Smectic Crystal Phases Research Articles

Diastereomeric Effect on Bulk Photovoltaic Property and Polarized Electroluminescence in Ferroelectric Liquid Crystals Containing an Extended π-Conjugated Unit

Abstract We synthesized two diastereomers comprising the same π-conjugated unit. One diastereomer exhibited a smectic crystal phase in which the chromophores tilted 45 degrees from the layer normal and macroscopic polarization was induced by a DC bias application in a cooling process from the high temperature phase to the smectic crystal phase. The other diastereomer exhibited a smectic crystal phase in which the chromophores were parallel to the layer normal and macroscopic polarization was not induced. The bulk photovoltaic effect and polarization-induced electroluminescence were observed only in the polarized smectic crystal phase in which the chromophores tilted from the layer normal. In the bulk photovoltaic effect in the tilted smectic crystal phase doped with fullerene derivative, the open circuit voltage and short circuit current were 1.03 V and 100 µAcm−2 for white light illumination (20 mWcm−2), respectively. In the polarization-induced electroluminescence in the tilted smectic crystal phase, linearly polarized emission with the dichroic ratio exceeding 10 was obtained and the axis of the linearly polarized emission could be rotated 90 degrees by an inversion of a DC bias of poling treatment.

High open-circuit voltage under the bulk photovoltaic effect for the chiral smectic crystal phase of a double chiral ferroelectric liquid crystal doped with a fullerene derivative

A bulk photovoltaic effect was studied in a chiral smectic crystal phase of a bisfluorophenylterthiophene derivative bearing two lactate moieties doped with a fullerene derivative.

Viscoelastic hydrodynamics and holography

We formulate the theory of nonlinear viscoelastic hydrodynamics of anisotropic crystals in terms of dynamical Goldstone scalars of spontaneously broken translational symmetries, under the assumption of homogeneous lattices and absence of plastic deformations. We reformulate classical elasticity effective field theory using surface calculus in which the Goldstone scalars naturally define the position of higher-dimensional crystal cores, covering both elastic and smectic crystal phases. We systematically incorporate all dissipative effects in viscoelastic hydrodynamics at first order in a long-wavelength expansion and study the resulting rheology equations. In the process, we find the necessary conditions for equilibrium states of viscoelastic materials. In the linear regime and for isotropic crystals, the theory includes the description of Kelvin-Voigt materials. Furthermore, we provide an entirely equivalent description of viscoelastic hydrodynamics as a novel theory of higher-form superfluids in arbitrary dimensions where the Goldstone scalars of partially broken generalised global symmetries play an essential role. An exact map between the two formulations of viscoelastic hydrodynamics is given. Finally, we study holographic models dual to both these formulations and map them one-to-one via a careful analysis of boundary conditions. We propose a new simple holographic model of viscoelastic hydrodynamics by adopting an alternative quantisation for the scalar fields.

Thermal behavior of novel catanionic cholates

In this article, we bring new insight into room temperature structure of catanionic cholates and complement their thermal behavior given by the conventional thermal techniques with the XRPD technique. The comparative study of the addition of each dodecyl chain and ammonium group is made bearing in mind the complete architecture of synthesized cholates. The examined samples are crystal smectic phases at room temperature, with proposed sandwich-type structure, promoted by cholates architecture. For most of the studied compounds, thermal behavior is characterized as formation of structural varieties and/or polymorphs as low-temperature phases and formation of high-temperature mesomorphic, lamellae-like phases. The exception is dimeric dicholate, which only forms SmA phase before its decomposition. The dependence of the isotropization temperatures, enthalpy and entropy changes, on the increasing ammonium headgroup number, points to the fact that thermal stability of these catanionics depends on the structure of cationic component that is its constituent, where cholate anion shows minor effect. The chemistry of amphiphiles, their supramolecular behavior and thermotropic affinity is at the frontier of the contemporary research and design of the new functional materials, because this is simple but effective way to control the nature and location of reactions. From that point of view, the systematic analysis of physico-chemical properties of various catanionic amphiphiles brings new findings of their chemical structure–properties relationship, therefore enabling simpler and reliable way of new materials synthesis with desired properties.

