Imaging of bacteria using chromonic liquid crystals

We explored adsorption isotherms of Escherichia coli (E.coli) and Salmonella over the poly-L-lysine (PLL) coated glass surface. The detection of the adsorbed bacteria was explored using 14 wt% di-sodium-chromo-glycate (DSCG) solution in water and 5CB. The textures of the optical cells made up of LCs and the adsorbed bacteria over PLL-coated glass substrate were obtained by using a polarized microscope in the transmission mode under crossed polars. We found that DSCG solution exhibits a dark spot on the adsorbed E.coli and Salmonella. In contrast to DSCG solution, 5CB did not show any dark spot.     

Modification in dielectric properties of SWCNT doped ferroelectric liquid crystals

Effect of single walled carbon nanotubes (SWCNT) in ferroelectric liquid crystal (FLC) geometry has been studied for low and high concentrations of dopant. The results are compared with the characteristics of pure FLC system. An appreciable change in dielectric permittivity, relaxation behavior and other vital parameters has been observed for SWCNT doped FLC system, which shows the adaptability of carbon nanotubes with that of pure FLC molecule. Under high electric field, highly concentrated SWCNT doped FLC shows enormously large values of dielectric loss. This is due to the high conductivity of SWCNT at higher electric field. Interestingly, such effect is not much prominent for the low concentration of the SWCNT doped FLC system.     

Functionalisation of cholesteric liquid crystals by direct laser writing

Cholesteric liquid crystals selectively reflect circularly polarised light with the same handedness as the helix. Because of their sensitivity to external stimuli, such as heat and electrical fields, various applications utilising their tunability have been proposed. Tuning is usually performed in the bulk, meaning that cholesteric liquid crystals usually possess a single pitch throughout the medium. However, when the helical structure is locally modulated, different optical properties arise, such as tunable photonic defect modes and multiple reflection bands. Here we show a technique to locally modulate the helical structure of cholesteric liquid crystals on a submicron scale, based on two-photon excitation direct laser lithography. Two examples of cholesteric liquid crystal structures with modulated helical structures will be presented.     

Spontaneous homeotropic alignment of nematic liquid crystals induced by a double-armed side chain liquid crystalline polymethacrylate

A liquid crystalline polymethacrylate having two cyclohexylphenyl mesogens on its side-chain (PMG0) was synthesized by the radical polymerization of the corresponding methacrylate monomer (MG0). PMG0 exhibited a smectic A phase around room temperature showing a focalconic fan texture in POM observations and a broad diffusion in a wide angle range of its WAXD profile. Upon slow cooling at ?1 °C min^?1 from the isotropic melt, PMG0 exhibited spontaneous homeotropic alignment between two native glass surfaces. A mixture of the commercial nematic liquid crystal (ZLI-4792) containing 1.0 wt% PMG0 also exhibited a homeotropic alignment, which easily covered hydrophilic surfaces such as glass or polyacrylamide.     

Colloidal structures in confined nematic liquid crystals

Colloidal structures in confined nematics offer novel routes for designing complex optical materials with micrometre and submicrometre functionality. In this paper, we review some of our recently assembled colloidal structures that form in confined nematic cells. We present effective elastic binding via nematic distortion as a mechanism for the assembly of two-dimensional colloidal crystals of elastic dipoles and elastic quadrupoles. We introduce entangled colloids as novel types of structures, where particles are topologically bound by delocalised defect loops, producing robust and possibly chiral structures. The concept of hierarchical assembly is demonstrated in colloids with particles of various scales. In cholesteric blue phases, the assembly of three-dimensional colloidal crystals is shown based on naturally occurring three-dimensional arrays of trapping sites produced by blue phases.     

Monte carlo simulations for blue-phase structure in liquid crystals

Blue-phase liquid crystals form three-dimensional structures in a self-organizing manner and are similar to living tissue structures such as the teeth of mice and collagen tissues. This study presents numerical results regarding the conditions under which blue-phase liquid crystals occur. The Monte Carlo simulations are performed by employing an improved Lennard–Jones potential that considers anisotropy and chirality. The conditions for the formation of the blue phase, which vary with respect to the chirality, are examined first. The relationship between the anisotropic parameters and the chiral parameter for the formation of the blue phase is discussed. Identical blue-phase structures are obtained, even when the cell size and molecular number are varied drastically. This discussion is useful for considering the scale-up problem, which is almost always a difficult issue for molecular-scale simulations.     

