Investigation of the structure and mechanisms of thermal motion in nanostructured undecylenic acid

Abstract

We have compared the structure, phase transitions and the thermal motion mechanisms of the undecylenic acid in bulk and inside a porous matrix using powder X-ray diffraction, calorimetry and IR-spectroscopy methods. The matrix used was a porous silicon with cylindrical pores (D?=?20?nm). The interaction between the walls of the porous silicon and the nanocrystals of the undecylenic acid results in a crystalline structure, which is significantly different from the structure of bulk undecylenic acid. A phase transition in the wall-adjacent layer of the undecylenic acid nanocrystals was shown to take place. The solid-state phase transition temperatures, as well as the melting point, were shown to be lower for nanocrystals. Topological soliton motion mechanism was suggested to explain the thermal motion of the undecylenic acid molecules in the rotator phase.     

Phase Diagram and Dielectric Studies in Hydrogen-Bonded Liquid Crystal System

The thermal and dielectric behaviors of mixtures were investigated for systems of p-n-hexyloxybenzoic acid (6OBA) and p-n-octyloxybenzoic acid (8OBA) by differential scanning calorimetry, polarized optical microscopy, and dielectric measurements. The T-X phase diagram was obtained for this system. Eutectic composition was calculated and received experimentally. Enthalpies of mixing were calculated to describe phase transitions physically. All mixtures show enantiotropic smectic and nematic phases. Dielectric permittivity has higher value for the mixture with fractional proportion of 30 to 70% mol for 8OBA than that for initial acid. It is assumed that co-crystallization of initial compound occurs when the ratio of components is close to equimolar ratio.     

New Mesogenic Compounds Exhibiting a Thermotropic Optically Isotropic Phase

Abstract

The only two series of carboxylic acids, 3-nitro- or 3-cyano-4-alkoxybiphenyl-4′-carboxylic acid, are known to exhibit the optically isotropic phase (S_D). Now we synthesised 4-(branched alkoxy)-anilinebenzylidene-4′-carboxylic acid series, all being racemic, and investigated their mesophase properties by means of DSC, optical microscopy and X-ray measurement. As a result, some branched azomethine derivatives were found to form a S_D phase. We also synthesised cinnamic acid derivatives with branched alkoxy tail that were turned out to exhibit either S_D phase or hexagonal columnar phase. We tried biphenyl or azobenzene core analogues which were found to produce a highly ordered smectic phase or no mesophase, respectively. At this stage, we suppose it plays an important role that the branch is introduced into the terminal chain and a certain dipole moment is located within the mesogenic core. These factors may allow the peculiar molecular packing that causes an optically isotropic property.     

Structural Phase Transition of an Intercalation Compound Mn1/4NbS2

Abstract

A structural phase transition of an intercalation compound Mn_1/4NbS₂ has been investigated by X-ray diffraction at high temperatures. The lattice parameter c exhibited a discontinuous change at 640K. The superlattice reflections observed below 640K disappeared suddenly above 640K. The phase transition at 640K took an aspect of the first-order phase transition. The precise structure analyses were performed at various temperatures above and below the phase-transition temperature. It was revealed that Mn atoms were arranged in disorder in the high-temperature phase, while the Mn atoms were ordered forming the 2a ₀ × 2a ₀ × c ₀ superlattice in the low-temperature phase. The Nb and S atoms around the ordered Mn atoms slightly shifted from the high-symmetry position in the low-temperature phase. The order parameters were the degree of order of the Mn atoms and the degree of displacement of the Nb and S atoms.     

Conoscopic image of a biaxial nematic phase in a sodium decyl sulfate – decanol – D2O mixture

ABSTRACT

The nematic phases of a lyotropic system NadS/ decanol/ heavy water are investigated using optical conoscopy and image processing. The phase diagram obtained from these lyotropic materials predicts the occurrence of a direct phase transition, which does not present the biaxial nematic phase, between the discotic (N_D) and calamitic (N_C) nematic phases. A biaxial nematic (N_B) phase is optically characterized and confirmed through conoscopic image, inside the biaxial range, between the two uniaxial nematic phases. Also, their respective transition points are determined by means of image processing. The N_B phase observed here is discussed as part of the nature of the micellar configuration of lyotropic materials which exhibit uniaxial nematic phases.     

Crystal structure,thermal analysis,and IR spectroscopic investigation of bis(2-amino-6-methyl) pyridinium sulfate

Synthesis, crystal structure refinement, phase transitions studied by thermal analysis, and IR spectroscopic investigation of 2C₆H₉N₂ < eqid2 > ⋅SO₄²⁻ are reported. The title compound crystallizes in the monoclinic space group C2/c (no. 15) with a = 10.5068(4) Å, b = 10.2225(5) Å, c = 14.0422(7) Å, and β = 104.489(3)^∘. A crystal packing diagram shows layers built by all the components of the structure and centered by planes z = 1/4 and 3/4. The pyridine substituents stack forming channels parallel to the c direction with dimensions of 4.163(1) Å and 5.148(4) Å. Thermal analysis shows that the anhydrous compound possesses an irreversible weak phase transition.     