The diversity in thermal behavior of novel catanionic cholates: The dominant effect of quaternary ammonium centers

Abstract The thermal behavior of novel catanionic compounds based on cholate anion was examined. The study explains the effect of the raising dodecyl chain number, as well as of the raising headgroup number in quaternary ammonium salts on their physico-chemical properties. The examined samples are crystal smectic phases at room temperature. Their rich and diverse thermal behavior is seen through polymorphic phase transitions, thermotropic mesomorphism of smectic nature and in some cases, kinetically managed crystallization that lasts in days. The changes of the cholates keto–enol isomer balance during thermal treatment are obtained. For both groups of samples temperatures of isotropisation and the thermodynamic parameters follow polynomial regression. Introduction of the new dodecyl chain leads to more ordered structure, while implementation the new headgroup leads to advanced polymer-like structure. The obtained results demonstrate an effort for getting and controlling the regularity of the physico-chemical and thermotropic properties for new compounds by systematic changing of cationic part of the molecule. These informations could provide in the future the easiest way for selection of potentially new and targeted applicable materials.

Amphiphilic Properties of Dodecylammonium Chloride/4‐(1‐Pentylheptyl) Benzene Sodium Sulfonate Aqueous Mixtures and Study of the Catanionic Complex

AbstractSurfactants are often used in supramolecular chemistry, due to their ability to self‐organize. Surfactant molecules aggregate spontaneously and reversibly to adopt a defined intermolecular arrangement. In this work, general phase behavior, adsorption and association in aqueous mixtures of dodecylammonium chloride, DACl and sodium 4‐(1‐pentylheptyl) benzenesulfonate, NaDBS, were studied by a combination of techniques including surface tension and conductivity measurements, light scattering and optical microscopy. The strong synergistic properties of the system were brought out with the Regular Solution Theory. Various colloidal objects are observed in wide range of composition: conventional small vesicles, large giant multilamellar or multivesicular vesicles. An excess of NaDBS provides extremely large tubular and elongated multilamellar vesicles. The new catanionic 1:1 complex, dodecylammonium‐4‐(1‐pentylheptyl) benzenesulfonate, formed in the equimolar conditions is a result of intramolecular charge neutralization. The thermal properties of this solid compound were examined by thermal polarizing microscopy, differential scanning calorimetry, and X‐ray diffraction. The most probable ion‐pair amphiphilic cluster of the crystal smectic phase, at room temperature, consists of ionic groups formed in ordered layers with dodecyl chains packed into somewhat disordered layers, tilted to the layer plane.

Adiabatic scanning calorimetry study of ionic liquid crystals with highly ordered crystal smectic phases

Adiabatic scanning calorimetry was used to study four ionic liquid crystals whose phase sequences include highly ordered crystal smectic phases (crystal smectic E or T phases). The ionic liquids were based on piperidinium or morpholinium cations with long alkyl chains; the anions were tetrafluoroborate or hexafluorophosphate. High-resolution heat capacity and enthalpy data were obtained, from which the total transition heat and latent heat for the observed phase transitions were determined. All transitions displayed a non-zero latent heat and were thus found to be first order.

Polymorphism and Mesomorphism of Oligomeric Surfactants: Effect of the Degree of Oligomerization

A series of cationic oligomeric surfactants (quaternary dodecyldimethylammonium ions with two, three, or four chains connected by an ethylene spacer at the headgroup level, abbreviated as dimer, trimer, and tetramer) were synthesized and characterized. The influence of the degree of oligomerization on their polymorphic and mesomorphic properties was investigated by means of X-ray diffraction, polarizing optical microscopy, thermogravimetry, and differential scanning calorimetry. All compounds display layered arrangements with interdigitated dodecyl chains. The increase in the degree of oligomerization increases the interlayer distance and decreases the ordering in the solid phase; whereas the dimer sample is fully crystalline with well-developed 3D ordering and the trimer and tetramer crystallize as highly ordered crystal smectic phases. The number of thermal phase transitions and sequence of phases are markedly affected by the number of dodecyl chains. Anhydrous samples exhibit polymorphism and thermotropic mesomorphism of the smectic type, with the exception of the tetramer that displays only transitions at higher temperature associated with decomposition and melting. All hydrated compounds form lyotropic mesophases showing reversible phase transitions upon heating and cooling. The sequence of liquid-crystalline phases for the dimer, typical of concentrated ionic surfactant systems, comprises a hexagonal phase at lower temperatures and a smectic phase at higher temperatures. In contrast, the trimer and tetramer reveal textures of the hexagonal phase.

