; Beeckman, Jeroen

    2016-03-01

    Most liquid crystal devices use transparent conductive electrodes such as indium tin oxide (ITO) to apply a potential difference in order to achieve electro-optic switching. As an alternative, we study a device with narrow metallic electrodes in combination with dielectric layers with large dielectric permittivity. In this approach the applied voltage can be a continuous function of the lateral distance from the electrode line. Simulations for a one-dimensional beam-steering device show that the switching of the liquid crystal (LC) director depends indeed on the distance from the addressing electrodes and on the value of the relative permittivity. We show that in a device with electrodes spaced 60 µm apart, the LC director halfway between the electrodes shows a considerable reorientation, when a dielectric layer with permittivity of Epsilonr = 550 is used, whereas no reorientation is observed for the uncoated reference sample at the same voltage. An added advantage is that the proposed configuration only contains dielectric materials, without resistive losses, which means that almost no heat is dissipated. This indicates that this technology could be used in low-power LC devices. The results show that using dielectric thin films with high relative permittivity in liquid crystal devices could form a cost-efficient and low-power alternative to many LC technologies where a gradient electric field is desirable.

  8. Intrachain flexibility constraints on phase stabilities and odd-even effects in multiple smectic-A and nematic liquid crystals

    SciTech Connect

    Dowell, F.

    1988-07-01

    The importance of the flexibility of n-alkyl tail chains in real liquid-crystal systems is reviewed. Two new microscopic, molecular statistical-physics theories (a full statistical theory and a simpler but accurate approximate theory) for the intrachain constraints on the n-alkyl tail-chain flexibility are presented and are compared with each other and with an old, more approximate theory for tail-chain flexibility used in earlier papers. The new approximate approach is computationally much faster than the full statistical method and is the first treatment to generate and explain odd-even effects in multiple smectic-A phases and the first treatment to generate and explain odd-even effects in smectic-A and nematic phases without resorting to ad hoc or arbitrarily adjustable fits to experimental data. Phase stabilities and odd-even effects for various thermodynamic and molecular ordering properties are calculated in the smectic-A/sub 1/, smectic-A/sub d/, and nematic liquid-crystal phases and the isotropic liquid phase using the new approximate method. Some predictions and accompanying physical explanations are made for various systems that have not yet been chemically synthesized and/or experimentally studied.

  9. Dichroic Liquid Crystal Displays

    NASA Astrophysics Data System (ADS)

    Bahadur, Birendra

    * Effect of Thickness * Impact of Order Parameter * Impact of the Host * Impact of Polarizer * Colour Applications * Multiplexing * QUARTER WAVE PLATE DICHROIC DISPLAYS * Operational Principle and Display Configuration11-13 * Electro-Optical Performance * DYE-DOPED TN DISPLAYS * Threshold Characteristic, Contrast Ratio and Switching Speed * PHASE CHANGE EFFECT DICHROIC LCDs * Theoretical Background * Threshold Characteristic and Molecular Orientation * MOLECULAR ORIENTATION DURING FIELD-INDUCED PHASE TRANSITION WITH HOMOGENEOUS WALL ALIGNMENT * MOLECULAR ORIENTATION DURING FIELD-INDUCED PHASE TRANSITION WITH HOMEOTROPIC WALL ALIGNMENT * Contrast Ratio, Transmission, Brightness and Switching Speed3,7,10,198-214 * Memory or Reminiscent Contrast * Electro-optical Performance vs. Temperature * Multiplexing Phase Change Dichroic LCDs * DOUBLE CELL DICHROIC LCDs3,9,14-17,232-234 * Double Cell Nematic Dichroic LCD3,8,9,14,15,233 * Double Cell One Pitch Cholesteric LCD16,17 * Double Cell Phase Change Dichroic LCD214,232 * POSITIVE MODE DICHROIC LCDS3,8,9 * Positive Mode Heilmeier Cells3,8,9,43,77,78,235-238 * USING PLEOCHROIC DYES3,8,9,43,235-238 * USING NEGATIVE DICHROIC DYES3,8,9,63,77,78156 * DUAL FREQUENCY ADDRESSED DICHROIC DISPLAYS75,238 * Positive Mode Dichroic LCDs Using λ/4 Plate * Positive Mode Double Cell Dichroic LCD * Positive Mode Dichroic LCDs Using Special Electrode patterns7,8,239-241 * Positive Mode Phase Change Dichroic LCDs3,8,9,230,243-248 * Dichroic LCDs Using an Admixture of Pleochroic and Negative Dichroic Dyes78,118 * SUPERTWIST DICHROIC EFFECT (SDE) DISPLAYS21-23 * FERROELECTRIC DICHROIC LCDs24-27 * Devices Using A Single Polarizer * Devices Using No Polarizer24-27 * POLYMER DISPERSED DICHROIC LCDs28-30,252-259 * DICHROIC POLYMER LIQUID CRYSTAL DISPLAYS * Heilmeier Type Displays * Guest-Host Cell Using an Admixture Of L.C. Polymer and Low Molecular Weight Liquid Crysta As Host * Polymeric Ferroelectric Dichroic LCDs * SMECTIC A DICHROIC LCDs * Laser

  10. Lipid Liquid-Crystal Phase Change Induced through near-Infrared Irradiation of Entrained Graphene Particles.

    PubMed

    Quinn, Matthew D J; Du, Joanne; Boyd, Ben J; Hawley, Adrian; Notley, Shannon M

    2015-06-23

    Lipid packing is intimately related to the geometry of the lipids and the forces that drive self-assembly. Here, the photothermal response of a cubic liquid-crystalline phase formed using phytantriol in the presence of low concentrations of pristine graphene was evaluated. Small-angle X-ray scattering showed the reversible phase changes from cubic to hexagonal to micellar due to localized heating through irradiation with near-infrared (NIR) light and back to cubic after cooling.

  11. Self-organization in phase separation of a lyotropic liquid crystal into cellular, network and droplet morphologies.

    PubMed

    Iwashita, Yasutaka; Tanaka, Hajime

    2006-02-01

    Phase separation is one of the most fundamental physical phenomena that controls the morphology of heterogeneous structures. Phase separation of a binary mixture of simple liquids produces only two morphologies: a bicontinuous or a droplet structure in the case of a symmetric or an asymmetric composition, respectively. For complex fluids, there is a possibility to produce other interesting morphologies. We found that a network structure of the minority phase can also be induced transiently on phase separation if the dynamics of the minority phase are much slower than those of the majority phase. Here we induce a cellular structure of the minority phase intentionally with the help of its smectic ordering, using phase separation of a lyotropic liquid crystal into the isotropic and smectic phase. We can control the three morphologies, cellular, network and droplet structures, solely by changing the heating rate. We demonstrate that the kinetic interplay between phase separation and smectic ordering is a key to the morphological selection. This may provide a new route to the formation of network and cellular morphologies in soft materials.

  12. Induced stabilization of columnar phases in binary mixtures of discotic liquid crystals.

    PubMed

    Cienega-Cacerez, Octavio; García-Alcántara, Consuelo; Moreno-Razo, José Antonio; Díaz-Herrera, Enrique; Sambriski, Edward John

    2016-01-28

    Three discotic liquid-crystalline binary mixtures, characterized by their extent of bidispersity in molecular thickness, were investigated with molecular dynamics simulations. Each equimolar mixture contained A-type (thin) and B-type (thick) discogens. The temperature-dependence of the orientational order parameter reveals that A-type liquid samples produce ordered phases more readily, with the (hexagonal) columnar phase being the most structured variant. Moderately and strongly bidisperse mixtures produce globally-segregated samples for temperatures corresponding to ordered phases; the weakly bidisperse mixture displays microheterogeneities. Ordered phases in the B-type liquid are induced partially by the presence of the A-type fluid. In the moderately bidisperse mixture, order is induced through orientational frustration: a mixed prenematic-like phase precedes global segregation to yield nematic and columnar mesophases upon further cooling. In the strongly bidisperse mixture, order is induced less efficiently through a paranematic-like mechanism: a highly-ordered A-type fluid imparts order to B-type discogens found at the interface of a fully-segregated sample. This ordering effect permeates into the disordered B-type domain until nematic and columnar phases emerge upon further cooling. At sufficiently low temperatures, all samples investigated exhibit the (hexagonal) columnar mesophase.

  13. The polymorphic phases of the hexaalkanoyloxytriphenylene liquid crystals, as studied by deuterium NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Goldfarb, D.; Lifshitz, E.; Zimmermann, H.; Luz, Z.

    1985-06-01

    Deuterium NMR spectra are reported for several specifically deuterated hexaalkanoyloxytriphenylenes in their corresponding liquid crystalline phases. The higher homologs of this series are polymorphic and exhibit a variety of discotic mesophases, including both biaxial (D0 and D1) and uniaxial (D2) columnar phases. The ordering characteristics of these phases are studied using the quadrupolar splittings of the aromatic and aliphatic deuterons. The results show that during the transition from the biaxial D1 to the axial D2 phase the major susceptibility tensor switch orientation, apparently due to strong tilting of the molecules with respect to the columnar axis in the biaxial phase. Characteristic features which appear in the spectra of these phases are interpreted in terms of intercolumnar jumps of mesogen molecules.

  14. Relaxational dynamics in the glassy, supercooled liquid, and orientationally disordered crystal phases of a polymorphic molecular material

    NASA Astrophysics Data System (ADS)

    Jiménez-Ruiz, M.; González, M. A.; Bermejo, F. J.; Miller, M. A.; Birge, Norman O.; Cendoya, I.; Alegría, A.

    1999-04-01

    The relaxational dynamics of the ambient pressure phases of ethyl alcohol are studied by means of measurements of frequency dependent dielectric susceptibility. A comparison of the α relaxation in the supercooled liquid and in the rotator phase crystal indicates that the molecular rotational degrees of freedom are the dominant contribution to structural relaxation at temperatures near the glass transition, the flow processes having lesser importance. Below the glass transition a secondary β relaxation is resolved for the orientational and structural glasses. Computer molecular-dynamics results suggest that localized molecular librations, strongly coupled to the low-frequency internal molecular motions, are responsible for this secondary relaxation.

  15. Optical real-time kinoform for on-axis phase-only correlation using liquid crystal television

    NASA Astrophysics Data System (ADS)

    Paul-Hus, Gilles; Sheng, Yunlong

    1994-01-01

    We use a commercially available liquid crystal television (LCTV) for encoding real-time on- axis continuous phase-only filter (POF) in a Vander Lugt type optical correlator. Theory and experiments show that the filter on the LCTV, that has phase mismatching and coupled amplitude modulation, retains a term, that is the true POF with a diffraction efficiency of about 70%, plus a zero order spot. The correlation output is a superposition of the POF correlation with an image of the input. The filter has advantages of on-axis POF correlation: high light efficiency and utilization of all the available space bandwidth product of the LCTV. Optical experimental results are shown.

  16. Voltage-controlled liquid-crystal terahertz phase shifter with indium-tin-oxide nanowhiskers as transparent electrodes.

    PubMed

    Yang, Chan-Shan; Tang, Tsung-Ta; Chen, Po-Han; Pan, Ru-Pin; Yu, Peichen; Pan, Ci-Ling

    2014-04-15

    Indium-tin-oxide nanowhiskers were employed as transparent electrodes in a liquid-crystal terahertz phase shifter. Transmittance of the device was as high as ∼75%. Phase shift exceeding π/2 at 1.0 THz is achieved in a ∼500  μm-thick cell. The driving voltage required for the device operating as a quarter-wave plate was as low as 17.68 V (rms), an improvement of nearly an order of magnitude over previous work.

  17. Improved high order grating method to realize wide angle beam steering on liquid crystal optical phased array

    NASA Astrophysics Data System (ADS)

    Wu, Liang; Wang, Xiangru; Xiong, Caidong; Huang, Ziqiang; Du, Jing; Tan, Qinggui; Li, Man; Wu, Shuanghong; Qiu, Qi

    2015-11-01

    To achieve a wider scanning range of liquid crystal optical phased array (LC-OPA), in this paper, a novel method of improved high order grating (i-HOG) is proposed in one device without introducing any other devices. The method of i-HOG breaks through the traditional ideas of modulo 𝟐𝛑 phase and takes the fringe effect into account to have a multi order extension. Subsequently, the method is verified by numerical simulation showing that it realizes a scanning range of wider than 20 degrees and even wider.

  18. Applying gray-scaled detour phase hologram on liquid crystal on silicon spatial light modulator (LCoS-SLM)

    NASA Astrophysics Data System (ADS)

    Sayem El-Daher, Moustafa

    2016-03-01

    In order to solve the representation problem of computer-generated holograms, multiple algorithms have been devised. One of which is the well-known detour phase method. This method has recently been modified to be optimized to display the generated hologram on twisted nematic spatial light modulators. In this paper, we apply the modified gray-scaled detour phase holograms on another type of spatial light modulators, which is of utmost importance in the field, namely the reflective liquid crystal on silicon spatial light modulator.

  19. Liquid-Crystal Point-Diffraction Interferometer

    NASA Technical Reports Server (NTRS)

    Mercer, Carolyn R.

    1996-01-01

    Liquid-crystal point-diffraction interferometer (LCPDI) invented to combine flexible control of liquid-crystal phase-shifts with robustness of point-diffraction interferometers. Produces interferograms indicative of shapes of wavefronts of laser beams having passed through or reflected from objects of interest. Interferograms combined in computers to produce phase maps describing wavefronts.

  20. Effects of nanoparticle doping on the phase transitional behaviour of ferroelectric liquid crystal Langmuir-Blodgett composite films

    NASA Astrophysics Data System (ADS)

    Kaur, Ramneek; Raina, K. K.

    2015-12-01

    Langmuir-Blodgett films of ferroelectric liquid crystals (FLCs) doped with a low concentration of functionalized Al: ZnO (AZO) nanoparticles were prepared and characterized. Pressure-area isotherms show that the nanoparticles as well as FLC composite systems have the capability to form stable monolayers at the air-water interface. The molecular interaction between nanoparticles and FLC molecules increased during barrier compression, which resulted in increased surface pressure. We observed various phases in isotherms with increasing concentration of nanoparticles in the FLC matrix. An X-ray diffraction profile at a low angle confirmed that FLCs retain their layer structure at a low concentration doping of AZO nanoparticles in the FLC matrix. Atomic force microscopy images indicate that low wt% composites are uniformly deposited without disturbing the translation behaviour of SmC* liquid crystals.

  1. Chirality-preserving growth of helical filaments in the B4 phase of bent-core liquid crystals.

    PubMed

    Chen, Dong; Maclennan, Joseph E; Shao, Renfan; Yoon, Dong Ki; Wang, Haitao; Korblova, Eva; Walba, David M; Glaser, Matthew A; Clark, Noel A

    2011-08-17

    The growth of helical filaments in the B4 liquid-crystal phase was investigated in mixtures of the bent-core and calamitic mesogens NOBOW and 8CB. Freezing-point depression led to nucleation of the NOBOW B4 phase directly from the isotropic phase in the mixtures, forming large left- and right-handed chiral domains that were easily observed in the microscope. We show that these domains are composed of homochiral helical filaments formed in a nucleation and growth process that starts from a nucleus of arbitrary chirality and continues with chirality-preserving growth of the filaments. A model that accounts for the observed local homochirality and phase coherence of the branched filaments is proposed. This model will help in providing a better understanding of the nature of the B4 phase and controlling its growth and morphology for applications, such as the use of the helical nanophase as a nanoheterogeneous medium. PMID:21692442

  2. Induction of ferroelectricity in the B2 phase of a liquid crystal composed of achiral bent-core molecules

    NASA Astrophysics Data System (ADS)

    Etxebarria, J.; Folcia, C. L.; Ortega, J.; Ros, M. B.

    2003-04-01

    We report the observation of a transition from the antiferroelectric B2 phase to a ferroelectric phase in a liquid crystal composed of achiral bent-core (banana-shaped) molecules. The transition is induced by an electric field of magnitude larger than the switching threshold and is not reversible, i.e., the original B2 phase does not reappear upon field removal. The transformation is accompanied by a dramatic texture change, resulting in an almost optically isotropic structure in the absence of field. The ferroelectric character assigned to the structure is based on the electro-optic behavior of the material and on previously reported dielectric measurements. A short-pitch smectic-C*-type structure is proposed for the ferroelectric phase.

  3. Determination of birefringence and slow axis distribution using an interferometric measurement system with liquid crystal phase shifter.

    PubMed

    Nose, Toshiaki; Kamata, Keisuke; Takeuchi, Toru; Okano, Keiju; Fujita, Naoko; Muraguchi, Hajime; Ozaki, Noriaki; Honma, Michinori; Ito, Ryouta

    2014-11-01

    It is known that liquid crystal (LC) cells are useful as compact and easy-to-handle phase shifters that are readily coupled into the optics of standard microscope systems. Here, a uniformly aligned molecular LC phase shifter is introduced into a polarization microscope to attain a birefringence imaging system, using the phase-shift interferometric technique. Since the birefringence can be determined accurately only when the optical axis of the sample is parallel or perpendicular to the slow axis (variable axis) of the LC phase shifter, an improved data analysis method is proposed for determining the birefringence independently of the direction; a simple method of determining the slow axis distribution is also demonstrated. Measurements of the birefringence and slow axis distribution properties of a potato starch particle are demonstrated to confirm the novel determination method. PMID:25402881

  4. Semiconductor liquid crystal composition and methods for making the same

    DOEpatents

    Alivisatos, A. Paul; Li, Liang-shi

    2005-04-26

    Semiconductor liquid crystal compositions and methods for making such compositions are disclosed. One embodiment of the invention is directed to a liquid crystal composition including a solvent and semiconductor particles in the solvent. The solvent and the semiconductor particles are in an effective amount in the liquid crystal composition to form a liquid crystal phase.

  5. Magnetically actuated liquid crystals.

    PubMed

    Wang, Mingsheng; He, Le; Zorba, Serkan; Yin, Yadong

    2014-07-01

    Ferrimagnetic inorganic nanorods have been used as building blocks to construct liquid crystals with optical properties that can be instantly and reversibly controlled by manipulating the nanorod orientation using considerably weak external magnetic fields (1 mT). Under an alternating magnetic field, they exhibit an optical switching frequency above 100 Hz, which is comparable to the performance of commercial liquid crystals based on electrical switching. By combining magnetic alignment and lithography processes, it is also possible to create patterns of different polarizations in a thin composite film and control over the transmittance of light in particular areas. Developing such magnetically responsive liquid crystals opens the door toward various applications, which may benefit from the instantaneous and contactless nature of magnetic manipulation.

  6. Electron paramagnetic resonance studies of a viscous nematic liquid crystal: Evidence counter to a second-order phase change

    NASA Technical Reports Server (NTRS)

    Shutt, W. E.; Gelerinter, E.; Fryburg, G. C.; Sheley, C. F.

    1972-01-01

    The ordering in a viscous, nematic, liquid crystal was studied using vanadyl acetyl acetonate and several nitroxides as paramagnetic probes. The ordering curve for VAAC at both K-band and X-band shows a slope discontinuity at a reduced temperature of 0.85. This discontinuity is caused by the tumbling time of the VAAC becoming comparable with the hyperfine splitting. The slope discontinuity is not present in the ordering curves of the nitroxides. The results are taken as evidence counter to the presence of a second-order phase transition.

  7. Research on the effect of coherent beam combination based on array of liquid crystal optical phased arrays

    NASA Astrophysics Data System (ADS)

    Yang, Zhenming; Kong, Lingjiang; Xiao, Feng; Chen, Jian

    2014-12-01

    On the basis of Coherent Beam Combination(CBC) based on Array of Liquid Crystal Optical Phased Arrays(LCOPA array), two major contributions are made in this article. Firstly, grating lobes and side lobes of combined beam are analyzed. Furthermore, according to interference theory the methods to suppress grating lobes and side lobes are put forward. Secondly, a new beam quality factor Q(θ0) is proposed to evaluate the beam quality of combined beam and several influence factors are discussed. These analysis results help to obtain combined beam with better beam quality.

  8. Fast response liquid crystal devices

    NASA Astrophysics Data System (ADS)

    Wu, Yung-Hsun

    LC-based VOA. In Chapter 7, we report a new device called axially-symmetric sheared polymer network liquid crystals (AS-SPNLC) and use it as LC devices. Through analyzing the structure of this axially-symmetric SPNLC, we construct a 3-D model to explain the observed phenomena. An axially-symmetric sheared polymer network liquid crystal has several attractive features: (1) it is polarization independent, (2) it has gradient phase change, and (3) its response time is fast. It can be used for polarization converter and divergent LC lens. In addition, a new method for simultaneously measuring the phase retardation and optic axis of a compensation film is demonstrated using an axially-symmetric sheared polymer network liquid crystal. By overlaying a tested compensation film with a calibrated SPNLC cell between crossed polarizers, the optic axis and phase retardation value of the compensation film can be determined. This simple technique can be used for simultaneously measuring the optic axis and phase retardations of both A- and C-plates. These compensation films have been used extensively in wide-view LCD industry. Therefore, this method will make an important impact to the LCD industry.

  9. The Effects of Highly Chiral Dopants on the Smectic Phases of Liquid Crystals Remarkably Wide Intermediate Phases

    SciTech Connect

    Jaradat,S.; Gleeson, H.; Roberts, N.; Wang, Y.

    2006-01-01

    A series of liquid crystalline mixtures that exhibit remarkably stable 4-layer intermediate phases, with phase ranges of around 30 {sup o}C, are reported. The mixtures are formed from a selenium-containing antiferroelectric material combined with up to 9% (by weight) of a highly chiral dopant. Various experimental methods including X-ray scattering and electro-optic techniques were employed in order to determine a set of physical parameters for each of the mixtures, such as smectic layer spacing, steric and optical tilt angles and spontaneous polarization. It is shown that the antiferroelectric phase is lost at dopant concentrations between 5 and 6%, when the stability of the 4-layer intermediate phase becomes significantly enhanced. This transition is associated with a decrease in the ratio of the spontaneous to flexoelectric coupling coefficients in the system. The combined observations suggest that molecular conformation is a more significant factor in stabilising the intermediate phases than chirality. The data are compared.

  10. Miniature Compressive Ultra-spectral Imaging System Utilizing a Single Liquid Crystal Phase Retarder

    NASA Astrophysics Data System (ADS)

    August, Isaac; Oiknine, Yaniv; Abuleil, Marwan; Abdulhalim, Ibrahim; Stern, Adrian

    2016-03-01

    Spectroscopic imaging has been proved to be an effective tool for many applications in a variety of fields, such as biology, medicine, agriculture, remote sensing and industrial process inspection. However, due to the demand for high spectral and spatial resolution it became extremely challenging to design and implement such systems in a miniaturized and cost effective manner. Using a Compressive Sensing (CS) setup based on a single variable Liquid Crystal (LC) retarder and a sensor array, we present an innovative Miniature Ultra-Spectral Imaging (MUSI) system. The LC retarder acts as a compact wide band spectral modulator. Within the framework of CS, a sequence of spectrally modulated images is used to recover ultra-spectral image cubes. Using the presented compressive MUSI system, we demonstrate the reconstruction of gigapixel spatio-spectral image cubes from spectral scanning shots numbering an order of magnitude less than would be required using conventional systems.

  11. Miniature Compressive Ultra-spectral Imaging System Utilizing a Single Liquid Crystal Phase Retarder

    PubMed Central

    August, Isaac; Oiknine, Yaniv; AbuLeil, Marwan; Abdulhalim, Ibrahim; Stern, Adrian

    2016-01-01

    Spectroscopic imaging has been proved to be an effective tool for many applications in a variety of fields, such as biology, medicine, agriculture, remote sensing and industrial process inspection. However, due to the demand for high spectral and spatial resolution it became extremely challenging to design and implement such systems in a miniaturized and cost effective manner. Using a Compressive Sensing (CS) setup based on a single variable Liquid Crystal (LC) retarder and a sensor array, we present an innovative Miniature Ultra-Spectral Imaging (MUSI) system. The LC retarder acts as a compact wide band spectral modulator. Within the framework of CS, a sequence of spectrally modulated images is used to recover ultra-spectral image cubes. Using the presented compressive MUSI system, we demonstrate the reconstruction of gigapixel spatio-spectral image cubes from spectral scanning shots numbering an order of magnitude less than would be required using conventional systems. PMID:27004447

  12. The role of hydrogen bonding in the phase behaviour of supramolecular liquid crystal dimers

    NASA Astrophysics Data System (ADS)

    Martínez-Felipe, Alfonso; Imrie, Corrie T.

    2015-11-01

    The phase behaviour of equimolar mixtures of 4-octyloxybenzoic acid, OOBA, and either 1-(4-butylazobenzene-4‧-oxy)-6-(4-oxypyridine)pentane, BuABO5OPyr, or 1-(4-butylazobenzene-4‧-oxy)-6-(4-oxypyridine)hexane, BuABO6OPyr, is reported. OOBA exhibits enantiotropic smectic C and nematic phases, whereas BuABO5OPyr and BuABO6OPyr are not liquid crystalline. Both the OOBA/BuABO5OPyr and OOBA/BuABO6OPyr equimolar mixtures show an enantiotropic smectic A phase identified using X-ray diffraction and polarised light microscopy. The liquid crystallinty of the mixtures is attributed, in part, to the formation of a 1:1 hydrogen-bonded complex between OOBA and either BuABO5OPyr or BuABO6OPyr. Differences in the transitional properties of the mixtures are accounted for in terms of the average shapes of these 1:1 complexes. Temperature dependent FTIR spectroscopy shows, however, that the formation of the complex is not quantitative in the mixtures but instead a complex mixture exists over the complete temperature range studied, involving the 1:1 complex, both cyclic and open acid dimers, free acid and hence, free BuABOnOPyr molecules.

  13. Tunable diffraction grating using ultraviolet-light-induced spatial phase modulation in dual-frequency liquid crystal

    SciTech Connect

    Lin, P.-T.; Liang Xiao; Ren Hongwen; Wu, S.-T.

    2004-08-16

    An electrically tunable diffraction phase grating using ultraviolet (UV)-light-induced spatial dielectric modulation of a dual-frequency liquid crystal (DFLC) cell is demonstrated. A photomask with transparent and opaque stripes was used for fabricating the grating. In the UV-exposed stripes, the negative dielectric anisotropy ({delta}{epsilon}) tolane compound of the DFLC mixture is partially polymerized resulting in a decreased threshold voltage as compared to that of the unexposed region. Upon applying a constant voltage, the phase difference between the adjacent pixels is produced. The first-order diffraction efficiency reaches {approx}60% which agrees well with the simulation results. Due to the dual-frequency addressing at 30 V{sub rms}, the response time of the DFLC phase grating was measured to be {approx}1 ms at room temperature.

  14. Tunable diffraction grating using ultraviolet-light-induced spatial phase modulation in dual-frequency liquid crystal

    NASA Astrophysics Data System (ADS)

    Lin, Pao-Tai; Liang, Xiao; Ren, Hongwen; Wu, Shin-Tson

    2004-08-01

    An electrically tunable diffraction phase grating using ultraviolet (UV)-light-induced spatial dielectric modulation of a dual-frequency liquid crystal (DFLC) cell is demonstrated. A photomask with transparent and opaque stripes was used for fabricating the grating. In the UV-exposed stripes, the negative dielectric anisotropy (Δɛ) tolane compound of the DFLC mixture is partially polymerized resulting in a decreased threshold voltage as compared to that of the unexposed region. Upon applying a constant voltage, the phase difference between the adjacent pixels is produced. The first-order diffraction efficiency reaches ˜60% which agrees well with the simulation results. Due to the dual-frequency addressing at 30Vrms, the response time of the DFLC phase grating was measured to be ˜1ms at room temperature.

  15. Phase Determination of Second-Order Surface Susceptibility Tensor of Liquid Crystal Monolayer Using Ultra-Thin Film Local Oscillator

    NASA Astrophysics Data System (ADS)

    Sei, Masaki; Nagayama, Kohei; Kajikawa, Kotaro; Ishii, Hisao; Seki, Kazuhiko; Kondo, Katsumi; Matsumoto, Yoshiyasu; Ouchi, Yukio

    1998-04-01

    We demonstrated full determination of second-order nonlinear susceptibility of a 4‧-n-octyl-4-cyanobiphenyl (8CB) liquid crystal (LC) monolayer adsorbed on a second-harmonic (SH) active polyimide (PI) substrate. In order to separate the SH signal of the LC film from that of the PI film, we adopted an interferometry technique of second-harmonic generation (SHG) using an ultra-thin film local oscillator. We have found a variety of phases in the components of susceptibility: those of χzii and χizi are almost the same but the phase of χzzz differs by 80° from the other two. The phases of the components of the surface susceptibility tensor are not always identical. This fact indicates that the surface SH response is more complicated than what we expected.

  16. Sequence of Four Orthogonal Smectic Phases in an Achiral Bent-Core Liquid Crystal: Evidence for the SmAPα Phase

    NASA Astrophysics Data System (ADS)

    Panarin, Y. P.; Nagaraj, M.; Sreenilayam, S.; Vij, J. K.; Lehmann, A.; Tschierske, C.

    2011-12-01

    The mesomorphic properties of an achiral bent-core liquid crystal derived from 4-cyanoresorcinol are studied by polarizing optical microscopy, x-ray diffraction, and second harmonic electro-optic response. It shows a novel sequence of four nontilted or orthogonal smectic phases on cooling: SmA-SmAPR-SmAPX-SmAPA. Here SmAPX is the new orthogonal polar uniaxial smectic phase. The electric-field-induced transformations in the SmAPX phase give rise to two biaxial states separated by a uniaxial one. The second harmonic electro-optic response in this phase is interpreted in terms of the polar interaction with the electric field. A comparison of the experimental results with the next-nearest-neighbor model for the structure of the SmAPX phase shows it to be an SmAPα phase.

  17. Molecular dynamics simulation of the nematic liquid crystal phase in the presence of an intense magnetic field

    NASA Astrophysics Data System (ADS)

    Satoh, Katsuhiko

    2006-04-01

    The influence of an intense external field on the dynamics of the nematic liquid crystal phase is investigated using a molecular dynamics simulation for the Gay-Berne nematogen under isobaric-isothermal conditions. The molecular dynamics as a function of the second-rank orientational order parameter ⟨P2⟩ for a system consisting of a nematic liquid crystal in the presence of an intense magnetic field is compared with that of a similar system without the field. The translational motion of molecules is determined as a function of the translational diffusion coefficient tensor and the anisotropy and compared with the values predicted theoretically. The rotational dynamics of molecules is analyzed using the first- and the second-rank orientational time correlation functions. The translational diffusion coefficient parallel with respect to the director is constrained by the intense field, although the perpendicular one is decreased as the ⟨P2⟩ is increased, just as it is in the system without the field. However, no essential effect of the strong magnetic field is observed in the rotational molecular dynamics. Further, the rotational diffusion coefficient parallel with respect to the director obtained from the first-rank orientational time correlation function in the simulation is qualitatively in agreement with that in the real nematic liquid crystalline molecules. The ⟨P2⟩ dependence of the rotational diffusion coefficient for the system with the intense magnetic field shows a tendency similar to that for the system without the field.

  18. Optical modulation in nematic phase of halogen substituted hydrogen bonded liquid crystals

    NASA Astrophysics Data System (ADS)

    Vijayakumar, V. N.; Madhu Mohan, M. L. N.

    2012-01-01

    A series of halogen-substituted hydrogen-bonded liquid crystalline complexes have been designed and synthesised. A successful attempt has been made to form complementary hydrogen bonding between the dodecyloxy benzoic acid (12BAO) and halogen-substituted benzoic acids and the physical properties exhibited by the individual complexes are studied. The complexes obtained are analysed by polarising optical microscope (POM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and dielectric studies. The formation of complementary hydrogen bond is confirmed through FTIR spectra. An interesting feature of this series is the observation of a field-induced transition (FiT) in nematic phase. Another interesting phenomenon is the observation of a new smectic X phase (worm-like texture) in all the synthesised complexes. Dielectric relaxation studies in the smectic C phase of these hydrogen bonded complexes along with the Arrhenius and the Cole-Cole plots are discussed. Optical tilt angle in smectic C phase and the corresponding fitted data analysis concur with the Mean field theory prediction.

  19. Fractional quantum Hall and nematic liquid crystal phases in a variable density two-dimensional electron system

    NASA Astrophysics Data System (ADS)

    Brandsen, S.; Pollanen, J.; Eisenstein, J. P.; Pfieffer, L. N.; West, K. W.

    2015-03-01

    At high magnetic field, Coulomb interactions in a two-dimensional electron system (2DES) lead to a wide variety of collective phases, including the fractional quantum Hall fluids and the nematic liquid crystals found at high Landau level occupancy. In order to examine the density dependence of these quantum states, we have developed a new sample architecture consisting of a highly doped, yet transparent, conducting cap layer grown atop a conventional modulation-doped heterojunction where the 2DES resides. Separate contacts to the 2DES and the cap layer allow the latter to function as a gate for tuning the 2DES density both before and after low temperature illumination. After illustrating the basic functioning of this structure, we will report results on the density dependence of various quantum Hall and nematic liquid crystal phases of the 2DES. This work was supported by the Institute for Quantum Information and Matter, an NSF Physics Frontiers Center with support of the Gordon and Betty Moore Foundation through Grant GBMF1250.

  20. Study of the isotropic to smectic-A phase transition in liquid crystal and acetone binary mixtures.

    PubMed

    Sigdel, Krishna P; Iannacchione, Germano S

    2010-11-01

    The first-order transition from the isotropic (I) to smectic-A (Sm A) phase in the liquid crystal 4-cyano-4(')-decylbiphenyl (10CB) doped with the polar solvent acetone (ace) has been studied as a function of solvent concentration by high-resolution ac-calorimetry. Heating and cooling scans were performed for miscible 10CB+ace samples having acetone mole fractions from x(ace)=0.05 (1 wt %) to 0.36 (10%) over a wide temperature range from 310 to 327 K. Two distinct first-order phase transition features are observed in the mixture whereas there is only one transition (I-Sm A) in the pure 10CB for that particular temperature range. Both calorimetric features reproduce on repeated heating and cooling scans and evolve with increasing x(ace) with the high-temperature feature relatively stable in temperature but reduced in size while the low-temperature feature shifts dramatically to lower temperature and exhibits increased dispersion. The coexistence region increases for the low-temperature feature but remains fairly constant for the high-temperature feature as a function of x(ace). Polarizing optical microscopy supports the identification of a smectic phase below the high-temperature heat capacity signature indicating that the low-temperature feature represents an injected smectic-smectic phase transition. These effects may be the consequence of screening the intermolecular potential of the liquid crystals by the solvent that stabilizes a weak smectic phase intermediate of the isotropic and pure smectic-A.

  1. Shape measurement by use of liquid-crystal display fringe projection with two-step phase shifting.

    PubMed

    Quan, Chenggen; Tay, Cho Jui; Kang, Xin; He, Xiao Yuan; Shang, Huai Min

    2003-05-01

    The use of an optical fringe projection method with two-step phase shifting for three-dimensional (3-D) shape measurement of small objects is described. In this method, sinusoidal linear fringes are projected onto an object's surface by a programmable liquid-crystal display (LCD) projector and a long-working-distance microscope (LWDM). The image of the fringe pattern is captured by another LWDM and a CCD camera and processed by a phase-shifting technique. Usually a minimum of three phase-shifted fringe patterns is necessary for extraction of the object shape. In this method, a new algorithm based on a two-step phase-shifting technique produces the 3-D object shape. Unlike in the conventional method, phase unwrapping is performed directly by use of an arccosine function without the need for a wrapped phase map. Hence, shape measurement can be speeded up greatly with this approach. A small coin is evaluated to demonstrate the validity of the proposed measurement method, and the experimental results are compared with those of the four-step phase-shifting method and the conventional mechanical stylus method. PMID:12737465

  2. Lipid-Based Liquid Crystals As Carriers for Antimicrobial Peptides: Phase Behavior and Antimicrobial Effect.

    PubMed

    Boge, Lukas; Bysell, Helena; Ringstad, Lovisa; Wennman, David; Umerska, Anita; Cassisa, Viviane; Eriksson, Jonny; Joly-Guillou, Marie-Laure; Edwards, Katarina; Andersson, Martin

    2016-05-01

    The number of antibiotic-resistant bacteria is increasing worldwide, and the demand for novel antimicrobials is constantly growing. Antimicrobial peptides (AMPs) could be an important part of future treatment strategies of various bacterial infection diseases. However, AMPs have relatively low stability, because of proteolytic and chemical degradation. As a consequence, carrier systems protecting the AMPs are greatly needed, to achieve efficient treatments. In addition, the carrier system also must administrate the peptide in a controlled manner to match the therapeutic dose window. In this work, lyotropic liquid crystalline (LC) structures consisting of cubic glycerol monooleate/water and hexagonal glycerol monooleate/oleic acid/water have been examined as carriers for AMPs. These LC structures have the capability of solubilizing both hydrophilic and hydrophobic substances, as well as being biocompatible and biodegradable. Both bulk gels and discrete dispersed structures (i.e., cubosomes and hexosomes) have been studied. Three AMPs have been investigated with respect to phase stability of the LC structures and antimicrobial effect: AP114, DPK-060, and LL-37. Characterization of the LC structures was performed using small-angle X-ray scattering (SAXS), dynamic light scattering, ζ-potential, and cryogenic transmission electron microscopy (Cryo-TEM) and peptide loading efficacy by ultra performance liquid chromatography. The antimicrobial effect of the LCNPs was investigated in vitro using minimum inhibitory concentration (MIC) and time-kill assay. The most hydrophobic peptide (AP114) was shown to induce an increase in negative curvature of the cubic LC system. The most polar peptide (DPK-060) induced a decrease in negative curvature while LL-37 did not change the LC phase at all. The hexagonal LC phase was not affected by any of the AMPs. Moreover, cubosomes loaded with peptides AP114 and DPK-060 showed preserved antimicrobial activity, whereas particles loaded

  3. Phase-field-crystal modeling of glass-forming liquids: spanning time scales during vitrification, aging, and deformation.

