Cholesteryl Nonanoate Research Articles

Optical activity of a side group cholesteric liquid crystalline silicone

We measured, using a phase modulation technique, the optical rotation in the isotropic and blue phases of a side group cholesteric liquid crystalline silicone polymer. For comparison, similar measurements were performed on cholesteryl nonanoate (CN) and CE6. The polymer has a selective reflection close to that of CE6 and a chiral mesogenic side group chemically similar to CN. The optical activity data for the polymer, unlike those for low molecular mass liquid crystals, does not follow a simple Landau-de Gennes temperature dependence.

Optical Properties of the Eu(Thenoyltrifluoroacetonate)3. (Cholesteryl Tetradecanoate or Nonanoate) Complexes

We report the optical properties study of two new europium coordination complexes Eu(Thenoyltrifluoroacetonate)3. (Cholesteryl Pelargonate), n H2O (EuTTA3P), Eu(Thenoyltrifluoroacetonate)3. (Cholesteryl Myristate), n H2O (EuTTA3M) and of an optically active cholesteric liquid crystal (CLC) mixture obtained doped with these two fluorescent complexes. Refractive indices of these coordination compounds and of the doped cholesteric liquid crystal mixture have been determined. Wavelength-dependent scattering of these doped cholesteric mixtures has been investigated. Optical absorption and luminescence bands of EuTTA3P and EuTTA3M have been measured and assigned to transitions between the energy levels of Eu3+. From these optical measurements and using Judd-Ofelt theory, intensity parameters Ω2, Ω4 and emission cross-section have been estimated.

Synthesis and Photoswitching Properties of Some Cholesterol Based Liquid Crystals

The synthesis and photoswitching properties of some azobenzene linked cholesterol derivatives (3a-d and 5a,b) have been described. Thermal properties of these compounds were studied by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) techniques. Compounds 3a and 3b exhibit a Smectic A phase, whereas 3d and 5b exhibit Smectic A, TGB and cholesteric phases. Compounds 3c and 5a show a cholesteric mesophase. The presence of azobenzene moiety imparts photochromic properties to these compounds. Trans-cis photoisomerization of the azo-moiety in these compounds in eutectic mixtures consisting of cholesteryl oleyl carbonate, cholesteryl chloride and cholesteryl nonanoate was studied by irradiating at 355 nm. Irradiation of the thin films of these mixtures lead to trans-cis isomerization of the azobenzene chromophore present in the mixture which is accompanied by a large shift in the reflectance band resulting in visual changes in the colour of these films.

Liquid Crystal Phase Transitions Using Fabry-Perot Etalon

Change in the phase of thermotropic liquid crystals occurs at definite phase transition temperatures. A spectroscopic technique using the Fabry-Perot etalon coupted with a spectrometer has been used to determine the mesophase transition temperatures of the liquid crystal — Cholesteryl pelargonate. New mesophase transitions have been detected and classified at the temperatures of 67°C. 75°C, 85°C and 89°C in addition to those reported by earlier workers at 77.5°C, 80.5°C and 92°C. These findings have been corroborated by the analysis of the thermal runs of the same samples using Differential scanning calorimetery.

Phase studies and thermal stability of binary systems of cholesteric liquid crystals

The binary mixture of cholesteryl oleyl carbonate (COC) and cholesteryl nonanoate (CN) with different ratios has been characterized by differential scanning calorimetry (DSC) to determine the phase diagrams. Their normal shelf-life and accelerated stability studies were also examined. A novel microscopic Fourier-transform infrared (FT-IR) spectrometer equipped with DSC was also used to measure simultaneously the chemical structural variation and the thermal response of these liquid crystals. The results indicate that the binary mixture might transform from smectic to cholesteric and then to isotropic liquid (CN composition 50%). Therefore, the 50% CN composition might play a critical role in the phase transition of the binary COC-CN mixture. The microscopic FT-IR/DSCsystem could also confirm the phase transition, but could measure the phase trasition temperature of liquid crystals more easily and sharply than the DSC method. The long-term accelerated thermal stability of the COC-CN mixture seemed to be more constant when stored at 4 °C than in any other temperature conditions.

