Fingerprint Texture Research Articles

Dislocation profile in cholesteric finger texture.

The displacement field around an isolated elementary dislocation in a medium with one-dimensional periodicity is established experimentally. The system studied is a cholesteric fingerprint texture with a macroscopic ( approximately 10 microm) periodicity. The characteristic elastic length is smaller than the "interlayer" distance. As a result, the experimental dislocation profile deviates from the classic pattern predicted by the linear elastic theory but fits well with the recently suggested nonlinear theory of dislocation [Phys. Rev. E 59, R4752 (1999)].

Chirality in Some Liquid Crystalline Association Chain Polymers

Two series of sequence random association chain liquid crystalline polymers have been synthesized by melt mixing a bispyridyl with dicarboxylic acids, which in their individual states are not liquid crystals. The phase behavior of two classes of polymer complexes was examined using hot stage polarized light microscopy. It is shown that polymer complexes consisting of (+)-3-methyl adipic acid exhibit a chiral nematic fingerprint texture even at low molar concentration (1.5%) while polymer complexes with an (L)-tartaric acid derivative exhibit a weak fingerprint texture only at high concentration. The effects of the random association chain structure on the thermal behavior of the polymer complexes are also discussed.

Dispersion of Cholesteric Liquid Crystals in Side-Chain Polymer Matrix

Cholesteric formulations (coco-cholesteryl esters:E7) were dispersed in commercial polymethylmethacrylate (PMMA) and in laboratory synthesized side-chain polymers (SCP). The side-chain copolymers were obtained via the ring opening reaction of a commercially available epon resin, ethyleneglycol diglycidyl ether, with the nematic 4-(ω -aminohexyloxy)-4′ -cyanobiphenyl and the twisted nematic cholesteryl 4-aminobutyrate. Switching properties of the resulting dispersions were evaluated. Cells using PMMA as matrix exhibited distinguishable droplet with bipolar and twisted radial configuration. A maximum voltage of 60 volts was needed to transform a 70:30 by weight (LC:PMMA) composite into a transparent state. LC formulations dispersed in the SCP bearing cholesteryl and cyanobiphenyl pendant groups were found to exhibit fingerprint texture. Compared to the LC/PMMA composite, the LC/SCP dispersions required lower voltage for switching.

Mesomorphic behaviour of N,N-dialkanoyl-2,3,5-trimethylbenzene1,4-diamines and 2,3,5,6-tetramethylbenzene-1,4-diamines

DSC and microscopic studies on several series of N, N'-dialkanoylbenzene-1,4-diamines are presented. The isotropization enthalpy is drastically reduced by the introduction of methyl groups into the aromatic nucleus. The trimethyl derivatives carrying octanoyl and nonanoyl groups generate metastable mesophases exhibiting a spherulitic texture; those carrying undecanoyl-to-octadecanoyl groups generate metastable or stable nematic phases exhibiting schlieren textures. The addition of the fourth methyl group to the nucleus results in an increase in the order of molecular arrangement and the enhancement of the thermal stability. A fingerprint texture is observed for many members of the tetramethyl derivatives and a transient schlieren texture for the octadecanoyl member.

Comparison of the pitch induced from lamellar and nematic regions in some lyotropic liquid crystal systems

Lamellar phases (Lalpha) composed of decylammonium chloride(DACl), NH4Cl and H2O were doped with cholesteryl-2-ethoxyethoxyethyl carbonate (CEEC) and with (L-MA) or its racemic mixture (DL-MA). Lalpha phases of the novel intrinsic optically active L-serine hydrochloride decylester (L-SDE) and its racemic mixture (DL-SDE) were also prepared. From the chiral Lalpha phases, cholesteric phases (ChD) were induced with increased temperature and it was found that the pitch length shortened as the temperature was raised. This phenomenon is new for micellar cholesterics. The non-chiral Lalpha phases gave pseudo-isotropic and nematic regions with increased temperature. On the basis of these results and those in the literature, a new interpretation of the distorted micelle shape and the formation of the fingerprint texture is presented. The pitches induced from Lalpha regions were always larger than those obtained from nematic regions. From these results it is inferred that the interactions between the micelles in the cholesteric state at room temperature are of 'ideal' type. In addition, the temperature dependence of the pitch in micellar cholesterics is discussed.

