Liquid crystal properties of new ionic liquid crystal compounds having a 1,3-dioxane ring

New pyridinium type chiral ionic liquid crystal materials having a 1,3-dioxane ring in the central core, (+)- N -2-methylbutyl-4-(5-alkyl-1,3-dioxan-2-yl)pyridinium bromides (6), were synthesized. Mixture A was made by adding 5.9 wt % of compound 6?3 to the ferroelectric liquid crystal mixture Merck 4655-100; its phase transitions and some liquid crystal properties were measured. In spite of a large decrease of P_s for mixture A, its response time A was the same as that of Merck 4655-100. The dielectric constants perpendicular to the molecular axis for the smectic C* and smectic A phases were measured for the mixture and Merck 4655?100: in the smectic C phase, these dielectric constants were almost the same (4.5～5.5), but in the smectic A phase, the perpendicular dielectric constant of the mixture was 47.0 and that of Merck 4655?100 was 4.5.     

New 1,3-dioxan-type ionic liquid crystal compounds having a large dielectric constant

New pyridinium-type thermotropic ionic liquid crystal materials having a 1,3-dioxan ring in its central core: N-substituted-4-(5-alkyl-1,3-dioxan-2-yl)pyridinium bromides (6) were synthesized. The mesomorphic behaviour of these compounds and dielectric constant perpendicular to the molecular axis were measured. The principal features of these compounds are that they exhibit a smectic A phase over a wide temperature range including room temperature - for example 6f: g -9 SmA 181 I (°C)-and they have a large dielectric constant perpendicular to the molecular axis.     

New 1,3-dioxan-type ionic liquid crystal compounds having a large dielectric constant

New pyridinium-type thermotropic ionic liquid crystal materials having a 1,3-dioxan ring in its central core: N-substituted-4-(5-alkyl-1,3-dioxan-2-yl)pyridinium bromides (6) were synthesized. The mesomorphic behaviour of these compounds and dielectric constant perpendicular to the molecular axis were measured. The principal features of these compounds are that they exhibit a smectic A phase over a wide temperature range including room temperature - for example 6f: g -9 SmA 181 I (°C)-and they have a large dielectric constant perpendicular to the molecular axis.     

New 1,3-dithiane type ionic liquid crystal compounds

New pyridinium type thermotropic ionic liquid crystal materials having a 1,3-dithiane ring in their central core, N -substituted-4-(5-alkyl-1,3-dithian-2-yl)pyridinium bromides ( 8 ), were synthesized. These compounds exhibited a smectic A phase over a very wide temperature range including room temperature.     

New ionic liquid crystal compounds having a 1,3-dithiane or 1,3-dioxane ring

New pyridinium type thermotropic ionic liquid crystal materials having a 1,3-dithiane ring in the central core N-substituted 4-(5-alkyl-1,3-dithian-2-yl)pyridinium bromides and the corresponding 1,3-dioxanes were synthesized and their mesomorphic behaviours compared. The principal feature of these compounds is to exhibit a smectic A phase over a very wide temperature range including room temperature.     

Atomistic simulations of liquid crystal mixtures of alkoxy substituted phenylpyrimidines 2PhP and PhP14

We study liquid crystal mixtures of alkoxy substituted phenylpyrimidines 2-[4-(butyloxy)phenyl]-5-(octyloxy)pyrimidine (2PhP) and 2-[4-(tetradecyloxy)phenyl]-5-(tetradecyloxy)pyrimidine (PhP14) using molecular dynamics simulations at the all atom level. The molecular length of PhP14 is 1.8 times that of 2PhP, resulting in an interesting binary mixture phase diagram. Our simulations are composed of 1000-1600 molecules for a total of 80,000-130,000 atomic sites, with total simulation times of 60-100 ns. We first show that a pure 2PhP system self-assembles into isotropic, nematic, smectic A and smectic C phases, and a pure PhP14 system self-assembles into isotropic and smectic C phases. Binary mixtures of PhP14 and 2PhP display a stabilization of the smectic A phase at the expense of the smectic C and nematic phases. We determine that the concentration-induced phase transition from the smectic C to the smectic A phase in the mixture is driven by an out-of-layer fluctuation arrangement of the molecules. We also observe that the tilt angle in the smectic C phases formed in the mixtures is concentration dependent. The results of our simulations are in good agreement with the experimental findings of Kapernaum et al. [J. Org. Chem. 5, 65 (2009)], thus showing that atomistic simulations are capable of reproducing the phase behavior of liquid crystal mixtures and can also provide microscopic details regarding the mechanisms that govern phase stability.     

New 1,3-dioxane type ionic liquid crystal materials having a terminal double bond

New 1,3-dioxane type ionic liquid crystal materials having a terminal double bond were synthesized. The mesomorphic behaviour of these compounds was measured. The principal features of these compounds are a smectic A phase over a very wide range including room temperature, and a low isotropic to mesophase transition temperature (for example, compound 6-1: Cr-22 SmA 25 I).     

