Oily Streak Texture Research Articles

Thermal and optical properties of amphitropic liquid crystals derived from cholesterol and cinnamic acid

ABSTRACT In this paper, we firstly demonstrate the synthesis of chiral amphitropic liquid crystals derived from cholesterol as well as their thermal and optical properties. Chiral monomeric cholesteryl-4-(6-acryloyloxyhexyloxy) cinnamate (CCM) derived from cholesterol and cinnamic acid has been synthesised showing amphitropic liquid crystal phases. The synthesised CCM exhibits oily streak textures under a polarised optical microscope (POM), corresponding to cholesteric liquid crystal phase formed after heating over 120°C and after being treated with organic solvents such as dichloromethane, chloroform, tetrahydrofuran and toluene. Both the thermotropic and lyotropic cholesteric liquid crystals exhibit selective light reflection, and the wavelength of the reflected light falls in the visible light region showing colourful appearances. The results suggest that CCM could be used for the development of sensors for both temperature and solvents. Homopolymer (Poly-CCM) was synthesised via free radical polymerisation. The synthesised polymer did not exhibit any mesomorphic behaviour either by heating or being treated with solvents. These results indicate that the long chain hydrocarbons and sidechains of CCM were disturbed and restricted after polymerisation leading to the loss of liquid crystalline properties. However, cholesteric construction of monomeric CCM was fixed via UV-polymerisation. The synthesised Poly-CCM film shows Bragg reflection significantly.

Synthesis, mesomorphic and photo-switching behaviours of novel azobenzene chiral liquid crystals containing (-)-menthyl

ABSTRACT A new series of chiral liquid crystal, Mt4AZOnAB (n = 2–18), containing a multi-chiral centre menthyl and an azobenzene moiety connected with a flexible butanedioyloxy and a varying length of alkanoyloxy in a terminal chain were designed and synthesised. The thermal properties and optical textures were investigated by differential scanning calorimetry and polarising optical microscopy. Selective reflection of the CLCs was measured by ultraviolet/visible spectrometer. Their photo-switching properties were well-demonstrated by UV irradiation. All CLCs show characteristic of selective reflection in heating stage and BPI/II texture in cooling course. Before and after irradiation, CLCs undergoes a transition from oily streak texture to focal conic texture; however, BPI/II texture in cooling stage shows a reversible phase transition.

The effect of various functional groups on mesophase behavior and optical property of blue phase liquid crystal compounds based on (−)‑menthol

In order to explore the effect of various functional groups on the mesomorphic properties, a series of menthol-based blue phase liquid crystal compounds (A, B1, B2, C1, C2, D1, D2) with various core structures in the molecules were synthesized. Their chemical structures and phase behavior were characterized with FT-IR, 1H NMR, differential scanning calorimeter (DSC) and polarizing optical microscopy (POM). The selective reflection and photoisomerization were investigated with ultraviolet/visible (UV/VIS) spectrometer. In our case, all BPLCs showed oily streak texture with selectively reflection and blue phase (BP), irrespective of the structure of mesogenic cores. This demonstrated that (−)‑menthol had high chirality, and via succinyloxy spacer group could drive molecules to arrangement in double twist cylinders of BP. The length-to-diameter ratio, the bridge bond in the aryl rings and the conjugate action in the mesogenic core had a significant effect on Tm, Ti and temperature range of BP. BPLC A without conjugated structure in three-benzene mesogenic core revealed a larger temperature range of BP than other BPLCs with conjugated structure.