Effect of Chiral Polymers on Lyotropic Liquid Crystals

Formation of the cholesteric phase in aqueous lyotropic liquid crystals doped with cellulose derivatives has been studied utilizing hot stage polarized microscopy. Three ionic surfactantssodium decyl sulfate, cesium pentadecafluorooctanoate, and myristyltrimethylammonium bromidewere employed to obtain anionic or cationic lyonematics. After addition of chiral polymers (at polymer concentration ∼0.05−0.750 wt %) the samples were sealed in flat glass capillaries, and a magnetic field was applied to enhance the homogeneous orientation and formation of the fingerprint texture. Out of seven various cellulosic derivatives (five nonionic, one cationic, and one anionic), nonionic hydroxypropyl cellulose was the only compound that induced the cholesteric phase. The effective helical twisting power (HTP) of hydroxypropyl cellulose is 3−4 times higher in anionic lyonematics than in cationics. In both cationic and anionic media, the HTP decreases with an increase in the molecular weight of the chiral polymer. This beh...

Magnetic-field alignment of cholesteric liquid-crystalline DNA

In moderately high fields (3.5 and 6.4 T) the cholesteric phase of liquid-crystalline DNA aligns with its twist axis parallel to the applied field. Thus when the field is applied in the plane of a thin sample, the well-known 'fingerprint' texture is observed with striations of width \ensuremath{\sim}1.1 \ensuremath{\mu}m orienting perpendicular to the field. In a 9.4 T field, the cholesteric aligns, still with the twist axis on average parallel to the field, but locally distorted into longer wavelength stripes. The orientation of these larger stripes is parallel to the magnetic field, thus perpendicular to the fingerprint striations. The field stabilizes the stripes, and upon removal from the magnet, the stripes anneal away. The time scale for relaxation of the stripes to an aligned fingerprint texture is several days. Defect sites present in the field-stabilized stripe structure persist and become quite mobile (in the presence of a concentration gradient) after the stripes have annealed away.

Structural transformations and viscoelastic response of sheared fingerprint cholesteric textures

Analysis and computer simulations of structural transformations and viscoelastic response functions are presented for the steady rectilinear simple shear flows of a flow-aligning cholesteric liquid crystal oriented with the helix axis along the vorticity direction of the flow; the helix orientation is known as the fingerprint texture. Computation and analysis of orientation and stress relaxation after cessation of shear are also given. The governing parameter that controls the orientation response to the imposed shear is the Ericksen number E (ratio of viscous to elastic effects). For a sufficiently high value of E, a sheared cholesteric liquid crystal with a fingerprint texture originally aligned along the vorticity axis is found to undergo the helix uncoiling transition and adopt the nematic flow-aligned ordering. On the other hand if the Ericksen number is low, the helix rotates driven by vorticity and the orientation state is characterized by traveling twist waves. The transition between the traveling twist wave mode and the stationary nematic mode is found to be mediated by the expansion of the cholesteric pitch, and occurs at a critical value of E, denoted by E c , Close form solutions for the helix pitch as a function of the Ericksen number and for the critical Ericksen number E c for helix uncoiling are obtained and shown to be in good agreement with the numerical solutions. The viscoelastic modes during shear are identified and analyzed. For steady shearing the classical three-region apparent viscosity curve is obtained. Stress relaxation after cessation of shear is computed and explained in terms of the governing scales of the model and in terms of elastic storage modes that operate during shear. Typical oscillatory underdamped stress relaxation oscillations generally present in liquid crystalline materials are found.