New 1,3-dioxane type ionic liquid crystal materials having a terminal double bond

New 1,3-dioxane type ionic liquid crystal materials having a terminal double bond were synthesized. The mesomorphic behaviour of these compounds was measured. The principal features of these compounds are a smectic A phase over a very wide range including room temperature, and a low isotropic to mesophase transition temperature (for example, compound 6-1: Cr-22 SmA 25 I).     

A sub-hertz frequency dielectric relaxation process in a ferroelectric liquid crystal material

Dielectric studies of the first order phase transition of a ferroelectric liquid crystal material having the phase sequence chiral nematic to smectic C* have been performed using thin (2.5 mum) cells in the frequency range 0.01 Hz to 12 MHz. For planar alignment, one of the cell electrodes was covered with a polymer and rubbed. Optically well defined alignment was obtained by applying an a.c. field below the N*-SmC* transition. Charge accumulation was enhanced by depositing a thick polymer aligning layer for the alignment of the liquid crystal molecules. A sub-hertz frequency dielectric relaxation process is detected in smectic C*, in the chiral nematic and a few degrees into the isotropic phase, due to the charge accumulation between the polymer layer and the ferroelectric liquid crystal material. The effect of temperature and bias field dependences on the sub-hertz dielectric relaxation process are reported and discussed.     

A sub-hertz frequency dielectric relaxation process in a ferroelectric liquid crystal material

Dielectric studies of the first order phase transition of a ferroelectric liquid crystal material having the phase sequence chiral nematic to smectic C* have been performed using thin (2.5 mum) cells in the frequency range 0.01 Hz to 12 MHz. For planar alignment, one of the cell electrodes was covered with a polymer and rubbed. Optically well defined alignment was obtained by applying an a.c. field below the N*-SmC* transition. Charge accumulation was enhanced by depositing a thick polymer aligning layer for the alignment of the liquid crystal molecules. A sub-hertz frequency dielectric relaxation process is detected in smectic C*, in the chiral nematic and a few degrees into the isotropic phase, due to the charge accumulation between the polymer layer and the ferroelectric liquid crystal material. The effect of temperature and bias field dependences on the sub-hertz dielectric relaxation process are reported and discussed.     

A small angle neutron scattering study of the conformation of a side chain liquid crystal poly(methacrylate) in the smectic C phase

The conformation of the backbone in the side chain liquid crystal polymer poly\[ omega (4-methoxybiphenyl-4-yloxy)butyl methacrylate] has been studied in the smectic C and nematic phases. Small angle neutron scattering experiments were performed on mixtures of molecules with perdeuteriated backbones and unlabelled molecules. The polymer is found to adopt an oblate conformation in the smectic C phase. The components of the radius of gyration parallel and perpendicular to the director are determined as a function of temperature from Guinier plots of the SANS data. The radii of gyration do not vary across the smectic phase and are found to be Rg,||=(27+/-1)A, Rg, =(42+/-1)A. These results are compared with recent SANS results for other side chain liquid crystal polymers.     

Dielectric, viscosity, and pitch measurements of a ferroelectric liquid crystal exhibiting the phase sequence smectic M-smectic C

A chiral liquid crystal compound exhibiting the ferroelectric smectic C phase and the recently discovered ferroelectric smectic M phase has been studied by measurements of the Goldstone-mode relaxation frequency and dielectric strength, the spontaneous polarization, the tilt angle and the helical pitch. The data allow the determination of the Goldstone-mode rotational viscosity and the pitch controlling elastic constant. The results indicate that the smectic M phase is characterized by a larger molecular order within the smectic layers compared to the smectic C phase confirming the assumption of a tilted hexatic structure for the smectic M phase.     

Static and dynamic properties of smectic liquid crystal side chain polymers

On the basis of models for the conformation of liquid crystal side chain polymers in the smectic phase, some dynamic aspects of such systems are considered using the reptation approach. The overall diffusion constants of the polymer along and perpendicular to the director of the side chains are derived.     

Dielectric permittivity properties of a fulgide dye guest-host liquid crystal

The dielectric permittivity of the nematic liquid crystalline mixture E7, doped with a low concentration of the photochromic material thiophene fulgide, was studied and compared with the properties of the pure E7. Fulgides are a group of thermally stable photochromic materials. On irradiation with ultraviolet light, a ring-closure occurs, giving an isomer which is stable if the dye is kept in the dark. The isomerism induces changes to the steric, dipolar and electronic conjugation properties of the species. A capacitive technique was used to determine the dielectric constants of the fulgide-doped liquid crystalline mixtures. The parallel and perpendicular components of dielectric constant were measured using a single cell, in the latter case in the presence of a magnetic field. Measurements were made on the photochromic system before and after ultraviolet irradiation and a marked variation in the dielectric properties of the mixture was observed. This was shown to be entirely due to the differences in phase transition temperatures between the irradiated and non-irradiated guest-host mixtures.     

