High-Resolution X-ray Study of the Smectic A-Smectic B Phase Transition and the Smectic B Phase in Butyloxybenzylidene Octylaniline

We have carried out a high resolution X-ray study of the smectic phases of Butyloxybenzylidene Octylaniline. We find that the phase previously identified as Smectic-B in this material is crystalline with in-plane order extending over at least 1.4 μm. The in-plane Bragg peaks are accompanied by anomalously strong diffuse scattering that can be described by a form 1/(q ²⊥ + γ² q ² _z). Unless the elastic constant C₄₄ is more than an order of magnitude smaller than previously reported values of ～ 10⁸ ergs/cm³ the diffuse scattering can not be due to acoustic phonons. The crystalline-B to Smectic-A melting transition is strongly first order with no observable pre-transition effects on either side of the transition.     

The Smectic A and the Smectic C Phase: A Coherent Molecular Picture

A molecular field theory of the smectic A and smectic C phase is presented which is based on an interaction derived in terms of the molecular polarizability, its anisotropy and the components of the static molecular quadrupole tensor. It is shown that this attractive interaction strongly depends on the anisotropy of the excluded molecular volume. The results obtained explain the stability of the A phase, the appearance of the tilt in the C phase and the A-C phase transition, without resource to adjustable parameters which indeed have no molecular significance.     

High Pressure Study of Phase Transitions in DMPC-Water System

We have carried out a detailed pressure study of the three phase transitions observed in hydrated dimyristoyl phosphatidylcholine (DMPC) containing 95% by weight of water. The P-T diagram shows a Gel III-Gel II-Gel I triple point at 3.5 kbar, 41[ddot]C. It is found that the Gel III phase can be obtained by pressure-annealing the sample for about 12 hours at room temperature.     

The Lyotropic Smectic Phase on the Flory Lattice

Abstract

The Flory lattice approach for rod-like molecules is extended to encompass the position-restricted (smectic-A) phase. The phase equilibria conditions are obtained from equity of relevant chemical potentials, together with minimization conditions of the Gibbs potential with respect to the system orientational (Flory disorder index, y) and positional (translational disorder index, ζ in the smectic phase) order.     

Biaxial Ordering of Deuterochloroform in a Smectic G Phase

The biaxial symmetry of the low temperature smectic phase of N-(4-n-hexyloxybenzylidene)-4-n-hexylaniline is demonstrated through observation of the deuterium NMR resonance of CDCl₃ probe molecules dissolved in this phase. The biaxial ordering is revealed in the observed powder spectrum as well as in a complete rotation study of a uniformly aligned sample.     

Investigation of a Twisted Phase between the Cholesteric and the Smectic A Phase

In a ternary mixture of two liquid crystals and a non-mesomorphic chiral dopant an intermediate state with an unusual texture was found between the cholesteric and the S_A phase which could be identified as a separate twisted mesophase. The reflection wavelength of this mesophase does not change with temperature whereas the transmission of unpolarized light decreases from 50 to 20%. The experimental findings point to the existence of a twisted grain boundary phase.     

A Novel Method for Study of a Smectic Phase Obtained from a Strongly-Deformed Nematic Texture

A simple method for the growth of conventional or reentrant smectic phases from strongly-deformed conventional or reentrant nematics, is proposed. It permits the formation of surface-induced and surface-governed conventional and/or reentrant smectic textures which can be studied from the scientific point of view or can be applied in the laser-addressed thermo-optic smectic liquid crystal storage displays for the creation of static figures. The simple method proposed might be applied for study of many smectics arrising either from conventional or reentrant nematic phases under cooling or heating.     

Smectic A-Nematic and Nematic-Isotropic Liquid Transitions in 8CB Liquid Crystal: Comparative Analysis

A differential heat flux calorimeter has been used to study the Smectic A-Nematic and Nematic-Isotropic Liquid transitions in 8CB liquid crystal. The Faktor and Hanks model under our working conditions enables us to distinguish first-order from second-order transitions by analysis of differential signal. The critical exponent values obtained justify the proportionality between Cp evolution and the normalized differential signal (differential signal divided by the scanning rate).     

Stimulation of the Electrohydrodynamic Instability in the Smectic a Phase

The electrooptical properties of 4-n-octyl-4′-cyano-biphenyl (8CB) in the smectic A phase were investigated. The electrohydrodynamic instability in the smectic A phase was observed, when a small quantity of any homologue (C₇, C₈, C₉) of 4-n-alkoxyben-zoic acid was adzed to this material. After the electrical field is turned off, the stable focal-conic texture is formed. A reverse focal-conic to homeotropic transition can be as well induced by means of an electric field.     

A Study on the First Order Phase Transitions in Hydrocarbon Crystals

A polarization hot stage microscopy study was made on the phase transitions in n-octacosane and n-hexatriacontane hydrocarbon crystals. Advancement rates of transition fronts of high temperature phase in low temperature phase were measured. Transition in the interior layers was detected. In order to explain the observations, we propose a model, which involves intrachain defects in the extended chain configuration. This model is an advanced stage of the model proposed by STROBL, basing on the SAXS results.     