Cross-sectional observations of the cholesteric texture in a Cano wedge cell

Abstract A novel procedure for an observation of a liquid crystal texture is proposed by using a UV curable liquid crystal. Optical observations from a cross-section of the Cano wedge cell are demonstrated and layered structures of cholesteric LC are visualized clearly. The structures near the Grandjean lines are then revealed in detail from images. From the observations, it is confirmed that the texture near the Grandjean line is similar to fingerprint texture

Melting and undercooled crystallisation of felsic xenoliths from minor intrusions (Jebilet massif, Morocco)

Granitic and gneissic xenoliths within microdiorite dykes from the Palaeozoic Jebilet massif (Morocco) contain up to 40% of granophyric intergrowths that occur as films along quartz-feldspar contacts and form an interconnected grain boundary network. The composition of the feldspar megacrysts — i.e. large embayed crystals surrounded by the granophyric intergrowths — implies high-temperature crystallisation ( T >900 °C) and the sievetexture (or finger-print texture) indicates that these crystals underwent incipient melting. Moreover, the microstructural position and bulk composition of the granophyre are similar to that of glass in partly molten felsic xenoliths from lavas or pyroclastics. It is argued that the granophyre originated after partial melting of the xenoliths when incorporated into the dioritic magma. Crystallisation of that melt resulted in most cases in the formation of vermicular and/or cuneiform granophyre, which testifies to moderate degrees of undercooling. A few occurrences of plumose granophyre i.e. very thin intergrowths that are close to quartz-bearing spherulites, indicate that some xenoliths crystallised at higher degrees of undercooling. Together with granophyric xenoliths, a number of microgranular inclusions also occur. These are characterized by phenocrysts of quartz and feldspar in a microgranular groundmass. Finger-print texture in feldspar suggests that these inclusions, like the granophyric xenoliths, underwent ultra-metamorphism and melting. The microgranular groundmass is most probably indicative of crystallisation at lower degrees of undercooling, but the relationships between the two types of xenoliths still remain to be explored in detail.

Phase behaviour of alkyl polyglucosides in combination with fatty alcohols and alkyl sulphates

Dilute C 12 14 alkyl polyglucoside (Glucopon600CS®) solutions containing small amounts of fatty alcohols (hydrocarbon chain length greater than 4) show three different lamellar phases (L αl, L α−h, L αh) which are characterized by increasing fatty alcohol: surfactant ratios. The middle lamellar phase appears, in some aspects, like a mixture of the lower and upper lamellar phases. The lower and middle lamellar phases are optically biaxial and are therefore probably in tilted crystalline states. The upper lamellar phase is in the liquid state and is uniaxial. On the addition of alkyl sulphates together with the appropriate amount of the fatty alcohols, to a 5% alkyl polyglucoside solution the middle lamellar phase predominates. Pentanol and hexanol favour the upper lamellar phase while longer-chain fatty alcohols favour the lower lamellar phase. A cholesteric phase with characteristic fingerprint texture appears in highly concentrated surfactant solutions containing decanol or higher fatty alcohols. The characteristic fingerprint texture of this phase is due to myelinic figures which occur in the two-phase region between the lower lamellar phase and an isotropic phase. The fingerprints can be oriented in strong magnetic fields. The cholesteric phase interacts strongly with polarized light which is travelling in the direction of the helical axis.

