Effects of Salt on the Orientational Order in Decylammonium Chloride/Ammonium Chloride/Water Systems

The effect of NH₄Cl on the temperature dependence of deuterium oxide splitting (water order) and proton line width (surfactant order) in decylammonium chloride (DACl), D₂O systems is reported. The molar ratio of DACl to D₂O was held constant at .085 and the molar ratio of NH₄Cl to D₂O was varied from .012 to .029. We find for the above concentration ranges that in the nematic range the relative temperature dependence of the D₂O splitting is little affected by changes on salt concentration. The slopes of the proton line widths as a function of temperature decrease with increasing salt concentration. The results are compared with earlier data on salt effects on order obtained with the disodium cromoglycate system.     

Optical Sign Determinations on Cholesteric Lyotropic Mesophases

Optical signs of type I and II micellar cholesteric lyotropic mesophases were for the first time determined. Lyomesophases were prepared from the following amphiphiles: potassium l-N-lauroyl-serinate, potassium laurate, sodium decylsulfate, cesium decylsulfate and decyl-ammonium chloride. Cholesterol was added to all mesophases in order to obtain the chevron pattern for magnetically oriented samples. The method involves the direct observation of the textures at the polarizing microscope. Using a quartz-wedge retardation plate the directions of the slow and fast light vibration components are determined. This method is simpler than the usual observation, under conoscopic illumination, of the basal interference figure which is hardly obtained in micellar lyotropic cholesteric mesophases. All type I cholesteric lyotropic mesophases here investigated exhibited a positive optical sign, whereas all type II cholesteric lyomesophases showed a negative birefringence.     

New Nematic Phase in Lyotropic Binary Liquid Crystals Detected by Positron Annihilation Techniquest

A new nematic phase in lyotropic binary liquid crystalline systems consisting of sodium dodecyl sulfate-water was detected, for the first time, in the absence of additives by utilizing positron annihilation techniques. Lyotropic and thermotropic phase transitions were also investigated by the same methods. The positron annihilation parameters have also indicated a better definition of the concentration ranges at which each phase exists in the system studied. Crossed polarized light microscopy was applied to substantiate these results.     

Nematic and Cholesteric PDLC Elaborated under Shear Stress

Abstract

The properties of nematic and cholesteric Polymer Dispersed Liquid Crystal (PDLC) with ellipsoidal droplets are reported. The shape of the droplets are modified by a shear stress during the preparation. Different values of the shear stress were used which permit an ellipticity ratio modification by a factor 10. The electro-optical properties are measured for different types of samples and compared with theoretical previsions: transmission or reflection under voltage, threshold voltage, response times. We also describe the preparation of the sample, the experimental apparatus used for the shear stress, and the expected theoretical quantities like response times. When the liquid crystals are nematics, we obtain an increase of the threshold voltages, as predicted. The relaxation time decreases with increasing deformation but the diminution is not as great as predicted. When the liquid crystals are cholesterics, the high deformations induce polygonal fields, which strongly modify the electro-optical properties of the micro-composite. The threshold voltages and response time at applied voltage decrease whereas the relaxation time is increasing.     

Inter and Intramolecular Contributions to the Proton Dipolar and Rotating Frame Spin-Lattice Relaxation Times in the Nematic Phase of the Liquid Crystal 5CB-d 11

An isotopic dilution study of the proton dipolar and rotating frame spin-lattice relaxation times (T ₁ D and T ₁ p) in the nematic liquid crystal 4-cyano-4′-n-pentyl-d ₁₁-biphenyl (5CB-d ₁₁) at 13.8 MHz over the nematic phase temperature range was used to separate the intermolecular and intramolecular contributions to the ring proton relaxation rates. This is the first such study to be reported. Combined with our earlier proton study of inter/intra Zeeman spin-lattice relaxation (T ₁) in 5CB-d ₁₁, these data permit a critical study of the soft-mode dynamics in the system. A qualitative explanation of the T ₁ D> results is presented, but a complete explanation of the T ₁ p results is not possible with existing theory.     

On the Transition between Cholesteric and Nematic Phases in Magnetic Field

Singularities at the critical lines bounding the cholesteric and nematic phases on the magnetic field versus temperature plane are investigated. Critical exponents, α and γ, of the specific heat and magnetic susceptibility are found both unities. By regarding the inverse of pitch of the cholesteric structure as an order parameter, it is found that the exponents β and δ are zero and infinity, respectively, and these exponents satisfy the scaling relations, α + 2β + γ = 2 and α + β (δ + 1) = 2. In relation to the discommensurate charge density wave in layer structure materials, it is noted that the transition from the nematic to cholesteric phase occurring with the change of magnetic field and/or temperature is interpreted as a condensation process of solitons.     

Influence of Curing Frequency on the Morphology and the Electro-Optical Property of Polymer-Stabilized Cholesteric Textures

The effect of curing frequency on the morphology of polymer networks and the electro-optical property of normal-mode polymer-stabilized cholesteric textures (PSCTs) has been investigated. The scanning electron microscopy indicates that the shape of polymer networks transforms from honeycomb-like to fiber-like due to the increased solubility of the monomer at higher curing frequencies. The PSCTs cured at lower frequencies with sufficiently large network voids show a two-stage reorientation process that correlates with two kinds of cholesteric liquid crystal (LC) under different environments. The threshold voltage decreases as the curing frequency increases from 1 Hz to 10,000 Hz, while the field-off response time increases.     