    PubMed

    Berry, Joel; Grant, Martin

    2014-06-01

    Two essential elements required to generate a glass transition within phase-field-crystal (PFC) models are outlined based on observed freezing behaviors in various models of this class. The central dynamic features of glass formation in simple binary liquids are qualitatively reproduced across 12 orders of magnitude in time by applying a physically motivated time scaling to previous PFC simulation results. New aspects of the equilibrium phase behavior of the same binary model system are also outlined, aging behavior is explored in the moderate and deeply supercooled regimes, and aging exponents are extracted. General features of the elastic and plastic responses of amorphous and crystalline PFC solids under deformation are also compared and contrasted. PMID:25019772

  4. Smectic order, pinning, and phase transition in a smectic-liquid-crystal cell with a random substrate.

    PubMed

    Zhang, Quan; Radzihovsky, Leo

    2013-02-01

    We study smectic-liquid-crystal order in a cell with a heterogeneous substrate imposing surface random positional and orientational pinnings. Proposing a minimal random elastic model, we demonstrate that, for a thick cell, the smectic state without a rubbed substrate is always unstable at long scales and, for weak random pinning, is replaced by a smectic glass state. We compute the statistics of the associated substrate-driven distortions and the characteristic smectic domain size on the heterogeneous substrate and in the bulk. We find that for weak disorder, the system exhibits a three-dimensional temperature-controlled phase transition between a weakly and strongly pinned smectic glass states akin to the Cardy-Ostlund phase transition. We explore experimental implications of the predicted phenomenology and suggest that it provides a plausible explanation for the experimental observations on polarized light microscopy and x-ray scattering. PMID:23496537

  5. Smectic order, pinning, and phase transition in a smectic-liquid-crystal cell with a random substrate

    NASA Astrophysics Data System (ADS)

    Zhang, Quan; Radzihovsky, Leo

    2013-02-01

    We study smectic-liquid-crystal order in a cell with a heterogeneous substrate imposing surface random positional and orientational pinnings. Proposing a minimal random elastic model, we demonstrate that, for a thick cell, the smectic state without a rubbed substrate is always unstable at long scales and, for weak random pinning, is replaced by a smectic glass state. We compute the statistics of the associated substrate-driven distortions and the characteristic smectic domain size on the heterogeneous substrate and in the bulk. We find that for weak disorder, the system exhibits a three-dimensional temperature-controlled phase transition between a weakly and strongly pinned smectic glass states akin to the Cardy-Ostlund phase transition. We explore experimental implications of the predicted phenomenology and suggest that it provides a plausible explanation for the experimental observations on polarized light microscopy and x-ray scattering.

  6. Smectic order, pinning, and phase transition in a smectic-liquid-crystal cell with a random substrate.

    PubMed

    Zhang, Quan; Radzihovsky, Leo

    2013-02-01

    We study smectic-liquid-crystal order in a cell with a heterogeneous substrate imposing surface random positional and orientational pinnings. Proposing a minimal random elastic model, we demonstrate that, for a thick cell, the smectic state without a rubbed substrate is always unstable at long scales and, for weak random pinning, is replaced by a smectic glass state. We compute the statistics of the associated substrate-driven distortions and the characteristic smectic domain size on the heterogeneous substrate and in the bulk. We find that for weak disorder, the system exhibits a three-dimensional temperature-controlled phase transition between a weakly and strongly pinned smectic glass states akin to the Cardy-Ostlund phase transition. We explore experimental implications of the predicted phenomenology and suggest that it provides a plausible explanation for the experimental observations on polarized light microscopy and x-ray scattering.

  7. Phase-field-crystal modeling of glass-forming liquids: spanning time scales during vitrification, aging, and deformation.

    PubMed

    Berry, Joel; Grant, Martin

    2014-06-01

    Two essential elements required to generate a glass transition within phase-field-crystal (PFC) models are outlined based on observed freezing behaviors in various models of this class. The central dynamic features of glass formation in simple binary liquids are qualitatively reproduced across 12 orders of magnitude in time by applying a physically motivated time scaling to previous PFC simulation results. New aspects of the equilibrium phase behavior of the same binary model system are also outlined, aging behavior is explored in the moderate and deeply supercooled regimes, and aging exponents are extracted. General features of the elastic and plastic responses of amorphous and crystalline PFC solids under deformation are also compared and contrasted.

  8. Simultaneous calorimetric and polarization microscopy investigations of light induced changes over phase transitions in a liquid crystal-napthopyran mixture

    NASA Astrophysics Data System (ADS)

    Paoloni, S.; Mercuri, F.; Marinelli, M.; Pizzoferrato, R.; Zammit, U.; Kosa, T.; Sukhomlinova, L.; Taheri, B.

    2015-10-01

    We have studied the specific heat and the thermal conductivity in a 4-(n-octyl)-4'-cyanobiphenyl liquid crystal (LC)-photochromic molecules mixture, before, during, and after the photo-activation of the dispersed photochromic molecules, over both the smectic A-nematic and the nematic-isotropic phase transitions. The evaluation of the specific heat has enabled the determination of the changes of the phase transition characteristics induced by the photochromic molecules photoisomerization, while that of the thermal conductivity could be used to monitor the modifications induced in the average LC molecular orientation. The polarization microscopy imaging of the sample texture constituted a valuable support for the interpretation of the obtained thermal conductivity results.

  9. Liquid crystal orientation control in photonic liquid crystal fibers

    NASA Astrophysics Data System (ADS)

    Chychlowski, M. S.; Nowinowski-Kruszelnicki, E.; Woliński, T. R.

    2011-05-01

    Similarly to liquid crystal displays technology in photonic liquid crystal fibers (PLCFs) a molecular orientation control is a crucial issue that influences proper operation of PLCF-based devices. The paper presents two distinct configurations: planar and radial escaped orientation of the LC molecules inside capillaries as well as methods of their application to photonic liquid crystal fibers. Possibilities of LC orientation control influence both: attenuation and transmitting spectra of the PLCF The orienting method is based on creation of an additional orienting layer on the inner surface of the capillary or air hole of the photonic liquid crystal fiber. Aligning materials used in the experiment are commercially available polyimides SE1211 and SE130 which induce liquid crystal homeotropic and planar anchoring conditions. The orienting layer increase an order parameter of the liquid crystal improving propagation properties and stability of photonic liquid crystal fiber-based devices.

  10. Investigations into complex liquid crystal mixtures

    NASA Astrophysics Data System (ADS)

    Kirchhoff, Jennifer

    Liquid crystal phases exhibit physical characteristics that lie between those of liquid and crystal phases. The many liquid crystal sub-phases are defined based on the degree of positional and orientational ordering the molecules have and the materials that make up these liquid crystal phases. This thesis presents a study of the molecular packing and physical properties of complex liquid crystal phases using dopants to better examine the stability and packing mechanisms of these phases. It also looks at the dispersion of quantum dots in liquid crystal materials, examining the electro-optical properties of the mixtures. The main goal of this thesis is to examine the effects of dopants on the properties of liquid crystal phases using optical microscopy, differential scanning calorimetry, electro-optical measurements, and X-ray scattering. For those mixtures with quantum dots fluorescence microscopy and photoluminescence measurements were also conducted. Rod-like liquid crystals are commonly used in display applications when the material is in a nematic liquid crystal phase, which is the least ordered phase exhibiting no positional ordering. The more complicated chiral smectic liquid crystal phases, which have a one dimensional layer structure, show potential for faster and tri-stable switching. A chiral rod-like liquid crystal material is doped with both chiral and achiral rod-like liquid crystals to examine the stability of one of the chiral smectic sub-phase, the SmC* FI1 phase. This phase consists of tilted molecules rotating about the cone defined by the tilt angle with a periodicity of three layers and an overall helical structure. The SmC*FI1 phase is stabilized by the competition between antiferroelectric and ferroelectric interactions, and small amounts of the achiral dopant broadens the range of this phase by almost 5°C. Higher dopant concentrations of the achiral material result in the destabilization of not just the SmC*FI1 phase but all tilted sub-phases

  11. Anomalous diffusion and cage effects in the isotropic phase of a liquid crystal.

    PubMed

    De Gaetani, Luca; Prampolini, Giacomo; Tani, Alessandro

    2007-07-01

    The translational motion of 4-n-hexyl-4'-cyanobiphenyl (6CB) in its isotropic phase has been studied by atomistic molecular dynamics simulation from 280 to 330 K. The mean square displacement shows evidence of a subdiffusive dynamics, with a plateau that becomes very apparent at the lowest temperatures. A three-time self-intermediate scattering function reveals that this plateau is connected with a homogeneous dynamics that, at longer times, becomes heterogeneous and finally exponential. These features are shared by, for example, a high-density system of hard spheres, which supports the universal character of the translational dynamics of liquids in their supercooled condition. As predicted by the idealized version of the mode-coupling theory (MCT), the diffusion coefficient dependence upon temperature is well described by a power law, with a critical temperature very close to that obtained by experimental measurements on orientational relaxation. This agreement might indicate a complete freezing of both rotational and translational intradomain dynamics. The time-temperature superposition principle also holds. The shape of the cage that surrounds a 6CB molecule has been reconstructed, and this analysis suggests a preferential side-by-side arrangement of molecules, which locally tend to align their long axes even in the isotropic phase. PMID:17567066

  12. Oblique incidence effect on steering efficiency of liquid crystal polarization gratings used for optical phased array beam steering amplification

    NASA Astrophysics Data System (ADS)

    Xiangjie, Zhao; Jiazhu, Duan; Dayong, Zhang; Cangli, Liu; Yongquan, Luo

    2016-10-01

    A liquid crystal polarization grating (LCPG) is proposed that amplifies the steering angle of a liquid crystal optical phased array for non-mechanical beam steering, taking advantage of its high steering efficiency under normal incidence. However, oblique incidence may play an important role in the overall steering efficiency. The effect of oblique incidence on steering efficiency of a LCPG was analyzed by numerically solving the extended Jones matrix and considering propagation crosstalk. The results indicate that the outgoing laser beam is amplitude-modulated under the effect of oblique incidence and behaves as a sinusoidal-modulated amplitude grating, which diffracts certain energies to non-blazed orders. Over-oblique incidence may even eliminate the steering effect of the incident beam. The modulation depth of the induced amplitude grating was found to be proportional to the product of sinusoidal value of oblique incidence angle and the LC layer thickness, and inversely proportional to the periodic pitch length of the LCPG. Both in-plane incidence and out-of-plane incidence behave similarly to influence the steering efficiency. Finally, the overall steering efficiency for cascaded LCPGs was analyzed and a difference of up to 11 % steering efficiency can be induced between different LCPG configurations, even without considering the over-oblique incidence effect. Both the modulation depth and final steering efficiency can be optimized by varying the LC birefringence and layer thickness.

  13. Imaging the oxidation effects of the Fenton reaction on phospholipids at the interface between aqueous phase and thermotropic liquid crystals.

    PubMed

    Zhang, Minmin; Jang, Chang-Hyun

    2015-08-01

    The lipid peroxidation process has attracted much attention because of the growing evidence of its involvement in the pathogenesis of age-related diseases. Herein, we report a simple, label-free method to study the oxidation of phospholipids by the Fenton reaction at the interface between an aqueous phase and immiscible liquid crystals (LCs). The different images produced by the orientation of 4-cyano-4'-pentylbiphenyl (5CB) corresponded to the presence or absence of oxidized 1,2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt (DOPG). The oxidation effects of the Fenton reaction on DOPG were evaluated by monitoring the orientational response of liquid crystals upon contact with the oxidized DOPG solutions. DOPG was oxidized into chain-changed products containing hydroxy, carbonyl, or aldehyde groups, resulting in the rearrangement of the phospholipid layer. This induced the orientational transition of LCs from homeotropic to planar states; therefore, a dark to bright optical shift was observed. This shift was due to the Fenton reaction preventing DOPG to induce the orientational alignment of LCs at the aqueous/LC interface. We also used an ultraviolet spectrophotometer to confirm the effects of oxidation on phospholipids by the Fenton reaction. Using this simple method, a new approach for investigating phospholipid oxidation was established with high resolution and easy accessibility. PMID:25656072

  14. Imaging the oxidation effects of the Fenton reaction on phospholipids at the interface between aqueous phase and thermotropic liquid crystals.

    PubMed

    Zhang, Minmin; Jang, Chang-Hyun

    2015-08-01

    The lipid peroxidation process has attracted much attention because of the growing evidence of its involvement in the pathogenesis of age-related diseases. Herein, we report a simple, label-free method to study the oxidation of phospholipids by the Fenton reaction at the interface between an aqueous phase and immiscible liquid crystals (LCs). The different images produced by the orientation of 4-cyano-4'-pentylbiphenyl (5CB) corresponded to the presence or absence of oxidized 1,2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt (DOPG). The oxidation effects of the Fenton reaction on DOPG were evaluated by monitoring the orientational response of liquid crystals upon contact with the oxidized DOPG solutions. DOPG was oxidized into chain-changed products containing hydroxy, carbonyl, or aldehyde groups, resulting in the rearrangement of the phospholipid layer. This induced the orientational transition of LCs from homeotropic to planar states; therefore, a dark to bright optical shift was observed. This shift was due to the Fenton reaction preventing DOPG to induce the orientational alignment of LCs at the aqueous/LC interface. We also used an ultraviolet spectrophotometer to confirm the effects of oxidation on phospholipids by the Fenton reaction. Using this simple method, a new approach for investigating phospholipid oxidation was established with high resolution and easy accessibility.

  15. Oblique incidence effect on steering efficiency of liquid crystal polarization gratings used for optical phased array beam steering amplification

    NASA Astrophysics Data System (ADS)

    Xiangjie, Zhao; Jiazhu, Duan; Dayong, Zhang; Cangli, Liu; Yongquan, Luo

    2016-07-01

    A liquid crystal polarization grating (LCPG) is proposed that amplifies the steering angle of a liquid crystal optical phased array for non-mechanical beam steering, taking advantage of its high steering efficiency under normal incidence. However, oblique incidence may play an important role in the overall steering efficiency. The effect of oblique incidence on steering efficiency of a LCPG was analyzed by numerically solving the extended Jones matrix and considering propagation crosstalk. The results indicate that the outgoing laser beam is amplitude-modulated under the effect of oblique incidence and behaves as a sinusoidal-modulated amplitude grating, which diffracts certain energies to non-blazed orders. Over-oblique incidence may even eliminate the steering effect of the incident beam. The modulation depth of the induced amplitude grating was found to be proportional to the product of sinusoidal value of oblique incidence angle and the LC layer thickness, and inversely proportional to the periodic pitch length of the LCPG. Both in-plane incidence and out-of-plane incidence behave similarly to influence the steering efficiency. Finally, the overall steering efficiency for cascaded LCPGs was analyzed and a difference of up to 11 % steering efficiency can be induced between different LCPG configurations, even without considering the over-oblique incidence effect. Both the modulation depth and final steering efficiency can be optimized by varying the LC birefringence and layer thickness.

  16. Solid-liquid surface tensions of critical nuclei and nucleation barriers from a phase-field-crystal study of a model binary alloy using finite system sizes.

    PubMed

    Choudhary, Muhammad Ajmal; Kundin, Julia; Emmerich, Heike; Oettel, Martin

    2014-08-01

    Phase-field-crystal (PFC) modeling has emerged as a computationally efficient tool to address crystal growth phenomena on atomistic length and diffusive time scales. We use a two-dimensional phase-field-crystal model for a binary system based on Elder et al. [Phys. Rev. B 75, 064107 (2007)] to study critical nuclei and their liquid-solid phase boundaries, in particular the nucleus size dependence of the liquid-solid interface tension as well as of the nucleation barrier. Critical nuclei are stabilized in finite systems of various sizes, however, the extracted interface tension as function of the nucleus radius r is independent of system size. We suggest a phenomenological expression to describe the dependence of the extracted interface tension on the nucleus radius r for the liquid-solid system. Moreover, the numerical PFC results show that this dependency can not be fully described by the nonclassical Tolman formula. PMID:25215738

  17. Solid-liquid surface tensions of critical nuclei and nucleation barriers from a phase-field-crystal study of a model binary alloy using finite system sizes

    NASA Astrophysics Data System (ADS)

    Choudhary, Muhammad Ajmal; Kundin, Julia; Emmerich, Heike; Oettel, Martin

    2014-08-01

    Phase-field-crystal (PFC) modeling has emerged as a computationally efficient tool to address crystal growth phenomena on atomistic length and diffusive time scales. We use a two-dimensional phase-field-crystal model for a binary system based on Elder et al. [Phys. Rev. B 75, 064107 (2007), 10.1103/PhysRevB.75.064107] to study critical nuclei and their liquid-solid phase boundaries, in particular the nucleus size dependence of the liquid-solid interface tension as well as of the nucleation barrier. Critical nuclei are stabilized in finite systems of various sizes, however, the extracted interface tension as function of the nucleus radius r is independent of system size. We suggest a phenomenological expression to describe the dependence of the extracted interface tension on the nucleus radius r for the liquid-solid system. Moreover, the numerical PFC results show that this dependency can not be fully described by the nonclassical Tolman formula.

  18. Reexamination of the mean-field phase diagram of biaxial nematic liquid crystals: Insights from Monte Carlo studies.

    PubMed

    Kamala Latha, B; Jose, Regina; Murthy, K P N; Sastry, V S S

    2015-07-01

    Investigations of the phase diagram of biaxial liquid-crystal systems through analyses of general Hamiltonian models within the simplifications of mean-field theory (MFT), as well as by computer simulations based on microscopic models, are directed toward an appreciation of the role of the underlying molecular-level interactions to facilitate its spontaneous condensation into a nematic phase with biaxial symmetry. Continuing experimental challenges in realizing such a system unambiguously, despite encouraging predictions from MFT, for example, are requiring more versatile simulational methodologies capable of providing insights into possible hindering barriers within the system, typically gleaned through its free-energy dependences on relevant observables as the system is driven through the transitions. The recent paper from this group [Kamala Latha et al., Phys. Rev. E 89, 050501(R) (2014)], summarizing the outcome of detailed Monte Carlo simulations carried out employing an entropic sampling technique, suggested a qualitative modification of the MFT phase diagram as the Hamiltonian is asymptotically driven toward the so-called partly repulsive regions. It was argued that the degree of (cross) coupling between the uniaxial and biaxial tensor components of neighboring molecules plays a crucial role in facilitating a ready condensation of the biaxial phase, suggesting that this could be a plausible factor in explaining the experimental difficulties. In this paper, we elaborate this point further, providing additional evidence from curious variations of free-energy profiles with respect to the relevant orientational order parameters, at different temperatures bracketing the phase transitions.

  19. Anomaly of pretransitional behavior at the nematic-smectic-A phase transition of amphiphilic liquid crystals with a hydrophilic group.

    PubMed

    Kimoto, Yasuhiro; Nishizawa, Ayumi; Takanishi, Yoichi; Yoshizawa, Atsushi; Yamamoto, Jun

    2013-05-23

    In order to clarify the origin of the X-ray diffraction peak corresponding to the smectic-like layer ordering appearing even in the nematic phase over a wide temperature range above the nematic-smectic A (NA) phase transition in liquid crystal (LC) molecules with a hydroxy group, we investigated the critical behavior of bend elastic constants and the correlation length of the smectic-like ordering in the N phase. It is found that cybotactic clusters with the transient layer ordering grow up extremely even far above the NA phase transition, and the critical exponent of the correlation length of the cybotactic clusters is estimated anomalously larger than that of conventional LC materials. Furthermore, we measured diffusion constants parallel and perpendicular to the director in the N phase, and concluded that cybotactic clusters with the smectic layer ordering create a finite potential barrier to prevent diffusion of the molecules parallel to the director as well as the true smectic A layer structure.

  20. Improvement of the performance of the twisted-nematic liquid-crystal display as a phase modulator.

    PubMed

    Ma, Baiheng; Yao, Baoli; Li, Ze; Ye, Tong

    2011-06-10

    A twisted-nematic liquid-crystal display (TN-LCD) placed between two linear polarizers (P) generally produces coupled intensity and phase modulations. For the purpose of phase-only modulation, quarter-wave plates (QWPs) are often used in front of or behind the LCD. In this paper, we demonstrate theoretically and experimentally the QWPs' effect on the modulation properties of the TN-LCD based on the general Jones matrix descriptions for all the devices, which circumvents the inconvenience of the traditional method on the basis of the TN-LCD's internal parameters. We prove that the phase modulation depth of the TN-LCD can be further increased in the configuration of P1-QWP1-LCD-QWP2-P2 with each component properly oriented, provided that the mean intensity transmission is decreased to a lower level. By observing the diffracted patterns of the Ronchi phase grating or blazed grating addressed onto the TN-LCD, we verify the validity of the proposed method. Improved reconstructed image quality from the kinoform loaded on the TN-LCD is obtained in this configuration. This approach is valuable when the TN-LCD is employed as a phase modulator, especially for the modern, thinner TN-LCD. PMID:21673760

  1. Bent core liquid crystal elastomers

    SciTech Connect

    Verduzco, R.; DiMasi, E.; Luchette, P.; Ho Hong, S.; Harden, J.; Palffy-Muhoray, P.; Kilbey II, S.M.; Sprunt, S.; Gleeson, G.T. Jakli, A.

    2010-07-28

    Liquid crystal (LC) elastomers with bent-core side-groups incorporate the properties of bent-core liquid crystals in a flexible and self-supporting polymer network. Bent-core liquid crystal elastomers (BCEs) with uniform alignment were prepared by attaching a reactive bent-core LC to poly(hydrogenmethylsiloxane) and crosslinking with a divinyl crosslinker. Phase behavior studies indicate a nematic phase over a wide temperature range that approaches room temperature, and thermoelastic measurements show that these BCEs can reversibly change their length by more than a factor of two upon heating and cooling. Small-angle X-ray scattering studies reveal multiple, broad low-angle peaks consistent with short-range smectic C order of the bent-core side groups. A comparison of these patterns with predictions of a Landau model for short-range smectic C order shows that the length scale for smectic ordering in BCEs is similar to that seen in pure bent-core LCs. The combination of rubber elasticity and smectic ordering of the bent-core side groups suggests that BCEs may be promising materials for sensing, actuating, and other advanced applications.

  2. Solid-phase laser-induced forward transfer of variable shapes using a liquid-crystal spatial light modulator

    NASA Astrophysics Data System (ADS)

    Pohl, R.; Jansink, M.; Römer, G. R. B. E.; Huis in `t Veld, A. J.

    2015-08-01

    Laser-induced forward transfer is a promising method for 3D printing of various materials, including metals. The ejection mechanism is complex and depends strongly on the experimental parameters, such as laser fluence and donor layer thickness. However, the process can be categorized by the physical condition of the ejected material, i.e., the donor layer is transferred in liquid phase or the material is transferred as a `pellet' in solid phase. Currently, solid-phase transfer faces several problems. Large shearing forces, occurring at the pellet perimeter during transfer, limit the similarity between the desired pellet shape and the deposited pellet shape. Furthermore, the deposited pellet may be surrounded by debris particles formed by undesired transferred donor material. This work introduces a novel approach for laser-induced forward transfer of variable shaped solid-phase pellets. A liquid-crystal spatial light modulator (SLM) is used to apply grayscale intensity modulation to an incident laser beam to shape the intensity profile. Optimized beams consist of a high fluence perimeter around an interior characterized by a lower fluence level. These beams are used successfully to transfer solid-phase pellets out of a 100-nm Au donor layer using a single laser pulse. The flexibility of the SLM allows a variable desired pellet shape. The shapes of the resulting deposited pellets show a high degree of similarity to the desired shapes. Debris-free deposited pellets are achieved by pre-machining the donor layer, prior to the transfer, using a double-pulse process.

  3. Optical studies of a binary liquid crystal mixture exhibiting induced smectic A phase

    NASA Astrophysics Data System (ADS)

    Thingujam, Kiranmala; Bhattacharjee, Ayon; Choudhury, Basana; Sarkar, S. D.

    2016-08-01

    A binary liquid crystalline mixture of a monotropic polar compound 4-cyanophenyl 4'- n-pentyl benzoate (CPPB) and an enantiotropic non-polar compound 4- n-hexyl phenyl 4- n'-pentyloxy benzoate (ME5O.6) shows the presence of an induced smectic A phase in the region 0.1 ≤ x CPPB ≤ 0.82, where x CPPB is the mole fraction of CPPB. The results of texture study, density study and refractive index measurements of the eutectic mixture along with those of the pure samples are reported in this paper. The density values of the eutectic mixture are found to be much higher than that of the pure samples. The determination of order parameters of the pure samples and eutectic mixture has been carried out. In order to determine the order parameters of the samples, we have used different methods, Vuks', Neugebauer's, modified Vuks' and direct extrapolation method. The results of order parameters obtained from the different approaches are compared and analysed in detail.

  4. Dispersive Stabilization of Liquid Crystal-in-Water with Acrylamide Copolymer/Surfactant Mixture: Nematic Curvilinear Aligned Phase Composite Film.

    PubMed

    Park; Lee

    1999-11-01

    The effect of nonionic surfactant, (H(OCH(2)-CH(2))(8)-OC(6)H(4)-C(9)H(19)), on the dispersion stabilization of liquid crystal (LC)-in-water with acrylamide copolymer containing the related nonylphenyl groups was studied. It was observed that the addition of nonionic surfactant increases the stability of LC dispersions and improves the electrooptical properties of the nematic curvilinear aligned phase (NCAP) composite film. On the basis of the surface tension, reduced viscosity, cloud point, and coalescence time measurements, it was proposed that formation of an integrated structure induced by interactions between hydrophobic groups in the polymer chains is probably important to fabrication of a polymer composite film made of LC and polymer matrix. Copyright 1999 Academic Press.

  5. Phase transitions in nanocomposites of hydrogen-bonded dimeric liquid crystals with mesogenic and non-mesogenic components

    NASA Astrophysics Data System (ADS)

    Katranchev, Boyko; Petrov, Minko

    2016-02-01

    Microtextural polarization, phase transitions, and electro-optical effects are studied in a series of nanocomposites, grown by mixing alkyloxybenzoic acids (nOBAs), displaying hydrogen-bonded dimeric liquid crystal (LC) state, with non-mesogens (single-walled carbon nanotubes (SWCNTs), perfluorooctanoic acid) or mesogens (bent-core LC compound D14F3). Each of the studied nanocomposites, in which the nOBA serves as a matrix, forms complexes with bent-shaped dimeric, caused by the interaction between the dopant structural units and the dimer rings. This feature, coordinated with the surface anchoring, bulk and electrical effects, leads to drastic reduction of the LC system symmetry. As a result, transitions from achiral (characteristic for the pristine nOBA) to chiral states (including ferroelectric smectic C with C2 symmetry and ferroelectric smectic CG with the lowest C1 triclinic one) take place. The functionalization of the SWCNTs causes drastic increase of the ferroelectricity.

  6. Quantitative analysis of the x-ray diffraction intensities of undulated smectic phases in bent-core liquid crystals

    SciTech Connect

    Folcia, C. L.; Etxebarria, J.; Ortega, J.

    2007-07-15

    X-ray diffraction diagrams of undulated smectic phases in bent-core liquid crystals have been theoretically studied. The intensities of the reflections have been obtained for different layer modulations, and a general expression has been deduced for orthogonal cells in terms of the different harmonics of the distortion. The case of sinusoidal modulation is especially simple and has been studied also in oblique cells. High-quality x-ray measurements of three compounds reported in the literature have been analyzed as examples. In all cases it has been deduced that the modulation is sinusoidal and its amplitude has been easily obtained by fitting the experimental intensities. Equatorial (h0) reflections have been also considered to obtain information about the structure of defects at the maxima and minima of the undulation.

  7. Dynamical studies of the mechanisms for optical nonlinearities of methyl-red dye doped blue phase liquid crystals.

    PubMed

    Chen, Chun-Wei; Lin, Tsung-Hsien; Khoo, Iam Choon

    2015-08-24

    Dynamical grating diffraction experiments and reflection/transmission polarization spectroscopy have been conducted on azo-dye doped Blue-Phase Liquid Crystal (BPLC) to investigate the mechanisms responsible for laser induced refractive index changes. The underlying mechanisms for the transient grating diffraction components are attributed to thermal indexing and lattice distortion, whereas the persistent component is due to lattice distortion/expansion caused by laser excited dye molecule isomerization. These mechanisms were distinguishable by their response dynamics and gave rise to the observed reflection spectra and photonic bandgap shift, polarization dependency and optical activity. Some preliminary studies have demonstrated the feasibility of using these mechanisms for coherent holographic and direct image writing operations. PMID:26368144

  8. Photopyroelectric ac calorimetric study of the nematic-smectic-A phase-transition line in binary liquid crystal mixtures with injected smectic-A phases.

    PubMed

    Caerels, J; Glorieux, C; Thoen, J

    2002-03-01

    Using a recently developed photopyroelectric ac calorimetric technique we investigate two binary liquid crystal mixtures with so-called injected smectic-A phases. Characteristic of these systems is the occurrence of nematic-to-smectic-A transition lines in the phase diagram of mixtures of pure compounds having only a nematic phase. The two binary systems are pentylcyanobiphenyl with either 4-n-propylcyclohexyl-carboxylate or 4-n-pentylphenyl 4(')-n-pentyloxybenzoate. Both these systems have domelike smectic-A ranges with narrow nematic ranges at the top. Near the top the N-SmA transitions are of first order and are crossing over to second order at a tricritical point on either side of the top with the increasing width of the nematic range. The obtained critical exponents are almost completely Fisher renormalized because of the strong concentration dependence of the nematic-to-smectic-A transition temperatures.

  9. Role of Molecular Structure on X-ray Diffraction in Uniaxial and Biaxial Phases of Thermotropic Liquid Crystals

    SciTech Connect

    Acharya, Bharat R.; Kang, Shin-Woong; Prasad, Veena; Kumar, Satyendra

    2009-04-29

    X-ray diffraction is one of the most definitive methods to determine the structure of condensed matter phases, and it has been applied to unequivocally infer the structures of conventional calamitic and lyotropic liquid crystals. With the advent of bent-core and tetrapodic mesogens and the discovery of the biaxial nematic phase in them, the experimental results require more careful interpretation and analysis. Here, we present ab-initio calculations of X-ray diffraction patterns in the isotropic, uniaxial nematic, and biaxial nematic phases of bent-core mesogens. A simple Meier-Saupe-like molecular distribution function is employed to describe both aligned and unaligned mesophases. The distribution function is decomposed into two, polar and azimuthal, distribution functions to calculate the effect of the evolution of uniaxial and biaxial nematic orientational order. The calculations provide satisfactory semiquantitative interpretations of experimental results. The calculations presented here should provide a pathway to more refined and quantitative analysis of X-ray diffraction data from the biaxial nematic phase.

  10. Role of Molecular Structure on X-ray Diffraction in Thermotropic Uniaxial and Biaxial Nematic Liquid Crystal Phases

    SciTech Connect

    Acharya, Bharat R.; Kang, Shin-Woong; Prasad, Veena; Kumar, Satyendra

    2009-08-27

    X-ray diffraction is one of the most definitive methods to determine the structure of condensed matter phases, and it has been applied to unequivocally infer the structures of conventional calamitic and lyotropic liquid crystals. With the advent of bent-core and tetrapodic mesogens and the discovery of the biaxial nematic phase in them, the experimental results require more careful interpretation and analysis. Here, we present ab-initio calculations of X-ray diffraction patterns in the isotropic, uniaxial nematic, and biaxial nematic phases of bent-core mesogens. A simple Meier-Saupe-like molecular distribution function is employed to describe both aligned and unaligned mesophases. The distribution function is decomposed into two, polar and azimuthal, distribution functions to calculate the effect of the evolution of uniaxial and biaxial nematic orientational order. The calculations provide satisfactory semiquantitative interpretations of experimental results. The calculations presented here should provide a pathway to more refined and quantitative analysis of X-ray diffraction data from the biaxial nematic phase.

  11. Adaptive correction of vortex laser beam in a closed-loop system with phase only liquid crystal spatial light modulator

    NASA Astrophysics Data System (ADS)

    Ma, Haotong; Liu, Zejin; Wu, Huiyun; Xu, Xiaojun; Chen, Jinbao

    2012-03-01

    We propose and demonstrate the wave front correction of a vortex laser beam by using dual phase only liquid crystal spatial light modulators (LC-SLMs) and a stochastic parallel gradient descent (SPGD) algorithm. One phase only LC-SLM is used to generate vortex laser beam by loading spiral phase screen onto the wave front of input quasi-Gaussian beam. The other phase only LC-SLM under SPGD controller based on the subzone control method adaptively compensates the wave front of vortex laser beam. Numerical simulation and experimental results show that after correction, vortex doughnut like beam is focused into a beam with airy disk pattern distribution in the far field. The adaptive corrections of vortex laser beam with different optical topological charges are studied. The results show that the optical topological charge has little influence on adaptive correction. The powers in the main lobe of far field intensity distributions of vortex laser beams with different optical topological charges are all greatly improved by adaptive correction. The technique proposed in this paper can be used in optical communication, relay mirror and atmospheric turbulence correction.

  12. Interferometric method for phase calibration in liquid crystal spatial light modulators using a self-generated diffraction-grating.

    PubMed

    Fuentes, José Luis Martínez; Fernández, Enrique J; Prieto, Pedro M; Artal, Pablo

    2016-06-27

    An auto-referenced interferometric method for calibrating phase modulation of parallel-aligned liquid crystal (PAL) spatial light modulators (SLM) is described. The method is experimentally straightforward, robust, and requires solely of a collimated beam, with no need of additional optics. This method uses the SLM itself to create a tilted plane wave and a reference wave which mutually interfere. These waves are codified by means of a binary diffraction grating and a uniformly distributed gray level area (piston) into the SLM surface. Phase shift for each gray level addressed to the piston section can then be evaluated. Phase modulation on the SLM can also be retrieved with the proposed method over spatially resolved portions of the surface. Phase information obtained with this novel method is compared to other well established calibration procedures, requiring extra elements and more elaborated optical set-ups. The results show a good agreement with previous methods. The advantages of the new method include high mechanical stability, faster performance, and a significantly easier practical implementation. PMID:27410574

  13. Nonequilibrium molecular dynamics of liquid crystals

    NASA Astrophysics Data System (ADS)

    Sarman, S. S.; Cummings, P. T.; Evans, D. J.

    1994-11-01

    During the last 15 years, noneyuilibrium molecular dynamics (NEMD) has been successfully applied to study transport phenomena in fluids that are isotropic at equilibrium. A natural extension is therefore to study liquid crystals, which are anisotropic al equilibrium. The lower symmetry of these systems means that the linear transport coefficients are considerably more complicated than in an isotropic system. Part of the reason for this is that there are crosscouplings between tensors of different rank and parity. Such couplings arc symmetry-forbidden in isotropic phases. In this paper. we review some of fundamental theoretical results we have derived concerning the rheology of liquid crystals. report NEMD simulations of thermal conductivity and shear viscosity of liquid crystals, and present NEMD simulations of shear cessation phenomena. All of the NEMD results are presented for a model liquid crystal fluid which is a modification of the Gay-Borne fluid. The results obtained are in qualitative agreement with experimental measurements on liquid crystal systems.