Optically Active Homogeneous Mixtures of Cholesteric Liquid Crystals and a New Coordination Compound: Eu(Thenoyltrifluoroacetonate)3. (Cholesteryl Tetradecanoate or Nonanoate)

The reactions of cholesteryl pelargonate (P) or myristate (M) with Eu(thenoyltrifluoroacetonate)3.3H2O (EuTTA3 ) at room temperature give the corresponding complexes Eu(thenoyltrifluoroacetonate)3. (Cholesteryl pelargonate), n H2O (1) and Eu(thenoyltrifluoroacetonate)3. (Cholesteryl myristate), n H2O (2) respectively. When adding these two fluorescent complexes to liquid crystal compounds, optically active and aggregate free mixtures are obtained, containing up to 2.5 molar percent of dopant without loosing the mesogenic properties. The different phases exhibited by these mixtures have been identified. The luminescence properties of these Eu3+ complexes in cholesteric phases have been investigated.

Anomalous Viscosity in the Blue Phases of Cholesteryl Nonanoate

Rheological property, shear stress vs. shear rate, of cholesteryl nonanoate (CN) is measured in a temperature region including the blue phases (BPs). From the measurement of the temperature dependence, an anomalous increase in the viscosity, accompanied by a non-Newtonian flow, is observed between 363.4 K and 367.5 K. The anomalous temperature region of 4.1 K obtained from the rheological measurement is wider than the BP region of 0.8 K determined from the thermal analysis, suggesting that the BP region is enlarged under an application of the steady shear flow.

Smectic A-Cholesteric liquid crystal phase transition: A density study

The present work is focused on density measurements near the smectic A-cholesteric liquid crystal phase transition for cholesteryl myristate (C14), cholesteryl nonanoate (C9) and binary mixtures of C14 and C9 and cholesteryl caproate (C6) and C9. The results have evidenced that the transition crosses over from first to second order when both the mean molecular length and the reduced temperature, r (ratio between the smectic A-cholesteric and cholesteric-isotropic phase transition temperatures), decrease in the system. The occurrence of a second order phase transition is observed for a concentration very near 63.1 molar percent of C9 in the C6−C9 mixture at r≅ 0.92.

Calorimetric Study of the Diastereomeric Interactions of Enantiomeric Iso-octyl-benzoyloxybenzoate Solutes with a Chiral Liquid Crystal

Precision differential scanning calorimetric (DSC) analysis of the effect of doping cholesteryl nonanoate with the enantiomers of 4-(4-n-hexyloxybenzoyloxy)-isooctyl benzoate (R811 and S811) has been performed. Depressions of the enthalpies of both phase transitions, from crystalline to cholesteric and from cholesteric to isotropic phases, were found to be ∼ 1.5 times greater for the samples of cholesteryl nonanoate doped with left-handed S811. Depressions of the temperatures of phase transitions are also more pronounced in the case of S811. Thus, the left-handed enantiomer S811 affects the molecular packing of cholesteryl nonanoate much more strongly than its right-handed counterpart R811. Remarkably, the difference between the enthalpy of melting of samples containing only 1 wt% of either enantiomer reaches ∼ 20% of the enthalpy of fusion of pure cholesteryl nonanoate, indicating strong diastereomeric discrimination in the system. This calorimetric manifestation of diastereomer discrimination of S811 and R811 in cholesteryl nonanoate is in agreement with earlier observed nonsymmetrical effects of these enantiomers on the pitch of cholesteric liquid crystals; that is the left-handed S811 enantiomer constricts the pitch nine times more strongly than the right-handed R811 expands the helix.

Dielectric Anisotropy and AC Conductivity of Bicomponent Mixtures of Liquid Crystals Cholesteryl Pelargonate and Nonyloxybenzoic Acid

Dielectric constant (ε′) and electrical conductivity ([sgrave]) of the binary mixtures of cholesteryl pelargonate (ChP) and nonyloxybenzoic acid (NOBA) of different concentrations have been measured in the frequency range of 100 Hz to 10 MHz from room temperature to 150°C both in planar and homeotropic alignments. These mixtures do not show the dielectric dispersion upto 10 MHz. Dielectric constants parallel and perpendicular to helical axes (ε′∥ and ε′⊥) and the dielectric anisotropy (Δε′ = ε′∥ - ε′⊥) have been determined in different mesophases. Dielectric anisotropy (Δε′) of the mixtures changes sign from negative to a positive value for NOBA concentrations above 75 mole %. From the measured frequency dependent conductivity [sgrave](f), d.c. conductivity [sgrave](dc) has been obtained using the universal power law equation. Activation energy (W a) of the d.c. conduction process has been determined in different mesophases.