Alkyloxy azo-cinnamate ester based thermotropic liquid crystals and their photophysical investigations

Two series of rod shaped Schiff base containing azo-cinnamate thermotropic liquid crystalline compounds were synthesized and characterized. These molecules have four different alkyl spacers (n = 6, 8, 10, and 12) at one end and a dodecyloxy chain at another end (n = 12) which influence their liquid crystalline properties. Liquid crystallinity commence from six methylene spacer onwards in the series exhibiting with Nematic to Smectic-C mesophases. Analytical data confirm the molecular structures of homologues series of compounds. The characteristic texture of liquid crystalline phases obtained using polarizing‐light microscope with a heating stage. The structural transformation of these liquid crystals was confirmed by differential scanning calorimetry. All the compounds exhibited various calamitic mesophases with wide mesomorphic temperature ranges. The relationship between structure and mesomorphic properties was discussed in framework of geometrical configuration of central unit, linking part, and length of alkoxy chains. Photosensitive azobenzene group undergoes photoisomerization under UV light and monitored by UV-Visible spectroscopy.     

Synthesis of four liquid crystals and study of alkyl chain effect on the nematic range for application in GC

Four liquid crystals (LCs) compounds which contain the 1,3,4-oxadiazole group were synthesized and characterized with spectroscopic techniques (IR, ¹H- and ¹³C NMR), their thermal properties were analyzed by the Differential Scanning Calorimetry (DSC) and the polarizing microscope (POM). A comparative study of the mesomorphic properties of these LCs and three other compounds which have already been used as a stationary phase in gas chromatography (GC) was carried out. These compounds have the same main nucleus. LCs V1, LC1, LC2 and LC3 gave a nematic (N) phase to the heating, LCs V2 and V3 recorded smectic A (SmA) and N phases. However, the range (N) has disappeared in V4.     

A pitch of helicoid of chiral liquid crystals and surface plasmon excitation: A theoretical study

ABSTRACT

Surface plasmon resonance (SPR) is widely used in different types of optical detection schemes and for light manipulation. There are a lot of experimental and theoretical investigations about the influence of different media, adjacent to the metal layer, on SPR. However, the influence of liquid crystal (LC) layer is not fully revealed. There are only few publications considering Kretshmann configuration with LC layer sandwiched between the prism and metal layer. Respectively, a lot of questions regarding the influence of LC properties on the surface plasmon resonance (SPR) are still open. The aim of this paper is to fill this gap.     

Supramolecular liquid crystals displaying competitive hydrogen bonding: Small molecule mesogens assembled through different hydrogen bond assemblies

A series of supramolecular assemblies created through competitive hydrogen bonding of a n-alkoxy benzoic acid hydrogen bond donor and a mixture of hydrogen bond acceptors: a liquid crystal-forming rigid bi-pyridyl and a non-mesogenic tetrafunctional pyridyl species. The associative chain structures displayed mesogenic characteristics at loadings dependent on the concentration of the disruptive tetrafunctional agent- systems eliminated liquid crystallinity at 85% inclusion in heating transitions and 90% in cooling. The assembled structures displayed considerable mesophase stability. This was observed through long liquid crystalline lifetimes even at high compositions of 4PD, which generally dampened due to a generalized eutectic effect. It is believed that the freedom of mobility inherent in the C8 Acid allows for the reorganization of the hydrogen bonds in the liquid crystalline state providing for a very high loading of disruptor and long mesophase lifetimes.     