  14. Liquid crystal device and method thereof

    DOEpatents

    Shiyanovskii, Sergij V; Gu, Mingxia; Lavrentovich, Oleg D

    2012-10-23

    The invention provides a liquid crystal device and method thereof. Subsequent to applying a first electrical voltage on a liquid crystal to induce a reorientation of the liquid crystal, a second electrical voltage with proper polarity is applied on the liquid crystal to assist the relaxation of the reorientation that was induced by the first electrical voltage. The "switch-off" phase of the liquid crystal can therefore be accelerated or temporally shortened, and the device can exhibit better performance such as fast response to on/off signals. The invention can be widely used LCD, LC shutter, LC lens, spatial light modulator, telecommunication device, tunable filter, beam steering device, and electrically driven LC device, among others.

  15. Biosensing using smectic and cholesteric liquid crystals

    NASA Astrophysics Data System (ADS)

    Popov, Piotr; Mann, Elizabeth; Jakli, Antal

    2015-03-01

    Liquid-crystal-based biosensors utilize liquid crystal alignment's high sensitivity to the presence of lipids and proteins self-assembled at the liquid crystal/aqueous solution interface. The optical response of the bulk liquid crystal to the interface offers inexpensive, easy optical detection of such biologically relevant molecules. Present technique uses nematic liquid crystal phase state that typically has a planar-to-homeotropic response only. Here we show that smectic and cholesteric phase states of liquid crystals can be used as new sensing modes that can provide additional information or improve the characteristics of a potential biosensor device. Smectic-A phase extends the detection range both toward the lower and higher concentration. Cholesteric phase (nematic with a chiral dopant) may be sensitive to the chirality of biological surface-active molecules such as phospholipids. Additionally, the ``finger-print'' texture of a cholesteric phase may show the differences between biomolecule homologues, thus providing a promising way of distinguishing between subtle differences of hydrocarbon chain or head-group size and structure.

  16. Liquid Crystals in Tribology

    PubMed Central

    Carrión, Francisco-José; Martínez-Nicolás, Ginés; Iglesias, Patricia; Sanes, José; Bermúdez, María-Dolores

    2009-01-01

    Two decades ago, the literature dealing with the possible applications of low molar mass liquid crystals, also called monomer liquid crystals (MLCs), only included about 50 references. Today, thousands of papers, conference reports, books or book chapters and patents refer to the study and applications of MLCs as lubricants and lubricant additives and efforts are made to develop new commercial applications. The development of more efficient lubricants is of paramount technological and economic relevance as it is estimated that half the energy consumption is dissipated as friction. MLCs have shown their ability to form ordered boundary layers with good load-carrying capacity and to lower the friction coefficients, wear rates and contact temperature of sliding surfaces, thus contributing to increase the components service life and to save energy. This review includes the use of MLCs in lubrication, and dispersions of MLCs in conventional polymers (PDMLCs). Finally, new lubricating system composed of MLC blends with surfactants, ionic liquids or nanophases are considered. PMID:19865534

  17. Chemical and biological sensing using liquid crystals

    PubMed Central

    Carlton, Rebecca J.; Hunter, Jacob T.; Miller, Daniel S.; Abbasi, Reza; Mushenheim, Peter C.; Tan, Lie Na; Abbott, Nicholas L.

    2014-01-01

    The liquid crystalline state of matter arises from orientation-dependent, non-covalent interaction between molecules within condensed phases. Because the balance of intermolecular forces that underlies formation of liquid crystals is delicate, this state of matter can, in general, be easily perturbed by external stimuli (such as an electric field in a display). In this review, we present an overview of recent efforts that have focused on exploiting the responsiveness of liquid crystals as the basis of chemical and biological sensors. In this application of liquid crystals, the challenge is to design liquid crystalline systems that undergo changes in organization when perturbed by targeted chemical and biological species of interest. The approaches described below revolve around the design of interfaces that selectively bind targeted species, thus leading to surface-driven changes in the organization of the liquid crystals. Because liquid crystals possess anisotropic optical and dielectric properties, a range of different methods can be used to read out the changes in organization of liquid crystals that are caused by targeted chemical and biological species. This review focuses on principles for liquid crystal-based sensors that provide an optical output. PMID:24795857

  18. Interaction and Response of a Smectic-A liquid crystal to a 2 nm Nanometer Particle: Phase transition due to the Functionalization Compound

    NASA Astrophysics Data System (ADS)

    Martinez-Miranda, Luz J.; Kurihara, Lynn K.

    2009-03-01

    We have studied the in-plane (parallel to the magnetic field) alignment of 8CB mixed with FeCo nanoparticles covered with different funtionalization compounds. The functionalization compounds are Polyethelene glycol (PEG (3000)), hydroxyl succinimide (NHS), aminopropyl tri-ethoxy silane (APTS) and mercapto hexa-decanoic acid (MHDA). We have studied them using X-ray scattering. We have found that the inverse integrated intensity of the X-ray scans in the plane of the magnetic field is a good measure of how much energy the system (liquid crystal, nanoparticles, functionalization compound) will need to reorient the liquid crystal in the magnetic field. In addition, we have observed that the orientation the liquid crystal adopts with respect to the nanoparticles can result in a phase transition that takes the liquid crystal to a more disordered and symmetric phase that favors the rotation, as happens in the smectic-nematic transition, observed in the sample with APTS. We relate the disordering to the changes observed in the transition for the liquid crystal and this termination to recent heat capacity measurements by Cordoyiannis et al. [1]. References [1] Cordoyiannis, G., Kurihara, L.K., Martinez-Miranda, L. J, Glorieux, C., Thoen, J., submitted to PRE (2008).

  19. Fluctuation-induced dielectric permittivity in the isotropic phase of cholesteric liquid crystals

    NASA Astrophysics Data System (ADS)

    Mukherjee, Prabir K.; Das, Asok K.

    2016-03-01

    The temperature and pressure dependence of the static dielectric permittivity in the isotropic phase of the isotropic to cholesteric phase transition is calculated using Landau-de Gennes’s fluctuation theory, allowing spatial variation of the orientational order parameter. A comparison is made with experimental data available in the isotropic phase of the isotropic to cholesteric phase transition.

  20. Swimming bacteria in liquid crystal

    NASA Astrophysics Data System (ADS)

    Sokolov, Andrey; Zhou, Shuang; Aranson, Igor; Lavrentovich, Oleg

    2014-03-01

    Dynamics of swimming bacteria can be very complex due to the interaction between the bacteria and the fluid, especially when the suspending fluid is non-Newtonian. Placement of swimming bacteria in lyotropic liquid crystal produces a new class of active materials by combining features of two seemingly incompatible constituents: self-propelled live bacteria and ordered liquid crystals. Here we present fundamentally new phenomena caused by the coupling between direction of bacterial swimming, bacteria-triggered flows and director orientations. Locomotion of bacteria may locally reduce the degree of order in liquid crystal or even trigger nematic-isotropic phase transition. Microscopic flows generated by bacterial flagella disturb director orientation. Emerged birefringence patterns allow direct optical observation and quantitative characterization of flagella dynamics. At high concentration of bacteria we observed the emergence of self-organized periodic texture caused by bacteria swimming. Our work sheds new light on self-organization in hybrid bio-mechanical systems and can lead to valuable biomedical applications. Was supported by the US DOE, Office of Basic Energy Sciences, Division of Materials Science and Engineering, under the Contract No. DE AC02-06CH11357.

  1. Incorporation of carbon nanotubes into a lyotropic liquid crystal by phase separation in the presence of a hydrophilic polymer.

    PubMed

    Xin, Xia; Li, Hongguang; Wieczorek, Stefan A; Szymborski, Tomasz; Kalwarczyk, Ewelina; Ziebacz, Natalia; Gorecka, Ewa; Pociecha, Damian; Hołyst, Robert

    2010-03-01

    Single-walled carbon nanotubes (SWNTs) were incorporated into a lyotropic liquid crystal (LLC) matrix formed by n-dodecyl octaoxyethene monoether (C(12)E(6)) at room temperature through spontaneous phase separation induced by nonionic hydrophilic polymer poly(ethylene glycol) (PEG). The quality of SWNTs/LLC composite was evaluated by polarized microscopy observations and small-angle X-ray scattering (SAXS) measurements. The results obtained clearly indicated that SWNTs have been successfully incorporated into the LLC matrix up to a considerable high content without destroying the LLC matrix, although interesting changes of the LLC matrix were also induced by SWNTs incorporation. By varying the ratio of PEG to C(12)E(6), the type of LLC matrix can be controlled from hexagonal phase to lamellar phase. Temperature was found to have a significant influence on the quality of SWNTs/LLC composite, and tube aggregation can be induced at higher temperature. When SWNTs were changed to multiwalled carbon nanotubes (MWNTs), they became difficult to be incorporated into LLC matrix because of an increase in the average tube diameter.

  2. Muoniated spin probes in the discotic liquid crystal HHTT: rapid electron spin relaxation in the hexagonal columnar and isotropic phases.

    PubMed

    McKenzie, Iain; Cammidge, Andrew N; Gopee, Hemant; Dilger, Herbert; Scheuermann, Robert; Stoykov, Alexey; Jayasooriya, Upali A

    2013-01-01

    Avoided level crossing muon spin resonance (ALC-μSR) spectroscopy was used to study radicals produced by the addition of the light hydrogen isotope muonium (Mu) to the discotic liquid crystal (DLC) 2,3,6,7,10,11-hexahexylthiotriphenylene (HHTT). Mu adds to the secondary carbon atoms of HHTT to produce a substituted cyclohexadienyl radical, whose identity was confirmed by comparing the measured hyperfine coupling constants with values obtained from DFT calculations. ALC-μSR spectra were obtained in the isotropic (I), hexagonal columnar (Col(h)), helical (H), and crystalline (Cr) phases. In the I and Col(h) phases the radicals, which are incorporated within the stacks of HHTT molecules as isolated paramagnetic defects, undergo extremely rapid electron spin relaxation, on the order of a hundredfold faster than in the H or Cr phases. The electron spin relaxation rate increases significantly with increasing temperature and appears to be caused by the liquidlike motion within the columns, which modulates the overlap between the π system of the radical and the π systems of the neighboring HHTT molecules, and hence, the hyperfine coupling constants. Rapid electron spin relaxation should occur for any π radical incorporated within the columns of a DLC, which may limit the utility of DLCs for future spin-based technologies.

  3. Reentrant smectic-[ital C] and smectic-[ital C][sup *] phases in liquid crystals under an electric field

    SciTech Connect

    Benguigui, L. ); Jacobs, A.E. )

    1994-05-01

    Kondo [ital et] [ital al]. [Jpn. J. Appl. Phys. 22, L43 (1983)] discovered that both the smectic-[ital C] and smectic-[ital C][sup *] phases in the liquid crystal [ital p]-[ital n]-decyloxybenzylidene-[ital p]-amino-2-methylbutyl-cinnamate are reentrant with temperature for a range of electric fields. We show that the Landau theory with no adjustable parameters provides a semiquantitative explanation of the phase diagram. The double reentrance is due to two fourth-order terms, one chiral and the other achiral, and is intimately related to the maximum in the pitch, unlike the reentrance under magnetic field. The Sm-C--Sm-C[sup *] transition curve displays both main types of second-order phase transition, instability, and nucleation, separated by a first-order segment. [ital p]-azoxy-cinnamate-methyl-2-butanol and other compounds with divergent pitch should also show the double reentrance, but the physical origin is different.

  4. Phase polymorphism and electro-optical properties of a ferroelectric liquid crystal containing the biphenyl system

    NASA Astrophysics Data System (ADS)

    Zalewski, Sławomir; Ossowska-Chruściel, Mirosława D.

    2016-04-01

    In this article we present results concerning phase transitions and physical properties of the ferroelectric phase of the compound (S)-4-(1-methylheptyloxy)biphenyl-4'-(heptyloxy phenyl)-4-carboxylate (MHOBOPO7). The compound has the following phases: smectic ferroelectric C (SmC*), chiral nematic N*, and two defected phases, TGBC and blue phase. The mesomorphic properties were investigated by means of three complementary methods: differential scanning calorimetry, polarizing light optical microscopy, and transmitted light intensity. The electro-optical measurements were carried out on an ordered sample in a middle electric field during very slow cooling from the nematic phase to the ferroelectric phase.

  5. Computer simulations of liquid crystals

    NASA Astrophysics Data System (ADS)

    Smondyrev, Alexander M.

    Liquid crystal physics is an exciting interdisciplinary field of research with important practical applications. Their complexity and the presence of strong translational and orientational fluctuations require a computational approach, especially in the studies of nonequlibrium phenomena. In this dissertation we present the results of computer simulation studies of liquid crystals using the molecular dynamics technique. We employed the Gay-Berne phenomenological model of liquid crystals to describe the interaction between the molecules. Both equilibrium and non-equilibrium phenomena were studied. In the first case we studied the flow properties of the liquid crystal system in equilibrium as well as the dynamics of the director. We measured the viscosities of the Gay-Berne model in the nematic and isotropic phases. The temperature-dependence of the rotational and shear viscosities, including the nonmonotonic behavior of one shear viscosity, are in good agreement with experimental data. The bulk viscosities are significantly larger than the shear viscosities, again in agreement with experiment. The director motion was found to be ballistic at short times and diffusive at longer times. The second class of problems we focused on is the properties of the system which was rapidly quenched to very low temperatures from the nematic phase. We find a glass transition to a metastable phase with nematic order and frozen translational and orientational degrees of freedom. For fast quench rates the local structure is nematic-like, while for slower quench rates smectic order is present as well. Finally, we considered a system in the isotropic phase which is then cooled to temperatures below the isotropic-nematic transition temperature. We expect topological defects to play a central role in the subsequent equilibration of the system. To identify and study these defects we require a simulation of a system with several thousand particles. We present the results of large

  6. Wetting of cholesteric liquid crystals.

    PubMed

    Silvestre, Nuno M; Figueirinhas Pereira, Maria Carolina; Bernardino, Nelson R; Telo da Gama, Margarida M

    2016-02-01

    We investigate theoretically the wetting properties of cholesteric liquid crystals at a planar substrate. If the properties of substrate and of the interface are such that the cholesteric layers are not distorted, the wetting properties are similar to those of a nematic liquid crystal. If, on the other hand, the anchoring conditions force the distortion of the liquid crystal layers the wetting properties are altered, the free cholesteric-isotropic interface is non-planar and there is a layer of topological defects close to the substrate. These deformations can either promote or hinder the wetting of the substrate by a cholesteric, depending on the properties of the cholesteric liquid crystal.

  7. Reexamination of the mean-field phase diagram of biaxial nematic liquid crystals: Insights from Monte Carlo studies

    NASA Astrophysics Data System (ADS)

    Kamala Latha, B.; Jose, Regina; Murthy, K. P. N.; Sastry, V. S. S.

    2015-07-01

    Investigations of the phase diagram of biaxial liquid-crystal systems through analyses of general Hamiltonian models within the simplifications of mean-field theory (MFT), as well as by computer simulations based on microscopic models, are directed toward an appreciation of the role of the underlying molecular-level interactions to facilitate its spontaneous condensation into a nematic phase with biaxial symmetry. Continuing experimental challenges in realizing such a system unambiguously, despite encouraging predictions from MFT, for example, are requiring more versatile simulational methodologies capable of providing insights into possible hindering barriers within the system, typically gleaned through its free-energy dependences on relevant observables as the system is driven through the transitions. The recent paper from this group [Kamala Latha et al., Phys. Rev. E 89, 050501(R) (2014), 10.1103/PhysRevE.89.050501], summarizing the outcome of detailed Monte Carlo simulations carried out employing an entropic sampling technique, suggested a qualitative modification of the MFT phase diagram as the Hamiltonian is asymptotically driven toward the so-called partly repulsive regions. It was argued that the degree of (cross) coupling between the uniaxial and biaxial tensor components of neighboring molecules plays a crucial role in facilitating a ready condensation of the biaxial phase, suggesting that this could be a plausible factor in explaining the experimental difficulties. In this paper, we elaborate this point further, providing additional evidence from curious variations of free-energy profiles with respect to the relevant orientational order parameters, at different temperatures bracketing the phase transitions.

  8. Effects of fullerene addition on the thermo-optical properties of smectic liquid crystals at the vicinity of the nematic-smectic-A phase transition.

    PubMed

    Omena, Lidiane; de Melo, Pedro B; Pereira, Maria S S; de Oliveira, Italo N

    2014-05-01

    The present work is devoted to the study of the thermo-optical properties of liquid crystals doped with traces of fullerene C(60) at the vicinity of the nematic-smectic-A phase transition. By using the time-resolved Z-scan technique, we measure the temperature dependence of the thermo-optical coefficient and the thermal diffusivity. Our results reveal that the critical behavior of the thermal diffusivity is strongly affected by the fullerene addition. We provide a detailed discussion under the light of the distinct mechanisms behind the thermal transport in liquid-crystal samples.

  9. Study on optical characterization of TGB and reentrant smectic-A phases in binary mixture of two liquid crystals

    NASA Astrophysics Data System (ADS)

    Govindaiah, T. N.; Sreepad, H. R.

    2015-04-01

    In this work, our investigation is to study the optical and thermal properties of the binary mixture of cholesteric and nematic compounds, namely, cholesteryl nonanoate and p-methoxybenzylidene-p-ethylaniline, which exhibits a very interesting liquid crystalline twisted grain boundary (TGB) phase and reentrant smectic-A phase. The chiral liquid crystalline TGB phases and reentrant smectic-A phases have been observed at different concentrations and at different temperatures. The existence of TGB and reentrant smectic-A phases is confirmed by differential scanning calorimetry and optical microscopic studies. The variation of optical anisotropy has been discussed. The helical pitch of the cholesteric phase has also been discussed.

  10. Study and characterization of the smectic X* phase in binary mixtures of thermotropic double hydrogen bonded ferroelectric liquid crystals

    NASA Astrophysics Data System (ADS)

    Sangameswari, G.; Pongali Sathya Prabu, N.; Madhu Mohan, M. L. N.

    2015-09-01

    Thermotropic double hydrogen bonded ferroelectric liquid crystals (DHBFLCs) composed of N-carbamyl-L-glutamic acid (CGA) and p-n-alkyloxy benzoic acids (BAO) have been investigated. Variation in the molar proportion of X and Y (where X = CGA + 5BAO and Y = CGA + 6BAO, CGA + 7BAO, and CGA + 8BAO) composed of three series yielded 27 binary mixtures. Optical and thermal properties of these mixtures are meticulously studied in the present article. A novel smectic ordering, namely smectic X*, is observed in all the three series. The aim of the investigation is to obtain an abundance occurrence of smectic X* and hence the proportions of the binary mixtures are so chosen that the preamble task is accomplished. Phase diagrams of three series are constructed from the data obtained from polarizing optical microscope (POM) and differential scanning calorimetry (DSC) studies. Odd-even effect, order of the phase transition, thermal stability factor, thermal equilibrium, and optical tilt angle are also premeditated.

  11. Crystallization of undercooled liquid fenofibrate.

    PubMed

    Amstad, Esther; Spaepen, Frans; Weitz, David A

    2015-11-28

    Formulation of hydrophobic drugs as amorphous materials is highly advantageous as this increases their solubility in water and therefore their bioavailability. However, many drugs have a high propensity to crystallize during production and storage, limiting the usefulness of amorphous drugs. We study the crystallization of undercooled liquid fenofibrate, a model hydrophobic drug. Nucleation is the rate-limiting step; once seeded with a fenofibrate crystal, the crystal rapidly grows by consuming the undercooled liquid fenofibrate. Crystal growth is limited by the incorporation of molecules into its surface. As nucleation and growth both entail incorporation of molecules into the surface, this process likely also limits the formation of nuclei and thus the crystallization of undercooled liquid fenofibrate, contributing to the good stability of undercooled liquid fenofibrate against crystallization.

  12. Transitions between paraelectric and ferroelectric phases of bent-core smectic liquid crystals in the bulk and in thin freely suspended films.

    PubMed

    Eremin, Alexey; Floegel, Martin; Kornek, Ulrike; Stern, Stephan; Stannarius, Ralf; Nádasi, Hajnalka; Weissflog, Wolfgang; Zhu, Chenhui; Shen, Yongqiang; Park, Cheol Soo; Maclennan, Joseph; Clark, Noel

    2012-11-01

    We report on the contrasting phase behavior of a bent-core liquid crystal with a large opening angle between the mesogenic units in the bulk and in freely suspended films. Second-harmonic generation experiments and direct observation of director inversion walls in films in an applied electric field reveal that the nonpolar smectic C phase observed in bulk samples becomes a ferroelectric "banana" phase in films, showing that a mesogen with a small steric moment can give a phase with polar order in freely suspended films even when the corresponding bulk phase is paraelectric.

  13. A decoupled energy stable scheme for a hydrodynamic phase-field model of mixtures of nematic liquid crystals and viscous fluids

    NASA Astrophysics Data System (ADS)

    Zhao, Jia; Yang, Xiaofeng; Shen, Jie; Wang, Qi

    2016-01-01

    We develop a linear, first-order, decoupled, energy-stable scheme for a binary hydrodynamic phase field model of mixtures of nematic liquid crystals and viscous fluids that satisfies an energy dissipation law. We show that the semi-discrete scheme in time satisfies an analogous, semi-discrete energy-dissipation law for any time-step and is therefore unconditionally stable. We then discretize the spatial operators in the scheme by a finite-difference method and implement the fully discrete scheme in a simplified version using CUDA on GPUs in 3 dimensions in space and time. Two numerical examples for rupture of nematic liquid crystal filaments immersed in a viscous fluid matrix are given, illustrating the effectiveness of this new scheme in resolving complex interfacial phenomena in free surface flows of nematic liquid crystals.

  14. Electron paramagnetic resonance study of alinement induced by magnetic fields in two smectic-A liquid crystals not exhibiting nematic phases

    NASA Technical Reports Server (NTRS)

    Fryburg, G. C.; Gelerinter, E.

    1972-01-01

    Using vanadyl acetylacetonate (VAAC) as a paramagnetic probe, the molecular ordering in two smectic-A liquid crystals that do not display nematic phases were studied. Reproducible alinement was attained by slow cooling throughout the isotropic smectic-A transition in dc magnetic fields of 1.1 and 2.15 teslas. The degree of order attained is small for a smectic-A liquid crystal. Measurements were made of the variation of the average hyperfine splitting of the alined samples as a function of orientation relative to the dc magnetic field of the spectrometer. This functional dependence is in agreement with the theoretical prediction except where the viscosity of the liquid crystal becomes large enough to slow the tumbling of the VAAC, as indicated by asymmetry in the end lines of the spectrum.

  15. Investigations into complex liquid crystal mixtures

    NASA Astrophysics Data System (ADS)

    Kirchhoff, Jennifer

    Liquid crystal phases exhibit physical characteristics that lie between those of liquid and crystal phases. The many liquid crystal sub-phases are defined based on the degree of positional and orientational ordering the molecules have and the materials that make up these liquid crystal phases. This thesis presents a study of the molecular packing and physical properties of complex liquid crystal phases using dopants to better examine the stability and packing mechanisms of these phases. It also looks at the dispersion of quantum dots in liquid crystal materials, examining the electro-optical properties of the mixtures. The main goal of this thesis is to examine the effects of dopants on the properties of liquid crystal phases using optical microscopy, differential scanning calorimetry, electro-optical measurements, and X-ray scattering. For those mixtures with quantum dots fluorescence microscopy and photoluminescence measurements were also conducted. Rod-like liquid crystals are commonly used in display applications when the material is in a nematic liquid crystal phase, which is the least ordered phase exhibiting no positional ordering. The more complicated chiral smectic liquid crystal phases, which have a one dimensional layer structure, show potential for faster and tri-stable switching. A chiral rod-like liquid crystal material is doped with both chiral and achiral rod-like liquid crystals to examine the stability of one of the chiral smectic sub-phase, the SmC* FI1 phase. This phase consists of tilted molecules rotating about the cone defined by the tilt angle with a periodicity of three layers and an overall helical structure. The SmC*FI1 phase is stabilized by the competition between antiferroelectric and ferroelectric interactions, and small amounts of the achiral dopant broadens the range of this phase by almost 5°C. Higher dopant concentrations of the achiral material result in the destabilization of not just the SmC*FI1 phase but all tilted sub-phases

  16. Tunable liquid crystal photonic devices

    NASA Astrophysics Data System (ADS)

    Fan, Yun-Hsing

    2005-07-01

    Liquid crystal (LC)-based adaptive optics are important for information processing, optical interconnections, photonics, integrated optics, and optical communications due to their tunable optical properties. In this dissertation, we describe novel liquid crystal photonic devices. In Chap. 3, we demonstrate a novel electrically tunable-efficiency Fresnel lens which is devised for the first time using nanoscale PDLC. The tunable Fresnel lens is very desirable to eliminate the need of external spatial light modulator. The nanoscale LC devices are polarization independent and exhibit a fast response time. Because of the small droplet sizes, the operating voltage is higher than 100 Vrms. To lower the driving voltage, in Chap. 2 and Chap. 3, we have investigated tunable Fresnel lens using polymer-network liquid crystal (PNLC) and phase-separated composite film (PSCOF). The operating voltage is below 12 Vrms. The PNLC and PSCOF devices are polarization dependent. To overcome this shortcoming, stacking two cells with orthogonal alignment directions is a possibility. Using PNLC, we also demonstrated LC blazed grating. The diffraction efficiency of these devices is continuously controlled by the electric field. We also develop a system with continuously tunable focal length. A conventional mechanical zooming system is bulky and power hungry. In Chap. 4, we developed an electrically tunable-focus flat LC spherical lens and microlens array. A huge tunable range from 0.6 m to infinity is achieved by the applied voltage. In Chap. 5, we describe a LC microlens array whose focal length can be switched from positive to negative by the applied voltage. The fast response time feature of our LC microlens array will be very helpful in developing 3-D animated images. In Chap. 6, we demonstrate polymer network liquid crystals for switchable polarizers and optical shutters. The use of dual-frequency liquid crystal and special driving scheme leads to a sub-millisecond response time. In

  17. Large-angle and high-efficiency tunable phase grating using fringe field switching liquid crystal.

    PubMed

    Xu, Daming; Tan, Guanjun; Wu, Shin-Tson

    2015-05-01

    We propose a switchable phase grating using fringe field switching (FFS) cells. The FFS phase grating possesses several attractive features: large diffraction angle, high diffraction efficiency, fast response time, and high contrast ratio. It can diffract >32% light to ± 2nd orders with a large diffraction angle of 12.1°. Meanwhile, its response time remains relatively fast even at -40°C. A simulation model is developed to explain the experimental results and good agreement is obtained. We also demonstrate a blazed phase grating to achieve tunable beam steering between 0th, 1st and 2nd orders. PMID:25969314

  18. Tunable Meta-Liquid Crystals.

    PubMed

    Liu, Mingkai; Fan, Kebin; Padilla, Willie; Powell, David A; Zhang, Xin; Shadrivov, Ilya V

    2016-02-24

    Meta-liquid crystals, a novel form of tunable 3D metamaterials, are proposed and experimentally demonstrated in the terahertz frequency regime. A morphology change under a bias electric field and a strong modulation of the transmission are observed. In comparison to conventional liquid crystals, there is considerable freedom to prescribe the electromagnetic properties through the judicious design of the meta-atom geometry.

  19. Liquid phase adsorption of Crystal violet onto activated carbons derived from male flowers of coconut tree.

    PubMed

    Senthilkumaar, S; Kalaamani, P; Subburaam, C V

    2006-08-25

    Adsorption of Crystal violet, a basic dye onto phosphoric and sulphuric acid activated carbons (PAAC and SAAC), prepared from male flowers coconut tree has been investigated. Equilibrium data were successfully applied to study the kinetics and mechanism of adsorption of dye onto both the carbons. The kinetics of adsorption was found to be pseudo second order with regard to intraparticle diffusion. The pseudo second order is further supported by the Elovich model, which in turn intensifies the fact of chemisorption of dye onto both the carbons. Quantitative removal of dye at higher initial pH of dye solution reveals the basic nature of the Crystal violet and acidic nature of the activated carbons. Influence of temperature on the removal of dye from aqueous solution shows the feasibility of adsorption and its endothermic nature. Mass transfer studies were also carried out. The adsorption capacities of both the carbons were found to be 60.42 and 85.84 mg/g for PAAC and SAAC, respectively. Langmuir's isotherm data were used to design single-stage batch adsorption model.

  20. Anomalous viscoelasticity near the isotropic-nematic phase transition in liquid crystals.

    PubMed

    Jose, Prasanth P; Bagchi, Biman

    2004-10-01

    Recent optical Kerr effect experiments have shown that orientational relaxation of nematogens shows a pronounced slow down of the response function at intermediate times and also a power law decay near the isotropic-nematic (I-N) transition. In many aspects, this behavior appears to be rather similar to the ones observed in the supercooled liquid near-glass transition. We have performed molecular dynamics simulations of model nematogens (Gay-Berne with aspect ratio 3) to explore the viscoelasticity near the I-N transition and also investigated the correlation of viscoelasticity (if any) with orientational relaxation. It is found that although the viscosity indeed undergoes a somewhat sharper than normal change near the I-N transition, it is not characterized by any divergence-like behavior (like the ones observed in the supercooled liquid). The rotational friction, on the other hand, shows a much sharper rise as the I-N transition is approached. Interestingly, the probability distribution of the amplitude of the three components of the stress tensor shows anisotropy near the I-N transition-similar anisotropy has also been seen in the deeply supercooled liquid. Frequency dependence of viscosity shows several unusual behaviors: (a) There is a weak, power law dependence on frequency [eta(')(omega) approximately omega(-alpha)] at low frequencies and (b) there is a rapid increase in the sharp peak observed in eta(')(omega) in the intermediate frequency on approach to the I-N transition density. These features can be explained from the stress-stress time correlation function. The angular velocity correlation function also exhibits a power law decay in time. The reason for this is discussed. PMID:15473759

  1. Geometrical aspects of the frustration in the cubic phases of lyotropic liquid crystals.

    PubMed Central

    Anderson, D M; Gruner, S M; Leibler, S

    1988-01-01

    Bicontinuous cubic phases, composed of bilayers arranged in the geometries of periodic minimal surfaces, are found in a variety of different lipid/water systems. It has been suggested recently that these cubic structures arrive as the result of competition between two free-energy terms: the curvature energy of each monolayer and the stretching energy of the lipid chains. This scenario, closely analogous to the one that explains the origin of the hexagonal phases, is investigated here by means of simple geometrical calculations. It is first assumed that the lipid bilayer is of constant thickness and the distribution of the (local) mean curvature of the phospholipid-water interfaces is calculated. Then, assuming the mean curvature of these interfaces is constant, the distribution of the bilayer's thickness is calculated. Both calculations quantify the fact that the two energy terms are frustrated and cannot be satisfied simultaneously. However, the amount of the frustration can be smaller for the cubic phase than for the lamellar and hexagonal structures. Therefore, this phase can appear in the phase diagram between the other two, as observed in many recent experiments. PMID:3399497

  2. Modulation of phase behaviors and charge carrier mobilities by linkage length in discotic liquid crystal dimers.

    PubMed

    Wang, Yi-Fei; Zhang, Chun-Xiu; Wu, Hao; Zhang, Ao; Wang, Jian-Chuang; Zhang, Shuai-Feng; Pu, Jia-Ling

    2015-01-28

    A clear structure-property relationship was revealed in a series of triphenylene-based dimers, which contained two triphenylene nuclei each bearing five β-OC4H9 substituents and are linked through a flexible O(CH2)nO polymethylene chain (n=6-12). Dimers with the linkage close to twice the length of the free side chains (n=8, 9) exhibited a single Colhp phase, while others with the linkage shorter (n=6, 7) or longer (n=10, 11, 12) showed multiphase behaviors with a transition from the Colhp phase to Colh phase; hole mobilities of Colhp phases reached 1.4×10(-2) cm2 V(-1) s(-1) in the dimer for which the linkage is exactly twice the length of the free side chains (n=8), and decreased regularly both with linkage length becoming shorter or longer. This modulation of phase behaviors and charge carrier mobilities was demonstrated to be generated by various steric perturbations introduced by linkages with different lengths, which result in different degrees of lateral fluctuations of discotic moieties in the columns. PMID:25467212

  3. Modeling liquid crystal polymeric devices

    NASA Astrophysics Data System (ADS)

    Gimenez Pinto, Vianney Karina

    The main focus of this work is the theoretical and numerical study of materials that combine liquid crystal and polymer. Liquid crystal elastomers are polymeric materials that exhibit both the ordered properties of the liquid crystals and the elastic properties of rubbers. Changing the order of the liquid crystal molecules within the polymer network can induce shape change. These materials are very valuable for applications such as actuators, sensors, artificial muscles, haptic displays, etc. In this work we apply finite element elastodynamics simulations to study the temperature induced shape deformation in nematic elastomers with complex director microstructure. In another topic, we propose a novel numerical method to model the director dynamics and microstructural evolution of three dimensional nematic and cholesteric liquid crystals. Numerical studies presented in this work are in agreement with experimental observations and provide insight into the design of application devices.

  4. A model for the Pockels effect in distorted liquid crystal blue phases

    SciTech Connect

    Castles, F.

    2015-09-07

    Recent experiments have found that a mechanically distorted blue phase can exhibit a primary linear electro-optic (Pockels) effect [F. Castles et al., Nat. Mater. 13, 817 (2014)]. Here, it is shown that flexoelectricity can account for the experimental results and a model, which is based on continuum theory but takes into account the sub-unit-cell structure, is proposed. The model provides a quantitative description of the effect accurate to the nearest order of magnitude and predicts that the Pockels coefficient(s) in an optimally distorted blue phase may be two orders of magnitude larger than in lithium niobate.

  5. A ferroelectric liquid crystal conglomerate composed of racemic molecules

    PubMed

    Walba; Korblova; Shao; Maclennan; Link; Glaser; Clark

    2000-06-23

    We describe the design and synthesis of a ferroelectric liquid crystal composed of racemic molecules. The ferroelectric polarization results from spontaneous polar symmetry breaking in a fluid smectic. The ferroelectric phase is also chiral, resulting in the formation of a mixture of macroscopic domains of either handedness at the isotropic-to-liquid crystal phase transition. This smectic liquid crystal is thus a fluid conglomerate. Detailed investigation of the electrooptic and polarization current behavior within individual domains in liquid crystal cells shows the thermodynamically stable structure to be a uniformly tilted smectic bow-phase (banana phase), with all layer pairs homochiral and ferroelectric (SmC(S)P(F)).

  6. Order-parameter-aided temperature-accelerated sampling for the exploration of crystal polymorphism and solid-liquid phase transitions

    SciTech Connect

    Yu, Tang-Qing Vanden-Eijnden, Eric; Chen, Pei-Yang; Chen, Ming; Samanta, Amit; Tuckerman, Mark

    2014-06-07

    The problem of predicting polymorphism in atomic and molecular crystals constitutes a significant challenge both experimentally and theoretically. From the theoretical viewpoint, polymorphism prediction falls into the general class of problems characterized by an underlying rough energy landscape, and consequently, free energy based enhanced sampling approaches can be brought to bear on the problem. In this paper, we build on a scheme previously introduced by two of the authors in which the lengths and angles of the supercell are targeted for enhanced sampling via temperature accelerated adiabatic free energy dynamics [T. Q. Yu and M. E. Tuckerman, Phys. Rev. Lett. 107, 015701 (2011)]. Here, that framework is expanded to include general order parameters that distinguish different crystalline arrangements as target collective variables for enhanced sampling. The resulting free energy surface, being of quite high dimension, is nontrivial to reconstruct, and we discuss one particular strategy for performing the free energy analysis. The method is applied to the study of polymorphism in xenon crystals at high pressure and temperature using the Steinhardt order parameters without and with the supercell included in the set of collective variables. The expected fcc and bcc structures are obtained, and when the supercell parameters are included as collective variables, we also find several new structures, including fcc states with hcp stacking faults. We also apply the new method to the solid-liquid phase transition in copper at 1300 K using the same Steinhardt order parameters. Our method is able to melt and refreeze the system repeatedly, and the free energy profile can be obtained with high efficiency.

