An experimental study of adsorption interference in binary mixtures flowing through activated carbon

The isothermal transmission through activated carbon adsorber beds at 25 C of acetaldehyde-propane and acetylene-ethane mixtures in a helium carrier gas was measured. The inlet concentration of each component was in the range between 10 ppm and 500 ppm. The constant inlet volumetric flow rate was controlled at 200 cc (STP)/min in the acetaldehyde-propane experiments and at 50 cc (STP)/min in the acetaldehyde-ethane experiments. Comparison of experimental results with the corresponding single-component experiments under similar conditions reveals interference phenomena between the components of the mixtures as evidenced by changes in both the adsorption capacity and the dispersion number. Propane was found to displace acetaldehyde from the adsorbed state. The outlet concentration profiles of propane in the binary mixtures tend to become more diffuse than the corresponding concentration profiles of the one-component experiments. Similar features were observed with mixtures of acetylene and ethane; however, the displacement of acetylene by ethane is less pronounced

Molecular simulation of hierarchical structures in bent-core nematics

The structure of nematic liquid crystals formed by bent-core mesogens (BCMs) is studied in the context of Monte Carlo simulations of a simple molecular model that captures the symmetry, shape and flexibility of achiral BCMs. The results indicate the formation of (i) clusters exhibiting local smectic order, orthogonal or tilted, with strong in-layer polar correlations and anti-ferroelectric juxtaposition of successive layers and (ii) large homochiral domains through the helical arrangement of the tilted smectic clusters, whilst the orthogonal clusters produce achiral (untwisted) nematic states.Comment: 14 pages, 2 figure

Tilt order parameters, polarity and inversion phenomena in smectic liquid crystals

The order parameters for the phenomenological description of the smectic-{\it A} to smectic-{\it C} phase transition are formulated on the basis of molecular symmetry and structure. It is shown that, unless the long molecular axis is an axis of two-fold or higher rotational symmetry, the ordering of the molecules in the smectic-{\it C} phase gives rise to more than one tilt order parameter and to one or more polar order parameters. The latter describe the indigenous polarity of the smectic-{\it C} phase, which is not related to molecular chirality but underlies the appearance of spontaneous polarisation in chiral smectics. A phenomenological theory of the phase transition is formulated by means of a Landau expansion in two tilt order parameters (primary and secondary) and an indigenous polarity order parameter. The coupling among these order parameters determines the possibility of sign inversions in the temperature dependence of the spontaneous polarisation and of the helical pitch observed experimentally for some chiral smectic-{\it $C^{\ast}$} materials. The molecular interpretation of the inversion phenomena is examined in the light of the new formulation.Comment: 12 pages, 5 figures, RevTe

Symmetries and alignment of biaxial nematic liquid crystals

The possible symmetries of the biaxial nematic phase are examined against the implications of the presently available experimental results. Contrary to the widespread notion that biaxial nematics have orthorhombic symmetry, our study shows that a monoclinic ($C_{2h}$) symmetry is more likely to be the case for the recently observed phase biaxiality in thermotropic bent-core and calamitc tetrapode nematic systems. The methodology for differentiating between the possible symmetries of the biaxial nematic phase by NMR and by IR spectroscopy measurements is presented in detail. The manifestations of the different symmetries on the alignment of the biaxial phase are identified and their implications on the measurement and quantification of biaxiality as well as on the potential use of biaxial nematic liquid crystals in electro-optic applications are discussed.Comment: 24 pages, 4 figure

Flexoelectricity and piezoelectricity - reason for rich variety of phases in antiferroelectric liquid crystals

The free energy of antiferroelectric liquid crystal which takes into account polar order explicitly is presented. Steric, van der Waals, piezoelectric and flexoelectric interactions to the nearest layers and dipolar electrostatic interactions to the nearest and to the next nearest layers induce indirect tilt interactions with chiral and achiral properties, which extend to the third and to the fourth nearest layers. Chiral indirect interactions between tilts can be large and induce helicoidal modulations even in systems with negligible chiral van der Waals interactions. If indirect chiral interactions compete with chiral van der Waals interactions, the helix unwinding is possible. Although strength of microscopic interactions change monotonically with decreasing temperature, effective interlayer interactions change nonmonotonically and give rise to nonmonotouous change of modulation period through various phases. Increased enatiomeric excess i.e. increased chirality changes the phase sequence.Comment: 4 pages, 1 figur

Resistivity Measurements on Aligned Amphiphilic Liquid Crystalline States

[[abstract]]We measured the resistivity of a ternary liquid mixture consisting of decylammoniumchloride, ammoniumchloride and water (45:5:50 wt%). The mixture forms a nematic phase between 41°C and 61°C; below 41°C a neat soap, and above 61°C an isotropic micellar solution. The resistivity decreases with increasing temperature. In the nematic and in the neat soap phases the resistivity is anisotropic, and it is higher for currents parallel to the director. The anisotropy increases strongly with decreasing temperature, due to a much stronger temperature dependence of the resistivity parallel to the director. The changes accompanying the phase transitions are small. The surprisingly small change of the resistivity parallel to the director at the nematic to neat soap transition indicates that the lamellae in the neat soap contain a large number of defects.[[notice]]補正完畢[[journaltype]]國外[[booktype]]紙本[[countrycodes]]US

AN EXTENSION OF THE LENNARD-JONES AND DEVONSHIRE MODEL TO LIQUID CRYSTALLINE PHASES

Une théorie à pression constante sur la fusion est présentée. Cette théorie prédit une phase caractérisée par un ordre translationnel dans une dimension. Des théories semblables ont été déjà développées par un réseau incompressible. Ce modèle, qui est une extension de celui présenté par Lennard-Jones et Devonshire, utilise un double réseau associé à deux réseaux conjugués, ce qui donne deux modes de fusion. Le premier correspond à la fusion dans les plans, le second à la fusion smectique. La distinction entre les deux modes est attribuée à l'ordre orientationnel à large distance. Le dernier n'est pas inclus directement dans le modèle statistique. Un terme quadratique représentant l'ordre orientationnel est ajouté à l'expression de l'énergie libre. Les valeurs du parametre d'ordre nématique sont obtenues à partir d'une équation de self-consistance. En utilisant les facteurs de compressibilité tabulés on obtient les isothermes pour discuter les transitions de phase cristal-nématique et smectique-nématique.A constant pressure theory of melting is presented which predicts a phase characterized by translational order in one direction. Similar theories have been already developed for an incompressible lattice. The present model, which is an extension of the one developed by Lennard-Jones and Devonshire, uses a twin lattice, along with the conjugate lattices, and hence allows for two modes of melting. One mode corresponds to the melting within the planes, the second represents the smectic melting. The distinction between the two modes is attributed to the long-range orientational order. The latter is not included directly in the statistical model ; instead, a quadratic term representing the orientational order is added to the expression for the free energy. The values of the nematic order parameter are derived from a separate self-consistency equation. Using tabulated compressibility factors we obtain the isotherms, which are used to discuss the crystal to smectic and smectic to nematic phase transitions