Pyrrolidinium Ionic Liquid Crystals with Pendant Mesogenic Groups

New ionic liquid crystals (including ionic metallomesogens) based on the pyrrolidinium core are presented. N-Methylpyrrolidine was quaternized with different mesogenic groups connected to a flexible, omega-bromosubstituted alkyl spacer. The length of the flexible alkyl spacer between the cationic head group and the rigid mesogenic group was varied. The substituted pyrrolidinium cations were combined with bromide, bis(trifluoromethylsulfonyl)imide, tetrakis(2-thenoyltrifluoroacetonato)europate(III), and tetrabromouranyl anions. The influence of the type of mesogenic unit, the lengths of the flexible spacer and terminal alkyl chain, the size of the mesogenic group, and the type of anion on the thermotropic mesomorphic behavior was investigated. Furthermore, the phase behavior was thoroughly compared with the previously reported mesomorphism of N-alkyl-N-methylpyrrolidinium salts. Low-ordered smectic A phases of the de Vries type, smectic C phases, higher-ordered smectic F/I phases, as well as crystal smectic phases (E and G, J, H, or K) were observed and investigated by polarizing optical microscopy, differential scanning calorimetry, and powder X-ray diffraction.

Structures and Phase Transformations of Asymmetric Bent Main-Chain Liquid Crystalline Polyesters

A series of new asymmetric bent main-chain liquid crystalline (LC) polyesters (BPE-Cn) were synthesized through the condensation polymerization of A−B type asymmetric α,ω-carboxylic acid−hydroxyl-terminated monomers containing different even numbers of methylene spacers (BPCA-Cn-PmOH, where n = 6, 8, and 10). Differential scanning calorimetry results showed three phase transition processes in this series of BPE-Cn samples. The phase change with the lowest transition temperature is cooling rate dependent, while the two higher temperature transitions are cooling rate independent. One-dimensional (1D) powder wide-angle X-ray diffraction (WAXD) results at different temperatures revealed that during cooling this series of polymers exhibits a low-ordered LC phase and a highly ordered smectic crystal phase before developing a crystalline phase at lower temperatures. The phase structures and symmetry were identified by 2D WAXD and selected area electron diffraction (SAED). On the basis of 2D fiber WAXD patterns, the low ordered LC phase was identified to be an anticlinically tilted SmC (SmCA) phase, which was constructed by an alternating synclinic SmC phase in each chemical repeating unit layer along the fiber drawn direction. The highly ordered smectic phase was an anticlinically tilted SmH (SmHA) phase, which was again constructed by an alternating synclinic SmH phase in neighboring layers. On the basis of the crystallographic point of view, this smectic crystal phase had an orthorhombic unit cell. The crystalline structure was determined to be an orthorhombic unit cell (KO) with Pna21 symmetry in these three polyesters. The crystalline structures and symmetry were also confirmed by SAED experiments. As the number of methylene units increased, the dimensions of the crystal structures also increased, yet they retained a zigzag conformation. A two-chain packing model of the KO phase with four chemical repeating units was proposed on the basis of the experimental diffraction patterns and qualitatively supported by simulated structural diffractions. Additionally, the phase identifications were also supported by the observation of texture changes in polarized light microscopy. Even though the zigzag molecular arrangement remains in the low ordered SmCA and the highly ordered SmHA phases which mimics the bent-core small molecules, chiral characteristics such as helical supramolecular structures are not observed due to the covalent bonding connections in this series of BPE-Cn polymers.

EPR of the first Fe(III)-containing spin-crossover metallomesogens

The low-spin (LS) to high-spin (HS) transition in two mesogenic Fe(III) complexes with alkyloxysalicyliden-N′-ethyl-N-ethylendiamine as ligands is studied by electron paramagnetic resonance (EPR). The symmetrization of the crystal field around the Fe(III) ion under first heating of a polycrystalline sample from the room temperature was observed in the spectra of HS complexes. The line narrowing (from 45 to 15 mT) under the crystal-smectic phase transition is explained by the strengthening of the intermolecular exchange interaction, as a result of the structural reorganization of layers in the smectic phase. A feature of both mesogenic spin-transition systemsis an unusual field-induced spin instability which leads to the hysteresis of the HS-LS composition. This instability is detected by EPR and magnetic susceptibility methods. The alignment of systems by magnetic field in the mesophase and a complete or partial orientational order under cooling the mesophase to the glass state are the main reason for this hysteresis. The influence of EPR-silent LS complexes reveals itself in the line broadening of HS compounds’ when the temperature is lowered from 220 K.