  7. Order-parameter-aided temperature-accelerated sampling for the exploration of crystal polymorphism and solid-liquid phase transitions

    NASA Astrophysics Data System (ADS)

    Yu, Tang-Qing; Chen, Pei-Yang; Chen, Ming; Samanta, Amit; Vanden-Eijnden, Eric; Tuckerman, Mark

    2014-06-01

    The problem of predicting polymorphism in atomic and molecular crystals constitutes a significant challenge both experimentally and theoretically. From the theoretical viewpoint, polymorphism prediction falls into the general class of problems characterized by an underlying rough energy landscape, and consequently, free energy based enhanced sampling approaches can be brought to bear on the problem. In this paper, we build on a scheme previously introduced by two of the authors in which the lengths and angles of the supercell are targeted for enhanced sampling via temperature accelerated adiabatic free energy dynamics [T. Q. Yu and M. E. Tuckerman, Phys. Rev. Lett. 107, 015701 (2011)]. Here, that framework is expanded to include general order parameters that distinguish different crystalline arrangements as target collective variables for enhanced sampling. The resulting free energy surface, being of quite high dimension, is nontrivial to reconstruct, and we discuss one particular strategy for performing the free energy analysis. The method is applied to the study of polymorphism in xenon crystals at high pressure and temperature using the Steinhardt order parameters without and with the supercell included in the set of collective variables. The expected fcc and bcc structures are obtained, and when the supercell parameters are included as collective variables, we also find several new structures, including fcc states with hcp stacking faults. We also apply the new method to the solid-liquid phase transition in copper at 1300 K using the same Steinhardt order parameters. Our method is able to melt and refreeze the system repeatedly, and the free energy profile can be obtained with high efficiency.

  8. Molecular ordering in the high-temperature nematic phase of an all-aromatic liquid crystal.

    PubMed

    Vita, Francesco; Hegde, Maruti; Portale, Giuseppe; Bras, Wim; Ferrero, Claudio; Samulski, Edward T; Francescangeli, Oriano; Dingemans, Theo

    2016-02-28

    We report the structural characterization of the nematic phase of 2,6-biphenyl naphthalene (PPNPP). This lath-like all-aromatic mesogen provides a valuable benchmark for classical theories of nematic order. PPNPP exhibits a very high temperature nematic phase (417-489 °C) above an enantiotropic smectic A phase. X-ray diffraction reveals a surprisingly strong tendency towards molecular layering in the nematic phase, indicative of "normal cybotaxis" (i.e. SmA-like stratification within clusters of mesogens). Although stronger at low temperatures, the layering is evident well above the smectic A-nematic transition. The nematic order parameter is evaluated as a function of temperature from the broadening of the wide-angle diffuse diffraction feature. Measured values of the orientational order parameter are slightly larger than those predicted by the Maier-Saupe theory over the entire nematic range except for a narrow region just below the clearing point where they significantly drop below the theoretical prediction.

  9. Liquid-liquid phase transition in a two-dimensional system with anomalous liquid properties.

    PubMed

    Urbic, Tomaz

    2013-12-01

    The phase diagram of the two-dimensional particles interacting through a smooth version of Stell-Hemmer interaction was studied using Monte Carlo computer simulations. By evaluating the pressure-volume isotherms, we observed liquid-liquid, liquid-gas phase transitions and three stable crystal phases. The model shows the liquid-liquid critical point in stable liquid phase and is confirmed by observing properties of other thermodynamic functions such as heat capacity and isothermal compressibility, for example. The liquid-gas and the liquid-liquid critical points were estimated within the thermodynamic limit.

  10. Nanoparticles in liquid crystals, and liquid crystals in nanoparticles

    NASA Astrophysics Data System (ADS)

    de Pablo, Juan

    2015-03-01

    Liquid crystals are remarkably sensitive to interfacial interactions. Small perturbations at a liquid crystal interface, for example, can be propagated over relatively long length scales, thereby providing the basis for a wide range of applications that rely on amplification of molecular events into macroscopic observables. Our recent research efforts have focused on the reverse phenomenon; that is, we have sought to manipulate the interfacial assembly of nanoparticles or the organization of surface active molecules by controlling the structure of a liquid crystal. This presentation will consist of a review of the basic principles that are responsible for liquid crystal-mediated interactions, followed by demonstrations of those principles in the context of two types of systems. In the first, a liquid crystal is used to direct the assembly of nanoparticles; through a combination of molecular and continuum models, it is found that minute changes in interfacial energy and particle size lead to liquid-crystal induced attractions that can span multiple orders of magnitude. Theoretical predictions are confirmed by experimental observations, which also suggest that LC-mediated assembly provides an effective means for fabrication of plasmonic devices. In the second type of system, the structure of a liquid crystal is controlled by confinement in submicron droplets. The morphology of the liquid crystal in a drop depends on a delicate balance between bulk and interfacial contributions to the free energy; that balance can be easily perturbed by adsorption of analytes or nanoparticles at the interface, thereby providing the basis for development of hierarchical assembly of responsive, anisotropic materials. Theoretical predictions also indicate that the three-dimensional order of a liquid crystal can be projected onto a two-dimensional interface, and give rise to novel nanostructures that are not found in simple isotropic fluids.

  11. Optical simulation of in-plane-switching blue phase liquid crystal display using the finite-difference time-domain method

    NASA Astrophysics Data System (ADS)

    Dou, Hu; Ma, Hongmei; Sun, Yu-Bao

    2016-09-01

    The finite-difference time-domain method is used to simulate the optical characteristics of an in-plane switching blue phase liquid crystal display. Compared with the matrix optic methods and the refractive method, the finite-difference time-domain method, which is used to directly solve Maxwell’s equations, can consider the lateral variation of the refractive index and obtain an accurate convergence effect. The simulation results show that e-rays and o-rays bend in different directions when the in-plane switching blue phase liquid crystal display is driven by the operating voltage. The finite-difference time-domain method should be used when the distribution of the liquid crystal in the liquid crystal display has a large lateral change. Project supported by the National Natural Science Foundation of China (Grant Nos. 11304074, 61475042, and 11274088), the Natural Science Foundation of Hebei Province, China (Grant Nos. A2015202320 and GCC2014048), and the Key Subject Construction Project of Hebei Province University, China.

  12. Charge transfer reactions in nematic liquid crystals

    SciTech Connect

    Wiederrecht, G.P.; Wasielewski, M.R. |; Galili, T.; Levanon, H.

    1998-07-01

    Ultrafast transient absorption studies of intramolecular photoinduced charge separation and thermal charge recombination were carried out on a molecule consisting of a 4-(N-pyrrolidino)naphthalene-1,8-imide donor (PNI) covalently attached to a pyromellitimide acceptor (PI) dissolved in the liquid crystal 4{prime}-(n-pentyl)-4-cyanobiphenyl (5CB). The temperature dependencies of the charge separation and recombination rates were obtained at temperatures above the nematic-isotropic phase transition of 5CB, where ordered microdomains exist and scattering of visible light by these domains is absent. The authors show that excited state charge separation is dominated by molecular reorientation of 5CB perpendicular to the director within the liquid crystal microdomains. They also show that charge recombination is adiabatic and is controlled by the comparatively slow collective reorientation of the liquid crystal microdomains relative to the orientation of PNI{sup +}-PI{sup {minus}}. They also report the results of time resolved electron paramagnetic resonance (TREPR) studies of photoinduced charge separation in a series of supramolecular compounds dissolved in oriented liquid crystal solvents. These studies permit the determination of the radical pair energy levels as the solvent reorganization energy increases from the low temperature crystalline phase, through the soft glass phase, to the nematic phase of the liquid crystal.

  13. Models for a liquid-liquid phase transition

    NASA Astrophysics Data System (ADS)

    Buldyrev, S. V.; Franzese, G.; Giovambattista, N.; Malescio, G.; Sadr-Lahijany, M. R.; Scala, A.; Skibinsky, A.; Stanley, H. E.

    2002-02-01

    We use molecular dynamics simulations to study two- and three-dimensional models with the isotropic double-step potential which in addition to the hard core has a repulsive soft core of larger radius. Our results indicate that the presence of two characteristic repulsive distances (hard core and soft core) is sufficient to explain liquid anomalies and a liquid-liquid phase transition, but these two phenomena may occur independently. Thus liquid-liquid transitions may exist in systems like liquid metals, regardless of the presence of the density anomaly. For 2D, we propose a model with a specific set of hard core and soft core parameters, that qualitatively reproduces the phase diagram and anomalies of liquid water. We identify two solid phases: a square crystal (high density phase), and a triangular crystal (low density phase) and discuss the relation between the anomalies of liquid and the polymorphism of the solid. Similarly to real water, our 2D system may have the second critical point in the metastable liquid phase beyond the freezing line. In 3D, we find several sets of parameters for which two fluid-fluid phase transition lines exist: the first line between gas and liquid and the second line between high-density liquid (HDL) and low-density liquid (LDL). In all cases, the LDL phase shows no density anomaly in 3D. We relate the absence of the density anomaly with the positive slope of the LDL-HDL phase transition line.

  14. Development of optical biosensor based on photonic crystal made of TiO2 using liquid phase deposition

    NASA Astrophysics Data System (ADS)

    Aono, Keigo; Aki, Shoma; Sueyoshi, Kenji; Hisamoto, Hideaki; Endo, Tatsuro

    2016-08-01

    We fabricated a titanium dioxide (TiO2)-based photonic crystal (PhC) using liquid phase deposition (LPD) to develop highly sensitive optical biosensors. The optical characteristics of the PhCs in the visible region were sensitive to the change in the refractive index of the surrounding medium due to an antigen–antibody reaction; thus, applications using the optical biosensor are expected to be highly sensitive. However, a base material with a high refractive index is indispensable for the fabrication of the PhC. Here, TiO2, which has optical transparency in the visible region, was selected as the high refractive index base material. The present LPD method allowed fabrication using low-cost apparatus. Furthermore, the mild conditions of the LPD method led to formation of TiO2-based PhC with fewer crack structures. Finally, the anti-neuron-specific enolase antibody was immobilized onto the TiO2-based PhC surface, and 1–1000 ng/mL of the neuron-specific enolase antigen was successfully detected.

  15. Development of optical biosensor based on photonic crystal made of TiO2 using liquid phase deposition

    NASA Astrophysics Data System (ADS)

    Aono, Keigo; Aki, Shoma; Sueyoshi, Kenji; Hisamoto, Hideaki; Endo, Tatsuro

    2016-08-01

    We fabricated a titanium dioxide (TiO2)-based photonic crystal (PhC) using liquid phase deposition (LPD) to develop highly sensitive optical biosensors. The optical characteristics of the PhCs in the visible region were sensitive to the change in the refractive index of the surrounding medium due to an antigen-antibody reaction; thus, applications using the optical biosensor are expected to be highly sensitive. However, a base material with a high refractive index is indispensable for the fabrication of the PhC. Here, TiO2, which has optical transparency in the visible region, was selected as the high refractive index base material. The present LPD method allowed fabrication using low-cost apparatus. Furthermore, the mild conditions of the LPD method led to formation of TiO2-based PhC with fewer crack structures. Finally, the anti-neuron-specific enolase antibody was immobilized onto the TiO2-based PhC surface, and 1-1000 ng/mL of the neuron-specific enolase antigen was successfully detected.

  16. Polarization independent Fabry-Pérot filter based on polymer-stabilized blue phase liquid crystals with fast response time.

    PubMed

    Chen, Yan-Han; Wang, Chun-Ta; Yu, Chin-Ping; Lin, Tsung-Hsien

    2011-12-01

    This work demonstrates a polarization-independent electrically tunable Fabry-Pérot (FP) filter that is based on polymer-stabilized blue phase liquid crystals (PSBPLCs). An external vertical electric field can be applied to modulate the effective refractive index of the PSBPLCs along the optical axis. Therefore, the wavelength-tuning property of the FP filter is completely independent of the polarization state of the incident light. The change in the birefringence in PSBPLCs is governed by Kerr effect-induced isotropic-to-anisotropic transition, and so the PSBPLCs based FP filter has a short response time. The measured tunability and free spectral range of the FP filter are 0.092 nm/ V and 16nm in the visible region, and 0.12nm/ V and 97nm in the NIR region, respectively, and the response time is in sub-millisecond range. The fast-responding polarization-independent electrically tunable FP filter has substantial potential for practical applications.

  17. Orientational fluctuations near the smectic A to smectic C phase transition in two "de Vries"-type liquid crystals.

    PubMed

    Nonnenmacher, Dorothee; Jagiella, Stefan; Song, Qingxiang; Lemieux, Robert P; Giesselmann, Frank

    2013-09-16

    On the basis of thorough analysis of 2D X-ray diffraction patterns from smectic monodomains, we examine the influence of orientational fluctuations on the weakly first-order smectic A (SmA) to smectic C (SmC) transitions in two nonchiral organosiloxane "de Vries"-type liquid crystals. We find that these materials exhibit very large molecular tilt fluctuations with magnitudes of up to 35°--thus larger than the average tilt itself. This is essential to understand the underlying molecular mechanism behind the practical absence of smectic layer contraction in these materials: in the SmA phase, the nematic order parameter is very low (molecular fluctuations correspondingly high), and the expected layer shrinkage at the SmA to SmC transition is almost fully compensated by the increase in orientational order, as the fluctuations diminish with decreasing temperature. In addition to the general tilt fluctuations, we observe intrinsic soft-mode fluctuations. They have a λ-shaped temperature dependence that peaks at the SmA-SmC transition with a maximum amplitude of about 2°.

  18. Bichromatic coherent random lasing from dye-doped polymer stabilized blue phase liquid crystals controlled by pump light polarization

    NASA Astrophysics Data System (ADS)

    Wang, Lei; Wang, Meng; Yang, Mingchao; Shi, Li-Jie; Deng, Luogen; Yang, Huai

    2016-09-01

    In this paper, we investigate the bichromatic coherent random lasing actions from the dye-doped polymer stabilized blue phase liquid crystals. Two groups of lasing peaks, of which the full widith at half maximum is about 0.3 nm, are clearly observed. The shorter- and longer-wavelength modes are associated with the excitation of the single laser dye (DCM) monomers and dimers respectively. The experimental results show that the competition between the two groups of the lasing peaks can be controlled by varying the polarization of the pump light. When the polarization of the pump light is rotated from 0° to 90°, the intensity of the shorter-wavelength lasing peak group reduces while the intensity of the longer-wavelength lasing peak group increases. In addition, a red shift of the longer-wavelength modes is also observed and the physical mechanisms behind the red-shift phenomenon are discussed. Project supported by the National Natural Science Foundation of China (Grant Nos. 11474021 and 51333001), the Key Program for International S&T Cooperation Projects of China (Grant No. 2013DFB50340), the Issues of Priority Development Areas of the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20120001130005), and the Key (Key Grant) Project of Chinese Ministry of Education (Grant No. 313002).

  19. Bichromatic coherent random lasing from dye-doped polymer stabilized blue phase liquid crystals controlled by pump light polarization

    NASA Astrophysics Data System (ADS)

    Wang, Lei; Wang, Meng; Yang, Mingchao; Shi, Li-Jie; Deng, Luogen; Yang, Huai

    2016-09-01

    In this paper, we investigate the bichromatic coherent random lasing actions from the dye-doped polymer stabilized blue phase liquid crystals. Two groups of lasing peaks, of which the full widith at half maximum is about 0.3 nm, are clearly observed. The shorter- and longer-wavelength modes are associated with the excitation of the single laser dye (DCM) monomers and dimers respectively. The experimental results show that the competition between the two groups of the lasing peaks can be controlled by varying the polarization of the pump light. When the polarization of the pump light is rotated from 0° to 90°, the intensity of the shorter-wavelength lasing peak group reduces while the intensity of the longer-wavelength lasing peak group increases. In addition, a red shift of the longer-wavelength modes is also observed and the physical mechanisms behind the red-shift phenomenon are discussed. Project supported by the National Natural Science Foundation of China (Grant Nos. 11474021 and 51333001), the Key Program for International S&T Cooperation Projects of China (Grant No. 2013DFB50340), the Issues of Priority Development Areas of the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20120001130005), and the Key (Key Grant) Project of Chinese Ministry of Education (Grant No. 313002).

  20. A Dual Modulated Homochiral Helical Nanofilament Phase with Local Columnar Ordering Formed by Bent Core Liquid Crystals: Effects of Molecular Chirality.

    PubMed

    Li, Lin; Salamonczyk, Miroslaw; Jákli, Antal; Hegmann, Torsten

    2016-08-01

    Helical nanofilament (HNF) phases form as a result of an intralayer mismatch between top and bottom molecular halves in bent-core liquid crystals (BC-LCs) that is relieved by local saddle-splay geometry. HNFs are immensely attractive for photovoltaic and chiral separation applications and as templates for the chiral spatial assembly of guest molecules. Here, the synthesis and characterization of two unichiral BC-LCs and one racemic mixture with tris-biphenyl-diester cores featuring chiral (R,R) and (S,S) or racemic 2-octyloxy aliphatic side chains are presented. In comparison to the achiral compound with linear side chains forming an intralayer modulated HNF phase (HNFmod ), synchrotron small angle X-ray diffraction indicates that the unichiral derivatives form a dual modulated HNF phase with intra- as well as interlayer modulations (HNFmod2 ) suggesting a columnar local structure of the nanofilaments. Transmission electron microscopy and circular dichroism spectropolarimetry confirm that the unichiral materials exclusively form homochiral HNFs with a twist sense-matching secondary twist. A contact preparation provides the first example of two identical chiral liquid crystal phases only differing in their handedness that do not mix and form an achiral liquid crystal phase with an entirely different structure in the contact zone.

  1. A Dual Modulated Homochiral Helical Nanofilament Phase with Local Columnar Ordering Formed by Bent Core Liquid Crystals: Effects of Molecular Chirality.

    PubMed

    Li, Lin; Salamonczyk, Miroslaw; Jákli, Antal; Hegmann, Torsten

    2016-08-01

    Helical nanofilament (HNF) phases form as a result of an intralayer mismatch between top and bottom molecular halves in bent-core liquid crystals (BC-LCs) that is relieved by local saddle-splay geometry. HNFs are immensely attractive for photovoltaic and chiral separation applications and as templates for the chiral spatial assembly of guest molecules. Here, the synthesis and characterization of two unichiral BC-LCs and one racemic mixture with tris-biphenyl-diester cores featuring chiral (R,R) and (S,S) or racemic 2-octyloxy aliphatic side chains are presented. In comparison to the achiral compound with linear side chains forming an intralayer modulated HNF phase (HNFmod ), synchrotron small angle X-ray diffraction indicates that the unichiral derivatives form a dual modulated HNF phase with intra- as well as interlayer modulations (HNFmod2 ) suggesting a columnar local structure of the nanofilaments. Transmission electron microscopy and circular dichroism spectropolarimetry confirm that the unichiral materials exclusively form homochiral HNFs with a twist sense-matching secondary twist. A contact preparation provides the first example of two identical chiral liquid crystal phases only differing in their handedness that do not mix and form an achiral liquid crystal phase with an entirely different structure in the contact zone. PMID:27334846

  2. Nanostructures of Liquid Crystal Phases in Mixtures of Bent-core and Rod-shaped Molecules

    SciTech Connect

    S Hong; R Verduzco; J Gleeson; S Sprunt; A Jakli

    2011-12-31

    We report small angle x-ray scattering (SAXS) studies of isotropic, nematic, and smectic mesophases formed by binary mixtures of bent-core (BC) and rod-shaped (RS) molecules. While optical studies indicate that the components are fully miscible, SAXS reveals fascinating structures that are consistent with segregation on a nanoscopic scale. We find that tilted smectic clusters, which have been previously reported in both the nematic and isotropic states of the pure BC materials, are also present in mixtures with up to 50 wt% of the RS compound; this is consistent with previous dielectric and flexoelectric studies on such mixtures. Unexpectedly in this concentration range the clusters are present in the isotropic and in the induced smectic phase range, as well as throughout the nematic phase. The results in the smectic phase also reveal complex layering phenomena, providing important insight into the interaction between bent and rod-shaped molecules. These studies will be crucial in the design of promising new functional nanomaterials.

  3. Helical phase of chiral nematic liquid crystals as the Bianchi VII0 group manifold.

    PubMed

    Gibbons, G W; Warnick, C M

    2011-09-01

    We show that the optical structure of the helical phase of a chiral nematic is naturally associated with the Bianchi VII(0) group manifold, of which we give a full account. The Joets-Ribotta metric governing propagation of the extraordinary rays is invariant under the simply transitive action of the universal cover E(2) of the three-dimensional Euclidean group of two dimensions. Thus extraordinary light rays are geodesics of a left-invariant metric on this Bianchi type VII(0) group. We are able to solve, by separation of variables, both the wave equation and the Hamilton-Jacobi equation for this metric. The former reduces to Mathieu's equation, and the latter to the quadrantal pendulum equation. We discuss Maxwell's equations for uniaxial optical materials where the configuration is invariant under a group action and develop a formalism to take advantage of these symmetries. The material is not assumed to be impedance matched, thus going beyond the usual scope of transformation optics. We show that for a chiral nematic in its helical phase Maxwell's equations reduce to a generalized Mathieu equation. Our results may also be relevant to helical phases of some magnetic materials and to light propagation in certain cosmological models. PMID:22060392

  4. Helical phase of chiral nematic liquid crystals as the Bianchi VII0 group manifold.

    PubMed

    Gibbons, G W; Warnick, C M

    2011-09-01

    We show that the optical structure of the helical phase of a chiral nematic is naturally associated with the Bianchi VII(0) group manifold, of which we give a full account. The Joets-Ribotta metric governing propagation of the extraordinary rays is invariant under the simply transitive action of the universal cover E(2) of the three-dimensional Euclidean group of two dimensions. Thus extraordinary light rays are geodesics of a left-invariant metric on this Bianchi type VII(0) group. We are able to solve, by separation of variables, both the wave equation and the Hamilton-Jacobi equation for this metric. The former reduces to Mathieu's equation, and the latter to the quadrantal pendulum equation. We discuss Maxwell's equations for uniaxial optical materials where the configuration is invariant under a group action and develop a formalism to take advantage of these symmetries. The material is not assumed to be impedance matched, thus going beyond the usual scope of transformation optics. We show that for a chiral nematic in its helical phase Maxwell's equations reduce to a generalized Mathieu equation. Our results may also be relevant to helical phases of some magnetic materials and to light propagation in certain cosmological models.

  5. Nanostructures of liquid crystal phases in mixtures of bent-core and rod-shaped molecules

    SciTech Connect

    Hong, S. H.; Gleeson, J. T.; Sprunt, S.; Verduzco, R.; Jakli, A.

    2011-06-15

    We report small angle x-ray scattering (SAXS) studies of isotropic, nematic, and smectic mesophases formed by binary mixtures of bent-core (BC) and rod-shaped (RS) molecules. While optical studies indicate that the components are fully miscible, SAXS reveals fascinating structures that are consistent with segregation on a nanoscopic scale. We find that tilted smectic clusters, which have been previously reported in both the nematic and isotropic states of the pure BC materials, are also present in mixtures with up to 50 wt% of the RS compound; this is consistent with previous dielectric and flexoelectric studies on such mixtures. Unexpectedly in this concentration range the clusters are present in the isotropic and in the induced smectic phase range, as well as throughout the nematic phase. The results in the smectic phase also reveal complex layering phenomena, providing important insight into the interaction between bent and rod-shaped molecules. These studies will be crucial in the design of promising new functional nanomaterials.

  6. Nanostructures of liquid crystal phases in mixtures of bent-core and rod-shaped molecules.

    PubMed

    Hong, S H; Verduzco, R; Gleeson, J T; Sprunt, S; Jákli, A

    2011-06-01

    We report small angle x-ray scattering (SAXS) studies of isotropic, nematic, and smectic mesophases formed by binary mixtures of bent-core (BC) and rod-shaped (RS) molecules. While optical studies indicate that the components are fully miscible, SAXS reveals fascinating structures that are consistent with segregation on a nanoscopic scale. We find that tilted smectic clusters, which have been previously reported in both the nematic and isotropic states of the pure BC materials, are also present in mixtures with up to 50 wt% of the RS compound; this is consistent with previous dielectric and flexoelectric studies on such mixtures. Unexpectedly in this concentration range the clusters are present in the isotropic and in the induced smectic phase range, as well as throughout the nematic phase. The results in the smectic phase also reveal complex layering phenomena, providing important insight into the interaction between bent and rod-shaped molecules. These studies will be crucial in the design of promising new functional nanomaterials.

  7. LIGHT NONAQUEOUS PHASE LIQUIDS

    EPA Science Inventory

    Nonaqueous phase liquids (NAPLS) are hydrocarbons that exist as a separate, immiscible phase when in contact with water and/or air. ifferences in the physical and chemical properties of water and NAPL result in the formation of a physical interface between the liquids which preve...

  8. Electric-field-induced switchable dark conglomerate phases in a bent-core liquid crystal exhibiting reverse columnar phases.

    PubMed

    Deepa, G B; Radhika, S; Sadashiva, B K; Pratibha, R

    2013-06-01

    Electric-field-induced transitions into switchable dark conglomerate (DC) phases from two types of reverse columnar mesophases have been observed in the bent-core (BC) compound 2,7-naphthylene bis[4-(3-methyl-4-n-tetradecyloxybenzoyloxy)] benzoate. Optical and x-ray studies show that the higher temperature columnar phase corresponds to the orthogonal B(1rev) phase, whereas the lower temperature columnar phase is a variant of the B(1revtilt) phase. As the layer fragments in this phase are modulated in order to relieve the steric hindrance caused by an anticlinic tilting in adjacent blocks, it has been named B(1revtiltM). The shape of the chiral domains are different in the DC phases viz. DC-B(1rev) and DC-B(1revtiltM) obtained by applying the electric field in the B(1rev) and B(1revtiltM) phases, respectively. While the chiral domains in the DC-B(1rev) phase appear similar to those observed in other DC phases, the shape of the domains in the DC-B(1revtiltM) phase appear to have some similarity to the domains in the banana leaf texture in the B(1revtiltM) phase implying that the detailed structure in this DC phase may be different. Optical observations, electro-optics, and dielectric studies show that the DC-B(1rev) and DC-B(1revtiltM) phases are both switchable and possess a local SmC(S)P(F) type of structure. As the temperature is decreased the switching behavior changes from ferroelectric to antiferroelectric. The temperature at which this changeover starts occurring coincides with the temperature at which the layer modulation occurs to overcome anticlinic tilt and the B(1rev) to B(1revtiltM) phase transition takes place without the application of the electric field. The change in switching behavior is attributed to a transformation into flat layers with the SmC(A)P(A) type of structure as also evidenced by the nucleation of bright regions alongside the chiral domains.

  9. Novel ferroelectric liquid crystals consisting glassy liquid crystal as chiral dopants

    NASA Astrophysics Data System (ADS)

    Chen, Huang-Ming Philip; Tsai, Yun-Yen; Lin, Chi-Wen; Shieh, Han-Ping David

    2006-08-01

    A series of ferroelectric liquid crystals consisting new glassy liquid crystals (GLCs) as chiral dopants were prepared and evaluated for their potentials in fast switching ability less than 1 ms. The properties of pure ferroelectric glassy liquid crystals (FGLCs) and mixtures were reported in this paper. In particular, the novel FGLC possessing wide chiral smectic C mesophase over 100 °C is able to suppress smectic A phase of host. The mixture containing 2.0 % GLC-1 performs greater alignment ability and higher contrast ratio than R2301 (Clariant, Japan) in a 2 μm pre-made cell (EHC, Japan). These results indicate that novel FLC mixtures consisting glassy liquid crystals present a promising liquid crystal materials for fast switching field sequential color displays.

  10. Pressure sensor using liquid crystals

    NASA Technical Reports Server (NTRS)

    Parmar, Devendra S. (Inventor); Holmes, Harlan K. (Inventor)

    1994-01-01

    A pressure sensor includes a liquid crystal positioned between transparent, electrically conductive films (18 and 20), that are biased by a voltage (V) which induces an electric field (E) that causes the liquid crystal to assume a first state of orientation. Application of pressure (P) to a flexible, transparent film (24) causes the conductive film (20) to move closer to or farther from the conductive film (18), thereby causing a change in the electric field (E'(P)) which causes the liquid crystal to assume a second state of orientation. Polarized light (P.sub.1) is directed into the liquid crystal and transmitted or reflected to an analyzer (A or 30). Changes in the state of orientation of the liquid crystal induced by applied pressure (P) result in a different light intensity being detected at the analyzer (A or 30) as a function of the applied pressure (P). In particular embodiments, the liquid crystal is present as droplets (10) in a polymer matrix (12) or in cells (14) in a polymeric or dielectric grid (16) material in the form of a layer (13) between the electrically conductive films (18 and 20). The liquid crystal fills the open wells in the polymer matrix (12) or grid (16) only partially.

  11. Liquid encapsulated crystal growth

    NASA Technical Reports Server (NTRS)

    Morrison, Andrew D. (Inventor)

    1987-01-01

    Low-defect crystals are grown in a closed ampoule under a layer of encapsulant. After crystal growth, the crystal is separated from the melt and moved into the layer of encapsulant and cooled to a first temperature at which crystal growth stops. The crystal is then moved into the inert gas ambient in the ampoule and further cooled. The crystal can be separated from the melt by decanting the melt into and adjacent reservoir or by rotating the ampoule to rotate the crystal into the encapsulant layer.

  12. Liquid encapsulated crystal growth

    NASA Technical Reports Server (NTRS)

    Morrison, Andrew D. (Inventor)

    1989-01-01

    Low-defect crystals are grown in a closed ampoule under a layer of encapsulant. After crystal growth, the crystal is separated from the melt and moved into the layer of encapsulant and cooled to a first temperature at which crystal growth stops. The crystal is then moved into the inert gas ambient in the ampoule and further cooled. The crystal can be separated from the melt by decanting the melt into an adjacent reservoir or by rotating the ampoule to rotate the crystal into the encapsulant layer.

  13. Dynamic Theory of Polydomain Liquid Crystal Elastomers.

    PubMed

    Duzgun, Ayhan; Selinger, Jonathan V

    2015-10-30

    When liquid crystal elastomers are prepared without any alignment, disordered polydomain structures emerge as the materials are cooled into the nematic phase. These polydomain structures are often attributed to quenched disorder in the cross-linked polymer network. As an alternative explanation, we develop a theory for the dynamics of the isotropic-nematic transition in liquid crystal elastomers, and show that the dynamics can induce a polydomain structure with a characteristic length scale, through a mechanism analogous to the Cahn-Hilliard equation for phase separation. PMID:26565497

  14. Dynamic Theory of Polydomain Liquid Crystal Elastomers

    NASA Astrophysics Data System (ADS)

    Duzgun, Ayhan; Selinger, Jonathan V.

    2015-10-01

    When liquid crystal elastomers are prepared without any alignment, disordered polydomain structures emerge as the materials are cooled into the nematic phase. These polydomain structures are often attributed to quenched disorder in the cross-linked polymer network. As an alternative explanation, we develop a theory for the dynamics of the isotropic-nematic transition in liquid crystal elastomers, and show that the dynamics can induce a polydomain structure with a characteristic length scale, through a mechanism analogous to the Cahn-Hilliard equation for phase separation.

  15. Critical behavior at transitions from uniaxial to biaxial phases in a smectic liquid-crystal mixture.

    PubMed

    Sasaki, Y; Ema, K; Le, K V; Takezoe, H; Dhara, S; Sadashiva, B K

    2010-07-01

    We report results of calorimetric and optical investigations of binary mixtures of rodlike and bent-shaped molecules. We find that the observed critical heat anomaly associated with the smectic-A2 to biaxial smectic-A2b transition is well described with a Fisher-renormalized form of the usual scaling expression. The effect of renormalization is large in this system in part because of the moderately steep slope of the phase boundary (dT(c)/ dX∼100 K, where X is the mole fraction of the bent-core molecules) and in part because of the proximity to the tricritical point. The magnitude of heat anomaly at the smectic-A2-smectic-A2b transition showed a drastic decrease as X becomes smaller. Moreover, the nematic-smectic-A2 transitions investigated turned out to be always first order and the transition enthalpy showed only weak dependence on the concentration X. The results imply that the energy fluctuations around the smectic-A2-smectic-A2b transition are very sensitive to the underlying ordering of the smectic-A2 background.

  16. Biological liquid crystal elastomers.

    PubMed

    Knight, David P; Vollrath, Fritz

    2002-02-28

    Liquid crystal elastomers (LCEs) have recently been described as a new class of matter. Here we review the evidence for the novel conclusion that the fibrillar collagens and the dragline silks of orb web spiders belong to this remarkable class of materials. Unlike conventional rubbers, LCEs are ordered, rather than disordered, at rest. The identification of these biopolymers as LCEs may have a predictive value. It may explain how collagens and spider dragline silks are assembled. It may provide a detailed explanation for their mechanical properties, accounting for the variation between different members of the collagen family and between the draglines in different spider species. It may provide a basis for the design of biomimetic collagen and dragline silk analogues by genetic engineering, peptide- or classical polymer synthesis. Biological LCEs may exhibit a range of exotic properties already identified in other members of this remarkable class of materials. In this paper, the possibility that other transversely banded fibrillar proteins are also LCEs is discussed.

  17. Tetrahedral Order in Banana Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Radzihovsky, Leo

    2005-03-01

    Bent-core liquid crystal molecules can exhibit phases that require a third-rank symmetric-traceless tensor order parameter, as well as a vector order parameter and the usual second-rank nematic order parameter. The combination gives rise to a rich variety of spatially homogeneous phases ranging from the well-known nematic to novel tetrahedratic and chiral liquids. I discuss experimental signatures of these phases and phase transitions between them.[0.3cm] L. Radzihovsky and T.C. Lubensky, Europhys. Lett.54, 206 (2001); Phys. Rev.E 66, 031704 (2002).

  18. Key Developments in Ionic Liquid Crystals.

    PubMed

    Alvarez Fernandez, Alexandra; Kouwer, Paul H J

    2016-05-16

    Ionic liquid crystals are materials that combine the classes of liquid crystals and ionic liquids. The first one is based on the multi-billion-dollar flat panel display industry, whilst the latter quickly developed in the past decades into a family of highly-tunable non-volatile solvents. The combination yields materials with a unique set of properties, but also with many challenges ahead. In this review, we provide an overview of the key concepts in ionic liquid crystals, particularly from a molecular perspective. What are the important molecular parameters that determine the phase behavior? How should they be introduced into the molecules? Finally, which other tools does one have to realize specific properties in the material?

  19. Key Developments in Ionic Liquid Crystals

    PubMed Central

    Alvarez Fernandez, Alexandra; Kouwer, Paul H. J.

    2016-01-01

    Ionic liquid crystals are materials that combine the classes of liquid crystals and ionic liquids. The first one is based on the multi-billion-dollar flat panel display industry, whilst the latter quickly developed in the past decades into a family of highly-tunable non-volatile solvents. The combination yields materials with a unique set of properties, but also with many challenges ahead. In this review, we provide an overview of the key concepts in ionic liquid crystals, particularly from a molecular perspective. What are the important molecular parameters that determine the phase behavior? How should they be introduced into the molecules? Finally, which other tools does one have to realize specific properties in the material? PMID:27196890

  20. A novel light trapping concept for liquid phase crystallized poly-Si thin-film solar cells on periodically nanoimprinted glass substrates

    NASA Astrophysics Data System (ADS)

    Preidel, V.; Amkreutz, D.; Sontheimer, T.; Back, F.; Rudigier-Voigt, E.; Rech, B.; Becker, C.

    2013-09-01

    Large grained polycrystalline silicon (poly-Si) absorbers were realized by electron beam induced liquid phase crystallization on 2 μm periodically patterned glass substrates and processed into a-Si:H/poly-Si heterojunction thin-film solar cells. The substrates were structured by nanoimprint lithography using a UV curable hybrid polymer sol-gel resist, resulting in a glassy high-temperature stable micro-structured surface. Structural analysis yielded high quality poly-Si material with grain sizes up to several hundred micrometers. An increase of absorption and an enhancement of the external quantum efficiency in the NIR as a consequence of light trapping due to the micro-structured poly-Si/substrate interface were observed. Up to now, only moderate solar cell parameters, a maximum open-circuit voltage of 413 mV and a short-circuit current density of 8 mA cm-2, were measured being significantly lower to what can be achieved with liquid phase crystallized poly-Si thin-film solar cells on planar glass substrates indicating that the substrate texture has impact on the electrical material quality. By reduction of the SiC interlayer thickness at the micro-structured poly- Si/substrate interface defect-related parasitic absorption was considerably minimized. This encourages the implementation of nanoimprinted tailored substrate textures for light trapping in liquid phase crystallized poly-Si thinfilm solar cells.

