The H2-phase of the lyotropic liquid crystal sodium 3,4,5-tris(omega-acryloyloxyundecyloxy)benzoate

The phase behaviour of the lyotropic liquid crystal sodium 3,4,5-tris(omega-acryloyloxyundecyloxy)-benzoate was investigated by small angle X-ray scattering. The water content of the lyotropic liquid crystal phase was varied between 8 and 20wt% and the investigations were performed in a temperature range up to 70^oC. A reversed hexagonal structure (H₂-phase) as well as the isotropic phase were observed. The lattice constant of the H₂-phase was found to be independent of the water content. An extremely small dependence on temperature could be found. Based on the shape of the molecules and the observed structural properties, a model for the arrangement of the molecules within the H₂-phase is given. The transition temperature from the H₂-phase to the isotropic phase decreases significantly from 60^oC for the sample with 8wt% water content to 30^oC for the sample with 20wt% water content.     

Aqueous Phase Behavior of Diglycerol Fatty Acid Esters

We have studied the phase behavior of homologous series of diglycerol fatty acid esters (Qn‐D, for n=10, 12, 14, and 16, where n represents the carbon number in the alkyl chain length of amphiphile) in aqueous solution as a function of temperature and surfactant concentration. The different equilibrium phases present over a wide range of composition and temperature studied were characterized by means of visual observation under normal and polarized light, and x‐ray scattering techniques at small (SAXS) and wide angle (WAXS) regions. In diglycerol monocaprate (Q10‐D) and diglycerol monolaurate (Q12‐D)/H₂O systems, lamellar liquid crystal (L_α) phase is present in the surfactant rich region and it swallows an appreciable amount of water. The amount of water swallowed by the L_α phase was determined by plotting the interlayer spacing, d, as a function of reciprocal of the surfactant weight fraction W_s . In the dilute regions, dispersion of L_α phase in water is observed over a wide range of temperature. At higher temperatures, the L_α phase melts to isotropic two‐liquid phases in water rich region whereas to isotropic reverse micellar solution (O_m) in surfactant rich region. The L_α‐O_m transition temperature is increased on increasing the hydrocarbon chain length of the surfactant from Q10‐D to Q12‐D. There is surfactant solid phase in equilibrium with water up to 25°C in diglycerol monomyristate (Q14‐D)/H₂O system and the solid phase could solubilize 25 wt% water. The melting temperature of solid phase is practically constant in a wide range of compositions. Both the solid present region and the extent of water solubilization are increased in diglycerol monopalmitate (Q16‐D)/H₂O system. At lower surfactant concentrations, excess water appears and dispersion of solid in water is formed. The structure of the solid is identified by WAXS measurement and it is confirmed to α‐solid. Normal vesicular aggregates are formed in L_α+W regions in the Q14‐D/H₂O system at 25°C.     

An isotopic effect in the dielectric spectra of Ark. 9/water systems

Dielectric spectra of H₂O and D₂O molecules in the L_α liquid crystalline phase of nonylphenoxy-poly(ethylenoxy)ethanol(Ark. 9)/water lyotropic systems have been investigated by dielectric time domain spectroscopy in the frequency range from 10 MHz to 10 GHz. By fitting the Cole-Cole formula to the dielectric spectra, obtained at different temperatures the dielectric increments, the relaxation times and the distribution parameters have been calculated. A strong retardation of water molecules has been found for the lamellar phase with low water content, i.e. 10 water molecules (H₂O or D₂O) per one Ark. 9 molecule. The relaxation times obtained at room temperature for the light and heavy water are 63 and 93 ps, respectively. It means that the retardation factor for D₂O molecules in the L_α phase is close to 1.5 and higher than that found for pure heavy water (1.25). Any decomposition of the dielectric spectra obtained seems to be unsubstantiated. The temperature dependences of the relaxation times acquired for both kinds of water obey the Arrhenius behaviour.     

Molecular dynamics and alignment studies of silica-filled 4-pentyl-4′-cyanobiphenyl (5CB) liquid crystal

A comprehensive study of the dielectric properties of 4-pentyl-4′-cyanobiphenyl (5CB) liquid crystal filled with silica particles (particle size 30–80 nm, concentration 2, 3, 5, 10 and 15 wt%). Dielectric spectroscopy in the frequency range 100 to 10 7 Hz was applied to investigate the influence of the filler on the dynamic behaviour of the liquid crystal molecules in both the nematic and isotropic phases. In this frequency range one relaxation process is observed (at f>10⁶ Hz). The dynamical behaviour of the 5CB liquid crystal is described by the Cole-Cole relaxation function. The temperature dependence of the relaxation time obeys the empirical Arrhenius equation. The activation energies are approximately 75 kJ mol¹ for the pure 5CB sample in the nematic phase and 50 kJ mol¹ for the 5 wt% silica-filled 5CB sample. These values are compared with the corresponding literature values. The reversible electro-mechanical response of these samples under the influence of an applied a.c. electric field is investigated.     