Synthesis and characterization of new chiral liquid crystal monomers containing steroid unit

To reduce the bulky steric hindrance, improve the reactivity of diosgenin and cholesterol, and obtain mesophase of their derivatives, the commercially available cholesterol and diosgenin were allowed to be structurally modified. Four new chiral LC intermediate compounds (c∼f) and the corresponding monomers (M1−M4) with different longer spacer were synthesized. The chemical structures, optical texture, thermal behavior and mesophase structure of all the mesogenic compounds obtained in this study were characterized by FT-IR, 1H-NMR, polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction measurements. The experimental results showed that the intermediate compounds containing diosgenyl groups c and d only showed a mesophase and exhibited fan-shaped texture of a smectic A (SA) phase, while the compounds containing terminal cholesteryl groups e and f showed two mesophases and exhibited fan-shaped texture of a SA phase, and oily streak texture and focal conic texture of cholesteric phase, respectively. The four chiral monomers M1−M4 all revealed cholesteric oily streak texture and focal conic texture. In addition, the melting temperature (Tm) and isotropic temperature (Ti) of the mesogenic compounds decreased with increasing the flexible spacer length. Compared with the intermediate compounds or monomers based on cholesterol, the compounds or monomers based on diosgenin showed higher Tm and Ti.

Persistence of Smectic-A Oily Streaks into the Nematic Phase by UV Irradiation of Reactive Mesogens

Thin smectic liquid crystal films with competing boundary conditions (planar and homeotropic at opposing surfaces) form well-known striated structures known as “oily streaks”, which are a series of hemicylindrical caps that run perpendicular to the easy axis of the planar substrate. The streaks vanish on heating into the nematic phase, where the film becomes uniform and exhibits hybrid alignment. On adding sufficient reactive mesogen and polymerizing, the oily streak texture is maintained on heating through the entire nematic phase until reaching the bulk isotropic phase, above which the texture vanishes. Depending on the liquid crystal thickness, the oily streak structure may be retrieved after cooling, which demonstrates the strong impact of the polymer backbone on the liquid crystal texture. Polarizing optical, atomic force, and scanning electron microscopy data are presented.

Synthesis and properties of new (−)-menthol-derived chiral liquid crystal compounds with alkyl or alkoxy terminal groups

ABSTRACTTwo series of chiral mesogenic compounds derived from (−)-menthol with varying length of alkyl or alkoxy terminal groups respectively were designed and synthesised. Their chemical structures were characterised by FT-IR and 1H-NMR spectra. The thermal properties and optical textures were investigated by differential scanning calorimetry and polarising optical microscopy. Bragg selective reflection spectra of the compounds with the alkoxy chain in the N* phase were measured by ultraviolet/visible spectrometer. The results showed that the alkyl series homologues melt directly to the isotropic phase on heating and display cubic blue phase and focal conic textures of chiral nematic phase on cooling, whereas the alkoxy series displayed oily streak textures with iridescent colours on heating, and platelet textures of blue phase and focal conic textures were observed on cooling cycles. The chain structure and length of the terminal groups have profound influence on the isotropic temperature and a large odd–even effect is observed for the compounds. The selective reflection colours of alkoxy series shifted to longer wavelength with the increasing of temperature.

Branched-arm macromolecule liquid crystals-containing fluorine and isosorbide-structure and properties

A new series of cholesteric fluorated branched-arm liquid crystals (CHFBALCs) compound (MFA1–MFA4), with isosorbide as chiral core, was synthesized. Four precursors of branched-arm FA1–FA4 were obtained firstly and then were esterized separately with isosorbide to get four chiral branched-arm liquid crystalline (MFA1–MFA4). The structures and properties were characterized by conventional spectrum methods, thermal analysis and texture analysis. The results showed that FA1–FA4 all were nematic phase with schlieren, threaded-like or droplet texture. When the isosorbide was successfully inducted, the phase of FA1–FA4 turned into cholesteric phase with oily streak texture, finger print texture or cholesteric droplets. The values of melting point and clearing point for FA1–FA4 and MFA1–MFA4 all changed irregularly, which may be due to the effect of different branched arm, warping of chiral agent and fluorine atom. MFA1–MFA4 had the same handedness as isosorbide core and did not show selective reflection. MFA3 and MFA4 were hopeful to realize the combination of the processability of polymers and the mobility of small molecules.