  1. Nanotube networks in liquid crystals

    NASA Astrophysics Data System (ADS)

    Urbanski, Martin; Lagerwall, Jan Peter F.; Scalia, Giusy

    2016-03-01

    Liquid crystals (LCs) are very attractive hosts for the organization of anisotropic nanoparticles such as carbon nanotubes (CNTs) because of the macroscopic organization resulting in properties of nanoparticles manifest at a macroscopic scale. Different types of LCs have demonstrated the ability to organize nanotubes, showing the generality of the approach, i.e., that the liquid crystallinity per se is the driving factor for the organization. Compared to standard nanotube composites (e.g. with disordered polymer hosts) the introduction of carbon nanotubes into an LC allows not only the transfer of the outstanding CNT properties to the macroscopic phase, providing strength and conductivity, but these properties also become anisotropic, following the transfer of the orientational order from the LC to the CNTs. The LC molecular structure plays an important even if ancillary role since it enters in the surface interactions, fulfilling a mediating action between the particle and the bulk of the LC. Isolated nanotubes can be obtained by optimized dispersions at lower concentrations and this process requires the use or development of tailored strategies like using solvents or even another LC for pre-dispersing CNTs. Aggregates or networks can be observed in poor dispersions and at higher nanoparticle concentrations. In those, due to surface interactions, the LC behaviour can be strongly affected with changes in phase sequences or transition temperatures and the effect is expected to be more pronounced as the concentration of nanotubes increases. We present preliminary investigations and observations on nanotube - LC systems based on a smectic LC host.

  2. Adaptive Liquid Crystal Windows

    SciTech Connect

    Taheri, Bahman; Bodnar, Volodymyr

    2011-12-31

    Energy consumption by private and commercial sectors in the U.S. has steadily grown over the last decade. The uncertainty in future availability of imported oil, on which the energy consumption relies strongly, resulted in a dramatic increase in the cost of energy. About 20% of this consumption are used to heat and cool houses and commercial buildings. To reduce dependence on the foreign oil and cut down emission of greenhouse gases, it is necessary to eliminate losses and reduce total energy consumption by buildings. To achieve this goal it is necessary to redefine the role of the conventional windows. At a minimum, windows should stop being a source for energy loss. Ideally, windows should become a source of energy, providing net gain to reduce energy used to heat and cool homes. It is possible to have a net energy gain from a window if its light transmission can be dynamically altered, ideally electronically without the need of operator assistance, providing optimal control of the solar gain that varies with season and climate in the U.S. In addition, the window must not require power from the building for operation. Resolution of this problem is a societal challenge and of national interest and will have a broad global impact. For this purpose, the year-round, allclimate window solution to provide an electronically variable solar heat gain coefficient (SHGC) with a wide dynamic range is needed. AlphaMicron, Inc. (AMI) developed and manufactured 1ft × 1ft prototype panels for the world’s first auto-adjusting Adaptive Liquid Crystal Windows (ALCWs) that can operate from sunlight without the need for external power source and demonstrate an electronically adjustable SHGC. This novel windows are based on AlphaMicron’s patented e-Tint® technology, a guesthost liquid crystal system implemented on flexible, optically clear plastic films. This technology is suitable both for OEM and aftermarket (retro-fitting) lamination to new and existing windows. Low level of

  3. Tactoids of chiral liquid crystals

    NASA Astrophysics Data System (ADS)

    Palacio-Betancur, Viviana; Villada-Gil, Stiven; Zhou, Ye; Armas-Pérez, Julio C.; de Pablo, Juan José; Hernández-Ortiz, Juan Pablo

    The phase diagram of chiral liquid crystals confined in ellipsoids is obtained, by following a theoretically informed Monte Carlo relaxation of the tensor alignment field Q. The free energy of the system is described by a functional in the framework of the Landau-de Gennes formalism. This study also includes the effect of anchoring strength, curvature, and chirality of the system. In the low chirality region of the phase diagram we found the twist bipolar (BS) phase and some cholesteric phases such as the radial spherical structure (RSS), twist cylinder (TC) and double twist cylinder (DTC) whose axis of rotation is not necessarily aligned with the major axis of the geometry. For high chirality scenarios, the disclination lines are twisted or bent near the surface preventing the formation of symmetric networks of defects, although an hexagonal pattern is formed on the surface which might serve as open sites for collocation of colloids. By analyzing the free energies of isochoric systems, prolate geometries tend to be more favorable for high chirality and low anchoring conditions. Universidad Nacional de Colombia Ph.D. grant and COLCIENCIAS under the Contract No. 110-165-843-748. CONACYT for Postdoctoral Fellowships Nos. 186166 and 203840.

  4. Tetrahedral Order in Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Pleiner, Harald; Brand, Helmut R.

    2016-10-01

    We review the impact of tetrahedral order on the macroscopic dynamics of bent-core liquid crystals. We discuss tetrahedral order comparing with other types of orientational order, like nematic, polar nematic, polar smectic, and active polar order. In particular, we present hydrodynamic equations for phases, where only tetrahedral order exists or tetrahedral order is combined with nematic order. Among the latter, we discriminate between three cases, where the nematic director (a) orients along a fourfold, (b) along a threefold symmetry axis of the tetrahedral structure, or (c) is homogeneously uncorrelated with the tetrahedron. For the optically isotropic T d phase, which only has tetrahedral order, we focus on the coupling of flow with, e.g., temperature gradients and on the specific orientation behavior in external electric fields. For the transition to the nematic phase, electric fields lead to a temperature shift that is linear in the field strength. Electric fields induce nematic order, again linear in the field strength. If strong enough, electric fields can change the tetrahedral structure and symmetry leading to a polar phase. We briefly deal with the T phase that arises when tetrahedral order occurs in a system of chiral molecules. To case (a), defined above, belong (i) the non-polar, achiral, optically uniaxial D2d phase with ambidextrous helicity (due to a linear gradient free energy contribution) and with orientational frustration in external fields, (ii) the non-polar tetragonal S4 phase, (iii) the non-polar, orthorhombic D2 phase that is structurally chiral featuring ambidextrous chirality, (iv) the polar orthorhombic C2v phase, and (v) the polar, structurally chiral, monoclinic C2 phase. Case (b) results in a trigonal C3v phase that behaves like a biaxial polar nematic phase. An example for case (c) is a splay bend phase, where the ground state is inhomogeneous due to a linear gradient free energy contribution. Finally, we discuss some experiments

  5. X-ray studies of the surface and bulk structure of the isotropic and nematic phase of a lyotropic liquid crystal

    SciTech Connect

    Swislow, G.; Schwartz, D.; Ocko, B.M.; Pershan, P.S. ); Litster, J.D. )

    1991-06-15

    We have used x-ray specular reflection to study the structure of the air--liquid-crystal interface of the lyotropic liquid crystal formed from binary mixtures of cesium perfluoro-octanoate (CsPFO) and water. In the isotropic phase the surface is coated with a monolayer of CsPFO separated by layers of water from one or more smectic bilayers of CsPFO. As for the case of thermotropic liquid crystals, the isotropic-to-nematic phase transition has no effect on the surface structure, and as the temperature is lowered towards the nematic--to--smectic-{ital A} transition temperature, the number of surface-induced smectic layers increases dramatically (e.g., approximately 100 layers were observed). Theoretical modeling of the reflectivity excludes the possibility that the surface bilayers are arrays of micelles. X-ray scattering from critical smectic short-range order in the bulk, studied by tuning the spectrometer away from the specular condition, indicates that the scattering is fundamentally different from short-range smectic order in thermotropic systems.

  6. Calorimetric study of the nematic to smectic- A and smectic- A to smectic- C phase transitions in liquid-crystal-aerosil dispersions

    NASA Astrophysics Data System (ADS)

    Roshi, A.; Iannacchione, G. S.; Clegg, P. S.; Birgeneau, R. J.; Neubert, M. E.

    2005-11-01

    A high-resolution calorimetric study has been carried out on nanocolloidal dispersions of aerosils in the liquid crystal 4-n -pentylphenylthiol- 4'-n -octyloxybenzoate (8¯S5) as a function of aerosil concentration and temperature spanning the smectic- C to nematic phases. Over this temperature range, this liquid crystal possesses two continuous XY phase transitions: a fluctuation-dominated nematic to smectic- A transition with α≈αXY=-0.013 and a mean-field smectic- A to smectic- C transition. The effective critical character of the N-SmA transition remains unchanged over the entire range of the introduced quenched random disorder while the peak height and enthalpy can be well described by considering a cutoff length scale to the quasicritical fluctuations. The robust nature of the N-SmA transition in this system contrasts with cyanobiphenyl-aerosil systems and may be due to the mesogens being nonpolar and having a long nematic range. The character of the SmA-SmC transition changes gradually with increasing disorder but remains mean field like. The heat capacity maximum at the SmA-SmC transition scales as ρS-0.5 with an apparent evolution from tricritical to a simple mean-field step behavior. These results may be generally understood as a stiffening of the liquid crystal (both the nematic elasticity as well as the smectic layer compression modulus B ) with silica density.

  7. Deuteron and proton NMR study of D2, p-dichlorobenzene and 1,3,5-trichlorobenzene in bimesogenic liquid crystals with two nematic phases

    NASA Astrophysics Data System (ADS)

    Burnell, E. E.; Ahmed, Z.; Welch, C.; Mehl, G. H.; Dong, R. Y.

    2016-08-01

    The solutes dideuterium, 1,3,5-trichlorobenzene and p-dichlorobenzene (pdcb) are co-dissolved in a 61/39 wt% mixture of CBC9CB/5CB, a bimesogenic liquid crystal with two nematic phases. NMR spectra are collected for each solute. The local electric field gradient (FZZ) is obtained from the dideuterium spectrum. A double Maier-Saupe potential (MSMS) is used to rationalize the order parameters of pdcb. The liquid-crystal fields G1 and G2 are taken to be due to size and shape interactions and interactions between the solute molecular quadrupole and the mean FZZ of the medium. The FZZ 's obtained from D2 and G2 (from pdcb) are compared and discussed.

  8. Pretransitional effects near the smectic-A-smectic-C* phase transition of hydrophilic and hydrophobic aerosil networks dispersed in ferroelectric liquid crystals

    SciTech Connect

    Cordoyiannis, George; Kralj, Samo; Nounesis, George; Kutnjak, Zdravko; Zumer, Slobodan

    2007-02-15

    A detailed x-ray scattering and high-resolution ac calorimetric study has been carried out near the smectic-A to chiral smectic-C phase transition of liquid-crystal compounds 4-(2-methyl butyl) phenyl 4-n-octylbiphenyl-4-carboxylate (CE8) and p-(n-decyloxy) benzylidene-p-amino-(2-methylbutyl) cinnamate (DOBAMBC) confined in hydrophilic and hydrophobic aerosil nanoparticle networks. The character of the transition, which is mean field near a tricritical point in bulk, is changed dramatically with an increase of aerosil-induced disorder. X-ray measurements revealed pretransitional behavior and compression of the smectic layers, phenomena that are strongly pronounced in high aerosil concentrations. A theoretical model that takes into account the interplay of relevant mechanisms is proposed to explain the observed phenomena. The effect of chirality on the interaction of liquid crystals with aerosils is discussed.

  9. Hierarchical Organization in Liquid Crystal-in-Liquid Crystal Emulsions

    PubMed Central

    Mushenheim, Peter C.

    2014-01-01

    We report the formation and characterization of hierarchical ordering in systems comprised of micrometer-sized droplets of thermotropic nematic liquid crystals (LCs) dispersed in continuous nematic phases of a lyotropic chromonic LC (disodium cromoglycate (DSCG)). Significantly, we find the orientations of the two LC phases to be coupled, with nematic droplets of 4′-pentyl-4-cyanobiphenyl (5CB) exhibiting a bipolar configuration with an axis of symmetry aligned orthogonal to the far-field director of the DSCG phase. We determine that this coupling of orientations does not result from either anisometric LC droplet shape or interfacial ionic phenomena but rather is consistent with the influence of van der Waals interactions that arise from the anisotropic polarizabilities of nematic 5CB (Δn = + 0.18) and DSCG (Δn = − 0.02) phases. We also find that it is possible to rotate and uniformly align the nematic droplets by using a weak magnetic field (B ∼ 0.3 T). An analysis of the dynamics of relaxation of the orientations of the 5CB droplets following removal of the magnetic field reveals the DSCG and 5CB droplets to be coupled by energies of ∼104kT, consistent with a simple theoretical estimate of the influence of anisotropic van der Waals interactions. We also observed the nematic 5CB droplets to form dimers and larger assemblies mediated by the elasticity of the nematic DSCG. Overall, these results reveal that LC-in-LC emulsions define a new class of hierarchically ordered soft matter in which both thermotropic and lyotropic LCs are coupled in their ordering. PMID:25278032

  10. Diastereomeric liquid crystal domains at the mesoscale.

    PubMed

    Chen, Dong; Tuchband, Michael R; Horanyi, Balazs; Korblova, Eva; Walba, David M; Glaser, Matthew A; Maclennan, Joseph E; Clark, Noel A

    2015-08-07

    In many technologies used to achieve separation of enantiomers, chiral selectors are designed to display differential affinity for the two enantiomers of a chiral compound. Such complexes are diastereomeric, differing in structure and free energy for the two enantiomers and enabling chiral discrimination. Here we present evidence for strong diastereomeric interaction effects at the mesoscale, manifested in chiral liquid crystal guest materials confined in a chiral, nanoporous network of semi-crystalline helical nanofilaments. The nanoporous host is itself an assembly of achiral, bent-core liquid crystal molecules that phase-separate into a conglomerate of 100 micron-scale, helical nanofilament domains that differ in structure only in the handedness of their homogeneous chirality. With the inclusion of a homochiral guest liquid crystal, these enantiomeric domains become diastereomeric, exhibiting unexpected and markedly different mesoscale structures and orientation transitions producing optical effects in which chirality has a dominant role.

  11. Diastereomeric liquid crystal domains at the mesoscale

    NASA Astrophysics Data System (ADS)

    Chen, Dong; Tuchband, Michael R.; Horanyi, Balazs; Korblova, Eva; Walba, David M.; Glaser, Matthew A.; Maclennan, Joseph E.; Clark, Noel A.

    2015-08-01

    In many technologies used to achieve separation of enantiomers, chiral selectors are designed to display differential affinity for the two enantiomers of a chiral compound. Such complexes are diastereomeric, differing in structure and free energy for the two enantiomers and enabling chiral discrimination. Here we present evidence for strong diastereomeric interaction effects at the mesoscale, manifested in chiral liquid crystal guest materials confined in a chiral, nanoporous network of semi-crystalline helical nanofilaments. The nanoporous host is itself an assembly of achiral, bent-core liquid crystal molecules that phase-separate into a conglomerate of 100 micron-scale, helical nanofilament domains that differ in structure only in the handedness of their homogeneous chirality. With the inclusion of a homochiral guest liquid crystal, these enantiomeric domains become diastereomeric, exhibiting unexpected and markedly different mesoscale structures and orientation transitions producing optical effects in which chirality has a dominant role.

  12. Molecular dynamics of biaxial nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Sarman, Sten

    1996-01-01

    We devise a constraint algorithm that makes the angular velocity of the director of a liquid crystal a constant of motion. When the angular velocity is set equal to zero, a director based coordinate system becomes an inertial frame. This is a great advantage because most thermodynamic properties and time correlation functions of a liquid crystal are best expressed relative to a director based coordinate system. One also prevents the director reorientation from interfering with the tails of the time correlation functions. When the angular velocity is forced to be zero the constraints do not do any work on the system. This makes it possible to prove that ensemble averages of phase functions and time correlation functions are unaffected by the director constraint torques. The constraint algorithm also facilitates generalization of nonequilibrium molecular dynamics algorithms to liquid crystal phases. In order to test the algorithm numerically we have simulated a biaxial nematic phase of a variant of the Gay-Berne fluid [J. G. Gay and B. J. Berne, J. Chem. Phys. 74, 3316 (1981)]. The director constraint algorithm works very well. We have calculated the velocity autocorrelation functions and the self diffusion coefficients. In a biaxial nematic liquid crystal there are three independent components of the self-diffusion tensor. They have been found to be finite and different thus proving that we really simulate a liquid rather than a solid and that the symmetry is biaxial. Simulation of biaxial liquid crystals requires fairly large systems. We have therefore developed an algorithm that we run on a parallel computer instead of an ordinary work station.

  13. Colloidal cholesteric liquid crystal in spherical confinement.

    PubMed

    Li, Yunfeng; Jun-Yan Suen, Jeffrey; Prince, Elisabeth; Larin, Egor M; Klinkova, Anna; Thérien-Aubin, Héloïse; Zhu, Shoujun; Yang, Bai; Helmy, Amr S; Lavrentovich, Oleg D; Kumacheva, Eugenia

    2016-01-01

    The organization of nanoparticles in constrained geometries is an area of fundamental and practical importance. Spherical confinement of nanocolloids leads to new modes of packing, self-assembly, phase separation and relaxation of colloidal liquids; however, it remains an unexplored area of research for colloidal liquid crystals. Here we report the organization of cholesteric liquid crystal formed by nanorods in spherical droplets. For cholesteric suspensions of cellulose nanocrystals, with progressive confinement, we observe phase separation into a micrometer-size isotropic droplet core and a cholesteric shell formed by concentric nanocrystal layers. Further confinement results in a transition to a bipolar planar cholesteric morphology. The distribution of polymer, metal, carbon or metal oxide nanoparticles in the droplets is governed by the nanoparticle size and yields cholesteric droplets exhibiting fluorescence, plasmonic properties and magnetic actuation. This work advances our understanding of how the interplay of order, confinement and topological defects affects the morphology of soft matter. PMID:27561545

  14. Colloidal cholesteric liquid crystal in spherical confinement

    PubMed Central

    Li, Yunfeng; Jun-Yan Suen, Jeffrey; Prince, Elisabeth; Larin, Egor M.; Klinkova, Anna; Thérien-Aubin, Héloïse; Zhu, Shoujun; Yang, Bai; Helmy, Amr S.; Lavrentovich, Oleg D.; Kumacheva, Eugenia

    2016-01-01

    The organization of nanoparticles in constrained geometries is an area of fundamental and practical importance. Spherical confinement of nanocolloids leads to new modes of packing, self-assembly, phase separation and relaxation of colloidal liquids; however, it remains an unexplored area of research for colloidal liquid crystals. Here we report the organization of cholesteric liquid crystal formed by nanorods in spherical droplets. For cholesteric suspensions of cellulose nanocrystals, with progressive confinement, we observe phase separation into a micrometer-size isotropic droplet core and a cholesteric shell formed by concentric nanocrystal layers. Further confinement results in a transition to a bipolar planar cholesteric morphology. The distribution of polymer, metal, carbon or metal oxide nanoparticles in the droplets is governed by the nanoparticle size and yields cholesteric droplets exhibiting fluorescence, plasmonic properties and magnetic actuation. This work advances our understanding of how the interplay of order, confinement and topological defects affects the morphology of soft matter. PMID:27561545

  15. Colloidal cholesteric liquid crystal in spherical confinement

    NASA Astrophysics Data System (ADS)

    Li, Yunfeng; Jun-Yan Suen, Jeffrey; Prince, Elisabeth; Larin, Egor M.; Klinkova, Anna; Thérien-Aubin, Héloïse; Zhu, Shoujun; Yang, Bai; Helmy, Amr S.; Lavrentovich, Oleg D.; Kumacheva, Eugenia

    2016-08-01

    The organization of nanoparticles in constrained geometries is an area of fundamental and practical importance. Spherical confinement of nanocolloids leads to new modes of packing, self-assembly, phase separation and relaxation of colloidal liquids; however, it remains an unexplored area of research for colloidal liquid crystals. Here we report the organization of cholesteric liquid crystal formed by nanorods in spherical droplets. For cholesteric suspensions of cellulose nanocrystals, with progressive confinement, we observe phase separation into a micrometer-size isotropic droplet core and a cholesteric shell formed by concentric nanocrystal layers. Further confinement results in a transition to a bipolar planar cholesteric morphology. The distribution of polymer, metal, carbon or metal oxide nanoparticles in the droplets is governed by the nanoparticle size and yields cholesteric droplets exhibiting fluorescence, plasmonic properties and magnetic actuation. This work advances our understanding of how the interplay of order, confinement and topological defects affects the morphology of soft matter.

  16. Orientational transitions in antiferromagnetic liquid crystals

    NASA Astrophysics Data System (ADS)

    Zakhlevnykh, A. N.; Petrov, D. A.

    2016-09-01

    The orientational phases in an antiferromagnetic liquid crystal (ferronematic) based on the nematic liquid crystal with the negative anisotropy of diamagnetic susceptibility are studied in the framework of the continuum theory. The ferronematic was assumed to be compensated; i.e., in zero field, impurity ferroparticles with the magnetic moments directed parallel and antiparallel to the director are equiprobably distributed in it. It is established that under the action of a magnetic field the ferronematic undergoes orientational transitions compensated (antiferromagnetic) phase-non-uniform phase-saturation (ferrimagnetic) phase. The analytical expressions for threshold fields of the transitions as functions of material parameters are obtained. It is shown that with increasing magnetic impurity segregation parameter, the threshold fields of the transitions significantly decrease. The bifurcation diagram of the ferronematic orientational phases is built in terms of the energy of anchoring of magnetic particles with the liquid-crystal matrix and magnetic field. It is established that the Freedericksz transition is the second-order phase transition, while the transition to the saturation state can be second- or first-order. In the latter case, the suspension exhibits orientational bistability. The orientational and magnetooptical properties of the ferronematic in different applied magnetic fields are studied.

  17. Liquid crystal thermography in boiling heat transfer

    SciTech Connect

    Klausner, J.F.; Mei, R.; Chen, W.C.

    1995-12-31

    The utilization of liquid crystal thermography to study heterogeneous boiling phenomena has gained popularity in recent years. In order not to disturb the nucleation process, which occurs in the microstructure of the heating surface, the crystals are applied to the backside of a thin heater. This work critically examines the ability of liquid crystal thermography to quantitatively capture the thermal field on the boiling surface. The thermal field identified experimentally through liquid crystal thermography is compared against that computed in the vicinity of a growing vapor bubble using a simulation which considers the simultaneous heat transfer between three phases: the solid heater, the liquid microlayer, and the growing vapor bubble. The temperature history beneath a growing vapor bubble elucidates the high frequency response required to capture the transient thermal fields commonly encountered in boiling experiments. Examination of the governing equations and numerical results reveal that due to the heater thermal inertia, the temperature variation on the bottom of the heater is significantly different than that on the boiling surface. In addition, the crystals themselves have a finite spatial resolution and frequency response which filter out much of the microscale phenomenon associated with boiling heat transfer. Analysis of existing pool and flow boiling liquid crystal thermographs indicate that the typical spacial resolution is on the order of 0.25 mm and the response time is on the order of 5 ms which are insufficient to resolve the fine spacial and temporal details of the heating surface thermal field. Thus the data obtained from liquid crystal thermography applied to boiling heat transfer must be cautiously interpreted.

  18. M3B2 and M5B3 Formation in Diffusion-Affected Zone During Transient Liquid Phase Bonding Single-Crystal Superalloys

    NASA Astrophysics Data System (ADS)

    Sheng, Naicheng; Hu, Xiaobing; Liu, Jide; Jin, Tao; Sun, Xiaofeng; Hu, Zhuangqi

    2015-04-01

    Precipitates in the diffusion-affected zone (DAZ) during transient liquid phase bonding (TLP) single-crystal superalloys were observed and investigated. Small size and dendritic-shaped precipitates were identified to be M3B2 borides and intergrowth of M3B2/M5B3 borides. The orientation relationships among M3B2, M5B3, and matrix were determined using transmission electron microscope (TEM). Composition characteristics of these borides were also analyzed by TEM energy-dispersive spectrometer. Because this precipitating phenomenon deviates from the traditional parabolic transient liquid phase bonding model which assumed a precipitates free DAZ during TLP bonding, some correlations between the deviation of the isothermal solidification kinetics and these newly observed precipitating behaviors were discussed and rationalized when bonding the interlayer containing the high diffusivity melting point depressant elements and substrates of low solubility.

  19. Phase diagrams of binary mixtures of liquid crystals and rodlike polymers in the presence of an external field.

    PubMed

    Matsuyama, Akihiko; Ueda, Tomomi

    2012-06-14

    We theoretically study phase separations in mixtures of a low molecular-weight-liquid crystalline molecule (LC) and a rigid-rodlike polymer (rod) under an external field, such as magnetic or electric fields. By taking into account two orientational order parameters of the rod and the LC, we define four nematic phases (N(0), N(1), N(2), N(3)) on the temperature-concentration plane. Depending on the sign of the dielectric anisotropy Δε(i) of the rod (i = 1) and LC(i = 2), we examine the phase behavior of rod/LC mixtures in the case of Δε(1) > 0, Δε(2) > 0 (a), Δε(1) < 0, Δε(2) > 0 (b), Δε(1) > 0, Δε(2) < 0 (c), and Δε(1) < 0, Δε(2) < 0 (d). We predict a variety of phase separations induced by an external field. PMID:22713070

  20. Detection of a new 'nematic-like' phase in liquid crystal-amphiphile mixture by differential scanning calorimetry

    NASA Astrophysics Data System (ADS)

    Dan, Kaustabh; Roy, Madhusudan; Datta, Alokmay

    2014-04-01

    Differential Scanning Calorimetry (DSC) studies on phase transitions of the pure liquid crystalline material N-4-methoxybenzylidene-4-butylaniline (MBBA) and mixtures of MBBA and the amphiphile Stearic Acid (StA) show significant changes in the behavior of mixture from pure MBBA, as regards the nematic-isotropic (N-I) transition temperature (Tc) and other thermodynamic parameters like enthalpy, specific heat and activation energy with concentration of StA. In particular, the convexity of the Arrhenius plot in pure MBBA vanishes with StA concentration pointing to the formation of a new, perhaps 'nematic-like', phase in the mixtures.

  1. Detection of a new 'nematic-like' phase in liquid crystal-amphiphile mixture by differential scanning calorimetry

    SciTech Connect

    Dan, Kaustabh Roy, Madhusudan Datta, Alokmay

    2014-04-24

    Differential Scanning Calorimetry (DSC) studies on phase transitions of the pure liquid crystalline material N-4-methoxybenzylidene-4-butylaniline (MBBA) and mixtures of MBBA and the amphiphile Stearic Acid (StA) show significant changes in the behavior of mixture from pure MBBA, as regards the nematic-isotropic (N-I) transition temperature (T{sub c}) and other thermodynamic parameters like enthalpy, specific heat and activation energy with concentration of StA. In particular, the convexity of the Arrhenius plot in pure MBBA vanishes with StA concentration pointing to the formation of a new, perhaps 'nematic-like', phase in the mixtures.

  2. A liquid crystal adaptive lens

    NASA Technical Reports Server (NTRS)

    Kowel, S. T.; Cleverly, D.

    1981-01-01

    Creation of an electronically controlled liquid crystal lens for use as a focusing mechanism in a multi-element lens system or as an adaptive optical element is analyzed. Varying the index of refraction is shown to be equivalent to the shaping of a solid refracting material. Basic characteristics of liquid crystals, essential for the creation of a lens, are reviewed. The required variation of index of refraction is provided by choosing appropriate electrode voltages. The configuration required for any incoming polarization is given and its theoretical performance in terms of modulation transfer function derived.

  3. Liquid crystal Fresnel lens display

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Qian; Abhishek Kumar, Srivastava; Alwin Tam, Ming-Wai; Zheng, Zhi-Gang; Shen, Dong; Vladimir, Chigrinov G.; Kwok, Hoi-Sing

    2016-09-01

    A novel see-through display with a liquid crystal lens array was proposed. A liquid crystal Fresnel lens display (LCFLD) with a holographic screen was demonstrated. The proposed display system has high efficiency, simple fabrication, and low manufacturing cost due to the absence of a polarizer and color filter. Project supported by Partner State Key Laboratory on Advanced Displays and Optoelectronics Technologies HKUST, China, the National Natural Science Foundation of China (Grant Nos. 61435008 and 61575063), and the Fundamental Research Funds for the Central Universities, China (Grant No. WM1514036).

  4. Liquid crystal Fresnel lens display

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Qian; Abhishek Kumar, Srivastava; Alwin Tam, Ming-Wai; Zheng, Zhi-Gang; Shen, Dong; Vladimir, Chigrinov G.; Kwok, Hoi-Sing

    2016-09-01

    A novel see-through display with a liquid crystal lens array was proposed. A liquid crystal Fresnel lens display (LCFLD) with a holographic screen was demonstrated. The proposed display system has high efficiency, simple fabrication, and low manufacturing cost due to the absence of a polarizer and color filter. Project supported by Partner State Key Laboratory on Advanced Displays and Optoelectronics Technologies HKUST, China, the National Natural Science Foundation of China (Grant Nos. 61435008 and 61575063), and the Fundamental Research Funds for the Central Universities, China (Grant No. WM1514036).

  5. Synthesis and Phase Behaviors of Supramolecular Liquid Crystals Based on 4-Octyldecyloxybenzoic Acid and 4-Hexadecyloxy Benzoic Acid in Binary Mixtures

    NASA Astrophysics Data System (ADS)

    Zhu, Lin-Jiang; Chen, Shao-Jun; Ban, Jian-Feng

    2016-05-01

    A series of supramolecular liquid crystals, named mOOBA-HOBA (m, which is the molar ratio of OOBA to HOBA) were successfully synthesized via mixing different molar ratio of 4-Octyldecyloxybenzoic acid (OOBA) and 4-hexadecyloxy benzoic acid (HOBA). The chemical and phase structures were investigated by the combination of techniques, including FT-IR, DSC, X-ray and POM. The experimental results revealed that the LC phase structures of the original symmetrical dimmers in OOBA and HOBA were both dissociated while a new asymmetrical dimmer was formed between OOBA with HOBA through hydrogen bonding in the binary mixture. DSC results show that the phase transition for entering into LC phase shifts to lower temperature, and the nematic-isotropic phase transition also shifts to lower temperature. These different phase transition behaviors should be ascribed to the asymmetrical dimmers between OOBA with HOBA. POM demonstrated that these OOBA-HOBA binary mixtures tend to show a lower liquid crystalline phase temperature and broad temperature range.

  6. Photoinduced crystal-to-liquid phase transitions of azobenzene derivatives and their application in photolithography processes through a solid-liquid patterning.

    PubMed

    Norikane, Yasuo; Uchida, Emi; Tanaka, Satoko; Fujiwara, Kyoko; Koyama, Emiko; Azumi, Reiko; Akiyama, Haruhisa; Kihara, Hideyuki; Yoshida, Masaru

    2014-10-01

    The direct and reversible transformation of matter between the solid and liquid phases by light at constant temperature is of great interest because of its potential applications in various manufacturing settings. We report a simple molecular design strategy for the phase transitions: azobenzenes having para-dialkoxy groups with a methyl group at the meta-position. The photolithography processes were demonstrated using the azobenzene as a photoresist in a single process combining development and etching of a copper substrate.

  7. Ionic Liquid Crystals: Versatile Materials.

    PubMed

    Goossens, Karel; Lava, Kathleen; Bielawski, Christopher W; Binnemans, Koen

    2016-04-27

    This Review covers the recent developments (2005-2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive overview of the "state-of-the-art" in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.

  8. Surfaces and chirality in liquid crystals

    NASA Astrophysics Data System (ADS)

    Kang, Daeseung

    1999-10-01

    The effects of surfaces and chirality in liquid crystals were studied in this thesis. Four different experiments were presented to investigate the different aspects of their role in liquid crystal physics. A liquid crystal cell treated for homeotropic alignment with different surfactants at the two surfaces was subjected to an electric field E in the plane of the cell. The longitudinal polarization at the surface couples with the external field, and in consequence exerts a torque on molecules. The differential optical retardation deltaalpha due to a slight deformation was found to be linear in field over a frequency range 10 < o < 105 Hz, where d(deltaalpha)/dE is proportional to o -1. As a different aspect of the surface, the phenomenon of a chiral liquid crystal in highly restricted geometry was also investigated, where the random surface dominates the bulk. The optical rotatory power of the chiral liquid crystal in the porous medium was drastically altered from that of the bulk liquid crystal. The observed behavior may be attributed to a combination of surface interactions and finite size effects, which are discussed in terms of an infrared cutoff in the orientational pair correlation function. Chirality manifests itself not only as an optical activity in nematics, but more strikingly in forms of ferroelectric and antiferroelectric phases in smectics. The anticlinic interlayer coupling coefficient U between smectic layers was evaluated for a pitch-compensated antiferroelectric liquid crystal by optical observation of the optic mode response to an in-plane electric field. The result is in good agreement with Us estimated from the threshold field for the onset of solitary waves, and provides a strong support for the switching model based on the free energy. Finally, a new trimer liquid crystal based on a terminal-lateral-lateral-terminal connection was investigated. Magnetically induced Freedericksz measurements were performed to extract the elastic constants of

  9. Bistable liquid crystal device fabricated via microscale liquid crystal alignment

    NASA Astrophysics Data System (ADS)

    Honma, Michinori; Toyoshima, Wataru; Nose, Toshiaki

    2016-10-01

    Bistable liquid crystal (LC) molecular orientation properties in micropatterned LC cells were investigated experimentally and theoretically. When an LC cell was heated to the phase-transition temperature and then cooled, an LC orientation with ±π/2-twist domains (±π/2-twist mode) was obtained. Furthermore, a different LC orientation with ±π-twist domains (±π-twist mode) was observed when a 10-V potential was applied across a sample LC cell. Both orientation states were stably retained over a long period. Herein, cross-sectional LC orientation models in the ±π/2- and ±π-twist modes are proposed to explain the generation and behavior of two different disclination lines. The total energies within one period in the ±π/2- and ±π-twist modes (F±π/2 and F±π, respectively) were estimated theoretically. These energies were found to depend on the LC layer thickness and to cross over at a certain thickness; this indicates that F±π is equal to F±π/2 at this equilibrium thickness. The best temporal stability is likely attained at this equilibrium thickness. We demonstrated a bistable color-switching device by combining a full-wave plate and crossed polarizers. When these optical components were configured properly, stable bistable switching between two colors was achieved.

  10. Liquid-crystal prisms for tip-tilt adaptive optics.

    PubMed

    Love, G D; Major, J V; Purvis, A

    1994-08-01

    Results from an electrically addressed liquid-crystal cell producing continuous phase profiles are presented. The adaptive deflection of a beam of light for use in a tip-tilt adaptive optics system is demonstrated. We compare the optical performance of liquid-crystal prisms with experimental data on atmospheric seeing at the William Herschel Telescope.

  11. Liquid-crystal prisms for tip-tilt adaptive optics.

    PubMed

    Love, G D; Major, J V; Purvis, A

    1994-08-01

    Results from an electrically addressed liquid-crystal cell producing continuous phase profiles are presented. The adaptive deflection of a beam of light for use in a tip-tilt adaptive optics system is demonstrated. We compare the optical performance of liquid-crystal prisms with experimental data on atmospheric seeing at the William Herschel Telescope. PMID:19844566

  12. Electrically Tunable Microlens via Photopolymerization-Induced Phase Separation of Liquid Crystal/Monomer Mixtures Based on Four-Wave Mixing

    NASA Astrophysics Data System (ADS)

    Kyu, Thein; Nwabunma, Domasius

    2001-03-01

    We introduce a new method of fabricating electrically tunable liquid crystal (LC) microlens via photopolymerization-induced phase separation of LC/monomer mixtures using four-wave mixing technique, i.e., interference of two horizontal and two vertical waves. The microlens forming process was simulated based on a spatially modulated photopolymerization reaction coupled with the time-dependent Ginzburg-Landau (TDGL) Model C equations, which incorporate free energy densities due to isotropic mixing, LC ordering, and polymer network elasticity. Our simulation revealed that the calculated LC microlens are similar to the compound eyes found in the eyes of insects such as flies, ants, and wasps.

  13. Molecular reorientation of a nematic liquid crystal by thermal expansion

    PubMed Central

    Kim, Young-Ki; Senyuk, Bohdan; Lavrentovich, Oleg D.