Calorimetric studies of poly (2-phenoxyethylacrylate)/5CB mixtures

The thermophysical properties of mixtures of poly (2-phenoxyethylacrylate) and 4-cyano-4′-pentyl-biphenyl, 5CB, are investigated using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The polymer has a molar mass M _w = 181 000 g mol ^-1 the low molecular mass liquid crystal exhibits a nematic to isotropic transition at 35.3°C and crystallizes below 23°C. The phase diagram exhibits miscibility gaps in certain regions of temperature and composition where coexisting nematic and isotropic phases are found. From a practical point of view when considering the electro-optical applications of these systems, it proves to be useful to know precisely the amount of small liquid crystal molecules dissolved in the polymer matrix and the concentration of polymer in the nematic phase. The former quantity has a mechanical impact due to a plasticizing effect, an optical impact since it changes the polymer refractive index, while the polymer in the nematic phase shifts the transition temperatures influencing the electro-optical response of the liquid crystal. The present work addresses these important aspects using POM and DSC.     

The effects of some factors on the rheological properties of the lyotropic liquid crystals formed in Brij97/NaDC/IPM/water system: compositions,temperature and polyphenols

In this paper, interaction between Brij97 and NaDC in mixed micelles was studied by surface tension method. Phase behavior for Brij97/NaDC/IPM/H₂O system was investigated at the desire molar ratio of α_NaDC?=?0.42 and the human body temperature of 37?°C. Hexagonal and cubic liquid crystal were found in this system analyzed by small angle x-ray scattering (SAXS). some factors were changed to affect the rheological properties of liquid crystal. Rheological investigations showed: The higher content of water and lower experimental temperature favored the greater values of shear viscosity and viscoelastic modulus; The sample was closer to the plastic fluid and was more likely to recover from disturbed state to equilibrium state at lower ratio of NaDC; The curcumin and TP can influence the shear viscosity, viscoelastic properties and phase transition temperature, even change the structure of liquid crystal. This supplies a way to adjust rheological properties, structure and even phase transition by altering those factors.     

Influence of transitional metal ions on lyotropic liquid crystals of hydroxyethyl cellulose acetate in N,N-dimethylformamide

The influence of inorganic salts on the formation of lyotropic liquid crystals of hydroxyethyl cellulose acetate (HECA) in N,N′dimethylformamide (DMF) was studied. In the presence of CaCl₂, an inorganic salt of a principal group metal, the solution of HECA/DMF/CaCl₂ was a biphasic system. The temperature of the transformation from the liquid crystalline phase to the isotropic one increased with adding CaCl₂ because local HECA concentration increases in the HECA/DMF phase. When CuCl₂ or CoCl₂, inorganic salts of transitional metals, was added, the solutions were monophasic systems and the complexes of HECA with Cu²⁺ or Co²⁺ were formed in solutions, which results in the increase of the temperature of the transfomation from the liquid crystalline phase to the isotropic one.     

Determination of the electrochemical diffusion coefficient of methylene blue in SDS/n-C5H11OH/H2O system by non-probe microelectrode voltammetry

The diffusion coefficient of methylene blue (MB) is determined by the method of non-probe microelectrode voltammetry in sodium dodecyl sulfate (SDS)/n-C₅H₁₁OH/H₂O lyotropic liquid crystal system. The results obtained show that the diffusion coefficient of MB increases with water and n-pentanol contents in the microemulsions and the lyotropic liquid crystal but decreases with SDS content. The diffusion coefficient of SDS droplet in the microemulsions and the diffusion coefficient of SDS molecule in the lyotropic liquid crystal with MB all are less than those without MB. The magnitude order of the diffusion coefficient of MB is as follows: the coefficient in the oil-in-water (O/W) microemulsion is greater than the coefficient in the water-in-oil (W/O) microemulsion which is greater than the coefficient in the lamellar liquid crystal (LLC), which is also greater than the coefficient in the Hex.     

