Quantitative analysis of the x-ray diffraction intensities of undulated smectic phases in bent-core liquid crystals (original) (raw)
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Occurrence of Five Different Orthogonal Smectic Phases in a Bent-Core (BC) Liquid Crystal
Molecular Crystals and Liquid Crystals, 2015
Five orthogonal smectic phases (Sm-A, Sm-A b , Sm-AP R , Sm-AP AR , and Sm-AP A) were observed in a 4-cyanoresorcinol bisbenzoate with two terephthalate-based wings achiral bent-core (BC) compound. The phase behavior was investigated by polarising optical microscopy, second harmonic electro-optic response (EO 2) and dielectric spectroscopy. The field dependent biaxiality of polar and non-polar Sm-A phases was studied. It is obviously of enormous scientific significance and practical interest to find five different orthogonal smectic phases in a low molecular weight bent-core (BC) compound at relatively low temperatures.
The Journal of Physical Chemistry B, 2009
X-ray diffraction is one of the most definitive methods to determine the structure of condensed matter phases, and it has been applied to unequivocally infer the structures of conventional calamitic and lyotropic liquid crystals. With the advent of bent-core and tetrapodic mesogens and the discovery of the biaxial nematic phase in them, the experimental results require more careful interpretation and analysis. Here, we present ab-initio calculations of X-ray diffraction patterns in the isotropic, uniaxial nematic, and biaxial nematic phases of bent-core mesogens. A simple Meier-Saupe-like molecular distribution function is employed to describe both aligned and unaligned mesophases. The distribution function is decomposed into two, polar and azimuthal, distribution functions to calculate the effect of the evolution of uniaxial and biaxial nematic orientational order. The calculations provide satisfactory semiquantitative interpretations of experimental results. The calculations presented here should provide a pathway to more refined and quantitative analysis of X-ray diffraction data from the biaxial nematic phase.
Microscopic ordering in smectic phases of liquid crystals
Journal de Physique, 1990
2014 On a étudié par spectroscopie d'absorption infrarouge l'ordre orientationel dans les phases smectiques d'un matériau cristal liquide ferroélectrique, le décyloxy-4-thiobenzoate de [(2S, 3S)-chloro-2-méthyl-3-pentanoyloxy]-4'-phényle, en abrégé 10.S.C1Isoleu. Deux types d'échantillons orientés, l'un homéotrope, l'autre en configuration Clark-Lagerwall, ont été préparés et plusieurs bandes intenses en infrarouge, caractéristiques des différentes parties et orientations des molécules, ont été choisies. Les résultats montrent que l'inclinaison des parties centrales (c0153urs) des molécules varie très peu de la phase SA à la phase S*C, ce qui implique que les c0153urs des molécules sont déjà inclinés dans la phase SA. Leurs axes, qui sont désordonnés sur un cône dans la phase SA, s'alignent mais restent sur ce cône quand on passe en phase S*Cen abaissant la température. Ce modèle est en accord avec quelques résultats antérieurs. Abstract. 2014 Orientational order in smectic phases of a ferroelectric liquid-crystalline material 4'-(2S, 3S)-2"-chloro-3"-methylpentanoyloxyphenyl-4-decyloxy thiobenzoate, abbreviated 10.S.C1Isoleu, was examined by IR absorption spectroscopy. Oriented samples were prepared in both bookshelf and homeotropic alignment geometry. Several stronger IR vibrations were selected characterizing different parts and orientations of the molecules. Results show that the molecular tilt of the core
Crystals
We present the synthesis and mesomorphic properties of the new series of bent-core liquid crystals based on 3-hydroxybenzoic acid bearing a lateral substituent in the apex position. Four different substituents of various sizes and electronic properties have been used. We have found that only compounds substituted with fluorine are mesogenic and exhibit one mesophase, whose type differs when prolonging the terminal alkyl chain. For homologues with shorter alkyl chains (octyl, decyl), a columnar B1-type of a mesophase was observed, while materials with longer terminal chains (dodecyl, tetradecyl) exhibited a switchable lamellar SmCAPA phase. Calorimetric measurements, texture observations under a polarizing microscope were performed and electro-optical properties studied. Additionally, dielectric measurements were realized to characterize the molecular dynamics in the SmCAPA phase. All mesogenic compounds were further studied by X-ray measurements to confirm phase identification and o...