    2012-01-01

    A unique feature of nematic liquid crystals is orientational order of molecules that can be controlled by electromagnetic fields, surface modifications and pressure gradients. Here we demonstrate a new effect in which the orientation of nematic liquid crystal molecules is altered by thermal expansion. Thermal expansion (or contraction) causes the nematic liquid crystal to flow; the flow imposes a realigning torque on the nematic liquid crystal molecules and the optic axis. The optical and mechanical responses activated by a simple temperature change can be used in sensing, photonics, microfluidic, optofluidic and lab-on-a-chip applications as they do not require externally imposed gradients of temperature, pressure, surface realignment, nor electromagnetic fields. The effect has important ramifications for the current search of the biaxial nematic phase as the optical features of thermally induced structural changes in the uniaxial nematic liquid crystal mimic the features expected of the biaxial nematic liquid crystal. PMID:23072803

  14. CdSe nanoparticles dispersed in ferroelectric smectic liquid crystals: effects upon the smectic order and the smectic-A to chiral smectic-C phase transition.

    PubMed

    Thanassoulas, Angelos; Karatairi, Eva; Cordoyiannis, George; Kutnjak, Zdravko; Tzitzios, Vassilios; Lelidis, Ioannis; Nounesis, George

    2013-09-01

    Spherical CdSe nanoparticles, surface-treated with oleylamine and tri-octylphosphine, dispersed in ferroelectric liquid crystals, can efficiently target disclination lines, substantially altering the macroscopic properties of the host compound. Here we present an ac calorimetry and x-ray diffraction study demonstrating that for a large range of nanoparticle concentrations the smectic-A layer thickness increases monotonically. This provides evidence for enhanced accumulation of nanoparticles at the smectic layers. Our results for the Smectic-A (SmA) to chiral smectic-C (SmC) phase transition of the liquid crystal S-(+)4-(2'-methylbutyl)phenyl-4'-n-octylbiphenyl-4-carboxylate (CE8) reveal that the character of the transition is profoundly changed as a function of the nanoparticle concentration. Large transition temperature shifts are recorded. Moreover, the heat-capacity peaks exhibit a crossover trend to a step-like anomaly. This behavior may be linked to the weakening of the SmA and SmC order parameter coupling responsible for the observed near-tricritical, mean-field character of the transition in bulk CE8. At lower temperatures, the presence of nanoparticles disrupts the phase sequence involving the tilted hexatic phases most likely by obstructing the establishment of long-range bond-orientational order.

  15. Copper sulfate: Liquid or crystals?

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Two separate experiments were conducted to evaluate copper toxicity to channel catfish and free-swimming Ichthyophthirius multifiliis or Ich (the stage of Ich that can be treated); the compounds we used were CuSO4 crystals and a non-chelated liquid CuSO4 product. In 96 hr tests conducted in aquaria...

  16. Liquid-Crystal Optical Correlator

    NASA Technical Reports Server (NTRS)

    Liu, Hua-Kuang

    1989-01-01

    Optical correlator uses commercially-available liquid-crystal television (LCTV) screen as spatial light modulator. Correlations with this device done at video frame rates, making such operations as bar-code recognition possible at reasonable cost. With further development, such correlator useful in automation, robotic vision, and optical image processing.

  17. Experiments with Cholesteric Liquid Crystals

    ERIC Educational Resources Information Center

    Fergason, James L.

    1970-01-01

    Describes laboratory experiments designed to demonstrate (1) the properties of cholesteric liquid crystals, (2) thermal mapping, (3) thermal diffusivity, (4) adiabatic expansion of rubber, and (5) measurement of radiated energy by a point source. Contains all of the information on materials and apparatus needed to perform the experiments.…

  18. Phase behaviors of binary mixtures composed of electron-rich and electron-poor triphenylene discotic liquid crystals

    NASA Astrophysics Data System (ADS)

    An, Lingling; Jing, Min; Xiao, Bo; Bai, Xiao-Yan; Zeng, Qing-Dao; Zhao, Ke-Qing

    2016-09-01

    Disk-like liquid crystals (DLCs) can self-assemble to ordered columnar mesophases and are intriguing one-dimensional organic semiconductors with high charge carrier mobility. To improve their applicable property of mesomorphic temperature ranges, we exploit the binary mixtures of electronic donor-acceptor DLC materials. The electron-rich 2,3,6,7,10,11-hexakis(alkoxy)triphenylenes (C4, C6, C8, C10, C12) and an electron-deficient tetrapentyl triphenylene-2,3,6,10-tetracarboxylate have been prepared and their binary mixtures have been investigated. The mesomorphism of the 1:1 (molar ratio) mixtures has been characterized by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and small angel x-ray scattering (SAXS). The self-assembled monolayer structure of a discogen on a solid-liquid interface has been imaged by the high resolution scanning tunneling microscopy (STM). The match of peripheral chain length has important influence on the mesomorphism of the binary mixtures. Project supported by the National Natural Science Foundation of China (Grant Nos. 51273133 and 51443004).

  19. Controllable light diffraction in woodpile photonic crystals filled with liquid crystal

    SciTech Connect

    Ho, Chih-Hua; Zeng, Hao; Wiersma, Diederik S.; Cheng, Yu-Chieh; Maigyte, Lina; Trull, Jose; Cojocaru, Crina; Staliunas, Kestutis

    2015-01-12

    An approach to switching between different patterns of light beams transmitted through the woodpile photonic crystals filled with liquid crystals is proposed. The phase transition between the nematic and isotropic liquid crystal states leads to an observable variation of the spatial pattern transmitted through the photonic structure. The transmission profiles in the nematic phase also show polarization sensibility due to refractive index dependence on the field polarization. The experimental results are consistent with a numerical calculation by Finite Difference Time Domain method.

  20. Orthoconic liquid crystals--a case study.

    PubMed

    Lagerwall, Sven T

    2014-06-01

    Since the early investigations on liquid crystals it was realized how the confining surfaces often determine the textures and even properties of the material. This influence is particularly complex and important for chiral materials. When we come to chiral smectics the surfaces may have dramatic effects. These are illustrated on the ferroelectric liquid crystals; they then again increase in importance for the antiferroelectric liquid crystals where the most recent example is given by the orthoconic liquid crystals.

  1. Liquid crystal polyester thermosets

    DOEpatents

    Benicewicz, Brian C.; Hoyt, Andrea E.

    1992-01-01

    The present invention provides (1) curable liquid crystalline polyester monomers represented by the formula: R.sup.1 --A.sup.1 --B.sup.1 --A.sup.2 --B.sup.2 --A.sup.3 --R.sup.2 where R.sup.1 and R.sup.2 are radicals selected from the group consisting of maleimide, substituted maleimide, nadimide, substituted naimide, ethynyl, and (C(R.sup.3).sub.2).sub.2 where R.sup.3 is hydrogen with the proviso that the two carbon atoms of (C(R.sup.3).sub.2).sub.2 are bound on the aromatic ring of A.sup.1 or A.sup.3 to adjacent carbon atoms, A.sup.1 and A.sup.3 are 1,4-phenylene and the same where said group contains one or more substituents selected from the group consisting of halo, e.g., fluoro, chloro, bromo, or iodo, nitro lower alkyl, e.g., methyl, ethyl, or propyl, alkoxy, e.g., methoxy, ethoxy, or propoxy, and fluoroalkyl, e.g., trifluoromethyl, pentafluoroethyl and the like, A.sup.2 is selected from the group consisting of 1,4-phenylene, 4,4'-biphenyl, 2,6-naphthylene and the same where said groups contain one or more substituents selected from the group consisting of halo, e.g., fluoro, chloro, bromo, or iodo, nitro, lower alkyl, e.g., methyl, ethyl, and propyl, lower alkoxy, e.g., methoxy, ethoxy, or propoxy, and fluoroalkyl or fluoroalkoxy, e.g., trifluoromethyl, pentafluoroethyl and the like, and B.sup.1 and B.sup.2 are selected from the group consisting of --C(O)--O-- and --O--C(O)--, (2) thermoset liquid crystalline polyester compositions comprised of heat-cured segments derived from monomers represented by the formula: R.sup.1 --A.sup.1 --B.sup.1 --A.sup.2 --B.sup.2 --A.sup.3 --R.sup.2 as described above, (3) curable blends of at least two of the polyester monomers and (4) processes of preparing the curable liquid crystalline polyester monomers.

  2. Liquid crystal assemblies in biologically inspired systems

    PubMed Central

    Safinya, Cyrus R.; Deek, Joanna; Beck, Roy; Jones, Jayna B.; Leal, Cecilia; Ewert, Kai K.; Li, Youli

    2013-01-01

    In this paper, which is part of a collection in honor of Noel Clark's remarkable career on liquid crystal and soft matter research, we present examples of biologically inspired systems, which form liquid crystal (LC) phases with their LC nature impacting biological function in cells or being important in biomedical applications. One area focuses on understanding network and bundle formation of cytoskeletal polyampholytes (filamentous-actin, microtubules, and neurofilaments). Here, we describe studies on neurofilaments (NFs), the intermediate filaments of neurons, which form open network nematic liquid crystal hydrogels in axons. Synchrotron small-angle-x-ray scattering studies of NF-protein dilution experiments and NF hydrogels subjected to osmotic stress show that neurofilament networks are stabilized by competing long-range repulsion and attractions mediated by the neurofilament's polyampholytic sidearms. The attractions are present both at very large interfilament spacings, in the weak sidearm-interpenetrating regime, and at smaller interfilament spacings, in the strong sidearm-interpenetrating regime. A second series of experiments will describe the structure and properties of cationic liposomes (CLs) complexed with nucleic acids (NAs). CL-NA complexes form liquid crystalline phases, which interact in a structure-dependent manner with cellular membranes enabling the design of complexes for efficient delivery of nucleic acid (DNA, RNA) in therapeutic applications. PMID:24558293

  3. Fluctuations and phase transitions in Larkin-Ovchinnikov liquid-crystal states of a population-imbalanced resonant Fermi gas

    NASA Astrophysics Data System (ADS)

    Radzihovsky, Leo

    2011-08-01

    Motivated by a realization of imbalanced Feshbach-resonant atomic Fermi gases, we formulate a low-energy theory of the Fulde-Ferrell and the Larkin-Ovchinnikov (LO) states and use it to analyze fluctuations, stability, and phase transitions in these enigmatic finite momentum-paired superfluids. Focusing on the unidirectional LO pair-density-wave state, which spontaneously breaks the continuous rotational and translational symmetries, we show that it is characterized by two Goldstone modes, corresponding to a superfluid phase and a smectic phonon. Because of the liquid-crystalline “softness” of the latter, at finite temperature the three-dimensional state is characterized by a vanishing LO order parameter, quasi-Bragg peaks in the structure and momentum distribution functions, and a “charge”-4, paired-Cooper-pairs, off-diagonal long-range order, with a superfluid-stiffness anisotropy that diverges near a transition into a nonsuperfluid state. In addition to conventional integer vortices and dislocations, the LO superfluid smectic exhibits composite half-integer vortex-dislocation defects. A proliferation of defects leads to a rich variety of descendant states, such as the charge-4 superfluid and Fermi-liquid nematics and topologically ordered nonsuperfluid states, that generically intervene between the LO state and the conventional superfluid and the polarized Fermi liquid at low and high imbalance, respectively. The fermionic sector of the LO gapless superconductor is also quite unique, exhibiting a Fermi surface of Bogoliubov quasiparticles associated with the Andreev band of states, localized on the array of the LO domain walls.

  4. Fluctuations and phase transitions in Larkin-Ovchinnikov liquid-crystal states of a population-imbalanced resonant Fermi gas

    SciTech Connect

    Radzihovsky, Leo

    2011-08-15

    Motivated by a realization of imbalanced Feshbach-resonant atomic Fermi gases, we formulate a low-energy theory of the Fulde-Ferrell and the Larkin-Ovchinnikov (LO) states and use it to analyze fluctuations, stability, and phase transitions in these enigmatic finite momentum-paired superfluids. Focusing on the unidirectional LO pair-density-wave state, which spontaneously breaks the continuous rotational and translational symmetries, we show that it is characterized by two Goldstone modes, corresponding to a superfluid phase and a smectic phonon. Because of the liquid-crystalline ''softness'' of the latter, at finite temperature the three-dimensional state is characterized by a vanishing LO order parameter, quasi-Bragg peaks in the structure and momentum distribution functions, and a ''charge''-4, paired-Cooper-pairs, off-diagonal long-range order, with a superfluid-stiffness anisotropy that diverges near a transition into a nonsuperfluid state. In addition to conventional integer vortices and dislocations, the LO superfluid smectic exhibits composite half-integer vortex-dislocation defects. A proliferation of defects leads to a rich variety of descendant states, such as the charge-4 superfluid and Fermi-liquid nematics and topologically ordered nonsuperfluid states, that generically intervene between the LO state and the conventional superfluid and the polarized Fermi liquid at low and high imbalance, respectively. The fermionic sector of the LO gapless superconductor is also quite unique, exhibiting a Fermi surface of Bogoliubov quasiparticles associated with the Andreev band of states, localized on the array of the LO domain walls.

  5. Optical solitons in liquid crystals

    SciTech Connect

    Yung, Y.S.; Lam, L.; Los Alamos National Lab., NM )

    1989-01-01

    In this paper, we will discuss theoretically the possible existence of optical solitons in the isotropic liquid and in the nematic phase. For the same compound, when heated, the nematic phase will go through a first order transition at temperature T{sub c} to the isotropic liquid phase. As temperature increases from below T{sub c}, the orientation order parameter, Q, decreases, drops to zero abruptly at T{sub c} and remains zero for T > T{sub c}. 10 refs., 1 fig.

  6. Universal scaling of dielectric response of various liquid crystals and glass-forming liquids

    NASA Astrophysics Data System (ADS)

    Gałązka, M.; Juszyńska-Gałązka, E.; Osiecka, N.; Bąk, A.

    2016-04-01

    We present a new generalized scaling relationship accounting both for the real and imaginary parts of the complex permittivity data. The generalized scaling procedure has been successfully used for various relaxation processes in liquid crystals (4-bromobenzylidene-4‧-pentyloxyaniline, 4-bromobenzylidene-4‧-hexyloxyaniline, 4‧-butyl-4-(2-methylbutoxy)-azoxybenzene, 4-ethyl-4‧-octylazoxybenzene), and in glass-forming liquids (glycerol, propylene carbonate, salol, cresolphthalein-dimethylether). As it is shown, one obtains common master-curve for liquid-like phases (isotropic liquid, cholesteric, nematic, smectic A), solid-like phases (smectic B, conformationally disorder crystal) and supercooled liquid phase.

  7. Finite-size effects on liquid-solid phase coexistence and the estimation of crystal nucleation barriers.

    PubMed

    Statt, Antonia; Virnau, Peter; Binder, Kurt

    2015-01-16

    A fluid in equilibrium in a finite volume V with particle number N at a density ρ=N/V exceeding the onset density ρ_{f} of freezing may exhibit phase coexistence between a crystalline nucleus and surrounding fluid. Using a method suitable for the estimation of the chemical potential of dense fluids, we obtain the excess free energy due to the surface of the crystalline nucleus. There is neither a need to precisely locate the interface nor to compute the (anisotropic) interfacial tension. As a test case, a soft version of the Asakura-Oosawa model for colloid-polymer mixtures is treated. While our analysis is appropriate for crystal nuclei of arbitrary shape, we find the nucleation barrier to be compatible with a spherical shape and consistent with classical nucleation theory.

  8. Finite-Size Effects on Liquid-Solid Phase Coexistence and the Estimation of Crystal Nucleation Barriers

    NASA Astrophysics Data System (ADS)

    Statt, Antonia; Virnau, Peter; Binder, Kurt

    2015-01-01

    A fluid in equilibrium in a finite volume V with particle number N at a density ρ =N /V exceeding the onset density ρf of freezing may exhibit phase coexistence between a crystalline nucleus and surrounding fluid. Using a method suitable for the estimation of the chemical potential of dense fluids, we obtain the excess free energy due to the surface of the crystalline nucleus. There is neither a need to precisely locate the interface nor to compute the (anisotropic) interfacial tension. As a test case, a soft version of the Asakura-Oosawa model for colloid-polymer mixtures is treated. While our analysis is appropriate for crystal nuclei of arbitrary shape, we find the nucleation barrier to be compatible with a spherical shape and consistent with classical nucleation theory.

  9. Direct observation of smectic layers in thermotropic liquid crystals.

    PubMed

    Zhang, C; Gao, M; Diorio, N; Weissflog, W; Baumeister, U; Sprunt, S; Gleeson, J T; Jákli, A

    2012-09-01

    We demonstrate subnanometer resolution cryo-TEM imaging of smectic layers in the smectic and nematic phases of two bent-core liquid crystals. Our results show perfect periodicity over several hundred layers in the smectic phase and also provide the first direct evidence of smectic clusters on length scales of 30-50 nm in a nematic liquid crystal. The results are corroborated with small angle x-ray scattering measurements. The observation of smectic clusters in the nematic phase is of special interest in bent-core liquid crystals, where the smectic clusters are stable over wide temperature ranges, in contrast to the well-known pretransitional "cybotactic" clusters that appear only in the vicinity of a bulk smectic phase. The means to characterize and manipulate this nanoscale molecular order could open up completely new liquid crystal-based technologies.

  10. Using priority growth orientation of crystallite of the Monte Carlo method to study the process of crystal nucleation and growth in liquid phase

    NASA Astrophysics Data System (ADS)

    Shi, Yu; Chen, Manjiao; Huang, Jiankang; Gu, Yufen; Fan, Ding

    2016-01-01

    The technique of “crystallite growth preferred orientation” was presented based on the Monte Carlo (MC) simulations of grain growth, and its factor was used to establish a lattice coordinate tracking method. The nucleation and growth of crystal from the liquid phase throughout the whole simulation were examined. Changes in solid fraction and crystallite size were counted via simulation by lattice tracking. Results showed that the established model could properly reflect crystallite nucleation and growth. The model was also determined capable of accurately estimating the number of solid phase fraction and achieving change in crystallite size by the lattice tracking method. The change in solid fraction and MC step (MCS) satisfied the S curve during simulation. The crystallite growth index was 0.477, which was relatively close to the theoretical value of 0.5.

  11. Study of the smecticA-hexaticB phase transition in homeotropic single domain samples of 65OBC liquid crystal by photopyroelectric calorimetry

    NASA Astrophysics Data System (ADS)

    Mercuri, F.; Paoloni, S.; Marinelli, M.; Pizzoferrato, R.; Zammit, U.

    2013-02-01

    The smecticA-hexaticB phase transition was studied in a homeotropic single domain sample and in a non-aligned sample of n-hexyl-4'-n-pentyloxybiphenyl-4-carboxylate liquid crystal compound to probe the effect of different amount of defects on the phase transition. The specific heat, the thermal diffusivity and the enthalpy exchange were monitored over the transition and, at the same time, polarization microscopy observations could be carried out. The transition during the first cooling run was found to be accompanied by a considerably larger defect annealing in the non-aligned sample than in the homeotropic one, but the critical behaviour of the specific heat remained substantially the same.

  12. Characterization of a chiral phase in an achiral bent-core liquid crystal by polarization studies of resonant x-ray forbidden reflections

    SciTech Connect

    Ponsinet, V.; Pindak, R.; Barois, P.; Pan, L.; Wang, S.; Huang, C.C.; Wang, S.T.; Baumeister, U. and Weissflog, W.

    2011-07-15

    The chiral antiferroelectric structure of an achiral bent-core liquid crystal is characterized by resonant x-ray scattering at chlorine K edge. The 'forbidden' reflections resulting from the glide or screw symmetry elements are restored by the anisotropy of the tensor structure factor, which we calculate for two possible structural models. A careful analysis of the polarization states of the restored 'forbidden' reflections enables an unambiguous identification of a chiral structure (i.e., the so-called anticlinic, antiferroelectric smectic-C or Sm-C{sub A}P{sub A}) coexisting with the achiral synclinic antiferroelectric smectic-C or Sm-C{sub S}P{sub A}. The method proves to be quite powerful as it identifies the chiral structure within coexisting phases despite an imperfect orientation of the sample. The volume fraction of the chiral phase and the distribution of alignment are extracted from the data.

  13. Function Spaces for Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Bedford, Stephen

    2016-02-01

    We consider the relationship between three continuum liquid crystal theories: Oseen-Frank, Ericksen and Landau-de Gennes. It is known that the function space is an important part of the mathematical model and by considering various function space choices for the order parameters s, n, and Q, we establish connections between the variational formulations of these theories. We use these results to justify a version of the Oseen-Frank theory using special functions of bounded variation. This proposed model can describe both orientable and non-orientable defects. Finally we study a number of frustrated nematic and cholesteric liquid crystal systems and show that the model predicts the existence of point and surface discontinuities in the director.

  14. Fast liquid crystal adaptive mirror for wavefront correction

    NASA Astrophysics Data System (ADS)

    Anderson, Michael H.; Caldwell, Loren M., Jr.; Scheffler, Craig R.

    1999-11-01

    We have designed and constructed a prototype adaptive mirror using a nematic liquid crystal as the optical phase modulating material. The mirror has 127 hexagonal elements (actuators) in a 12 mm diameter clear aperture. The liquid crystal is a dual-frequency type that can be driven both parallel to, and orthogonal to, the external driving field by changing the drive frequency. With the dual-frequency liquid crystal we have achieved 1 micron of optical phase delay with full-cycle switching times of 6 ms. The electronic driver was designed to interface with an IBM compatible PC.

  15. Tracking transient temperatures with liquid crystals

    NASA Technical Reports Server (NTRS)

    Grodzka, P. G.; Facemire, B. R.

    1975-01-01

    The theoretical basis of the use of the liquid crystal technique to obtain transient thermal data is discussed. Results of calibrations of liquid crystal temperature sensors are given. The effects of crystal aging, lighting effects, observer bias, etc., on accuracy are discussed. The sensitivity of liquid crystal tapes as sensors of dynamic temperature changes is quite high. The accuracy of the technique is determined primarily by the type of calibration apparatus used.

  16. Structures of cyano-biphenyl liquid crystals

    NASA Technical Reports Server (NTRS)

    Chu, Yuan-Chao; Tsang, Tung; Rahimzadeh, E.; Yin, L.

    1989-01-01

    The structures of p-alkyl- p'-cyano- bicyclohexanes, C(n)H(2n+1) (C6H10)(C6H10) CN (n-CCH), and p-alkyl- p'-cyano- biphenyls, C(n)H(2n+1) (C6H4)(C6H4) CN (n-CBP), were studied. It is convenient to use an x ray image intensification device to search for symmetric x ray diffraction patterns. Despite the similarities in molecular structures of these compounds, very different crystal structures were found. For the smectic phase of 2CCH, the structure is close to rhombohedral with threefold symmetry. In contrast, the structure is close to hexagonal close-packed with two molecules per unit cell for 4CCH. Since intermolecular forces may be quite weak for these liquid crystals systems, it appears that crystal structures change considerably when the alkyl chain length is slightly altered. Different structures were also found in the crystalline phase of n-CBP for n = 6 to 9. For n = 7 to 9, the structures are close to monclinic. The structures are reminiscent of the smectic-A liquid crystal structures with the linear molecules slightly tilted away from the c-axis. In contrast, the structure is quite different for n = 6 with the molecules nearly perpendicular to the c-axis.

  17. Graphene chiral liquid crystals and macroscopic assembled fibres

    NASA Astrophysics Data System (ADS)

    Xu, Zhen; Gao, Chao

    2011-12-01

    Chirality and liquid crystals are both widely expressed in nature and biology. Helical assembly of mesophasic molecules and colloids may produce intriguing chiral liquid crystals. To date, chiral liquid crystals of 2D colloids have not been explored. As a typical 2D colloid, graphene is now receiving unprecedented attention. However, making macroscopic graphene fibres is hindered by the poor dispersibility of graphene and by the lack of an assembly method. Here we report that soluble, chemically oxidized graphene or graphene oxide sheets can form chiral liquid crystals in a twist-grain-boundary phase-like model with simultaneous lamellar ordering and long-range helical frustrations. Aqueous graphene oxide liquid crystals were continuously spun into metres of macroscopic graphene oxide fibres; subsequent chemical reduction gave the first macroscopic neat graphene fibres with high conductivity and good mechanical performance. The flexible, strong graphene fibres were knitted into designed patterns and into directionally conductive textiles.

  18. Graphene chiral liquid crystals and macroscopic assembled fibres

    PubMed Central

    Xu, Zhen; Gao, Chao

    2011-01-01

    Chirality and liquid crystals are both widely expressed in nature and biology. Helical assembly of mesophasic molecules and colloids may produce intriguing chiral liquid crystals. To date, chiral liquid crystals of 2D colloids have not been explored. As a typical 2D colloid, graphene is now receiving unprecedented attention. However, making macroscopic graphene fibres is hindered by the poor dispersibility of graphene and by the lack of an assembly method. Here we report that soluble, chemically oxidized graphene or graphene oxide sheets can form chiral liquid crystals in a twist-grain-boundary phase-like model with simultaneous lamellar ordering and long-range helical frustrations. Aqueous graphene oxide liquid crystals were continuously spun into metres of macroscopic graphene oxide fibres; subsequent chemical reduction gave the first macroscopic neat graphene fibres with high conductivity and good mechanical performance. The flexible, strong graphene fibres were knitted into designed patterns and into directionally conductive textiles. PMID:22146390

  19. Ice-Crystal Fallstreaks from Supercooled Liquid Water Parent Clouds

    NASA Technical Reports Server (NTRS)

    Campbell, James R.; O'C. Starr, David; Welton, Ellsworth J.; Spinhirne, James D.; Ferrare, Richard A.

    2003-01-01

    On 31 December 2001, ice-crystal fallstreaks (e.g., cirrus uncinus, or colloquially "Mare's Tails") from supercooled liquid water parent clouds were observed by ground-based lidars pointed vertically from the Atmospheric Radiation Measurement Southern Great Plains (SGP) facility near Lamont, Oklahoma. The incidence of liquid phase cloud with apparent ice-phase precipitation is investigated. Scenarios for mixed-phase particle nucleation, and fallstreak formation and sustenance are discussed. The observations are unique in the context of the historical reverence given to the commonly observed c h s uncinus fallstreak (wholly ice) versus this seemingly contradictory coincidence of liquid water begetting ice-crystal streaks.

  20. Modeling liquid-liquid phase transitions and quasicrystal formation

    NASA Astrophysics Data System (ADS)

    Skibinsky, Anna

    In this thesis, studies which concern two different subjects related to phase transitions in fluids and crystalline solids are presented. Condensed matter formation, structure, and phase transitions are modeled using molecular dynamics simulations of simple discontinuous potentials with attractive and repulsive interactions. Novel phase diagrams are proposed for quasicrystals, crystals, and liquids. In the first part of the thesis, the formation of a quasicrystal in a two dimensional monodisperse system is investigated using molecular dynamics simulations of hard sphere particles interacting via a two-dimensional square-well potential. It is found that for certain values of the square-well parameters more than one stable crystalline phase can form. By quenching the liquid phase at a very low temperature, an amorphous phase is obtained. When this the amorphous phase is heated, a quasicrystalline structure with five-fold symmetry forms. From estimations of the Helmholtz potentials of the stable crystalline phases and of the quasicrystal, it is concluded that within a specific temperature range, the observed quasicrystal phase can be the stable phase. The second part of the thesis concerns a study of the liquid-liquid phase transition for a single-component system in three dimensions, interacting via an isotropic potential with a repulsive soft-core shoulder at short distance and an attractive well at an intermediate distance. The potential is similar to potentials used to describe such liquid systems as colloids, protein solutions, or liquid metals. It is shown that the phase diagram for such a potential can have two lines of first-order fluid-fluid phase transitions: one separating a gas and a low-density liquid (LDL), and another between the LDL and a high-density liquid (HDL). Both phase transition lines end in a critical point, a gas-LDL critical point and, depending on the potential parameters, either a gas-HDL critical point or a LDL-HDL critical point. A

  1. Complementary interference method for determining optical parameters of liquid crystals

    NASA Astrophysics Data System (ADS)

    Kowiorski, K.; Kędzierski, J.; Raszewski, Z.; Kojdecki, M. A.; Chojnowska, O.; Garbat, K.; Miszczyk, E.; Piecek, W.

    2016-04-01

    Wedge cells of small apex angle, filled with liquid crystals, were used to determining optical characteristics as functions of temperature for three liquid crystalline mixtures recently produced and a reference nematic. The interference fringes appearing in polarised monochromatic light (of sodium yellow line) normally incident on the cell were exploited to measure the ordinary and extraordinary refractive indices in the reflection mode and birefringence in the transmission mode. The measurements were repeated using Abbe's refractometer for 6CHBT as the reference to verifying the precision. Additionally the order parameter was computed from birefringence as a function of temperature. The results confirm the usefulness of the method and provide the properties of two nematic liquid crystals of small and large birefringence and one smectic liquid crystal of medium birefringence, recently produced. The experimental systems served also to investigating phase transition between the liquid crystals and the isotropic liquid at near-clearing temperature.

  2. `Guest-host' effect in liquid crystal mixtures

    NASA Astrophysics Data System (ADS)

    Suchodolska, B.; Rudzki, A.; Ossowska-Chruściel, M. D.; Zalewski, S.; Chruściel, J.

    2015-01-01

    The most important goal of our research is to show the influence of the 'guest' (bent-core mesogen, 1,3-phenyldicarboxylatebis{4-[(4-octylbenzoyl)sulphanyl]phenyl} [IFOS8], banana-shaped liquid crystal [BLC]) on the 'host' (calamitic liquid crystal [CLC], (S)-(+)-1-methylheptyloxybiphenyl-(4-n-octylphenyl)thiobenzoate [MHOBS8]), on the stability and the destabilization of the antiferroelectric B2 and the ferroelectric smectic C* (SmC*) phases, and change of the temperature ranges of other phases in the binary liquid crystal mixtures. This work is focused on polymorphism of three new binary liquid crystal mixtures, exhibiting a 'guest-host' (guest liquid crystal-host liquid crystal [GH-LC]) effect. MHOBS8 has, among others, a ferroelectric SmC* phase, and IFOS8 assumes the B2 phase with antiferroelectric properties. The observed properties of the mixtures, such as variation of the phase transition temperatures, spontaneous polarization, tilt angle and switching time, are characteristic of a 'guest-host' mixture. The influence of BLC on the character of the interactions within the CLC host is discussed, with particular attention paid to electro-optical properties of the GH-LC mixtures.

  3. Phase comparison technique for measuring liquid-liquid phase equilibrium

    NASA Astrophysics Data System (ADS)

    Lu, Z.; Daridon, J. L.; Lagourette, B.; Ye, S.

    1999-04-01

    In this article, a new method is demonstrated to measure the liquid-liquid phase equilibrium for binary systems. A phase comparison technique was employed to real-time display the phase-time curve in a "wave form (time) object" of Hewlett-Packard visual engineering environment. It was found that the phase-time curve showed a distorted wave form when liquid-liquid phase transition took place. The abnormal curve can therefore be used to detect liquid-liquid phase transitions. Measurements were performed in several binary systems such as nitromethane+1-hexanol, nitromethane+butanol, and nitroethane+n-hexane. The experimental results are in good agreement with those in the literature.

  4. Effect of transient liquid phase (TLP) bonding on the ductility of a Ni-base single crystal superalloy in a stress rupture test

    SciTech Connect

    Liu, J.D. Jin, T.; Zhao, N.R.; Wang, Z.H.; Sun, X.F.; Guan, H.R.; Hu, Z.Q.

    2008-01-15

    A Ni-base single crystal superalloy was transient liquid phase (TLP) bonded using a Ni-Cr-B amorphous foil at 1230 deg. C for 8 h. Stress rupture tests of the TLP joint and a matrix sample were carried out at 982 deg. C/248 MPa and 1010 deg. C/248 MPa. The microstructures and fracture surfaces were studied using scanning electron microscopy (SEM). Transmission electron microscopy (TEM) investigations were performed after creep rupture testing to examine the deformation substructures. The results show that the stress rupture ductility of TLP joints is significantly decreased compared to the matrix sample. This reduction of the ductility of TLP joints can be attributed to solid solution strengthening by boron atoms, subgrain boundaries formed in the bonding zone and the concentration of creep cavities formed during the last stage of the stress rupture test.

  5. Thermodynamics of the adsorption of organic compounds from the gas phase over a monolayer of liquid crystal formed on the surface of a carbon adsorbent

    NASA Astrophysics Data System (ADS)

    Kopytin, K. A.; Bykov, E. S.; Onuchak, L. A.; Kudryashov, S. Yu.; Kuvshinova, S. A.; Burmistrov, V. A.

    2015-04-01

    Inverse gas-solid chromatography is used to study the adsorption of vapors of organic compounds with different structures and polarities on a carbon adsorbent modified with a monolayer of 4-(3-hydroxypropyloxy)-4'-formylazobenzene (HPOFAB) polar LIQUID crystal. The resulting thermodynamic characteristics of adsorption on the original and modified adsorbents are compared. The effect the nature and structure of adsorbate molecules and the liquid crystal modifier have on the thermodynamic characteristics of adsorption is considered.

  6. Influence of chemical moieties and the flexible chain for the tilted smectic phases in linear hydrogen bonded liquid crystals with Schiff based pyridene derivatives

    NASA Astrophysics Data System (ADS)

    Muniprasad, M.; Srinivasulu, M.; Chalapathi, P. V.; Potukuchi, D. M.

    2012-05-01

    A novel series of hydrogen bonded liquid crystals (HBLC's) prepared from non-mesogenic 4-pyridine carboxaldehyde, p-n-tetradecyl aniline and mesogenic 4-n-alkoxy benzoic acids (nOBA's) are isolated by a condensation reaction followed by an HB complexation. Formation of HB complex and purity of product is confirmed by 1H NMR and IR spectroscopic techniques. The phase variance exhibited by the present HBLC series of compounds viz., Py14BA:nOBA's (for n = 3-5, 7-9 and 12) is found to be AB in lower homologues and CF in higher homologues. Odd-even effect is exhibited by the series at I-SmA, I-SmC and LC to Solid transitions. Iso-SmA, Iso-SmC, SmA-SmB and SmC-SmF transitions are found to be of 1st order nature. The even higher homologues (for n = 8 and 12) exhibit a paramorphotic textural transition of 2nd order nature in their SmC phase. The influence of HB (soft-covalent) interaction and the inductomeric effect contributed by the end chains for the enhancement of transverse dipole moment μt, the stability of tilted LC phases (SmC and SmF) are discussed. An ACF Multi-Critical Point is predicted in the phase diagram for Py14BA:nOBA series of HBLC's in the vicinity of n = 5.

  7. Molecular orientation behavior of chiral nematic liquid crystals based on the presence of blue phases using polarized microscopic FT-IR spectroscopy

    NASA Astrophysics Data System (ADS)

    Matsumura, Masanori; Katayama, Norihisa

    2016-07-01

    Study on molecular orientation behavior of highly twisted chiral nematic liquid crystals (N∗LCs) expressing blue phases (BPs) is important for developing new devices. This study examines the change of molecular orientation of N∗LCs due to the presence of BPs. Polarized microscopic FT-IR spectroscopy was used to study the in- and out-of-plane molecular orientations of N∗LCs that undergo a phase transition involving BPs. The band intensity ratio of CN to CH2 stretching modes (CN/CH2) in the IR spectra was used to determine the orientation of N∗LC molecules. The measured spectra indicated that the helical axis of N∗LC molecules was perpendicular to the substrate before heating and inclined on the substrate after cooling the sample which has phase transition from BP I to chiral nematic (N∗). The N∗LC molecule in the cell of rubbed orientation film exhibited the in-plane anisotropy after a heating-cooling ramp only in samples that passed through BP I. These results indicate that the changes of molecular orientation of N∗LC by phase transition are affected by BP I.