Twisted Grain Boundary Phase in the Binary Mixture of Neuatic and Ceolesteryl Compounds

The binary mixture of cholesteryl nonanoate(CN) and 4,4′-hexyloxy azoxy benzene (HOB) exhibit a very interesting sesophases like blue phase, twisted grain boundary (TGB) phase, induced smectic A, smectic C and smectic B phases at different temperatures when the mixture is cooled from isotropic phase. The existence of TGB phase is confirmed by DSC and optical microscopic studies. The mixtures with concentration 30 to 45% of CN exhibit TGB phase at higher temperature. The optical anisotropy of cholesteric phase is estimated. Numerous interesting optical textures are also illustrated.

High pressure optical studies of the chirality and phase behaviour of liquid crystalline blue phases

The blue phase (BP) polymorphism of chiral S -(+)-4-(2-methylbutyl)phenyl-4-decyloxy benzoate (CE6) and S -(+)-4-(2-methylbutyl)phenyl-4-dodecyloxy benzoate (CE7) was studied at elevated transition pressures up to 280MPa using optical activity measurements. The increased density causes an increase in phase chirality which in the case of CE6 manifests itself in the disappearance of BP II (BP I-BP II-BP III triple point) and in the case of CE7 in the appearance of BP II. At atmospheric pressure, CE6 exhibits BP I, BP II and BP III, while CE7 only possesses BP I. This pressure behaviour of CE6 and CE7 is contrary to that of cholesteryl nonanoate, which has been investigated previously. This result is particularly interesting when discussed in connection with the effect of elongation of the terminal n alkylcarboxy chain of the cholesteryl n -alkanoates and of the terminal n -alkyloxy chain in the homologous series to which CE6 and CE7 belong. In the first case the phase chirality increases; in the second case it decreases. Since CE6 shows an obvious pretransitional optical activity in its isotropic liquid phase, pretransition and BP phase behaviour could be compared with each other at elevated transition pressures and temperatures. For those transition pressures or temperatures where anomalies in the BP phase behaviour occur, anomalies in the pretransition behaviour are also observed.

Thermodynamical Properties of Bicomponent Mixtures of Liquid Crystals Cholesteryl Pelargonate and Nonyloxybenzoic Acid

Abstract Transition temperatures, transition enthalpies and entropies of different mesophases of the binary mixture of cholesteryl pelargonate (ChP) and nonyloxybenzoic acid (NOBA) have been measured on a differential scanning calorimeter and optical textures of different mesophases have been confirmed on a polarizing microscope. Eutectic point has been observed at 28 ± 2 mole percent of NOBA from the variation of transition temperature, enthalpy and entropy of the crystal to mixed crystal phase and the mixed crystal phase to mesophase with concentration of NOBA. Stability of SmA phase increases on addition of NOBA. SmA* phase has been observed in between SmA and Ch phases for NOBA concentrations between 18 and 50 mole percent. A very wide cholesteric range of about 50 °C has been observed in cooling in the concentration range of 60 to 90 mole percent of NOBA.

Effect of γ-irradiation on liquid crystalline properties of cholesteryl pelargonate (nonanoate)

Effect of Co 60 γ-irradiation at a dose 500 kGy on dielectric and thermodynamic properties of cholesteryl pelargonate (nonanoate) (ChP) has been studied by differential scanning calorimeter (DSC) and electric impedance analyzer. From UV spectra of irradiated ChP a charge transfer complex peak has been observed at 290 nm besides the peak of pure ChP at 240 nm making it a bicomponent mixture. Irradiated sample shows depression in crystal-cholesteric (KCh) transition by 4.0°C and cholesteric-isotropic (ChI) transition by 9.8°C while cholesteric-smectic A (ChSmA) by 15.4°C. Enthalpies (ΔH) of the KCh, CSmA transitions are found to decrease on irradiation. The dielectric constants ϵ ⊥ ′ and ϵ ∥ ′ and losses( ϵ ⊥ ″ and ϵ ∥ ″ in planar and homeotropic alignmen the sample have been measured in the frequency range 100 Hz to 10 MHz at different temperatures between 30 to 100°C. The dielectric losses ( ϵ ⊥ ″ and ϵ ∥ ″) of irradiated sample are observed to increase significantly (150%) whereas the dielectric anisotropy Δϵ ( ϵ ⊥ K ′ − ϵ ∥ ′) decreases.