X-ray studies of the phases and phase transitions of liquid crystals
Acta Crystallographica Section A Foundations of Crystallography, 2005
A short review is given of recent X-ray diffraction studies of the phases and phase transitions of thermotropic liquid crystals. The areas covered are twistgrain-boundary phases, antiferroelectric phases studied with resonant X-ray diffraction and smectic phases within gel structures. In all areas, X-ray diffraction has played a key role. Nonetheless, open questions remain: the nature of the smectic C variant of the twist-grain-boundary phase, the origin of antiferroelectric phases, and whether novel Bragg glass states exist for smectic A gel samples.
Optically isotropic liquid-crystal phase of bent-core molecules with polar nanostructure
Physical Review E, 2005
We found that the optically isotropic (I M ) mesophase observed recently below the nematic phase of the bent core liquid crystal, 4-chlororesorcinol bis[4-(4-ndodecyloxybenzoyloxy)benzoate], shows ferroelectric-type switching. Polarizing microscopic, electric current, dielectric, and dynamic light scattering studies lead us to propose that the I M phase is composed of interconnected orthoconic racemic smectic (SmC a P F ) nano-domains with random layer orientations. Near the nematic phase, where the polarization can be saturated by electric fields, the system responds in a fashion analogous to the granular structure of a magnetic spin glass -in particular, we observed that the relaxation back to the non-poled structure follows a similar, inverse logarithmic rule.
A novel smectic liquid crystalline phase exhibited by W-shaped molecules
Journal of Materials Chemistry, 2003
A novel smectic phase has been discovered in the W-shaped molecular system of N,N'-bis[2-hydroxy-5-(4'-ntetradecylphenylazo)benzylidene]-4-nitro-1,3-phenylenediamine. On slowly cooling this material from the isotropic phase, fine filaments of a chiral nature appear. When they cover the whole surface, schlieren-like textures with two-brush defects are observed. In the texture, fine stripes formed by the filaments exist, which represent an orientational map. Each filament in a specific region has its own chiral character and forms chiral domains, as identified by uncrossed polarizers. According to X-ray analysis, a layer structure with a periodicity of the molecular length is clearly seen. Several diffuse but distinct wide-angle diffraction peaks are observed in the smectic phase and become sharp in the lower-temperature crystalline phases. Based on these experimental results, we can conclude the existence of a new phase with a chiral nature.
Unusual Sequences of Tilted Smectic Phases in Liquid Crystals of Bent-Shape Molecules
Physical Review Letters, 2002
The first theoretical description of the experimentally often-observed isotropic-polar smectic phase transitions of symmetric and asymmetric bent-shape molecules is presented. The isotropic-tilted polar smectic phase transition requires a coupling among three types of ordering processes: polar packing, director tilt, and layer ordering. For explaining the unusual triclinic-monoclinic phase transition with the lower symmetry phase at higher temperature, observed in fluoro-containing compounds recently, a mechanism is proposed in which the layer ordering triggers the simultaneous onset of the tilt and polar order.
Structural Investigations on Smectic Blue Phases
Physical Review Letters, 2001
Smectic blue phases (BP Sm) are thermotropic liquid crystalline phases which exhibit both threedimensional orientational order, such as classical blue phases, and smectic positional order. BP Sm appear as the three-dimensional counterpart of twist grain boundary phases. X-ray scattering and optical polarizing microscopy provide information on the hexagonal and cubic symmetries of these new phases.