An Inversion in the Chirality in an Amphiphilic Cholesteric Liquid Crystal Where the Chiral Dopant Is the Chloride of the Decyl Ester of L-Proline

The chloride of the decyl ester of L-proline has been used as a chiral dopant where the achiral host detergent was tetradecyltrimethylammonium bromide. The twist and the sense of the helix were measured as a function of the chiral dopant concentration, using the fingerprint texture and Grandjean planes observed under a polarizing microscope. The magnitude of the twist as a function of the chiral dopant concentration initially rose and fell, while the sense of helix was positive. At about 10% the twist magnitude passed through zero, and then with increasing amounts of the chiral dopant the sense of the helix became negative. This inversion in the twist sense is thought to be due to a concentration-dependent distribution of the cis and trans molecular rotamers derived from rotation around the >CH-CO 2 - bond

Wallrock Melting and Reaction Effects along the Higganum Diabase Dike in Connecticut: Contamination of a Continental Flood Basalt Feeder

The question of whether continental flood basalts are contaminated with crustal material during ascent through the lithosphere is addressed through a study of the feeder dike to the first of the Mesozoic flood basalts in the Hartford basin of Connecticut. Faulting associated with basin formation exposed the dike, not only where it connects with the flood basalt, but also at levels that may have been as deep as 10 km at the time of crystallization. Wallrocks at all levels of exposure and along the entire 250-km length of this 50–60 m wide dike show evidence of partial melting and contamination of the diabase magma. Melting of the wallrocks took place on grain boundaries between quartz and feldspar, especially where these boundaries were fluxed with water released from the breakdown of biotite. The melts were simple mixtures of quartz and the particular feldspar involved rather than equilibrium minimum compositions, probably because heating rates were faster than melting rates. The melts crystallized to form granophyre. Feldspars in direct contact with the diabase partly melted, with plagioclase developing the fingerprint texture and orthoclase being converted to an exceptionally fine-grained mixture of plagioclase and quartz. Melts generated in the wallrocks were forced into the margins of the dike by the volume expansion caused by melting. The earliest melts to enter the dike are preserved as felsic wisps in the chilled margins, but at distances of more than a few centimeters from the edge of the dike they appear to have been assimilated by the diabase magma. Melts that entered the dike after the margins had solidified were intruded as crosscutting granophyre veins. Chemical profiles across the dike reveal that the contaminants were not restricted to narrow marginal zones but entered the main body of the dike. Thus, by the time this magma had risen to the surface and erupted as the Talcott basalt it had assimilated a significant amount of crustal material, which accounts for the change from olivine normative compositions in the deepest level exposures of the dike to quartz normative ones in the basalt. Mass balance calculations indicate that the Talcott basalt may have had ˜6% granophyre added to it during the magma's ascent through the last 10 km of the crust. The amount assimilated in traversing the entire continental crust would therefore be greater than this.

Liquid-Crystalline Polymer Gels VI. Preparation and Swelling Behavior of Cross-Linked Hydrogels of Poly(L-glutamic acid) Possessing Cholesteric Order

Cross-linked gels of poly(L-glutamic acid) (PGA) possessing cholesteric liquid-crystalline order were prepared from the corresponding liquid-crystalline gels of poly(γ-benzyl L-glutamate). The PGA hydrogels were found to hold original liquid-crystalline order in the neutral pH range, but became isotropic at higher pH values. The phase change was reversible. The swelling with the increase of pH occurred through two stages. During the first stage that begins around pH=6, a finger-print texture was observed under crossed polarizers. After the second stage of the swelling that begins around pH=9, the finger-print texture was mostly disappeared. From a detailed study on the dissociation of PGA inside the gel, the first stage is attributed to a process of expansion of partially dissociated helical PGA chains and the second stage is the full expansion of fully dissociated PGA chains.

Lyotropic mesophase of imogolite, 3 observation of liquid crystal structure by scanning electron and noval polarized optical microscopy

AbstractThe mesophase (lyotropic liquid crystal) of the inorganic rod‐like polymer, imogolite, displays a typical fingerprint texture under a polarized optical microscope (POM), although the mesophase reveals no circular dichroism. The scanning electron microscope revealed a honeycomb structure of thin sheets having pleats in the freeze‐dried sample prepared from the mesophase solution, and POM shows also a fingerprint texture from the same sample. A novel polarized optical microscopic observation procedure was introduced to eliminate the contrast variation and extinction due to the zero amplitude effect which depends on the orientational variation of anisotropic bodies with respect to a polarizer direction under the crossed Nicols. Various textures of lyotropic imogolite liquid crystals were observed with the procedure, and the results were accounted for by a honey‐comb structure of curled thin sheats having pleats. The honey‐comb model is consistent with the observation by scanning electron microscopy on the freeze‐dried sample.