Synthesis and mesomorphic properties of chiral nematic liquid crystals based on cholesterol

A new series of mesogenic compounds having a cholesteryl moiety has been synthesised by condensing p-amino benzoate of cholesterol and methoxy substituted 4-n-alkoxy cinnamoyl chlorides and their liquid crystalline properties has been studied. All the members of the series are enantiotropic and exhibit chiral nematic (N*) mesophase. The plot of transition temperatures versus number of carbon atoms in the alkoxy chain exhibits odd–even effect and falling tendency for N*–isotropic transition temperatures. The compounds exhibit oily streak textures that on slight disturbance change to the plane textures and show iridescent colours. High anisotropy, linearity and intermolecular hydrogen bonding confer rich mesomorphic properties on the system. Intermolecular hydrogen bonding arising from amide linkage can lead to supramolecular motifs.

Syntheses and Characterization of Chiral Branched-Arm Liquid Crystals-Basing on Isosorbide as Chiral Core

A new series of two-arm (MB1, MB2), four-arm (MB3), six-arm (MB4) chiral liquid crystalline compound containing isosorbide as chiral core were first synthesized. Four precursors of branched-arm B1~B4 were obtained at first and then were esterized separately with isosorbide and got four chiral branched-arm liquid crystals (MB1~MB4). The chemical structures and LC properties of the liquid crystalline molecule were measured by spectrum and thermal analysis techniques. XRD curves of MB1~MB4 samples only showed broad peaks at wide-angle, but no sharp peak was seen for all the samples. The results showed that MB1~MB4 appeared cholesteric phase with oily streak texture or lined texture and finger print texture. Isosorbide successfully induced cholesteric phase. The values of melting point and clearing point for MB1~MB4 decreased. The quantity of branched-arm and chiral core had effects on their liquid crystalline properties.

The effect of different arms on the properties of chiral branched-arm liquid crystals based on isosorbide as the chiral core

A new series of two-arm ( MA1 , MA2 ), four-arm ( MA3 ) and six-arm ( MA4 ) chiral liquid crystalline compounds containing isosorbide as the chiral core were synthesised. Four precursors of branched-arm A1–A4 were first obtained, and then were esterised separately with isosorbide to obtain four chiral branched-arm liquid crystals ( MA1–MA4 ). The structure and properties have been characterised. The results show that MA1 was smectic–cholesteric phase with a fan-like and oily streak texture; MA2–MA4 showed a cholesteric phase with oily streak texture, or lined texture and finger print texture. Isosorbide successfully induced a cholesteric phase. The melting point and clearing point values for MA1–MA4 first increased and then decreased. The branched-arm and chiral core quantity affected the liquid crystalline properties. At the same time, the difference in side-arms resulted in different directions of rotation. MA1–MA2 showed right-handed rotation and had selective reflection; MA3–MA4 demonstrated left-handed rotation and did not have selective reflection.

Cholesteric mesophase in side-chain liquid crystalline polymers: influence of mesogen interdigitation and motional decoupling

In this paper, the thermal, optical and mesomorphic properties of side-chain liquid crystalline (SCLC) homopolymers (PNBCh-n), in which cholesteryl mesogens are linked to a polynorbornene backbone by different lengths of methylene spacer (n = 4, 5, 9, 10 and 15), are investigated. By doing so, the impact of flexible spacer length on the formation of different types of LC mesophase is explained. Because of comb-shaped SCLC polymer architecture, smectic mesophases are primarily found in PNBCh-n. Interestingly, cholesteric mesophases are identified only in PNBCh-9 and 10, which are proved by (1) the selective light reflection in UV-Vis analysis, (2) the characteristic oily streak texture under polarized optical microscope (POM) and (3) a long range periodicity in the cross-sectioned films from transmission electron microscope (TEM) investigation. Moreover, temperature-controlled X-ray scattering measurements are performed to examine mesomorphic structure evolution. By comparing the mesomorphic structures in this series of SCLC homopolymers, both extent of mesogen interdigitation and motional decoupling between backbone and mesogenic side-chains are found to play a critical role in the development of cholesteric mesophase. This structure–property study of PNBCh-n will help elucidate the importance of molecular structure, particularly the length of spacers, on the formation of cholesteric mesophase and its importance in the design of thermochromic devices.