Synthesis of aromatic liquid crystals with asymmetric diester based on rod-like multi-ring system by two-step esterification method

A novel method of two-step esterifications was developed to synthesize compounds with asymmetric double ester groups. By using this method, six rod-like double ester compounds were prepared with p-hydroxy benzaldehyde, p-hydroxy benzoic acid bicyclohexyl carboxylic acid, cyclohexyl benzoic acid and biphenyl carboxylic acid substituted by n-propyl and n-pentyl as main reactants. The structures and properties of target compounds were confirmed by IR, MS, ¹H NMR, elemental analysis, differential scanning calorimetry (DSC) and hot stage polarizing optical microscope (HS-POM). Typical yields of the target molecules were more than 70%. All the molecules have mesophases with the textures of nematic type, indicating a rod-like molecule with a longer rigid skeleton can keep its mesophases. There was no clearing point observed for any of the derivatives before they decomposed so that the temperature ranges of the mesophases could not be determined. The energy differences between frontier molecular orbitals (HOMO-LUMO) (E_g) of the compounds were calculated by cyclic voltammetry (CV). The terminal ring system has an obvious influence on the energy levels and the energy gaps (E_g).     

Chromonic liquid crystals: more questions than answers

While much liquid crystal research is on either thermotropic liquid crystals or on lyotopic, surfactant systems, a fascinating third class of materials is that of chromonic liquid crystals. These systems show fascinating properties but are, as yet, poorly understood. This article reports a recent meeting in which the status of our current knowledge is reviewed.     

Thermo‐morphological properties of the smectic C* mesophase in new chiral salicyaldimine liquid crystals

Specific textures and their temperature transformations in large temperature interval for the chiral smectic C* mesophase of new liquid crystalline materials, synthesized by our group, have been investigated in detail. Temperature dependences of the pitch of helical structure of the smectic C* mesophase have been determined for these materials. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Liquid crystals: applications and industry

Liquid crystals (LCs) are mesogenic phases of matter which combine liquid fluidity with crystalline solid properties. Precise knowledge of the molecular orientations – close to the boundaries and within the material bulk – is necessary for understanding their flow behaviour, especially in microfluidic settings. While the boundary conditions are set, passively, by surface-induced molecular orientations, the bulk orientation in flow is determined, actively, by the anisotropic coupling between the flow and the molecular orientation. Together, the surface and the bulk orientations offer a range of topological constraints within microfluidic channels, which affect the evolution and sustenance of flow-induced phenomena in LC-based systems. The concept of topological microfluidics can be extended to different classes of anisotropic fluids, allowing us to explore and to employ such fluids as complex functional materials for microfluidics, thereby significantly broadening the reach of conventional microfluidics.     

Liquid crystals,fractals and art

We discuss the aesthetic appeal of liquid crystal textures and take a brief polarising microscopic tour through the wealth of the appearances of nematic, cholesteric, smectic and banana phases. Some examples are given on how these textures may be used in a creative process employing digital image processing to produce ‘computer art’, including images exhibiting self-similarity. A discussion of the ‘art’ of computer-generated mathematical fractals leads us to examples of fractal structures observed in the phase-ordering process of some liquid crystalline phases. This includes a first brief report of dilatation invariance observed for aggregates of a conventional SmC phase and percolation simulations to quantitatively explain the obtained textures. The circle between liquid crystals, fractals and arts is closed by a discussion of self-similarity in modern arts, especially works of the movement known as abstract expressionism. More than 100 paintings of the artists Wassily Kandinsky, Jackson Pollock, Mark Tobey and Franz Kline were analysed, placing an emphasis of the discussion on the ‘drip-paintings’ of Pollock in relation to recent reports.     

Imidazolium based ionic liquid crystals: structure,photophysical and thermal behaviour of [Cnmim]Br·xH2O (n = 12, 14; x=0, 1)