Polarized infrared spectroscopic study on changes in molecular orientation and interaction during phase transitions of a ferroelectric liquid crystal with a naphthalene ring

Temperature-dependent polarized infrared spectra were measured over the temperature range 105-30°C for a ferroelectric liquid crystal with a naphthalene ring (FLC-1) in the isotropic, smectic A (SmA), and chiral smectic C (SmC*) phases to investigate its molecular conformation, interactions, and alignment in each phase. It has been found, from the temperaturedependent spectral changes in the 1610-1600 cm^-1 region, that the degree of twist between the naphthalene and benzene rings of FLC-1 changes with temperature. The peak intensity of the band at 1606 cm^-1 containing contributions from both the benzene and naphthalene ring stretching modes begins to decrease, not suddenly but gradually, upon going from the SmA phase to the SmC* phase, suggesting that the molecular orientation of the two rings changes gradually between the two phases. The frequencies of two CH₂ stretching bands suggest that the disorder of the alkyl chain of FLC-1 is similar for the liquid crystal phase and the isotropic liquid phase. The splitting of the core C=O stretching band indicates that the resonance system consisting of the benzene ring and the C=O group in the core part of FLC-1 is involved in two kinds of intermolecular interaction between adjacent molecules in the liquid crystal phase.     

3-D phase diagram of HPC/H2O/H3PO4 tertiary system

A 3-D phase diagram of the HPC/H₂O/H₃PO₄ tertiary system against various temperatures was established. Four distinct phases—the completely separated phase (S), the cloudy suspension phase (CS), the liquid crystalline miscible phase (LC), and the isotropically miscible phase (I)—were identified. The S phase shrank as the temperature increased, revealing that the HPC solubility increased with temperature, regardless of the LCST (lower critical solution temperature) characteristic. The addition of H₃PO₄ suppressed the formation of LC phase. However, as the temperature was raised sharply from 50 to 70?°C, the LC phase could only be maintained at high H₃PO₄ concentration region; it was a triangular shape, and the top apex of the triangle was the temperature-invariant L* point (HPC/H₂O/H₃PO₄ 38/9/53?wt%). The CS phase expanded considerably into the H₂O-rich but H₃PO₄-poor region when the temperature continued to increase over 48?°C. The LCST points of the CS phase that contained 0 and 15?wt% of H₃PO₄ were 34 and 38?°C, respectively. These CS results demonstrate that H₃PO₄ suppresses the occurrence of LCST behavior. Additionally, the binodal curve exhibits a weak or even zero dependence of binodal temperature on the HPC concentration at HPC concentrations of less than 30?wt% in a pure water system. A hypothesis concerning the sequential desorption of water molecules was proposed to explain such behavior.     

Thermotropic Liquid Crystals Based on Extended 2,5‐Disubstituted‐1,3,4‐Oxadiazoles: Structure–Property Relationships,Variable‐Temperature Powder X‐ray Diffraction,and Small‐Angle X‐ray Scattering Studies

A class of extended 2,5‐disubstituted‐1,3,4‐oxadiazoles R¹‐C₆H₄‐{OC₂N₂}‐C₆H₄‐R² (R¹=R²=C₁₀H₂₁O 1 a , p‐C₁₀H₂₁O‐C₆H₄‐C?C 3 a , p‐CH₃O‐C₆H₄‐C?C 3 b ; R¹=C₁₀H₂₁O, R²=CH₃O 1 b , (CH₃)₂N 1 c ; F 1 d ; R¹=C₁₀H₂₁O‐C₆H₄‐C?C, R²=C₁₀H₂₁O 2 a , CH₃O 2 b , (CH₃)₂N 2 c , F 2 d ) were prepared, and their liquid‐crystalline properties were examined. In CH₂Cl₂ solution, these compounds displayed a room‐temperature emission with λ_max at 340–471 nm and quantum yields of 0.73–0.97. Compounds 1 d , 2 a – 2 d , and 3 a exhibited various thermotropic mesophases (monotropic, enantiotropic nematic/smectic), which were examined by polarized‐light optical microscopy and differential scanning calorimetry. Structure determination by a direct‐space approach using simulated annealing or parallel tempering of the powder X‐ray diffraction data revealed distinctive crystal‐packing arrangements for mesogenic molecules 2 b and 3 a , leading to different nematic mesophase behavior, with 2 b being monotropic and 3 a enantiotropic in the narrow temperature range of 200–210 °C. The structural transitions associated with these crystalline solids and their mesophases were studied by variable‐temperature X‐ray diffractometry. Nondestructive phase transitions (crystal‐to‐crystal, crystal‐to‐mesophase, mesophase‐to‐liquid) were observed in the diffractograms of 1 b, 1 d , 2 b, 2 d , and 3 a measured at 25–200 °C. Powder X‐ray diffraction and small‐angle X‐ray scattering data revealed that the structure of the annealed solid residue 2 b reverted to its original crystal/molecular packing when the isotropic liquid was cooled to room temperature. Structure–property relationships within these mesomorphic solids are discussed in the context of their molecular structures and intermolecular interactions.     