Synthesis and optical activity of isosorbide chiral derivative containing fluorocarbon group as chiral dopant in liquid crystal materials

Novel isosorbide derivative containing perfluorocarbon group, bi(perfluorooctanesulfonyl)isosorbide ester as chiral dopant in liquid crystal, was synthesized. Chemical structure was characterized by elemental analysis, FT-IR, 1H NMR and 19F NMR. The optical texture of the mixture was observed by polarized optical microscopy (POM). Novel chiral dopant containing perfluorocarbon group had excellent optical activity. Its specific rotation and molar rotation were noticeable higher than those of bi(4-chloromethylbenzenecarbonic)isosorbide ester. The fluorocarbon group improved the molar rotation of chiral compound and did not affect optical rotation direction. The texture of the mixture added isosorbide derivative with fluorocarbon group showed the oily streak texture.

Synthesis and characterization of chiral compounds containing cationic groups as chiral dopants in liquid crystals

Novel chiral molecules containing cationic groups, (N-[4-triethylammoniomethyl]-benzoyl ester)-ethyl lactate chloride and bi-(N-[4-triethylammoniomethyl]-benzoyl ester)-isosorbide chloride, were designed and synthesized. Chemical structures of the molecules were characterized by elemental analysis, FT-IR, and 1H NMR. The photochemical properties of the chiral compounds and their textures in nematic liquid crystals (LCs) were investigated by optical rotation, circular dichroism (CD), and polarizing optical microscopy (POM). The novel chiral molecules exhibited good optical activity. The chiral compound based on a l-ethyl lactate chiral center had a left-handed configuration. The chiral compound based on an isosorbide chiral center had a right-handed configuration. The cationic polar groups did not affect the direction of optical rotation, but could effluence the molar rotation of chiral compounds. The mixtures with dopants showed oily streak textures. Doping of a nematic phase liquid crystal with the chiral molecules converted it to the cholesteric phase.

Synthesis, structure and mesomorphism of new cholesteric monomers and smectic comblike polymers

Seven new cholesteric monomers ( M-1− M-7) and the corresponding smectic comblike polymers containing cholesteryl groups ( P-1− P-7) were synthesized. The chemical structures and purity were characterized by FT-IR, 1H NMR, and elemental analyses. The specific optical rotations were evaluated with a polarimeter. The mesomorphism was investigated by polarizing optical microscopy, differential scanning calorimetry, thermogravimetric analysis, and X-ray diffraction. The specific optical rotation values of these monomers and polymers with the same numbers of phenyl ring and terminal groups were nearly equal, however, they decreased with increasing the aryl numbers in the mesogenic core. M-1− M-7 showed oily streak texture and focal conic texture, or fingerprint texture, or spiral texture of cholesteric phase. P-1− P-7 showed the smectic A phase. The melting, clearing, and glass transition temperatures increased, and the mesophase temperature ranges widened with increasing the aryl number in the mesogenic core. Surprisingly, although the molecular structures of M-6 and M-7 were similar to those of M-4, namely the mesogenic cores contained three phenyl rings, their phase behavior had a considerable difference, and T m and T i of M-6 and M-7 were less than those of M-4. In addition, M-6 and M-7 also showed an obvious glass transition. TGA showed that all the polymers had good thermal stabilities.