Field-induced spirals from a confined cholesteric

We have observed birefringent spirals induced by a field in a fingerprint texture of a cholesteric polymer in solution in a nematic low molar weight liquid crystal. This paper describes the conditions of nucleation of these spirals and the part of different parameters which determine their characteristics.

Synthesis and characterization of new chiral mesogenic monomers

Abstract New mesogenic monomers carrying substituted biphenylyl rings linked to acryloyl or methacryloyl moieties through straight or chiral flexible spacers have been synthesized. All the investigated monomers, independent of the side group chirality, have been found to form ordered smectic phases, most probably of the S1 type. The asymmetric methyl substitution on the flexible spacer leads to an expansion of the temperature range of mesophase stability. The chiral monomers induce a helical structure when mixed with appropriate nematogens. The fingerprint texture of a contact mixture of the chiral methacrylate prepared in this work, with a nematic methacrylate synthesized previously, has been found not to change after UV-initiated polymerization.

Electro-Optical Behavior of a Novel Strong-Weak and Weak-Weak Anchored Large-Pitch Cholesteric

Abstract The electro-optical behavior of strong-strong, strong-weak and weak-weak anchored tilted and reversely-tilted large-pitch cholesterics has been investigated. The weak anchoring has been achieved after rubbing with soap the previously mechanically-rubbed glass plates. Under a voltage excitation, the most important reversely-tilted weak-weak anchored cholesteric layers giving rise to a nearly-planar Grandjean-like texture showed the appearance of a Helfrich's instability, followed by a π/2 rotation of the helix and finally, a scroll texture which compactly disappeared into a completely unwinded cholesteric. When voltage was switched off, the unwinded cholesteric was returned to the initial Grandjean-like texture for the case of a low voltage (U < 3Uth, where Uth is the threshold voltage for the Helfrich's instability) or has been transformed into a finger-print texture for higher voltages. This novel boundary-induced bi-stability is related to the weakness of the surface anchoring. In addition, att...

Elastic Deformations and Electrohydrodynamic Instabilities in Large Pitch Cholesteric Liquid Crystals under an Electric Field

Abstract We report experimental observations on large pitch cholesteric liquid crystals in the planar geometry submitted to DC or low frequency AC fields applied along the helical axis. An electric field can cause orientation of the molecules in the field direction (tilting of the helical axis leading to a fingerprint texture and unwinding of the cholesteric spiral) or disruption of the orientation due to the hydrodynamic effect of current carriers (periodic two-dimensional deformations). The behavior of the samples depends upon the sign and the absolute value of the dielectric anisotropy ea. We have investigated a wide range of systems by using nematic matrices with ea between -4 and +33 doped with small amounts of cholesteryl chloride (ea > 0) and cholesteryl benzoate (ea < 0). Instabilities are observed in negative ea mixtures; depending upon the frequency, two regimes can be found, as in nematics. The behavior above threshold depends largely on the magnitude of the negative anisotropy. In the case of ...

On the Cholesteric-Nematic Phase-Change Transition in Layers with Homeotropically Orienting Surfaces

Lattice-model calculations of the energies of surface director-configurations are presented. These configurations mediate between the homeotropic surface conditions and the bulk fingerprint texture of cholesteric layers. Their energy determines the asymptotic behaviour of the cholesteric-nematic threshold field in the limit of thick layers. The dependence of their energies on the elastic constant ratios could be brought into a simple scaling form. This form is in agreement with existing and newly presented measurements.