Dielectric relaxation of water molecules in different lyotropic structures of nonylphenoxypoly(ethylenoxy)ethanol (Ark. 9)

Abstract

Dielectric relaxation of water molecules in the lamellar, L_α, cubic and hexagonal, H_α, lyotropic structures of nonylphenoxy-poly(ethylenoxy)ethanol (Ark. 9) has been studied by dielectric time domain spectroscopy in the frequency range between 10 MHz and 10 GHz. The values of the relaxation times, obtained at room temperature, are the following: 41 ps for the L_α phase, 29 ps for the cubic phase and 22 ps for the H_α phase. As is seen, the relaxation time of bound water is distinctly higher than that of pure water, and it depends strongly on the phase structure. The relaxation times measured for the liquid-crystalline phases as well as for pure Ark. 9 obey the Arrhenius law, and the energy barriers obtained have the following values: (20 ± 2) kJ/mol for all the liquid-crystalline phases, and (30 ± 3) kJ/mol for pure Ark. 9. The former is in good agreement with the value found for bound water in lipid systems whereas the latter is characteristic of the isotropic phase of thermotropic liquid crystals.     

Electrochemical polymerization of aniline in the SDS/n‐C5H11OH/H2SO4(aq) lyotropic liquid crystal

Electrochemical polymerization of aniline was performed by the method of ultramicroelectrode cyclic voltammetry in the lamellar liquid crystal and hexagonal liquid crystal of SDS/n‐C₅H₁₁OH/H₂SO₄(aq) system. The results indicate that the electrochemical polymerization of aniline can be catalyzed by the SDS/n‐C₅H₁₁OH/H₂SO₄(aq) lyotropic liquid crystal. The polymerization potential of aniline is smaller in the lyotropic liquid crystal system than that in the 0.10 mol L?1 sulfuric acid solution. The catalytic efficiency and polymerization rate of aniline increase with the n‐pentanol content, but decrease with the increase of the SDS content or [PhNH₂/H₂SO₄(aq)] content. Moreover, the catalytic efficiency of the lamellar liquid crystal exceeds that of the hexagonal liquid crystal in the SDS/n‐C₅H₁₁OH/H₂SO₄(aq) system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2388–2394, 2006     

The Effects of Alcohol with Different Chain Length on the Phase Equilibria of Nonionic Surfactant System

Addition of alcohol with longer chain length (C₆H₁₃OH, C₈H₁₇OH, and C₁₂H₂₁OH) caused a reduction the cloud point of a commercial nonionic surfactant, Tesgitol (T_15-s-9). The formation of lamellar liquid crystal (LLC) was favored so that isotropic liquid (L₁)-LLC two-phase region became wider with increasing temperature at an appropriate weight ratio of surfactant to alcohol. The isotropic liquid phase/liquid two phase transformation was replaced by a two-phase transformation to isotropic liquid/lamellar liquid crystal at the cloud point for the system without alcohol.     

Growth and Thermal,Electrical, Structural Characterization of Mixed Hydrated Single Crystal

Mixed single crystal was made by mixing saturated aqueous solutions of NiSO₄ · 6H₂O and CuSO₄ · 5H₂O by volume (80:20) and the mixture was kept to form the crystals at room temperature by slow evaporation process. After some days, big pieces of greenish blue, dark colored crystals were grown. To determine the weight of NiSO₄ · 6H₂O and CuSO₄ · 5H₂O in the crystal, Ni-DMG complexiometrical and EDTA gravimetrical analysis was done respectively. From this analysis it was concluded that 5.8 molecules of water of crystallization is present in the mixed single crystal. The crystals were characterized by UV-Visible, FTIR and single crystal X-ray diffraction studies. From single crystal XRD lattice parameters have been calculated. All these structural analysis confirms formation of new single crystal. Further, DTA-TGA, dc electrical conductivity and dielectric constant studies were done from the room temperature to 400 °C.From DTA studies it was observed that 5.8 molecules of water of crystallization get dehydrated in four major steps at temperature 115 °C, 150 °C, 240 °C and 325 °C respectively corresponding to the detachment of 1 mole, 3 moles, 1 mole and 0.8 mole of water of crystallization. DC electrical conductivity and dielectric constant studies also show close agreement to the dehydration steps. The observed peaks in the conductivity verses temperature graph have been explained on the basis of release of water molecules and subsequent dissociation of these released water molecules into H⁺ and OH⁻ ions.     