Side-chain polyesters derived from adipoyl chloride and α-(bis(2-hydroxyethyl)amino)-ω-(4'- methoxybiphenyl-4-oxy) alkanes

A series of polyesters derived from adipoyl chloride and α-(bis(2-hydroxy ethyl)amino)-ω-(4'-methoxybiphenyl-4-oxy)alkanes with different spacer lengths (Cn-diol, n=6,8,10) have been synthesized and characterized by NMR spectroscopy, SEC, DSC, and X-ray spectroscopy. All polyesters have a narrow distribution of molar masses (1.3–1.5), melting temperature of 55–62°C, and they melt in a narrow temperature range of 7–11°C. Although no liquid crystalline phase transitions were found, an ordered structure was observed by XRD experiments and was ascribed to a crystal smectic phase.

Small-angle X-ray diffraction study of the thermotropic and lyotropic phases of five alkyl cyclic and acyclic disaccharides: Influence of the linkage between the hydrophilic and hydrophobic moieties

We present a comparative study of the thermotropic and lyotropic phases of 5 surfactants with an aliphatic chain of 12 carbon atoms and a cyclic or acyclic sugar head with different linkages between the two moieties. These linkages can concern different chemical groups or different orientations between the head and the chain. The compounds included the α- and β-N dodecyl-D-maltosides, N-dodecylamino-1-deoxylactitol, N-dodecyl lactobionamide and N-acetyl N-dodecyl lactosylamine. The influence of the polar head (with closed- and opened-type sugars) and the linkage with the hydrocarbon chain on the phases obtained by the heating of the anhydrous compounds and after addition of water was studied by X-ray diffraction and optical microscopy. In the anhydrous state, the surfactants were either crystalline or amorphous. On heating, they went through a liquid crystal smectic phase which, in some cases, was preceded by solid-to-solid transitions. On addition of water, the sequence of phases from the micellar phase to the lamellar phase was accounted for in terms of the geometric model of Sadoc and Charvolin. However, with certain surfactants this sequence was not complete, and the domains of existence of phases were altered.

The synthesis, mesomorphism and mesophase structure of anisotropic imines and their complexes with rhenium(i)

Highly anisotropic imine ligands have been synthesised and complexed to Re(I). Two series of ligands and complexes were obtained with various chain lengths, showing smectic and nematic phases for the ligands and only a nematic phase for the complexes. The identity of the crystal smectic phase in the ligands was studied by X-ray diffraction and identified as a crystal J phase.

Phase Identification in a Series of Liquid Crystalline TPP Polyethers and Copolyethers Having Highly Ordered Mesophase Structures. 6. Structure Changes from Smectic to Columnar Phases in a Series of Copolyethers Containing Odd and Even Numbers of Methylene Units in Equal Molar Composition

A series of liquid crystalline copolyethers has been synthesized from 1-(4-hydroxy-4‘-biphenyl)-2-(4-hydroxyphenyl)propane and different α,ω-dibromoalkanes [coTPP(n/m)]. In this report, coTPPs having n = 5, 7, 9, 11 and m = 12 are studied, which represent copolyethers having both varying odd number and a fixed even number of methylene units. The compositions were fixed at an equal molar ratio (50/50). These coTPPs(n/m) show multiple phase transitions during cooling and heating in differential scanning calorimetry experiments. The undercooling dependence of these transitions is found to be small, indicating that these transitions are close to equilibrium. Although the coTPPs possess a high-temperature nematic (N) phase, the periodicity order along the chain direction is increasingly disturbed when the length of the odd-numbered methylene units decreases from n = 11 to 5. In the coTPPs(5/12, 7/12, and 9/12), wide-angle X-ray diffraction experiments at different temperatures show that, shortly after the N phase formation during cooling, the lateral molecular packing improves toward a hexagonal lattice, as evidenced by a gradual narrowing of the scattering halo. This process represents the possible existence of an exotic N phase, which serves as a precursor to the columnar (ΦH) phase. A further decrease in temperature leads to a ΦH phase having a long-range ordered, two-dimensional hexagonal lattice. In coTPP(11/12), the phase structures are categorized as highly ordered and tilted, smectic and smectic crystal phases, similar to homoTPPs, such as the smectic F (SF) and smectic crystal G (SCG) phases. An interesting observation is found for coTPP(9/12), wherein a structural change from the high-temperature ΦH phase to the low-temperature SF phase occurs. It can be proven that, upon heating, the well-defined layer structure disappears and the lateral packing remains hexagonal. The overall structural differences in this series of coTPPs between those of the columnar and highly ordered smectic phases are related to the disorders introduced into the layer structure by the dissimilarity of the methylene unit lengths in the comonomers.