Synthesis and mesomorphic properties of side-chain cholesteric liquid-crystalline polymers containing menthyl groups

A series of new cholesteric liquid-crystalline polysiloxanes (P1–P5) derived from menthyl groups were synthesized. The chemical structures of the monomers and polymers were characterized with Fourier transform infrared, 1H-NMR, 13C-NMR, and elemental analyses. The mesomorphic properties and thermal behavior were investigated with differential scanning calorimetry, polarizing optical microscopy, thermogravimetric analysis, and X-ray diffraction measurements. The influence of the polymer structure on the thermal behavior was discussed. The monomer diosgeninyl 4-allyloxybenzoate exhibited a typical cholesteric oily-streak texture and a focal-conic texture. Polymers P1–P5 showed thermotropic liquid-crystalline properties. P1 displayed a smectic fan-shaped texture, P2–P5 showed a cholesteric Grandjean texture, and P6 and P7 did not show mesomorphic properties. The experimental results demonstrated that the glass-transition temperature and the clearing temperature decreased, and the mesomorphic properties weakened with an increasing concentration of menthyl units. Moreover, P1–P5 exhibited wide mesophase temperature ranges and high thermal stability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5559–5565, 2006

Liquid Crystalline Phases of a Diacetylenic Phosphocholine Lipid

Abstract We have studied the liquid crystalline behavior of a polymerizable diacetylenic phosphocholine lipid l,2-bis(10,12-tricosadiynoyl-sn-glycero-3-phosphocholine (DC8,9PC). Optical polarized microscopy reveals several types of textures corresponding to normal as well as tilted smectic phases for the dry sample while only the oily streak texture of the Lα phase is seen for the sample with 5% water. X-ray diffraction data show that the lamellar order in the hydrated sample is more pronounced than that in the dry sample. Also, a pronounced change in the layer structure occurs for both the dry and 5% hydrated samples at the chain melting temperature. These structural changes are discussed in relation to the optical microscopic observations.

Effect of Magnetic Field on the Texture of (E-A)C/DCA Mesomorphic Solution

Abstract The ethyl-acetyl cellulose/dichloroacetic acid anisotropic solution film could form pseudoisotropic and oily streak textures in nature and the layers of ordered polymer chains tend to being parallel to the glass slide in the former texture and perpendicular to it in the latter one. Under the effect of the magnetic field, of which the intensity was smaller than the critical value, the changes of mesophase texture were obvious when the direction of the magnetic field (B) was parallel to the plane on which the helicoids lay but small when the B was normal to that. In the former case, the axial direction of helicoids (A) was more agreement with each other and the degree of anisotropy was higher than that without the effect of the magnetic field. But when the magnetic field was removed, the degree of anisotropy decreased gradually. The arrangement of the helicoids which were composed of the layers of ordered polymer chains played a very important role in the changes of mesophase texture.

Morphology of thermotropic polyesters with azoxybenzene moiety examined by optical microscopy.

Morphological observation of the texture of thermotropic polyester, poly (4, 4'-dioxy-2, 2'-dimethylazoxybenzene alkanedioyl) has been performed by using a polarized microscope equiped with a hot stage. The observation showed that the oily streak texture of the nematic phase changes dramatically in the nematic-isotropic biphasic region.

Textures of ethyl-cyanoethyl cellulose mesophase

Abstract The characteristic textures of the mesophase in ethyl-cyanoethyl cellulose/dichloroacetic acid cholesteric liquid crystalline solutions were studied under different conditions by means of a polarized light microscope with a hot stage. It was found that the mesophase textures were directly related to the concentration and the temperature of the solutions. With increasing concentration, the disk-like texture changed, first, into an oily-streak texture and then into a randomdomain texture. The disk-like and oily-streak mesophase textures also changed gradually with time into the focalconic texture or the pseudoisotropic texture. Changes in the texture with temperature were affected by thermodynamic and kinetic factors. In the equilibrium state, the mesophase aggregates were smaller at higher temperature than at lower temperature, but their birefringence did not decrease with the temperature.