Syntheses and Mesomorphic Properties of New Liquid Crystalline Materials Involving Piperazine Skeleton

Some mesogenic materials involving a piperazine skeleton were prepared and the thermal properties were examined by DSC and microscopic analyses. Although the piperazines have a thermal flexibility similar to cyclohexyl ring, a lateral interaction due to lone pair electrons of nitrogens largely enhances the thermal stability of the mesophase. The piperazine compounds tend to preserve a smectic arrangement.     

Synthesis,Characterization and Mesomorphic Properties of New Rod-like Thiophene Based Liquid Crystals

Two new mesogenic homologous series of Schiff base esters, 2-[4-(4′-n-Alkoxy benzoyloxy) benzylidenamino] 3-cyno thiophine (Series-A) and Schiff base cinnamates, 2-[4-(4′-n-alkoxy cinnamoyloxy) benzylidenamino] 3-cyano thiophene (Series-B), comprising a thiophene moiety were synthesized. Structural elucidation was carried out using elemental analysis and spectroscopic techniques such as FT-IR, ¹H-NMR and ¹³C-NMR, and mass spectrometry. The mesomorphic properties and thermal stabilities of the title compounds were studied by using differential scanning calorimetry and optical polarizing microscopy. All the derivatives are mesomorphic in nature showing the nematic phase, and the higher members of Series-A show a smectic C phase whereas Series-B exhibits only the nematic mesophase. The mesomorphic properties of the present series are compared with other structurally related compounds.     

Synthesis,spectroscopic studies and ab‐initio structure determination from X‐ray powder diffraction of bis‐(N‐3‐acetophenylsalicylaldiminato)copper(II)

The synthesis, spectroscopic studies and crystal structure determination from X‐ray powder diffraction have been carried out for bis‐(N‐3‐acetophenylsalicylaldiminato)copper(II). The structure is triclinic, space group P1 with unit cell dimensions a = 11.817(1) Å, b = 12.087(1) Å, c = 9.210(1) Å, α = 102.62(1)°, β = 111.16(1)°, γ = 86.15(1)°, V = 1197.0(2)ų, Z = 2. The structure has been solved by Monte Carlo simulated annealing approach and refined by GSAS package. The final Rp value was 8.68%. The coordination geometry around the copper atom in the complex is intermediate between square‐planar and tetrahedral with two salicylaldimine ligands in trans arrangement. Intermolecular C–H…O hydrogen bonds between molecules related by translation generate infinite chains along [010] direction. The molecular chains are linked via additional C–H…O hydrogen bonds to form a three‐dimensional supramolecular network. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and Crystal Structure of a New Coordination Polymer from Cadmium and V-Shape Ligand Bis(imidazol-1-yl) methane

Abstract  The new coordination polymer, [Cd(BIM)₂(NO₃)₂]_n, has been prepared from the reaction of bis(imidazol-1-yl) methane (BIM) with Cd(NO₃)₂ in methanol and water. The compound were characterized by single crystal X-ray diffraction and IR spectroscopy, it crystallizes in the monoclinic space group C2/m with a = 14.400(3) ?, b = 9.3894(18) ?, c = 8.6926(17) ?, β = 123.499(2)°, V = 980.1(3) ?³, Z = 2. The Cd atoms are coordinated to four nitrogen atoms from four different BIM ligands and two nitrates to form a slightly distorted octahedral geometry. Further, the BIM ligands act as a bridged ligand to form 1D infinite cationic double chain with a 16-membered macrometallacyclic tetragonal box structure. Graphical Abstract   Synthesis and Crystal Structure of a New Coordination Polymer from Cadmium and V-Shape Ligand Bis(imidazol-1-yl) methane Chuan-Ming Jin*, Ling-Yan Wu, Zhen-Xing Zhong A new coordination polymer with 1D infinite cationic double chain with a 16-membered macrometallacyclic tetragonal box structure has been prepared from the reaction of bis(imidazol-1-yl) methane (BIM) and Cd(NO₃)₂.      

A New Poly(aryleneethynylene) from the Cross-Coupling Condensation of 4-[(tert-Butyldimethylsiloxy)methyl]-1,6-heptadiyne and p-Diiodobenzene: Synthesis and Properties

A new poly(aryleneethynylene) was synthesized from the palladium-catalyzed carbon-carbon coupling condensation of 4-[(tert-butyldimethylsiloxy)methyl]-1,6-heptadiyne and p-diiodobenzene. This polymerization proceeded well in mild reaction conditions to give a high yield of polymer (92%). The polymer structure was characterized by such instrumental methods as infrared and NMR spectroscopies. This polymer was completely soluble in common organic solvents such as chloroform, chlorobenzene, toluene, and xylene. The X-ray diffractogram of polymer powder showed that this polymer is amorphous. In the DSC thermogram of polymer, a broad exothermic peak was observed around 205°C (started at 140°C) in the first heating, whereas there was no exothermic peak in the second heating. When this polymer was excited at 272 nm, it gave PL maximum emissions at 327 and 380 nm.