Study on Structure and Properties of Polymer Dispersed Cholesteric Liquid Crystals Ⅳ. The X-ray Diffraction of Poly(MMA-co-BMA)and Cholesteryl Nonanoate Mixtures

Study on Structure and Properties of Polymer Dispersed Cholesteric Liquid Crystals Ⅳ. The X-ray Diffraction of Poly(MMA-co-BMA)and Cholesteryl Nonanoate Mixtures

Study on Structure and Properties of Polymer Dispersed Cholesteric Liquid Crystals Ⅳ. The X-ray Diffraction of Poly(MMA-co-BMA)and Cholesteryl Nonanoate Mixtures

Study on Structure and Properties of Polymer Dispersed Cholesteric Liquid Crystals Ⅳ. The X-ray Diffraction of Poly(MMA-co-BMA)and Cholesteryl Nonanoate Mixtures

Latent heat measurements of the smectic A–cholesteric transition on binary mixtures

Abstract New differential scanning calorimetry measurements of the smectic A-cholesteric latent heat of transition for binary mixtures of cholesteryl nonanoate (C 9) and cholesteryl heptanoate (C 7), cholesteryl nonanoate and cholesteryl caproate (C 6) are reported for cooling cycles. These measurements give evidence of a tricritical point at approximately the reduced temperature T SACh/T Chl ≅ 0·92 for 63·1 mol per cent C 9 in the mixture of C 6 and C 9. This tricritical point occurs at reduced temperatures and concentrations different from those already obtained for heating cycles for the same mixture.

Thermische analyse binärer systeme von mesogenen cholesterylestern und azoxybenzolen

The binary systems of cholesteryl nonanoate with 4,4′-bis(hexyloxy)azoxybenzene (1) and with 4,4′-bis(heptyloxy)azoxybenzene (2) show induced smecticA phases with transition point maximum. Whereas in (1) the smecticA phase is transformed into the cholesteric phase on heating within the whole range of its existence, in (2) the maximum of the smectic phase is stabilized compared with the cholesteric phase and clears into the isotropic melt directly. The molecular ratio of the maximum is 1∶1 in both cases. Moreover in system (2) a smecticC phase was observed.Cholesterylhexadecanoate forms series of smectic and cholesteric mixed crystals of type I resp. III Roozeboom with cholesteryl nonanoate (3) and with cholesteryl tetradecanoate (4). As the unstable solid modifications of the components become relatively stabilized in some mixtures, additional metastable eutectics are formed, which hardly allow to be transformed into the thermodynamic stable solid crystals. Thus errors happened at previous investigations. In the systems (1) to (3) the solid crystals show simple eutectics, in system (4) mixed crystals type V Roozeboom are formed.

Phase transition behaviors and selective optical properties of a binary cholesteric liquid crystals system: Mixtures of oleyl cholesteryl carbonate and cholesteryl nonanoate

This paper deals with the phase transition behaviors of the mixtures of oleyl cholesteryl carbonate and cholesteryl nonanoate by means of optical and differential scanning calorimetry methods. The iridescent colors were measured by using the spectro multichannel photodetector. The phase diagrams show that the smectic mesophase appears in the whole concentration ranges under cooling, but only exists in heating with concentration less than 60%. The phase transition temperatures of the mixtures increase monotonically with increase of cholesteryl nonanoate (CN) contents. This phenomenon has been interpreted from the viewpoints of molecular configurations. The iridescent colors vary from red to violet as the temperature increases, and in reverse order when cooling. The concentration ranges of the iridescence are in agreement with those of smectic existence. Results also indicate that the color band shifts monotonically toward higher temperatures with an increased concentration of CN. This effect is accompanied by a gradual expansion of the temperature interval of the color band. The temperature dependence of the color shift may be explained with the pretransition of twist or untwist of the helical structures. Reflection bandwidth variations with temperature are also attributable to pretransitional effects. The temperature dependence of selectively reflected light intensity measurements reveals that the sensitivity decreases with increase in the wavelength. Moreover, 50% CN concentration is most sensitive, whether heating or cooling.

Phase transition of cholesteryl oleyl carbonate—cholesteryl nonanoate mixtures

Abstract A binary liquid crystals system of cholesteryl oleyl carbonate and cholesteryl nonanoate (CN) has been studied using a differential scanning calorimeter. Measurements of the phase transition enthalpies, entropies, and heat capacities indicate that the smectic mesophase appears throughout the whole concentration ranges under cooling, but it only exists at room temperature with CN content of less than 50%. The phase diagram points out that the two components mixed well with ramdon distribution and formed a solid solution. Phase transition temperatures increase monotonically with the increase in CN content. This phenomenon has been interpreted from the viewpoint of molecular configuration. Mixtures have no eutectic point but the mesomorphous ranges of suitable compositions are still notably larger than those of pure components. The most suitable compositions and the most appropriate conditions for the cholesteric formations are also determined.