Phase Transition Studies in Mixed Polymesomorphic Liquid Crystals with Cholesteric and Smectic A Phase

Cholesteric mesomorphism was induced in a polymesomorphic liquid crystal with nematic and smectic A phases by mixing it with a low pitch cholesteric. A variety of mixtures for a wide range of concentrations were studied. It was observed that the addition of cholesteric liquid crystal disrupts the smectic phase of the parent polymesomorphic liquid crystal. The measured valuses of ultrasound velocity and specific volume and their related parameters were found to exhibit anomalies near each of the phase transitions. The mean interaction parameter $ \bar \alpha $ was estimated for different mixtures and was found to decrease with increasing concentration of cholesteric liquid crystal in the mixture. It was observed that smectic A-cholesteric transition becomes second-order at a particular concentration in agreement with the theoretical predictions.     

Successive Phase Transitions in Lipid Membranes

On the basis of a statistical model previously proposed by the present authors, a new sort of phase transition recently observed in the fluid-like phase of DPL bilayer and mono-layer above the main transition temperature is investigated as successive orientational transitions accompanied with conformational changes. The effects of lateral pressure on the transition temperatures and latent entropies observed in DPL monolayer are also explained consistently. This type of phase transition is expected to occur in DML, DSL and DBL as well, although it has not been observed yet in the case of these molecules.     

Phase Transitions of A Quasi-One-Dimensional Fermi Gas

Phase transitions of a quasi-one-dimensional Fermi gas are studied by the use of the renormalization group method for the fermion system without the bosonization. Intrachain backward and forward scatterings, pair electron hopping between different chains and exchange scattering of electrons in different chains are taken account of. Pair electron hopping gives rise to the singlet and triplet superconductor phase transitions. Electron exchange scattering gives rise to the spin density wave and charge density wave transitions. Calculation is made by the use of the one-dimensional dispersion. Following Menyhárd's method (Ref. 1) for the model with interchain backward scattering only, the change of the fluctuation from the one-dimensional region to the three-dimensional region is described. The transition temperatures are given by the bare couplings at high temperatures.     

Solid-Solid Phase Transitions of Long-Chain n-Alkyltrimethylammonium Halides

Transition properties of some compounds of the type, n-C _n H_2n+1N⁺(CH₃)₃X_-, with n = 10, 12, 14, 18, 22, and X = Cl, Br, and I, were investigated. All these compounds show a solid-solid phase transition with a large enthalpy change in the range of temperature 350 ～ 400K. The transition behaviors were investigated by the aid of DSC, TG, X-ray, and optical microscope. The solid-solid phase transition is regarded to be caused by melting of the layer of hydrocarbon chains of the compounds, while the rigid ionic layer retains the regular arrangement. Some relationships between the physical properties and the structure of the compounds are discussed.     

Sequence of Phase Transitions in Solid Mbba

Combined neutron diffraction and Raman scattering measurements were carried out on a series of different phases of the same MBBA sample. The change in the diffraction patterns and in the optical spectra are used to indicate the transitions between the different phases investigated in the whole temperature range of interest. Besides the isotropic and nematic liquid crystalline phases, 7 different solid structures were found and a schematic phase diagram was constructed to show the thermal procedur for producing these phases.     

Transitions de Phase en Series Mesogenes:

The polymorphism of the di(4-alkylphenyl) and di(4-alkoxyphenyl) tetrathiafulvalene (TTF) is investigated by optical, crystallographic and calorimetric methods. All the studied derivatives are mesomorphic. The first mesophase is always a smectic G phase; the second one is a nematic N phase for short chains and a smectic C phase for long chains.

The entropies corresponding to the passage high-temperature crystalline phase C₁ → S_G and to the “melting” (C₁ → mesophases → isotropic phase I) increase with the length of the chain and with the presence of the oxygen atom in the radical.     

Phase Transitions in Chlorobenzene-Cis-Decalin Mixtures: A Nuclear Magnetic Resonance,Thermal Analysis and Phase Diagram Study

Using nuclear magnetic resonance and differential scanning calorimetry we have been able to observe the molecular rotation properties of chlorobenzene-cis-decalin mixtures in their glassy, amorphous and crystalline phases. The results indicate: that in “rapidly” cooled samples the behavior of the host dominates the properties of the mixtures; that reorientation of the guest molecule is less restricted in the amorphous phase than in the glassy phase; that when the material crystallizes from the amorphous phase on warming, reorientation again becomes severely restricted. The temperatures at which these phenomena occur agree with the phase diagram that has been determined for these materials. Similar experiments on t butyl chloride-cis-decalin mixtures support the above conclusions. These conclusions are in agreement with the previous dielectric studies.

Our magnetic resonance and thermal analysis experiments support the argument that the behavior of the CD host dominates the behavior of guest polar molecules in rapidly cooled mixtures. At the lowest temperature (110 K) CD forms a glassy phase unaccompanied by any heat of crystallization. On warming this glassy phase transforms near 150 K to an amorphous phase where considerable motion of both host and guest molecules occurs. Above 160 K the material crystallizes and reorientation is once again severely restricted up to the eutectic melting of 210 K. There appears to be no time dependence to these transformations and, as long as one stays below the crystallization temperature, the glassy-amorphous transition is reversible.     

Phase Transitions in Polypeptide Liquid Crystals: A Reentrant Isotropic Phase

Optical and C-13 NMR examinations of concentrated solutions of poly-γ-benzyl-L-glutamate (PBLG) in a mixed solvent system containing a denaturant acid, show that this polymer liquid crystal has both a low and high temperature isotropic phase. The latter is due to thermal disruption of long range orientational order of the elongated macromolecules. The former reentrant isotropic phase is a result of an intramolecular helix to random coil transition, which leads to a macromolecular conformation inconsistent with liquid crystallinity.