  8. Spatio-orientationally organized polymer microstructures obtained on self-assembled pattern-forming states of liquid crystals: Morphology, phase separation, and potential applications

    NASA Astrophysics Data System (ADS)

    Kang, Shin-Woong

    The main objective of the dissertation is to develop and exploit a novel technique for imparting multidimensional spatial and orientational order into polymer networks. This approach is based on the use of pattern-forming states of liquid crystals as templates for the network formation. To demonstrate the feasibility and flexibility of this concept, we describe various pattern-forming states observed from ordinary cholesteric and nematic/cholesteric dual-frequency liquid crystals. We present a variety of polymer microstuctures templated on those pattern-forming states. This clearly demonstrates the feasibility and flexibility of templating both orientational and positional order of host pattern-forming states into polymer network. We investigated possible driving forces behind this templating effect of LC pattern-forming states. These include effects of both spatial variations of UV intensity and gradients in elastic distortion caused by the spatial modulation of director field. The effects of the two mechanisms are separated through a series of experiments, including polarization-selective photopolymerization, FTIR imaging of the monomer distribution prior to UV-exposure and initiation of the photoreaction, the effect of temperature on the templated morphology, and the use of a thermal reactive monomer to remove the effect of possible optical inhomogeneities. The model derives from the concept of director gradient templating, whereby monomer phase separation is driven by a competition between reduction in elastic energy when monomer replaces liquid crystal in more (or less) distorted regions of the molecular director, and a consequent decrease in the entropy of mixing of the two species. Another emphasis of this dissertation is to study the control over the network morphology in the "third" dimension---perpendicular to UV wavefront---by relatively simple means of selecting the wavelength of UV light used in photopolymerization to be inside or outside a carefully

  9. Perspectives in active liquid crystals.

    PubMed

    Majumdar, Apala; Cristina, Marchetti M; Virga, Epifanio G

    2014-11-28

    Active soft matter is a young, growing field, with potential applications to a wide variety of systems. This Theme Issue explores this emerging new field by highlighting active liquid crystals. The collected contributions bridge theory to experiment, mathematical theories of passive and active nematics, spontaneous flows to defect dynamics, microscopic to continuum levels of description, spontaneous activity to biological activation. While the perspectives offered here only span a small part of this rapidly evolving field, we trust that they might provide the interested reader with a taste for this new class of non-equilibrium systems and their rich behaviour.

  10. Perspectives in active liquid crystals

    PubMed Central

    Majumdar, Apala; Cristina, Marchetti M.; Virga, Epifanio G.

    2014-01-01

    Active soft matter is a young, growing field, with potential applications to a wide variety of systems. This Theme Issue explores this emerging new field by highlighting active liquid crystals. The collected contributions bridge theory to experiment, mathematical theories of passive and active nematics, spontaneous flows to defect dynamics, microscopic to continuum levels of description, spontaneous activity to biological activation. While the perspectives offered here only span a small part of this rapidly evolving field, we trust that they might provide the interested reader with a taste for this new class of non-equilibrium systems and their rich behaviour. PMID:25332386

  11. Solvent-free Liquid Crystals and Liquids from DNA.

    PubMed

    Liu, Kai; Shuai, Min; Chen, Dong; Tuchband, Michael; Gerasimov, Jennifer Y; Su, Juanjuan; Liu, Qing; Zajaczkowski, Wojciech; Pisula, Wojciech; Müllen, Klaus; Clark, Noel A; Herrmann, Andreas

    2015-03-23

    As DNA exhibits persistent structures with dimensions that exceed the range of their intermolecular forces, solid-state DNA undergoes thermal degradation at elevated temperatures. Therefore, the realization of solvent-free DNA fluids, including liquid crystals and liquids, still remains a significant challenge. To address this intriguing issue, we demonstrate that combining DNA with suitable cationic surfactants, followed by dehydration, can be a simple generic scheme for producing these solvent-free DNA fluid systems. In the anhydrous smectic liquid crystalline phase, DNA sublayers are intercalated between aliphatic hydrocarbon sublayers. The lengths of the DNA and surfactant are found to be extremely important in tuning the physical properties of the fluids. Stable liquid-crystalline and liquid phases are obtained in the -20 °C to 200 °C temperature range without thermal degradation of the DNA. Thus, a new type of DNA-based soft biomaterial has been achieved, which will promote the study and application of DNA in a much broader context.

  12. Positron lifetime measurements in chiral nematic liquid crystals

    NASA Technical Reports Server (NTRS)

    Singh, Jag J.; Eftekhari, Abe; Parmar, Devendra S.

    1991-01-01

    Positron lifetimes in the isotropic phases of chiral nematic liquid crystal formulations and their mixtures up to the racemic level were measured. The lifetime spectra for all liquid crystal systems were analyzed into three components. Although the individual spectra in the left- and right-handed components are identical, their racemic mixtures exhibit much larger orthopositronium lifetimes; these larger lifetimes indicate the presence of larger microvoids. This result is consistent with the reportedly higher thermodynamic stability and color play range in the racemic mixtures of chiral nematic liquid crystals.

  13. Smectic layer instabilities in liquid crystals.

    PubMed

    Dierking, Ingo; Mitov, Michel; Osipov, Mikhail A

    2015-02-01

    Scientists aspire to understand the underlying physics behind the formation of instabilities in soft matter and how to manipulate them for diverse investigations, while engineers aim to design materials that inhibit or impede the nucleation and growth of these instabilities in critical applications. The present paper reviews the field-induced rotational instabilities which may occur in chiral smectic liquid-crystalline layers when subjected to an asymmetric electric field. Such instabilities destroy the so-named bookshelf geometry (in which the smectic layers are normal to the cell surfaces) and have a detrimental effect on all applications of ferroelectric liquid crystals as optical materials. The transformation of the bookshelf geometry into horizontal chevron structures (in which each layer is in a V-shaped structure), and the reorientation dynamics of these chevrons, are discussed in details with respect to the electric field conditions, the material properties and the boundary conditions. Particular attention is given to the polymer-stabilisation of smectic phases as a way to forbid the occurrence of instabilities and the decline of related electro-optical performances. It is also shown which benefit may be gained from layer instabilities to enhance the alignment of the liquid-crystalline geometry in practical devices, such as optical recording by ferroelectric liquid crystals. Finally, the theoretical background of layer instabilities is given and discussed in relation to the experimental data.

  14. Nanoscopic Manipulation and Imaging of Liquid Crystals

    SciTech Connect

    Rosenblatt, Charles S.

    2014-02-04

    This is the final project report. The project’s goals centered on nanoscopic imaging and control of liquid crystals and surfaces. We developed and refined techniques to control liquid crystal orientation at surfaces with resolution as small as 25 nm, we developed an optical imaging technique that we call Optical Nanotomography that allows us to obtain images inside liquid crystal films with resolution of 60 x 60 x 1 nm, and we opened new thrust areas related to chirality and to liquid crystal/colloid composites.

  15. Investigating the orientational order in smectic liquid crystals

    NASA Astrophysics Data System (ADS)

    Wang, Shun

    This thesis is composed of two projects. The first one is the investigation of a reversed phase sequence, which subsequently leads to the discovery of a novel Smectic-C liquid crystal phase. The 10OHFBBB1M7 (10OHF) compound shows a reversed phase sequence with the SmC*d4 phase occurring at a higher temperature than the SmC* phase. This phase sequence is stabilized by moderate doping of 9OTBBB1M7 (C9) or 11OTBBB1M7 (C11). To further study this unique phase sequence, the mixtures of 10OHFBBB1M7 and its homologs have been characterized by optical techniques. In order to perform the resonant X-ray diffraction experiment, we have added C9 and C11 compounds to the binary mixtures and pure 10OHF. In two of the studied mixtures, a new smectic-C* liquid crystal phase with six-layer periodicity has been discovered. Upon cooling, the new phase appears between the SmC*a phase having a helical structure and the SmC*d4 phase with four-layer periodicity. The SmC*d6 phase shows a distorted clock structure. Three theoretical models have predicted the existence of a six-layer phase. However, our experimental findings are not consistent with the theories. The second project involves the mixtures of liquid crystals with different shapes. The role of different interactions in stabilizing the antiferroelectric smectic liquid crystal phases have been a long-standing questions in the community. By mixing the antiferroelectric smectic liquid crystal with achiral liquid crystal molecules with rod and hockey-stick shapes, distinct different behaviors are obtained. In the case of the mixtures of chiral smectic liquid crystals with rod-like molecules, all the smectic-C* variant phases vanish with a small amount of doping. However, the hockey-stick molecule is much less destructive compared to the rod-like molecule. This suggests that the antiferroelectric smectic liquid crystal molecules may have a shape closer to a hockey-stick rather than a rod.

  16. GPU-Accelerated Molecular Dynamics Simulation to Study Liquid Crystal Phase Transition Using Coarse-Grained Gay-Berne Anisotropic Potential.

    PubMed

    Chen, Wenduo; Zhu, Youliang; Cui, Fengchao; Liu, Lunyang; Sun, Zhaoyan; Chen, Jizhong; Li, Yunqi

    2016-01-01

    Gay-Berne (GB) potential is regarded as an accurate model in the simulation of anisotropic particles, especially for liquid crystal (LC) mesogens. However, its computational complexity leads to an extremely time-consuming process for large systems. Here, we developed a GPU-accelerated molecular dynamics (MD) simulation with coarse-grained GB potential implemented in GALAMOST package to investigate the LC phase transitions for mesogens in small molecules, main-chain or side-chain polymers. For identical mesogens in three different molecules, on cooling from fully isotropic melts, the small molecules form a single-domain smectic-B phase, while the main-chain LC polymers prefer a single-domain nematic phase as a result of connective restraints in neighboring mesogens. The phase transition of side-chain LC polymers undergoes a two-step process: nucleation of nematic islands and formation of multi-domain nematic texture. The particular behavior originates in the fact that the rotational orientation of the mesogenes is hindered by the polymer backbones. Both the global distribution and the local orientation of mesogens are critical for the phase transition of anisotropic particles. Furthermore, compared with the MD simulation in LAMMPS, our GPU-accelerated code is about 4 times faster than the GPU version of LAMMPS and at least 200 times faster than the CPU version of LAMMPS. This study clearly shows that GPU-accelerated MD simulation with GB potential in GALAMOST can efficiently handle systems with anisotropic particles and interactions, and accurately explore phase differences originated from molecular structures. PMID:26986851

  17. GPU-Accelerated Molecular Dynamics Simulation to Study Liquid Crystal Phase Transition Using Coarse-Grained Gay-Berne Anisotropic Potential

    PubMed Central

    Cui, Fengchao; Liu, Lunyang; Sun, Zhaoyan; Chen, Jizhong; Li, Yunqi

    2016-01-01

    Gay-Berne (GB) potential is regarded as an accurate model in the simulation of anisotropic particles, especially for liquid crystal (LC) mesogens. However, its computational complexity leads to an extremely time-consuming process for large systems. Here, we developed a GPU-accelerated molecular dynamics (MD) simulation with coarse-grained GB potential implemented in GALAMOST package to investigate the LC phase transitions for mesogens in small molecules, main-chain or side-chain polymers. For identical mesogens in three different molecules, on cooling from fully isotropic melts, the small molecules form a single-domain smectic-B phase, while the main-chain LC polymers prefer a single-domain nematic phase as a result of connective restraints in neighboring mesogens. The phase transition of side-chain LC polymers undergoes a two-step process: nucleation of nematic islands and formation of multi-domain nematic texture. The particular behavior originates in the fact that the rotational orientation of the mesogenes is hindered by the polymer backbones. Both the global distribution and the local orientation of mesogens are critical for the phase transition of anisotropic particles. Furthermore, compared with the MD simulation in LAMMPS, our GPU-accelerated code is about 4 times faster than the GPU version of LAMMPS and at least 200 times faster than the CPU version of LAMMPS. This study clearly shows that GPU-accelerated MD simulation with GB potential in GALAMOST can efficiently handle systems with anisotropic particles and interactions, and accurately explore phase differences originated from molecular structures. PMID:26986851

  18. Stochastic rotation dynamics for nematic liquid crystals

    SciTech Connect

    Lee, Kuang-Wu Mazza, Marco G.

    2015-04-28

    We introduce a new mesoscopic model for nematic liquid crystals (LCs). We extend the particle-based stochastic rotation dynamics method, which reproduces the Navier-Stokes equation, to anisotropic fluids by including a simplified Ericksen-Leslie formulation of nematodynamics. We verify the applicability of this hybrid model by studying the equilibrium isotropic-nematic phase transition and nonequilibrium problems, such as the dynamics of topological defects and the rheology of sheared LCs. Our simulation results show that this hybrid model captures many essential aspects of LC physics at the mesoscopic scale, while preserving microscopic thermal fluctuations.

  19. Probing and controlling liquid crystal helical nanofilaments.

    PubMed

    Zhu, Chenhui; Wang, Cheng; Young, Anthony; Liu, Feng; Gunkel, Ilja; Chen, Dong; Walba, David; Maclennan, Joseph; Clark, Noel; Hexemer, Alexander

    2015-05-13

    We report the first in situ measurement of the helical pitch of the helical nanofilament B4 phase of bent-core liquid crystals using linearly polarized, resonant soft X-ray scattering at the carbon K-edge. A strong, anisotropic scattering peak corresponding to the half-pitch of the twisted smectic layer structure was observed. The equilibrium helical half-pitch of NOBOW is found to be 120 nm, essentially independent of temperature. However, the helical pitch can be tuned by mixing guest organic molecules with the bent-core host, followed by thermal annealing.

  20. Demonstrations of Some Optical Properties of Liquid Crystals.

    ERIC Educational Resources Information Center

    Nicastro, Anthony J.

    1983-01-01

    Discusses several properties of liquid crystal displays. Includes instructions for demonstrating liquid crystalline phase, ordering of the long axes of molecules along one direction, and electro-optic effects. The latter is accomplished with the use of an overhead projector following preparation of a sandwich cell. (JN)

  1. Chemical Programming of the Domain of Existence of Liquid Crystals.

    PubMed

    Dutronc, Thibault; Terazzi, Emmanuel; Guénée, Laure; Buchwalder, Kerry-Lee; Floquet, Sébastien; Piguet, Claude

    2016-01-22

    This work illustrates how enthalpy and entropy changes responsible for successive phase transitions of cyanobiphenyl-based liquid crystals can be combined to give cohesive free energy densities. These new parameters are able to rationalize and quantify the demixing of the melting and clearing processes that occur in thermotropic liquid crystals. Minor structural variations at the molecular level can be understood as pressure increments that alter either the melting or clearing temperatures in a predictable way. This assessment of microsegregation operating in amphiphilic molecules paves the way for the chemical programming of the domain of existence of liquid-crystalline phases.

  2. Theory of polymer-dispersed cholesteric liquid crystals

    SciTech Connect

    Matsuyama, Akihiko

    2013-11-07

    A mean field theory is presented to describe cholesteric phases in mixtures of a polymer and a cholesteric liquid crystal. Taking into account an anisotropic coupling between a polymer and a liquid crystal, we examine the helical pitch, twist elastic constant, and phase separations. Analytical expressions of the helical pitch of a cholesteric phase and the twist elastic constant are derived as a function of the orientational order parameters of a polymer and a liquid crystal and two intermolecular interaction parameters. We also find isotropic-cholesteric, cholesteric-cholesteric phase separations, and polymer-induced cholesteric phase on the temperature-concentration plane. We demonstrate that an anisotropic coupling between a polymer and a liquid crystal can stabilize a cholesteric phase in the mixtures. Our theory can also apply to mixtures of a nematic liquid crystal and a chiral dopant. We discuss the helical twisting power, which depends on temperature, concentration, and orientational order parameters. It is shown that our theory can qualitatively explain experimental observations.

  3. Polymer Crystallization at Curved Liquid/Liquid Interface

    NASA Astrophysics Data System (ADS)

    Wang, Wenda

    Liquid/liquid interface, either flat or curved, is a unique template for studying self-assembly of a variety of nanomaterials such as nanoparticles and nanorods. The resultant monolayer films can be ordered or disordered depending on the regularity of the nanomaterials. Integration of nanoparticles into two-dimensional structure leads to intriguing collective properties of the nanoparticles. Crystallization can also be guided by liquid/liquid interface. Due to the particular shape of the interface, crystallization can happen in a different manner comparing to the normal solution crystallization. In this dissertation, liquid/liquid interface is employed to guide the crystallization of polymers, mainly focusing on using curved liquid/liquid interface. Due to the unique shape of the interface and feasibility to control the curvature, polymer crystallization can take place in different manner and lead to the formation of curved or vesicular crystals. Curved liquid/liquid interface is typically created through o/w emulsions. With the presence of surfactant, the emulsions are controlled to be stable at least for the polymer crystallization periods. The difference to normal solution crystallization is: the nuclei will diffuse to the curved interface due to the Pickering effect and guide the crystallization along the curved liquid/liquid interface. If the supercooling can be controlled to be very small, crystal growth in the bulk droplets can be avoided. The advantages of this strategy are: 1) the formation process of vesicular type crystals can be monitored by controlling the polymer supply; 2) curved crystals, bowl-like structures and enclosed capsules can be easily obtained comparing to the self-assembly method for vesicle formation; 3) the obtained vesicles will be made of polymer crystals, which will possess the extraordinary mechanical properties. Based on the nucleation type, this dissertation is divided into two parts. The first part is focused on the self

  4. Shaping Crystal-Crystal Phase Transitions

    NASA Astrophysics Data System (ADS)

    Du, Xiyu; van Anders, Greg; Dshemuchadse, Julia; Glotzer, Sharon

    Previous computational and experimental studies have shown self-assembled structure depends strongly on building block shape. New synthesis techniques have led to building blocks with reconfigurable shape and it has been demonstrated that building block reconfiguration can induce bulk structural reconfiguration. However, we do not understand systematically how this transition happens as a function of building block shape. Using a recently developed ``digital alchemy'' framework, we study the thermodynamics of shape-driven crystal-crystal transitions. We find examples of shape-driven bulk reconfiguration that are accompanied by first-order phase transitions, and bulk reconfiguration that occurs without any thermodynamic phase transition. Our results suggest that for well-chosen shapes and structures, there exist facile means of bulk reconfiguration, and that shape-driven bulk reconfiguration provides a viable mechanism for developing functional materials.

  5. Planar optics with patterned chiral liquid crystals

    NASA Astrophysics Data System (ADS)

    Kobashi, Junji; Yoshida, Hiroyuki; Ozaki, Masanori

    2016-06-01

    Reflective metasurfaces based on metallic and dielectric nanoscatterers have attracted interest owing to their ability to control the phase of light. However, because such nanoscatterers require subwavelength features, the fabrication of elements that operate in the visible range is challenging. Here, we show that chiral liquid crystals with a self-organized helical structure enable metasurface-like, non-specular reflection in the visible region. The phase of light that is Bragg-reflected off the helical structure can be controlled over 0-2π depending on the spatial phase of the helical structure; thus planar elements with arbitrary reflected wavefronts can be created via orientation control. The circular polarization selectivity and external field tunability of Bragg reflection open a wide variety of potential applications for this family of functional devices, from optical isolators to wearable displays.

  6. Comparison of supramolecular hydrogen bonded liquid crystals

    NASA Astrophysics Data System (ADS)

    Pongali Sathya Prabu, N.; Vijayakumar, V. N.; Madhu Mohan, M. L. N.

    2012-01-01

    Supramolecular hydrogen bonded liquid crystals are formed by methoxy hydroquinone (MHQ) and alkyloxy benzoic acids are isolated and characterised. MHQ formed double hydrogen bonds with p-n-alkyloxy benzoic acids. Fourier Transform-Infrared studies confirm the hydrogen bond formation in the complex. Polarising Optical Microscopic (POM) studies revealed the textural information, while the transition and enthalpy values are experimentally deduced from Differential Scanning Calorimetry (DSC) studies. Phase diagram has been constructed from the POM and DSC data, respectively. Experimental data of optical tilt angle in Smectic C phase have been fitted to a power law and it has been observed that the temperature variation of the tilt angle follows Mean Field theory prediction. Present homologous are compared with hydroquinone alkyloxy benzoic acids complexes and the influence of methyl group on the occurrence of phases and its transition temperatures are discussed.

  7. Single-scan measurement of conductance of a quartz crystal microbalance array coupled with resonant markers for biosensing in liquid phase

    NASA Astrophysics Data System (ADS)

    Hsiao, Hsien-Yi; Chen, Richie L. C.; Cheng, Tzong-Jih

    2009-04-01

    This work presents a method for sensing the viscoelastic property of liquid/solid interface using a quartz crystal microbalance (QCM) array. Each sensor in a QCM array has a unique resonant frequency and can be identified by a single-scan measurement of admittance (or impedance). The resonant frequency encoding at each sensor in an array was realized by connecting a capacitor with a known capacitance, called a resonant marker, to the sensor in series. Changes in the resonant frequency of all sensors in an array can be determined using an impedance analyzer and a program that determines the frequencies at which the conductance is at a local maximum. The sensing method allows every sensor output (resonant frequency) to be obtained without the use of time-consuming multiplexed hardware and software. Adsorptions of biomolecules by multiple sensor are monitored in the liquid phase to demonstrate the feasibility of frequency encoding using resonant markers and the single-scan measurement of conductance of a QCM array.

  8. Single-scan measurement of conductance of a quartz crystal microbalance array coupled with resonant markers for biosensing in liquid phase

    SciTech Connect

    Hsiao, Hsien-Yi; Chen, Richie L. C.; Cheng, Tzong-Jih

    2009-04-15

    This work presents a method for sensing the viscoelastic property of liquid/solid interface using a quartz crystal microbalance (QCM) array. Each sensor in a QCM array has a unique resonant frequency and can be identified by a single-scan measurement of admittance (or impedance). The resonant frequency encoding at each sensor in an array was realized by connecting a capacitor with a known capacitance, called a resonant marker, to the sensor in series. Changes in the resonant frequency of all sensors in an array can be determined using an impedance analyzer and a program that determines the frequencies at which the conductance is at a local maximum. The sensing method allows every sensor output (resonant frequency) to be obtained without the use of time-consuming multiplexed hardware and software. Adsorptions of biomolecules by multiple sensor are monitored in the liquid phase to demonstrate the feasibility of frequency encoding using resonant markers and the single-scan measurement of conductance of a QCM array.

  9. Eutectic mixtures of ferroelectric liquid crystals

    SciTech Connect

    Goodby, J.W. ); Chin, E. ); Patel, J.S. )

    1989-11-30

    Ferroelectric liquid crystals show potential as the optically and electrically active media in a variety of applications. However, it is considered unlikely that a single individual compound will possess all of the desired properties required by device applications, and therefore it is to be expected that it will be necessary to mix compounds together in order to obtain a suitable blend. In this study we have examined how the pitch of the helix and the magnitude of the spontaneous polarization of the ferroelectric smectic C* phase vary as a function of concentration when two materials of opposite twist and with the same (or opposite) polarization directions are mixed together. In some cases the ferroelectric phase(s) was found to disappear in the central region of the phase diagram, only to be replaced by the nonferroelectric smectic B phase. This type of behavior was found to happen even when the two components were of the same generic family. Changes in phase type were detected optically and also from the switching behavior in individual mixtures. This second approach offers a new method of monitoring certain phase changes that occur in a phase diagram.

  10. Crystal phase identification

    DOEpatents

    Michael, Joseph R.; Goehner, Raymond P.; Schlienger, Max E.

    2001-01-01

    A method and apparatus for determining the crystalline phase and crystalline characteristics of a sample. This invention provides a method and apparatus for unambiguously identifying and determining the crystalline phase and crystalline characteristics of a sample by using an electron beam generator, such as a scanning electron microscope, to obtain a backscattered electron Kikuchi pattern of a sample, and extracting crystallographic and composition data that is matched to database information to provide a quick and automatic method to identify crystalline phases.

  11. Demonstrations with a Liquid Crystal Shutter

    ERIC Educational Resources Information Center

    Kraftmakher, Yaakov

    2012-01-01

    The experiments presented show the response of a liquid crystal shutter to applied electric voltages and the delay of the operations. Both properties are important for liquid crystal displays of computers and television sets. Two characteristics of the shutter are determined: (i) the optical transmittance versus applied voltage of various…

  12. Liquid Crystals in Education--The Basics

    ERIC Educational Resources Information Center

    Cepic, Mojca

    2012-01-01

    The introduction of teaching about liquid crystals is discussed from several points of view: the rationale why to teach them, the basics about liquid crystals or what the teacher should teach about them, the fundamental pre-knowledge of students required, the set of experiments accompanying the teaching and the brief report on the already…

  13. Liquid Crystalline Phases of Polymer Brushes

    NASA Astrophysics Data System (ADS)

    Amini, Kiana; Abukhdeir, Nasser; Matsen, Mark

    The phase behavior of liquid-crystal polymeric brushes in solvent are investigated using self-consistent field theory. The polymers are modeled as freely-jointed chain consisting of N rigid segments. The isotropic interactions between the polymer and the solvent are treated using the standard Flory-Huggins theory, while the anisotropic liquid-crystalline (LC) interactions between rigid segments are taken into account using the Mayer-Saupe theory. For weak LC interactions, the brush exhibits the conventional parabolic-like profile, while for strong LC interactions, the polymers crystallize into a dense brush with a step-like profile. At intermediate interaction strengths, we find the microphase-segregated phase observed previously for lattice-model calculations. In this phase, the brush exhibits a crystalline layer next to the grafting surface with an external layer similar to the conventional brush. This work was supported by NSERC of Canada.

  14. Relaxation time of molecular rotation about its long axis in the smectic-A phase of ferroelectricand antiferroelectric liquid crystals as observed by picosecond optical Kerr effect

    NASA Astrophysics Data System (ADS)

    Miyachi, Kouichi; Takanishi, Yoichi; Ishikawa, Ken; Takezoe, Hideo; Fukuda, Atsuo

    1997-02-01

    We have studied the molecular rotational motion about its long axis in ferroelectric chiral smectic-C (Sm-C) and antiferroelectric chiral smectic-Ca (Sm-C*>A) liquid crystals and observed a few tens of picosecond relaxation time. Previously reported results using degenerate four-wave mixing with 25-ps pump pulses [Lalanne et al., Phys. Rev. A 44, 6632 (1991)] claimed to show a critical slowing down in the temperature region more than 0.1 °C above the Sm-A-Sm-C phase transition. Our measurements of the optical Kerr effect with 130-fs pump pulses do not show any critical slowing down in the corresponding temperature region above the phase transition from Sm-A to Sm-C or Sm-C*>A. The result may indicate that the laser-induced molecular reorientation with τ~10-11 s scarcely couples with the tilt angle and the polarization. A possibility has been discussed that a slower rotational motion with τ>~10-10 s plays a primary role for the emergence of ferroelectricity and/or antiferroelectricity.

  15. Macroscopic biaxiality and electric-field-induced rotation of the minor director in the nematic phase of a bent-core liquid crystal

    NASA Astrophysics Data System (ADS)

    Nagaraj, Mamatha; Merkel, K.; Vij, J. K.; Kocot, A.

    2010-09-01

    Biaxiality in the nematic phase has been investigated for the bent-core liquid-crystal para-heptylbenzoate diester, using polarised IR spectroscopy. Anisotropic fluctuations of the nematic director are discussed in terms of the self-assembly of the chiral conformers. The ordering of the minor director for the homeotropicaly aligned sample is found to depend on the rubbing of the substrates of the cell and the amplitude of in-plane electric field. On increasing the in-plane electric field, the rotation of the minor director in the plane of the substrate is observed with an angle of approximately 45°, where initially the minor director is shown to lie along the rubbing direction. It is also shown that on the average the long axis of the molecules is normal to the substrate with surface treatment, with and without rubbing. The electric in-plane field combined with rubbing is shown to induce biaxial order in the nematic phase of a material with negative dielectic anisotropy for the first time.

  16. Detection of Significant Aprotic Solvent Effects on the Conformational Distribution of Methyl 4-Nitrophenyl Sulfoxide: From Gas-Phase Rotational to Liquid-Crystal NMR Spectroscopy.

    PubMed

    Celebre, Giorgio; De Luca, Giuseppina; Di Pietro, Maria Enrica; Giuliano, Barbara Michela; Melandri, Sonia; Cinacchi, Giorgio

    2015-08-01

    The conformational equilibrium of methyl 4-nitrophenyl sulfoxide (MNPSO) was experimentally investigated in the gas phase by using microwave spectroscopy and in isotropic and nematic liquid-crystal solutions, in which the solvents are nonaqueous and aprotic, by using NMR spectroscopy; moreover, it was theoretically studied in vacuo and in solution at different levels of theory. The overall set of results indicates a significant dependence of the solute conformational distribution on the solvent dielectric permittivity constant: when dissolved in low-polarity media, the most stable conformation of MNPSO proved to be strongly twisted with respect to that in more polar solvents, in which the conformational distribution maximum essentially coincides with that obtained in the gas phase. We discuss a possible explanation of this behavior, which rests on electrostatic solute-solvent interactions and is supported by calculations of the solute electric dipole moment as a function of the torsional angle. This function shows that the least polar conformation of MNPSO is located at a twist angle close to that of the conformational distribution maximum found in less-polar solvents. This fact, associated with a relatively flat torsional potential, can justify the stabilization of the twisted conformation by the less-polar solvents.

  17. Effect of surfactant/silica molar ratios on the formation of mesoporous molecular sieves: Inorganic mimicry of surfactant liquid-crystal phases and mechanistic implications

    SciTech Connect

    Vartuli, J.C.; Schmitt, K.D.; McCullen, S.B.; Hellring, S.D.; Beck, J.S.; Schlenker, J.L.; Olson, D.H.; Sheppard, E.W.; Kresge, C.T.; Roth, W.J.

    1994-12-01

    The influence of surfactant/silica molar ratio (Sur/Si) in the synthesis of mesoporous molecular sieve materials (M41S) was studied in a simple ternary synthesis system containing tetraethylorthosilicate (TEOS), water, and the cetyltrimethylammonium (CTMA) cation at 100{degrees}C. The resulting silicate materials were characterized by X-ray diffraction, {sup 29}Si NMR, and FTIR. As the Sur/Si molar ratio increased from 0.5 to 2, the siliceous products obtained could be classified into four separate groups: MCM-41 (hexagonal), MCM-48 (cubic), thermally unstable M41S, and a molecular species, the cubic octamer [(CTMA)SiO{sub 2.5}]{sub 8}. One of the thermally unstable structures has been identified as a lamellar phase. These results are consistent with known micellar phase transformations that occur at various surfactant concentrations and reinforce the concept that liquid-crystal structures serve as templating agents for the formation of M41S type materials. 48 refs., 13 figs., 5 tabs.

  18. Liquid crystal applications in photonics

    NASA Astrophysics Data System (ADS)

    Chigrinov, Vladimir G.

    2009-02-01

    Liquid crystal (LC) devices for Photonics applications is a hot topic of research. Such elements begin to appear in Photonics market. Passive elements for fiber optical communication systems (DWDM components) based on LC cells can successfully compete with the other elements used for the purpose, such as micro electromechanical (MEM), thermo-optical, opto-mechanical or acousto-optical devices. We have already successfully fabricated certain prototypes of the optical switches based on various electrooptic modes in ferroelectric and nematic LC materials. The electrooptical modes used for the purpose included the light polarization rotation, voltage controllable diffraction and fast switching of the LC refractive index. Use of photo-alignment technique pioneered by us makes it possible to develop new LC fiber components. Almost all the criteria of perfect LC alignment are met in case of azo-dye layers. We have already used azo-dye materials to align LC in superthin photonic holes, curved and 3D surfaces and as cladding layers in microring silicon based resonators. We have already used the photoaligning materials to align LC mixtures in small cavities, such as the holes and tubes of photonic crystals, having size of 1 μm and less and obtained excellent LC orientation inside the tubes by photoalignment. The prototypes of new LC efficient Photonics devices, such as optically rewritable LC waveguides and voltage controllable diffraction gratings are envisaged. The polarization controllers, polarization rotators, variable optical attenuators and other passive LC optical elements for fiber communication networks are under way.

  19. Patterned cholesteric liquid crystal polymer film.

    PubMed

    Hsu, Wei-Liang; Ma, Ji; Myhre, Graham; Balakrishnan, Kaushik; Pau, Stanley

    2013-02-01

    Herein, the ability to create arbitrarily patterned circular polarized optical devices is demonstrated by using cholesteric liquid crystal polymer. Photoalignment with polarized ultraviolet light is utilized to create aligned cholesteric liquid crystal films. Two different methods, thermal annealing and solvent rinse, are utilized for patterning cholesteric liquid crystal films over large areas. The patterned cholesteric liquid crystal films are measured using a Mueller matrix imaging polarimeter, and the polarization properties, including depolarization index, circular diattenuation (CD), and circular retardance are derived. Patterned nonlinearly polarized optical devices can be fabricated with feature sizes as small as 20 μm with a CD of 0.812±0.015. Circular polarizing filters based on polymer cholesteric liquid crystal films have applications in three-dimensional displays, medical imaging, polarimetry, and interferometry. PMID:23456060

  20. Influence of spacer moiety and length of end chain for the phase stability in complementary, double hydrogen bonded liquid crystals, MA:nOBAs

    NASA Astrophysics Data System (ADS)

    Ashok Kumar, A. V. N.; Chalapathi, P. V.; Srinivasulu, M.; Muniprasad, M.; Potukuchi, D. M.

    2015-01-01

    Supra molecular liquid crystals formed by the Hydrogen Bonding interaction between a non-mesogenic aliphatic dicarboxylic acid viz., COOHsbnd CH2sbnd COOH (Malonic Acid, MA); and mesogenic aromatic, N-(p-n-alkoxy benzoic)Acids, (i.e., nOBAs) for n = 3, 4, 5, 7, 8, 9, 10, 11 and 12, labeled as nOBA:COOHsbnd [CH2]msbnd COOH:nOBAs, abbreviated as MA:nOBAs are reported. 1H NMR and 13C NMR studies confirm the formation of HBLC complexes. Infrared (IR) studies confirm the complementary, double, alternative type of HB. Polarized Optical Microscopy (POM) and Differential Scanning Calorimetry (DSC) studies infer N, SmC, SmX, SmCRE, SmF, SmG LC phase variance. SmX phase exhibiting finger print texture grows in MA:nOBAs for n = 10, 11 and 12 by the interruption of SmC phase with decreasing temperature. Re-Entrant SmC (SmCRE) grows by the cooling of SmX. I-N, N-C, X-CRE, C-G, CRE-F, F-G and G-Solid transitions exhibit first order nature. C-X is found to be second order nature in n = 10 and 11. C-X in n = 12 and X-CRE and CRE-F transitions are found to be weak first order nature. Influence of lengths of end chain (n) and spacer (m) for the overall LC phase [ΔT]LC; tilted phase [ΔT]Tilt; SmC phase [ΔT]C and SmX phase [ΔT]X stabilities is discussed in the wake of data on other HBLCs with similar molecular structure. Prevalence of SmX phase in MA:nOBAs with m = 1 infers repulsive interaction between the π-electronic cloud of aromatic boards of nOBAs. Model molecule predicts a twisted configuration of π-cloud around the molecular long axis. Finger print texture of SmX validates the model.

  1. Lifshitz point in ferroelectric liquid crystals

    NASA Astrophysics Data System (ADS)

    Rananavare, Shankar B.; Pisipati, V. G.; Wong, E. W.

    1994-04-01

    Ferroelectric liquid crystals (FLCs) find many applications in display devices, waveguide switching and optical computing. These applications exploit the electrically alignable polarization of FLCs in the Smectic C* (SmC*) phase. In the absence of an electrical field, the SmC* phase exhibits helical modulation of the polarization vector resulting in no net bulk polarization. Pitch length and polarization properties of the phase are associated with the tilted structure and chirality of FLCs. Fundamentally, these physical properties constitute secondary order parameters of the SmA-SmC* (AC*) phase transitions. In this paper, we report a unique and startling ACC* multicritical point in mixtures of chiral DOBAMBC (p-(n- decyloxybenzylidene)-p-amino-(2-methyl-butyl) cinnamate and archiral 10O.8 (4- decyloxybenzylidene-4' octylaniline) where the SmA, C, and C* (ACC* point) phases meet. Studies of the phase diagram, tilt angle ((theta) ), polarization (P) and helix pitch (p) reveal an ACC* Lifshitz point that can be described in terms of the extended Landau theory. Specifically, the TAC* and maximum polarization (Pm) exhibit quadratic composition dependence while the helical pitch length (p equals 2(pi) /q) varies linearly. Both q and Pm vanish discontinuously at the C-C* phase boundary revealing its first order nature. Significantly, the composition dependence (x) of Pm and (theta) can be explained using percolation and thermodynamic scaling theories, respectively.

  2. Biomolecular interactions at phospholipid-decorated surfaces of liquid crystals.

    PubMed

    Brake, Jeffrey M; Daschner, Maren K; Luk, Yan-Yeung; Abbott, Nicholas L

    2003-12-19

    The spontaneous assembly of phospholipids at planar interfaces between thermotropic liquid crystals and aqueous phases gives rise to patterned orientations of the liquid crystals that reflect the spatial and temporal organization of the phospholipids. Strong and weak specific-binding events involving proteins at these interfaces drive the reorganization of the phospholipids and trigger orientational transitions in the liquid crystals. Because these interfaces are fluid, processes involving the lateral organization of proteins (such as the formation of protein- and phospholipid-rich domains) are also readily imaged by the orientational response of the liquid crystal, as are stereospecific enzymatic events. These results provide principles for label-free monitoring of aqueous streams for molecular and biomolecular species without the need for complex instrumentation.