The long chain imidazolium halides [C_nmim]Br·xH₂O (n = 10, 12; x = 0, 1) have been synthesized and their structural and thermal behaviour together with their photophysical properties characterized. X‐ray structure analyses of the monohydrates ([C₁₂mim]Br·H₂O: triclinic, P1, no. 2, Z = 2, Pearson code aP112, a = 550.0(5) pm, b = 779.4(5) pm, c = 2296.1(5) pm, α = 81.89(5)°, β = 83.76(5)°, γ = 78.102(5)°, 3523 unique reflections with I_o > 2σ(I_o), R₁ = 0.0263, wR₂ = 0.0652, GooF = 1.037, T = 263(2) K; [C₁₄mim]Br•H₂O: triclinic, P1, no. 2, Z = 12, Pearson code aP11, a = 549.86(8) pm, 782.09(13) pm, c = 2511.3(4) pm, α = 94.86(2)°, β = 94.39(2)°, γ = 101.83(2)°, 2063 unique reflections with I_o > 2σ(I_o), R₁ = 0.0429, wR₂ = 0.0690, GooF = 0.770, T = 293(2) K) show for both compounds similar bilayered structures. Sheets composed of hydrophilic structure regions constituted by positively charged imidazolium head groups, bromide anions and hydrogen bonded water alternate with hydrophobic areas formed by interdigitated long alkyl chains belonging to imidazolium cations with different orientation. Combined differential scanning calorimetry and polarizing optical microscopy shows that the monohydrates as well as the anhydrous imidazolium salts are thermotropic liquid crystals which adopt smectic mesophases. The mesophase region is larger in case of the monohydrates when compared to the anhydrous compounds indicating that water obviously stabilizes the mesophase. All compounds show an intense whitish photoluminescence with short lived (¹π←¹π*) and long lived (¹π←³π*) transitions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photo Alignment and Patterning of Liquid Crystal Polymer Films and Optical Devices by Side-Chain Photopolymers

Prerequisite for virtually all nematic field-effects on which liquid crystal displays (LCDs) are based is stable, uniaxial surface alignment with defined bias tilt angle between the long liquid crystal (LC) axes and their display boundaries. Since the invention of the TN-LCD [1 Schadt, M., & Helfrich, W. (1972). Mol. Cryst. Liq. Cryst., 17, 355.[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]] in 1970 until recently this was achieved by confining liquid crystals between mechanically brushed surfaces [2 Cognard, J. (1982). J. Mol. Cryst. Liq. Cryst. Suppl. Ser., 1, 1–74. [Google Scholar]–4 Aoyama, H., Yamazaki, Y., Matsuura, N., Mada, H., & Kobayashi, S. (1981). Mol. Cryst. Liq. Cryst. Lett., 72, 127.[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]]. We have first shown in the 1990s that, non-mechanical, uniaxial, tilted and patterned LC-alignment is possible by anisotropic Van der Waals surface interactions [5 Schadt, M., Seiberle, H., & Schuster, A. (1996). Nature, 381, 212. US Patent (1995) US-6, 215, 539.[Crossref], [Web of Science ®] , [Google Scholar]], namely by directional polymerization of photo-sensitive side-chain polymers films [5 Schadt, M., Seiberle, H., & Schuster, A. (1996). Nature, 381, 212. US Patent (1995) US-6, 215, 539.[Crossref], [Web of Science ®] , [Google Scholar], 6 Schadt, M., Schmitt, K., Kozinkov, V. & Chigrinov, V.G. (1992). Jpn. J. Appl. Phys., 31, 2155. US patent (1991) US 5,389,698.[Crossref], [Web of Science ®] , [Google Scholar]] by linear polarized UV light. The LPP model is reviewed and its applications enabling high resolution multi-domain liquid crystal displays operated in transmission and reflection are discussed. Examples are given for optical retarders integrated into LCDs, anisotropic liquid crystal polymer (LCP)-films for 3D imaging, interference color filters, wide-view films and anisotropic polymer surface topologies.     

Thermal conductivity and refractive indices of Nd:GdVO4 crystals

The thermal conductivities of Nd:YAG, M(Y,Gd)VO₄ crystals were measured at 298 K. The value of Nd:GdVO₄ crystal along <001> direction was 11.4 W/mK, which was higher than that of YAG crystal measured to be 10.7 W/mK. The principal refractive indices of Nd:GdVO₄ crystal in the temperature range from 20 °C to 170 °C were determined by auto‐collimation method. Based on the measured values of refractive indices, the Sellmeier equation and expression of temperature dependence of refractive indices have been obtained. The measured results show that the birefringence Δn is 0.22007 at 20 °C and temperature coefficient of birefringence is 4.33 × 10⁻⁶/°C for 1.064 μm. These results prove that the GdVO₄ crystal is a laser crystal with excellent thermal and birefringence properties. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)