Miscibility behavior of ternary lipidphospholipid/water systems

Differential-scanning-calorimetry was applied to study the lyotropic and thermotropic properties of the two ternary systems dimyristoylcephaline (di-(C14:0)-PE)/Palmitic acid (C₁₅COOH)/water (H₂O) and dimyristoylcephaline (di-(C14:0)-PE)/palmitic acid methyl ester (C₁₅COOMe)/water (H₂O) in dispersions with excess water (50 wt.%).The phase diagrams of both systems showed that the two systems differ in their miscibility behavior. The system di-(C14:0)-PE/C₁₅COOH/H₂O is completely miscible in its high-temperature phase. In the low-temperature phase the mixing gap was found within the concentration range of C₁₅COOH and was also indicated by a maximum value of the transition enthalpy of the pseudo-binary mixtures.In the pseudo-binary system di-(C14:0)-PC/C₁₅COOMe/H₂O, the tendency towards demixing is much more pronounced. It was observed that the incorporated C₁₅COOMe melted above its normal melting point, but below the transition temperature of di(C14:0)-PE/H₂O system; therefore, the phase transition started at lower temperature. In the low-temperature phase, both lipids are partially miscible. The demixing range of the phase diagram lies within the concentration region of C₁₅COOMe. Up to the mole fraction ofXC₁₅COOMe=0.43, C₁₅COOMe can be incorporated into theL-phase of the system di-(C14:0)-PE/H₂O.     

An X-ray scattering study of the lamellar/nematic/isotropic sequence of phases in decylammonium chloride/H2O/NH4Cl

Abstract

An X-ray scattering study is presented of the lamellar/nematic/isotropic sequence in the lyotropic system DACI/H₂O/NH₄Cl. The whole reciprocal space of monocrystalline samples oriented in magnetic fields are reconstructed from their two dimensional sections on photographic films. Intense diffuse scatterings are observed in the lamellar phase, around and away from the Bragg spots. Their evolution close to the lamellar/nematic transition reveals the presence of intense structural fluctuations. They take place over temperature ranges which are significantly greater than those associated with the smectic/nematic transitions in thermotropic liquid crystals. A similar situation is observed in the isotropic phase in the vicinity of the nematic/isotropic transition.     

Polymorphic tin dioxide synthesis via sol–gel mineralization of ethyl–cyanoethyl cellulose lyotropic liquid crystals

The polymorphic tin dioxide (SnO₂) was synthesized by calcinating the sol–gel mineralized hybrid of the tin source solution (SnCl₄/ethanol/H₂O) and the lyotropic liquid crystal of ethyl–cyanoethyl cellulose((E-CE)C)/acrylic acid (AA). The sub-micrometer SnO₂ spheres with bimodal distribution at 370 and 860 nm were obtained after calcinating the hybrid at 400°C for 5 h. When the hybrid was exposed to ultraviolet first and then calcinated the flying-saucer-like SnO₂ was formed. The exposure time was found to influence the morphology of the as-prepared SnO₂. Except for the spherical and the flying-saucer-like SnO₂, a small amount of well-developed polyhedral SnO₂ was also observed in the as-prepared samples. On this basis, the lyotropic liquid crystal of (E-CE)C/AA afforded a novel route to obtain polymorphic SnO₂.     

Density and refractive index measurements in hexaheptyloxytriphenylene,a discotic liquid crystal

Density and refractive index measurements in the discotic liquid crystal hexaheptyloxytriphenylene were performed in the hexagonal columnar Col_ho and isotropic I phases. The temperature dependence of the density ρ(T) for this compound was obtained by combining small angle X-ray data and capillary methods. The ordinary n _o extraordinary n _e and isotropic liquid n _i refractive indices were measured using a modified Abbe refractometer to an accuracy of about 10^?3. To check the consistency of the density and the refractometry experiments we used the Lorentz–Lorenz relation. An anomaly in the empirical relationship at the Col_ho–I phase transition, which holds for many uniaxial liquid crystals, was detected. A discrepancy between low birefringence Δn～0.109 and a relatively high local electric field anisotropy for hexaheptyloxytriphenylene is discussed.