  3. Dynamic self-stiffening in liquid crystal elastomers

    NASA Astrophysics Data System (ADS)

    Agrawal, Aditya; Chipara, Alin C.; Shamoo, Yousif; Patra, Prabir K.; Carey, Brent J.; Ajayan, Pulickel M.; Chapman, Walter G.; Verduzco, Rafael

    2013-04-01

    Biological tissues have the remarkable ability to remodel and repair in response to disease, injury and mechanical stresses. Synthetic materials lack the complexity of biological tissues, and man-made materials that respond to external stresses through a permanent increase in stiffness are uncommon. Here we report that polydomain nematic liquid crystal elastomers increase in stiffness by up to 90% when subjected to a low-amplitude (5%), repetitive (dynamic) compression. Elastomer stiffening is influenced by liquid crystal content, the presence of a nematic liquid crystal phase and the use of a dynamic as opposed to static deformation. Through rheological and X-ray diffraction measurements, stiffening can be attributed to a mobile nematic director, which rotates in response to dynamic compression. Stiffening under dynamic compression has not been previously observed in liquid crystal elastomers and may be useful for the development of self-healing materials or for the development of biocompatible, adaptive materials for tissue replacement.

  4. Dynamic self-stiffening in liquid crystal elastomers.

    PubMed

    Agrawal, Aditya; Chipara, Alin C; Shamoo, Yousif; Patra, Prabir K; Carey, Brent J; Ajayan, Pulickel M; Chapman, Walter G; Verduzco, Rafael

    2013-01-01

    Biological tissues have the remarkable ability to remodel and repair in response to disease, injury and mechanical stresses. Synthetic materials lack the complexity of biological tissues, and man-made materials that respond to external stresses through a permanent increase in stiffness are uncommon. Here we report that polydomain nematic liquid crystal elastomers increase in stiffness by up to 90% when subjected to a low-amplitude (5%), repetitive (dynamic) compression. Elastomer stiffening is influenced by liquid crystal content, the presence of a nematic liquid crystal phase and the use of a dynamic as opposed to static deformation. Through rheological and X-ray diffraction measurements, stiffening can be attributed to a mobile nematic director, which rotates in response to dynamic compression. Stiffening under dynamic compression has not been previously observed in liquid crystal elastomers and may be useful for the development of self-healing materials or for the development of biocompatible, adaptive materials for tissue replacement. PMID:23612280

  5. Dynamic Self-Stiffening in Liquid Crystal Elastomers

    PubMed Central

    Agrawal, Aditya; Chipara, Alin C.; Shamoo, Yousif; Patra, Prabir K.; Carey, Brent J.; Ajayan, Pulickel M.; Chapman, Walter G.

    2013-01-01

    Biological tissues have the remarkable ability to remodel and repair in response to disease, injury, and mechanical stresses. Synthetic materials lack the complexity of biological tissues, and man-made materials which respond to external stresses through a permanent increase in stiffness are uncommon. Here, we report that polydomain nematic liquid crystal elastomers increase in stiffness by up to 90% when subjected to a low-amplitude (5%), repetitive (dynamic) compression. Elastomer stiffening is influenced by liquid crystal content, the presence of a nematic liquid crystal phase and the use of a dynamic as opposed to static deformation. Through rheological and X-ray diffraction measurements, stiffening can be attributed to a nematic director which rotates in response to dynamic compression. Stiffening under dynamic compression has not been previously observed in liquid crystal elastomers and may be useful for the development of self-healing materials or for the development of biocompatible, adaptive materials for tissue replacement. PMID:23612280

  6. Holographic polymer-dispersed liquid crystal Bragg grating integrated inside a solid core photonic crystal fiber.

    PubMed

    Zito, Gianluigi; Pissadakis, Stavros

    2013-09-01

    A polymer/liquid crystal-based fiber Bragg grating (PLC-FBG) is fabricated with visible two-beam holography by photo-induced modulation of a prepolymer/liquid crystal solution infiltrated into the hollow channels of a solid core photonic crystal fiber (PCF). The fabrication process and effects related to the photonic bandgap guidance into the infiltrated PCF, and characterization of the PLC-FBG, are discussed. Experimental data presented here demonstrate that the liquid crystal inclusions of the PLC-FBG lead to high thermal and bending sensitivities. The microscopic behavior of the polymer/liquid crystal phase separation inside the PCF capillaries is examined using scanning electron microscopy, and is discussed further. PMID:23988927

  7. Numerical simulation of phase separation coupled with crystallization

    NASA Astrophysics Data System (ADS)

    Zhou, Douglas; Shi, An-Chang; Zhang, Pingwen

    2008-10-01

    The kinetics of liquid-liquid phase separation and polymer crystallization observed in double-quench experiments with blends of poly(ethylene-co-hexene) and poly(ethylene-co-butene) are studied using time-dependent Ginzburg-Landau Model. Numerical simulations demonstrate that our model can successfully reproduce three experimental phenomena: The decrease in number and size of crystallized spherulites with increasing time in phase separation, the preponderance of nuclei near the domain interface, and the subphase separation and subcrystallization occurring when the second quench is very deep. Moreover, the simulations are consistent with the recently proposed mechanism of "phase separation fluctuation assisted nucleation" in the crystallization process.

  8. PHASE CHANGE LIQUIDS

    SciTech Connect

    Susan S. Sorini; John F. Schabron

    2006-03-01

    Work is being performed to develop a new shipping system for frozen environmental samples (or other materials) that uses an optimal phase change liquid (PCL) formulation and an insulated shipping container with an on-board digital temperature data logger to provide a history of the temperature profile within the container during shipment. In previous work, several PCL formulations with temperatures of fusion ranging from approximately -14 to -20 C were prepared and evaluated. Both temperature of fusion and heat of fusion of the formulations were measured, and an optimal PCL formulation was selected. The PCL was frozen in plastic bags and tested for its temperature profile in a cooler using a digital temperature data logger. This testing showed that the PCL formulation can maintain freezer temperatures (< -7 to -20 C) for an extended period, such as the time for shipping samples by overnight courier. The results of the experiments described in this report provide significant information for use in developing an integrated freezer system that uses a PCL formulation to maintain freezer temperatures in coolers for shipping environmental samples to the laboratory. Experimental results show the importance of the type of cooler used in the system and that use of an insulating material within the cooler improves the performance of the freezer system. A new optimal PCL formulation for use in the system has been determined. The new formulation has been shown to maintain temperatures at < -7 to -20 C for 47 hours in an insulated cooler system containing soil samples. These results are very promising for developing the new technology.

  9. Hydrogen-Bonded Liquid Crystal Nanocomposites.

    PubMed

    Roohnikan, Mahdi; Toader, Violeta; Rey, Alejandro; Reven, Linda

    2016-08-23

    Nanoparticle-liquid crystal (NP-LC) composites based on hydrogen bonding were explored using a model system. The ligand shells of 3 nm diameter zirconium dioxide nanoparticles (ZrO2 NPs) were varied to control their interaction with 4-n-hexylbenzoic acid (6BA). The miscibility and effect of the NPs on the nematic order as a function of particle concentration was characterized by polarized optical microscopy (POM), fluorescence microscopy and (2)H NMR spectroscopy. Nonfunctionalized ZrO2 NPs have the lowest miscibility and strongest effect on the LC matrix due to irreversible binding of 6BA to the NPs via a strong zirconium carboxylate bond. The ZrO2 NPs were functionalized with 6-phosphonohexanoic acid (6PHA) or 4-(6-phosphonohexyloxy)benzoic acid (6BPHA) which selectively bind to the ZrO2 NP surface via the phosphonic acid groups. The miscibility was increased by controlling the concentration of the pendant CO2H groups by adding hexylphosphonic acid (HPA) to act as a spacer group. Fluorescence microscopy of lanthanide doped ZrO2 NPs showed no aggregates in the nematic phase below the NP concentration where aggregates are observed in the isotropic phase. The functionalized NPs preferably concentrate into LC defects and any remaining isotropic liquid but are still present throughout the nematic liquid at a lower concentration. PMID:27466705

  10. Hydrogen-Bonded Liquid Crystal Nanocomposites.

    PubMed

    Roohnikan, Mahdi; Toader, Violeta; Rey, Alejandro; Reven, Linda

    2016-08-23

    Nanoparticle-liquid crystal (NP-LC) composites based on hydrogen bonding were explored using a model system. The ligand shells of 3 nm diameter zirconium dioxide nanoparticles (ZrO2 NPs) were varied to control their interaction with 4-n-hexylbenzoic acid (6BA). The miscibility and effect of the NPs on the nematic order as a function of particle concentration was characterized by polarized optical microscopy (POM), fluorescence microscopy and (2)H NMR spectroscopy. Nonfunctionalized ZrO2 NPs have the lowest miscibility and strongest effect on the LC matrix due to irreversible binding of 6BA to the NPs via a strong zirconium carboxylate bond. The ZrO2 NPs were functionalized with 6-phosphonohexanoic acid (6PHA) or 4-(6-phosphonohexyloxy)benzoic acid (6BPHA) which selectively bind to the ZrO2 NP surface via the phosphonic acid groups. The miscibility was increased by controlling the concentration of the pendant CO2H groups by adding hexylphosphonic acid (HPA) to act as a spacer group. Fluorescence microscopy of lanthanide doped ZrO2 NPs showed no aggregates in the nematic phase below the NP concentration where aggregates are observed in the isotropic phase. The functionalized NPs preferably concentrate into LC defects and any remaining isotropic liquid but are still present throughout the nematic liquid at a lower concentration.

  11. Stabilization of DNA liquid crystals on doping with gold nanorods.

    PubMed

    Brach, Katarzyna; Matczyszyn, Katarzyna; Olesiak-Banska, Joanna; Gordel, Marta; Samoc, Marek

    2016-03-14

    We report on the impact of doping with gold nanorods (NRs) on the formation and stability of DNA liquid crystals (LCs). Cetyl trimethylammonium (CTAB)-stabilized gold NRs were synthesized using the wet chemistry method. Different textures of cholesteric and columnar mesophases, as well as phase transitions, were observed using a polarized light microscope. It was found that liquid crystalline phases formed in the samples were qualitatively the same and the phase appearance sequence was preserved in the samples regardless of the doping. We show that depending on the concentration of gold NRs present in the phase, nanoparticle-doped cholesteric and columnar hexagonal phases existed in wider temperature ranges compared to pure DNA LCs. The potential applications of these liquid crystal-nanoparticle hybrid systems may include the fabrication of new optoelectronic devices and sensors.

  12. Resonant X-Ray Diffraction Study of an Unusually Large Phase Coexistance in Smectic Liquid-Crystal Films

    SciTech Connect

    Pan L.; Pindak R.; Barois, P.; Liu, Z.Q.; McCoy, B.K. & Hyang, C.C.

    2012-01-19

    The recent discovery of the new smectic-C{sub d6}* (SmC{sub d6}*) phase [S. Wang et al. Phys. Rev. Lett. 104 027801 (2010)] also revealed the existence of a noisy region in the temperature window between the SmC{sub d6}* phase and the smectic-C{sub d4}* (SmC{sub d4}*) phase. Characterized by multiple resonant peaks spanning a wide region in Q{sub Z}, the corresponding structure of this temperature window has been a mystery. In this Letter, through a careful resonant x-ray diffraction study and simulations of the diffraction spectra, we show that this region is in fact an unusually large coexistence region of the SmC{sub d6}* phase and the SmC{sub d4}* phase. The structure of the noisy region is found to be a heterogeneous mixture of local SmC{sub d6}* and SmC{sub d4}* orders on the sub-{micro}m scale.

  13. Liquid crystal devices for photonics applications

    NASA Astrophysics Data System (ADS)

    Chigrinov, Vladimir G.

    2007-11-01

    Liquid crystal (LC) devices for Photonics applications is a hot topic of research. Such elements begin to appear in Photonics market. Passive elements for fiber optical communication systems (DWDM components) based on LC cells can successfully compete with the other elements used for the purpose, such as micro electromechanical (MEM), thermo-optical, opto-mechanical or acousto-optical devices. Application of nematic and ferroelectric LC for high speed communication systems, producing elements that are extremely fast, stable, durable, of low loss, operable over a wide temperature range, and that require small operating voltages and extremely low power consumption. The known LC applications in fiber optics enable to produce switches, filters, attenuators, equalizers, polarization controllers, phase emulators and other fiber optical components. Good robustness due to the absence of moving parts and compatibility with VLSI technology, excellent parameters in a large photonic wavelength range, whereas the complexity of the design and the cost of the device are equivalent to regular passive matrix LC displays makes LC fiber optical devices very attractive for mass production. We have already successfully fabricated certain prototypes of the optical switches based on ferroelectric and nematic LC materials. The electrooptical modes used for the purpose included the light polarization rotation, voltage controllable diffraction and fast switching of the LC refractive index. We used the powerful software to optimize the LC modulation characteristics. Use of photo-alignment technique pioneered by us makes it possible to develop new LC fiber components. Almost all the criteria of perfect LC alignment are met in case of azo-dye layers. We have already used azo-dye materials to align LC in superthin photonic holes, curved and 3D surfaces and as cladding layers in microring silicon based resonators. The prototypes of new LC efficient Photonics devices are envisaged. Controllable

  14. Anchoring transition in confined discotic columnar liquid crystal films

    NASA Astrophysics Data System (ADS)

    Brunet, Thomas; Thiebaut, Olivier; Charlet, Émilie; Bock, Harald; Kelber, Julien; Grelet, Éric

    2011-01-01

    We report the achievement of ultrathin films (down to 25 nm thick) of thermotropic columnar liquid crystals in homeotropic alignment (columns normal to the interface) confined between a glass slide and a thin metallic electrode (about 150 nm thick). The face-on orientation of the discotic compound is obtained by anchoring transition of a columnar liquid crystalline phase from a degenerate planar orientation to the homeotropic alignment without any phase transition to the isotropic liquid phase. The kinetic dependence on temperature of such anchoring transition is investigated revealing various diffusive growth regimes of the homeotropic domains. Finally, confining effects are also considered by varying the thickness of the columnar liquid crystal film to reach the typical value required in organic solar cells thus demonstrating the reliability of such alignment process in a photovoltaic context.

  15. Synthesis and Liquid Crystals Properties of α-Methylated Galactosides

    NASA Astrophysics Data System (ADS)

    Rodzi, N. Z. B. M.; Heidelberg, T.; Hashim, R.; Sugimura, A.; Minamikawa, H.

    Due to the amphiphilicity nature of glycolipids, some are known to exhibits liquid crystals phases both in thermotropic and lyotropic phases. Six different glycolipids have been synthesized using three steps process and their structures have been characterized by 1H-NMR and 13C-NMR in acetylated and deacytelated forms. Their liquid crystals properties were studied using optical polarising microscopy (OPM) and differential scanning calorimetry (DSC). The effect of α-methylated tails is comparedwith those of the straight chain glycolipids. The epimeric effect of the hydroxyl group at the C-4 of the sugar group was also commented.

  16. Structure of liquid crystal droplets with chiral propeller texture.

    PubMed

    Yang, Deng-Ke; Jeong, Kwang-Un; Cheng, S Z D

    2008-02-01

    We experimentally studied a nematic liquid crystal whose molecules form twisted head-to-head H-bonded dimers. We observed that when the material transformed from the isotropic to nematic phase, it formed droplets with chiral propeller textures. We carried out a computer simulation to investigate the liquid crystal director configuration inside the droplets and to study the effects of elastic constants and chirality on the droplet texture. Results of our study show it is likely that the material in the droplets had nonzero chirality due to spontaneous chiral phase separation.

  17. Electrically induced tilt in achiral bent-core liquid crystals.

    PubMed

    Eremin, Alexey; Stern, Stephan; Stannarius, Ralf

    2008-12-12

    We report an electric-field-induced SmA-SmC transition in a liquid crystal formed by achiral bent molecules. The steric moment of such molecules is too small to spontaneously induce the phases characteristic to the bent-core mesogens. On the other hand, its contribution to the thermodynamical properties of the mesophases make it possible to induce tilt and polar order by the action of the external electric field. This effect is unique for bent mesogens and its physical nature differs from an electroclinic effect observed in the SmA* phase of chiral liquid crystals.

  18. Two distinct crystallization processes in supercooled liquid.

    PubMed

    Tane, Masakazu; Kimizuka, Hajime; Ichitsubo, Tetsu

    2016-05-21

    Using molecular dynamics simulations we show that two distinct crystallization processes, depending on the temperature at which crystallization occurs, appear in a supercooled liquid. As a model for glass-forming materials, an Al2O3 model system, in which both the glass transition and crystallization from the supercooled liquid can be well reproduced, is employed. Simulations in the framework of an isothermal-isobaric ensemble indicate that the calculated time-temperature-transformation curve for the crystallization to γ(defect spinel)-Al2O3 exhibited a typical nose shape, as experimentally observed in various glass materials. During annealing above the nose temperature, the structure of the supercooled liquid does not change before the crystallization, because of the high atomic mobility (material transport). Thus, the crystallization is governed by the abrupt crystal nucleation, which results in the formation of a stable crystal structure. In contrast, during annealing below the nose temperature, the structure of the supercooled liquid gradually changes before the crystallization, and the formed crystal structure is less stable than that formed above the nose temperature, because of the restricted material transport. PMID:27208956

  19. Two distinct crystallization processes in supercooled liquid

    NASA Astrophysics Data System (ADS)

    Tane, Masakazu; Kimizuka, Hajime; Ichitsubo, Tetsu

    2016-05-01

    Using molecular dynamics simulations we show that two distinct crystallization processes, depending on the temperature at which crystallization occurs, appear in a supercooled liquid. As a model for glass-forming materials, an Al2O3 model system, in which both the glass transition and crystallization from the supercooled liquid can be well reproduced, is employed. Simulations in the framework of an isothermal-isobaric ensemble indicate that the calculated time-temperature-transformation curve for the crystallization to γ(defect spinel)-Al2O3 exhibited a typical nose shape, as experimentally observed in various glass materials. During annealing above the nose temperature, the structure of the supercooled liquid does not change before the crystallization, because of the high atomic mobility (material transport). Thus, the crystallization is governed by the abrupt crystal nucleation, which results in the formation of a stable crystal structure. In contrast, during annealing below the nose temperature, the structure of the supercooled liquid gradually changes before the crystallization, and the formed crystal structure is less stable than that formed above the nose temperature, because of the restricted material transport.

  20. Novel Microstructures for Polymer-Liquid Crystal Composite Materials

    NASA Technical Reports Server (NTRS)

    Magda, Jules J.

    2004-01-01

    There are a number of interface-dominated composite materials that contain a liquid crystalline (LC) phase in intimate contact with an isotropic phase. For example, polymer- dispersed liquid crystals, used in the fabrication of windows with switchable transparency, consist of micron size LC droplets dispersed in an isotropic polymer matrix. Many other types of liquid crystal composite materials can be envisioned that might have outstanding optical properties that could be exploited in novel chemical sensors, optical switches, and computer displays. This research project was based on the premise that many of these potentially useful LC composite materials can only be fabricated under microgravity conditions where gravity driven flows are absent. In the ground-based research described below, we have focused on a new class of LC composites that we call thermotropic- lyotropic liquid crystal systems (TLLCs). TLLCs consist of nanosize droplets of water dispersed in an LC matrix, with surfactants at the interface that stabilize the structure. By varying the type of surfactant one can access almost an infinite variety of unusual LC composite microstructures. Due to the importance of the interface in these types of systems, we have also developed molecular simulation models for liquid crystals at interfaces, and made some of the first measurements of the interfacial tension between liquid crystals and water.

  1. Advancements of vertically aligned liquid crystal displays.

    PubMed

    Kumar, Pankaj; Jaggi, Chinky; Sharma, Vandna; Raina, Kuldeep Kumar

    2016-02-01

    This review describes the recent advancements in the field of the vertical aligned (VA) liquid crystal displays. The process and formation of different vertical alignment modes such as conventional VA, patterned VA, multi-domain VA, and polymer stabilised VA etc are widely discussed. Vertical alignment of liquid crystal due to nano particle dispersion in LC host, bifunctional PR-SAM formed by silane coupling reaction to oxide surfaces, azo dye etc., are also highlighted and discussed. Overall, the article highlights the advances in the research of vertical aligned liquid crystal in terms of their scientific and technological aspects.

  2. Liquid Crystal Research Shows Deformation By Drying

    NASA Technical Reports Server (NTRS)

    2003-01-01

    These images, from David Weitz's liquid crystal research, show ordered uniform sized droplets (upper left) before they are dried from their solution. After the droplets are dried (upper right), they are viewed with crossed polarizers that show the deformation caused by drying, a process that orients the bipolar structure of the liquid crystal within the droplets. When an electric field is applied to the dried droplets (lower left), and then increased (lower right), the liquid crystal within the droplets switches its alignment, thereby reducing the amount of light that can be scattered by the droplets when a beam is shone through them.

  3. Liquid crystals for laser applications

    NASA Astrophysics Data System (ADS)

    Jacobs, S. D.; Marshall, K. L.; Schmid, A.

    1992-10-01

    This article highlights some of the advances made in the use of liquid crystals for laser applications from 1982 through 1992. New materials and new effects were discovered, many new devices were developed, and novel applications for well-understood phenomena were conceived. This was quite an eventful time period. Several new books were published on the broad subject of LC's, and the international scientific community organized a society devoted to encouraging further scientific and educational advancement in the field. Attention was focused on LC's in October of 1991 when the Nobel Prize in Physics was awarded to Pierre-Gilles de Gennes for his pioneering work toward understanding order phenomena in LC's and polymers. This article is divided into four sections. The first section discusses new materials, specifically ferroelectric LC's and LC polymers. The former have opened up the realm of submicrosecond response for LC devices, and the latter have significantly reduced the sensitivity of LC optics to temperature. Some new insights into the optical properties of materials are also mentioned. The second section reviews new developments in passive applications for cholesterics and nematics. Included here are the fabrication of cholesteric laser mirrors and apodizers, the use of LC polymers for notch filters and as optical storage media, and some novel nematic retarder concepts such as the distributed polarization rotator.

  4. Novel liquid-crystal alignment method using polarized laser light (Invited Paper)

    NASA Astrophysics Data System (ADS)

    Sun, Shao-Tang; Gibbons, Wayne M.; Shannon, Paul J.

    1992-10-01

    The control of liquid crystal alignment is of critical importance to the electro-optic performance of a liquid crystal display. Recently a new alignment method was discovered. Instead of the conventional buffing technique, polarized light is employed to treat the polymer alignment layer on the substrate of the display cell for the control of liquid crystal orientation. This non-contact method of aligning liquid crystals offers unique possibilities for display cell repair or reconfiguration after cell assembly. In addition, novel liquid crystal phase devices can be realized for use in optical processing.

  5. Photorefractive amplification of dynamic light signals using photoconductive ferroelectric liquid crystals

    NASA Astrophysics Data System (ADS)

    Sasaki, Takeo

    2015-05-01

    The photorefractive effect in photoconductive ferroelectric liquid crystal blends containing photoconductive chiral compounds was investigated. Terthiophene compounds possessing chiral structures were mixed with an achiral smectic C liquid crystal mixture. The blends exhibit the ferroelectric chiral smectic C phase. The photorefractivity of the liquid crystal blends was investigated by two-beam coupling experiments. The photoconductive ferroelectric liquid crystal blends prepared in this study exhibited a large gain coefficient of over 1200 cm-1 and a fast response time shorter than 1 ms. Amplification of an moving optical image signal of over 30 fps using the photorefractive ferroelectric liquid crystal was demonstrated.

  6. Liquid crystals: a new topic in physics for undergraduates

    NASA Astrophysics Data System (ADS)

    Pavlin, Jerneja; Vaupotič, Nataša; Čepič, Mojca

    2013-05-01

    This paper presents a teaching module about liquid crystals. Since liquid crystals are linked to everyday student experiences and are also a topic of current scientific research, they are an excellent candidate for a modern topic to be introduced into education. We show that liquid crystals can provide a pathway through several fields of physics such as thermodynamics, optics and electromagnetism. We discuss what students should learn about liquid crystals and what physical concepts they should know before considering them. In the presentation of the teaching module, which consists of a lecture and experimental work in a chemistry and physics laboratory, we focus on experiments on phase transitions, polarization of light, double refraction and colours. A pilot evaluation of the module was performed among pre-service primary school teachers who have no special preference for natural sciences. The evaluation shows that the module is very efficient in transferring knowledge. A prior study showed that the informally obtained pre-knowledge on liquid crystals of the first-year students from several different fields of study was negligible. Since social science students are the least interested in natural sciences, it can be expected that students in any study programme will on average achieve at least as good qualitative knowledge of phenomena related to liquid crystals as the group involved in the pilot study.

  7. Analyzing algorithms for nonlinear and spatially nonuniform phase shifts in the liquid crystal point diffraction interferometer. 1998 summer research program for high school juniors at the University of Rochester`s Laboratory for Laser Energetics: Student research reports

    SciTech Connect

    Jain, N.

    1999-03-01

    Phase-shifting interferometry has many advantages, and the phase shifting nature of the Liquid Crystal Point Diffraction Interferometer (LCPDI) promises to provide significant improvement over other current OMEGA wavefront sensors. However, while phase-shifting capabilities improve its accuracy as an interferometer, phase-shifting itself introduces errors. Phase-shifting algorithms are designed to eliminate certain types of phase-shift errors, and it is important to chose an algorithm that is best suited for use with the LCPDI. Using polarization microscopy, the authors have observed a correlation between LC alignment around the microsphere and fringe behavior. After designing a procedure to compare phase-shifting algorithms, they were able to predict the accuracy of two particular algorithms through computer modeling of device-specific phase shift-errors.

  8. Aqueous liquid crystals of graphene oxide.

    PubMed

    Xu, Zhen; Gao, Chao

    2011-04-26

    The formation of liquid crystals (LCs) is the most viable approach to produce macroscopic, periodic self-assembled materials from oriented graphene sheets. Herein, we have discovered that well-soluble and single-layered graphene oxide (GO) sheets can exhibit nematic liquid crystallinity in water and first established their isotropic-nematic solid phase diagram versus mass fraction and salt concentration. The zeta potential of GO dispersion is around -64 mV, and its absolute value decreases with increasing salt concentration, implying that the electrostatic repulsive force between negatively charged GO sheets is the dominant interaction in the system of GOLCs and also explaining the salt-dependent phase behavior. For single-layer GO sheets with average diameter of 2.1 μm and polydispersity index of 83%, the isotropic-nematic phase transition occurs at a mass concentration of ∼0.025%, and a stable nematic phase forms at ∼0.5%. Rheological measurements showed that GO aqueous dispersions performed as typical shear flows and confirmed the isotropic-nematic transition. The ordering of GO sheets in aqueous dispersions and the solid state is demonstrated by the characterizations of polarized-light optical microscopy, small-angle X-ray scattering, scanning electron microscopy, and transmission electron microscopy. The direct, real-time fluorescent inspections by confocal laser microscopy further reveal that the individually dispersed fluorescent GO sheets align with orientational directions along their long axes. These novel findings shed light on the phase behaviors of diversely topological graphenes and lay the foundation for fabrication of long-range, ordered nano-objects and macroscopically assembled graphene-based functional materials.

  9. Crystal-liquid interfacial free energy via thermodynamic integration

    SciTech Connect

    Benjamin, Ronald; Horbach, Jürgen

    2014-07-28

    A novel thermodynamic integration (TI) scheme is presented to compute the crystal-liquid interfacial free energy (γ{sub cl}) from molecular dynamics simulation. The scheme is applied to a Lennard-Jones system. By using extremely short-ranged and impenetrable Gaussian flat walls to confine the liquid and crystal phases, we overcome hysteresis problems of previous TI schemes that stem from the translational movement of the crystal-liquid interface. Our technique is applied to compute γ{sub cl} for the (100), (110), and (111) orientation of the crystalline phase at three temperatures under coexistence conditions. For one case, namely, the (100) interface at the temperature T = 1.0 (in reduced units), we demonstrate that finite-size scaling in the framework of capillary wave theory can be used to estimate γ{sub cl} in the thermodynamic limit. Thereby, we show that our TI scheme is not associated with the suppression of capillary wave fluctuations.

  10. Defect topologies in chiral liquid crystals confined to mesoscopic channels

    SciTech Connect

    Schlotthauer, Sergej Skutnik, Robert A.; Stieger, Tillmann; Schoen, Martin

    2015-05-21

    We present Monte Carlo simulations in the grand canonical and canonical ensembles of a chiral liquid crystal confined to mesochannels of variable sizes and geometries. The mesochannels are taken to be quasi-infinite in one dimension but finite in the two other directions. Under thermodynamic conditions chosen and for a selected value of the chirality coupling constant, the bulk liquid crystal exhibits structural characteristics of a blue phase II. This is established through the tetrahedral symmetry of disclination lines and the characteristic simple-cubic arrangement of double-twist helices formed by the liquid-crystal molecules along all three axes of a Cartesian coordinate system. If the blue phase II is then exposed to confinement, the interplay between its helical structure, various anchoring conditions at the walls of the mesochannels, and the shape of the mesochannels gives rise to a broad variety of novel, qualitative disclination-line structures that are reported here for the first time.

  11. Polymer single crystal membrane from liquid/liquid interface

    NASA Astrophysics Data System (ADS)

    Wang, Wenda; Li, Christopher; Soft Matter Research Group-Drexel University Team

    2013-03-01

    Vesicles, mimicking the structure of cell membrane at the molecular scale, are small membrane-enclosed sacks that can store or transport substances. The weak mechanical properties and the nature of environment-sensitivity of the current available vesicles: liposomes, polymersomes, colloidsomes limit their applications as an excellent candidate for targeting delivery of drugs/genes in biomedical engineering and treatment. Recently, we developed an emulsion-based method to grow curved polymer single crystals. Varying the polymer concentration and/or the emulsification conditions (such as surfactant concentration, water-oil volume ratio), curved crystals with different sizes and different openness could be obtained. This growing process was attributed to polymer crystal growth along the liquid/liquid interface. In addition, the liquid/liquid interfacial crystal growth is promising for synthesis of enclosed hollow sphere.

  12. Rapid leak detection with liquid crystals

    NASA Technical Reports Server (NTRS)

    Heisman, R. M.; Iceland, W. F.; Ruppe, E. P.

    1978-01-01

    Small leaks in vacuum lines are detected by applying liquid-crystal coating, warming suspected area, and observing color change due to differential cooling by leak jet. Technique is used on inside or outside walls of vacuum-jacketed lines.

  13. Liquid crystal television spatial light modulators

    NASA Technical Reports Server (NTRS)

    Liu, Hua-Kuang; Chao, Tien-Hsin

    1989-01-01

    The spatial light modulation characteristics and capabilities of the liquid crystal television (LCTV) spatial light modulators (SLMs) are discussed. A comparison of Radio Shack, Epson, and Citizen LCTV SLMs is made.

  14. Liquid crystal on subwavelength metal gratings

    NASA Astrophysics Data System (ADS)

    Palto, S. P.; Barnik, M. I.; Artemov, V. V.; Shtykov, N. M.; Geivandov, A. R.; Yudin, S. G.; Gorkunov, M. V.

    2015-06-01

    Optical and electrooptical properties of a system consisting of subwavelength metal gratings and nematic liquid crystal layer are studied. Aluminium gratings that also act as interdigitated electrodes are produced by focused ion beam lithography. It is found that a liquid crystal layer strongly influences both the resonance and light polarization properties characteristic of the gratings. Enhanced transmittance is observed not only for the TM-polarized light in the near infrared spectral range but also for the TE-polarized light in the visible range. Although the electrodes are separated by nanosized slits, and the electric field is strongly localized near the surface, a pronounced electrooptical effect is registered. The effect is explained in terms of local reorientation of liquid crystal molecules at the grating surface and propagation of the orientational deformation from the surface into the bulk of the liquid crystal layer.

  15. Slow light in liquid crystal media

    NASA Astrophysics Data System (ADS)

    Bortolozzo, Umberto; Wei, Dong; Huignard, Jean-Pierre; Residori, Stefania

    2014-10-01

    Liquid crystal media are characterized by large and tunable dispersive properties and hence allow achievement of large group delays. At the same time, liquid crystals provide large areas and are easily reconfigurable and highly sensitive devices; they are, therefore, well adapted for interferometric applications. Two different ways of achieving slow light in liquid crystals are presented. The first method consists of exploiting photoisomerization-induced transparency in dye-doped chiral liquid crystals, and the second method makes use of two-wave mixing optical resonance in pure nematics. In both mechanisms, two beams are sent to the medium, where they create a grating, either of absorption or of refractive index. Both physical mechanisms are elucidated in the context of slow light, then, as examples of sensing applications, Doppler shift measurements and adaptive holography are presented.

  16. Thermal Conductivity and Liquid Crystal Thermometers.

    ERIC Educational Resources Information Center

    Edge, R. D., Ed.

    1993-01-01

    Describes using stock liquid crystal postcards as inexpensive classroom thermometers. Also suggests using these postcards as a good visual temperature indicator for classroom demonstrations such as temperature gradients. One such activity is provided. (MVL)

  17. Liquid crystal on subwavelength metal gratings

    SciTech Connect

    Palto, S. P.; Barnik, M. I.; Artemov, V. V.; Shtykov, N. M.; Geivandov, A. R.; Yudin, S. G.; Gorkunov, M. V.

    2015-06-14

    Optical and electrooptical properties of a system consisting of subwavelength metal gratings and nematic liquid crystal layer are studied. Aluminium gratings that also act as interdigitated electrodes are produced by focused ion beam lithography. It is found that a liquid crystal layer strongly influences both the resonance and light polarization properties characteristic of the gratings. Enhanced transmittance is observed not only for the TM-polarized light in the near infrared spectral range but also for the TE-polarized light in the visible range. Although the electrodes are separated by nanosized slits, and the electric field is strongly localized near the surface, a pronounced electrooptical effect is registered. The effect is explained in terms of local reorientation of liquid crystal molecules at the grating surface and propagation of the orientational deformation from the surface into the bulk of the liquid crystal layer.

  18. Polychromatic Optical Vortex Generation from Patterned Cholesteric Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Kobashi, Junji; Yoshida, Hiroyuki; Ozaki, Masanori

    2016-06-01

    Generation of optical vortices is described in cholesteric liquid crystals with a singular point in the spatial distribution of a helix phase. The phenomenon uses the fact that a Bragg reflected light phase varies in proportion to the spatial phase of the helix, both at normal and oblique incidences. Our proposal enables high-efficiency, polychromatic generation of optical vortices without the need of a cumbersome fabrication process and fine-tuning.

  19. Polychromatic Optical Vortex Generation from Patterned Cholesteric Liquid Crystals.

    PubMed

    Kobashi, Junji; Yoshida, Hiroyuki; Ozaki, Masanori

    2016-06-24

    Generation of optical vortices is described in cholesteric liquid crystals with a singular point in the spatial distribution of a helix phase. The phenomenon uses the fact that a Bragg reflected light phase varies in proportion to the spatial phase of the helix, both at normal and oblique incidences. Our proposal enables high-efficiency, polychromatic generation of optical vortices without the need of a cumbersome fabrication process and fine-tuning. PMID:27391724

  20. Optically isotropic liquid crystal media formulated by doping star-shaped cyclic oligosiloxane liquid crystal surfactants in twin nematic liquid crystals.

    PubMed

    Kim, Namil; Kim, Dae-Yoon; Park, Minwook; Choi, Yu-Jin; Kim, Soeun; Lee, Seung Hee; Jeong, Kwang-Un

    2015-05-21

    The formation of optically isotropic liquid crystal (LC) media has been investigated by doping the star-shaped LC molecular surfactants (SiLC) into the rod-shaped twin LC host molecules (DiLC). The experimental phase diagram was constructed on the basis of differential scanning calorimetry (DSC) and then a theoretical calculation was conducted through a combined Flory-Huggins (FH)/Maier-Saupe-McMillan (MSM)/phase field (PF) model to account for the experimental results. The phase diagram of the SiLC/DiLC mixtures revealed the broad coexistence regions such as smectic A + crystal (SmA1 + Cr2), liquid + crystal (L1 + Cr2), and liquid + nematic (L1 + N2) at the intermediate composition along with the narrow single phase crystal (Cr2), smectic (SmA1), and nematic (N2) regions. The morphologies and structures of these coexistence regions were further confirmed by polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). At the 80/20 SiLC/DiLC composition, the optical anisotropy was induced under an alternating current (AC) electric field above its isotropization temperature. The formation of an optically isotropic LC medium in mixtures of the SiLC molecular surfactants and nematic LC host may allow us to develop new electro-optical devices.