Novel phase behaviour in two (smectic/cholesteric) liquid crystal mixtures

The phase behaviours of mixed liquid crystal systems having either Sm/N or Sm/Ch properties have been studied. The (smectic/nematic) binary system formed smectic phases over a wide and much enhanced range of temperature (42 C) and a broad concentration range (0-90 wt %). The ternary smectic/cholesteric system, in appropriate concentration ranges, exhibited the smectic A phase, a TGBA-like twist grain boundary A phase, the cholesteric phase and blue phases. The TGBA-like phase appeared in the cholesteric-smectic phase transition range. Three textures (chiral pitch, fan-shaped and scale-like) for the cholesteric phase of the ternary smectic/cholesteric mixtures were observed in the ranges 0-7, 7-43 and 43 wt % respectively, of cholesteric CB15, in a binary Sm/N mixture.     

Time resolved X-ray diffraction studies of electric field induced layer motion in a chevron geometry smectic A liquid crystal device

Small angle time-resolved X-ray diffraction was used to monitor the behaviour of the smectic layers during the electric field induced planar to homeotropic transition in a smectic A cell possessing a chevron layer geometry. The liquid crystal material used was S3, from Merck Ltd, and was sandwiched in a 15 mum parallel plate device. The main features of the transition are the cooperative rotation of layers and the creation of an asymmetric chevron structure during the early stages of switching. The time scale for the planar-to-homeotropic transition in the device is approximately 5 s, at a temperature of 3 C below the nematic-to-smectic A phase transition and for an applied electric field of 2 V mum -1 (rms).     

Biaxial smectic phases in non-linear optical properties and phase behaviour of an oxdiazole liquid crystal

A symmetric, low-molecular-mass liquid crystal based on the oxadiazole ring was synthesized and characterized. The symmetric position of the heterocyclic group in the centre of the liquid crystal, bis(4-hexyloxyphenyl)4,4-(1,3,4-oxadiazole-2,5-diyl)dicarboxylate, yields a very rigid and non-linear mesogenic core. Despite this non-linear structure, a broad liquid crystalline range with a smectic C and a smectic A phase was found. Conoscopic experiments on freely suspended films revealed the existence of two optical axes in the smectic A phase, indicating a phase symmetry anticipated for either a 'McMillan' biaxial smectic phase or a biaxial (achiral) ferroelectric smectic phase.     

An unusual chevron structure in an achiral smectic C liquid crystal device

The layer structure that occurs in an achiral smectic C liquid crystal device has been investigated as a function of temperature using the small angle X-ray scattering facility at the Synchrotron Radiation Source, Daresbury UK. The material studied shows a direct phase transition from the nematic to the smectic C phase. The layer structure proposed on the basis of the diffraction data is relatively complex, containing regions with chevron, quasi-bookshelf and curved structures. A rationale for the formation of the structure is presented, relying on both the phase transition characteristics of the system and the anisotropic layer elasticity in the smectic C phase. Qualitative analysis indicates that the layer constant A is greater than A 21, i.e. layer flexing is easier perpendicular to the plane of the director than parallel to it. It is also demonstrated that the surface chevron angle is several degrees different from the tilt angle of the smectic C phase at temperatures well below the smectic C to nematic phase transition. 12     

Induced smectic phases in phase diagrams of binary nematic liquid crystal mixtures

To elucidate induced smectic A and smectic B phases in binary nematic liquid crystal mixtures, a generalized thermodynamic model has been developed in the framework of a combined Flory-Huggins free energy for isotropic mixing, Maier-Saupe free energy for orientational ordering, McMillan free energy for smectic ordering, Chandrasekhar-Clark free energy for hexagonal ordering, and phase field free energy for crystal solidification. Although nematic constituents have no smectic phase, the complexation between these constituent liquid crystal molecules in their mixture resulted in a more stable ordered phase such as smectic A or B phases. Various phase transitions of crystal-smectic, smectic-nematic, and nematic-isotropic phases have been determined by minimizing the above combined free energies with respect to each order parameter of these mesophases. By changing the strengths of anisotropic interaction and hexagonal interaction parameters, the present model captures the induced smectic A or smectic B phases of the binary nematic mixtures. Of particular importance is the fact that the calculated phase diagrams show remarkable agreement with the experimental phase diagrams of binary nematic liquid crystal mixtures involving induced smectic A or induced smectic B phase.     

Dielectric,viscosity, and pitch measurements of a ferroelectric liquid crystal exhibiting the phase sequence smectic M–smectic C

Abstract

A chiral liquid crystal compound exhibiting the ferroelectric smectic C phase and the recently discovered ferroelectric smectic M phase has been studied by measurements of the Goldstone-mode relaxation frequency and dielectric strength, the spontaneous polarization, the tilt angle and the helical pitch. The data allow the determination of the Goldstone-mode rotational viscosity and the pitch controlling elastic constant. The results indicate that the smectic M phase is characterized by a larger molecular order within the smectic layers compared to the smectic C phase confirming the assumption of a tilted hexatic structure for the smectic M phase.