Anomalous Orientation Behavior in a Series of Copoly(ester imide)s Observed by Wide-Angle X-ray Diffraction

A series of copoly(ester imide)s (CPEIs) was synthesized by the esterification of N,N‘-dodecane-1,12-diylbis(trimellitimide) to two different acetylated diols, 4,4‘-dihydroxybiphenyl and hydroquinone, in varying proportions. On the basis of their compositions, six samples are designated as CPEI(A−F), in which CPEI(A) is a homopolymer having 100% of incorporated 4,4‘-dihydroxybiphenyl and CPEI(F), a homopolymer having 100% of incorporated hydroquinone. The composition ratios of the copolymers are 80/20 (B), 60/40 (C), 40/60 (D), and 20/80 (E). Except for CPEI(F), the five CPEI(A−E)s show enantiotropic liquid crystalline behavior during cooling from the isotropic melt. In all of the samples, highly ordered smectic crystal phases are assumed in the solid state. In the course of structural identification, it has been found that CPEI(A−E)s often exhibit anomalous wide-angle X-ray diffraction (WAXD) fiber patterns: the smectic layer normal is perpendicular to the fiber direction while the (hk0) reflections exhibit maxima along the meridian. Furthermore, the degree of orientation for the (hk0) reflections is apparently much lower than that of the layer structure. Crystallographic analysis is given to provide a quantitative explanation of experimentally obtained WAXD fiber patterns.

Synthesis and properties of copper(II) and oxovanadium(IV) complexes derived from polar Schiff's bases

The synthesis and mesogenic behaviour of copper(II) and oxovanadium(IV) complexes derived from Schiff's bases substituted with polar groups and of their corresponding ligands are reported. The polar groups studied are F, CF3, CN, and CH2CN in the 3 or 4 position of the aniline moiety. The ligands exhibited smectic C, smectic A and nematic phases, whereas the complexes showed smectic A and nematic phases, and in some cases oxovanadium(IV) complexes exhibited a smectic crystal phase.

Phase diagram of ultrathin ferromagnetic films with perpendicular anisotropy.

Ultrathin ferromagnetic films with perpendicular spin anisotropy can possess an alternating up-down stripe-domain structure, with widths L\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}. Considering the two inequivalent types of stripe domains to form a single unit, this structure may be thought of as a two-dimensional smectic crystal. It is subject to a weak stripe orientation energy. With increasing temperature the domain system changes from a smectic crystal phase to an ``Ising nematic'' phase, and then to a ``tetragonal liquid'' phase. We discuss its possible phase diagrams, in (${\mathit{H}}_{\mathrm{\ensuremath{\perp}}}$, ${\mathit{H}}_{\mathrm{\ensuremath{\parallel}}}$, T) space. This sequence of phases can occur whether or not the system ultimately undergoes a spin reorientation transition to a planar phase.

Scaling properties of soft-core parallel spherocylinders near the crystal-smectic-phase transition.

By carrying out constant-pressure molecular-dynamics simulations near the melting transition from crystal to smectic liquid crystal, the characterize the scaling properties of systems composed of soft-core parallel spherocylinders. Properties at the transition have a clear dependence on the length-to-width ratio of the cylinder. These scaling properties are explained by introducing the concept of the temperature dependence of the effective core of the spherocylinders. Utilizing these scaling properties, the equations of state of systems with different anisotropy can be scaled onto one another

Overview of partial orientational and positional ordering in concentrated systems

This paper provides an overview of the static behavior of systems with partial orientational and positional ordering of the species. The understanding of the static behavior provides the foundation needed to understand the dynamic properties of such systems, which are described in more detail in other papers in this issue. More specifically, this paper provides an overview of the fact that species of different dimensions exhibit similar types of partial ordering of the species. This paper further provides an overview of liquid crystalline (LC) phases and molecules, including discussions of types of chemical structures (both rigid and semiflexible) in LC molecules (both nonpolymeric and polymeric); thermotropic and lyotropic LCs; nematic and multiple smectic LC phases; reentrant nematic LC phases; cholesteric LC phases and blue phases; smectic crystal phases; columnar phases; micelles and lamellar LC structures; LC phase transitions; LC glasses; viscosities of LC phases; and dynamic textures and patterns in LC phases.