Foreword

Abstract

We have synthesized very thin nanosheets (NSs) of metal-organic frameworks (MOFs) in sandwich-like reaction fields (SRFs) inside the bilayers of a hyperswollen lyotropic lamellar (HL) phase. The obtained samples were characterized by means of infrared spectroscopy, atomic force microscopy, transmission electron microscopy and X-ray diffraction measurements. The thickness and horizontal width of the MOF-NSs obtained from the synthesis in the SRFs in the HL phase are a few nanometres and several hundreds of nanometres, respectively. The accumulation and reaction of ingredients in the highly separated bilayers in the HL phase should result in a dilute aqueous suspension of very thin MOF-NSs.     

Synthesis and Mesomorphic Properties of New T- Shaped Dimesogens

Abstract

Several new T- shaped liquid crystalline dimesogenic compounds were synthesized and their LC properties were characterized. These T-shaped dimesogens consist of substituted fluorene and substituted biphenyl units connected by flexible spacer units of varying lengths. The compounds were characterized for their liquid crystallinity by differential scanning calorimetry (DSC) and polarizing microscopy. All the compounds were found to exhibit enantiotropic nematic phase.     

Light Interference Study of Superionic Transition in Synthetic Metal—Solid Electrolyte Hybrid (BEDT-TTF)3AgxI8

Abstract

First order phase transition at 163–172 K is found in the (BEDT-TTF)₃Ag_xI₈ compound in close vicinity to the temperature range of superionic conductivity. This observation indicates formation of the mobile silver ions in the salt as a consequence of sublattice melting.     

Electrically tunable vector vortex coronagraphs based on liquid-crystal geometric phase waveplates

Abstract

In the present work we attempt to demonstrate the potential advantages of inserting an electrically tunable q-plate as phase mask in the design of a vector vortex coronagraph. The possibility of electrically adjusting the operation wavelength of the phase mask, joined with highly accuracy patterning capabilities, allow to push imaging contrast as high as possible. Azimuthally selective masks can be also envisaged, based on geometric phase, allowing to enhance contrast only where this is actually needed.     

Spectroscopy of Molecualr Crystals: A Bibliography for 1975

Abstract

Our previous thermodynamical approach was reexamined to study phase transition of anion radical salts, [(C₆H₅)₃PCH₃]⁺ _{1 ? x}[(C₆H₅)₃AsCH₃]⁺ _x(TCNQ)^? ₂,(0≤x≤1). The mechanism of the phase transition of the solid solution at 1 atm pressure was confirmed to be αy [(C₆H₅)₃PCH₃]⁺ _{1 ? x}[(C₆H₅)₃AsCH₃]⁺ _x(TCNQ)^? ₂,(0≤x≤1) βy, and the volume change assoiated with the phase transition was estimated to be ΔV =-1.3 (1-x) cm³/mol.     

Twist Grain Boundary Phases in the Binary Mixtures of Smectic and Cholesteryl Compounds

Abstract

The binary mixture of Terephthal-bis-p-n-hexadecylaniline (TB16A) and cholesteryl nonanoate (CN) exhibits I - N* - TGB _A - TGB _c*- Sm A - Sm I - Sm F - Sm G - K phases in the concentration region between 95 to 98% of TB16A at higher temperature range. The 90% of TB16A exhibits I - N* - TGB _A - TGB _c - Sm A - Sm I - Sm F - K phases. The mixtures of concentration between 50 to 80% of TB16A exhibits I - Sm A - Sm I - K phases. The frustrated blue phase is also observed in the mixtures of lower concentration of TB16A in CN at higher temperature. Optical, DSC and X-ray studies were carried out for the identification of the different phases. The phase diagram of the Chen-Lubensky model in this context is discussed.     

Bifurcated-tail chiral fluorinated organosiloxane liquid crystalline materials

Abstract

The synthesis and characterization of a series of chiral fluorinated low molar mass (bifurcated tail) organosiloxane materials is presented. The mesogenic moiety is similar to that in the TSiKN65F mesogen reported by Naciri et al., which displays a de Vries-type S_A^* phase. The one parameter varied across the series reported herein is the length of the alkyl chain linking the mesogen moiety to the bifurcated siloxane tail.     

Synthesis,crystal and molecular structures of 1,8-diaza-11,14-dioxacyclohexadeca-2,7-dione and 1,10-diaza-4,7-dioxacyclohexadeca-2,9-dione

1,8-Diaza-11,14-dioxacyclohexadeca-2,7-dione (3) has been synthesized under high-pressure conditions, whereas 1,10-diaza-4,7-dioxacyclohexadeca-2,9-dione (6) has been obtained under thermal conditions. Both compounds have been investigated in the solid state and in solution by X-ray structural and NMR methods, respectively. The crystals of3 are orthorhombic, space groupPbca; the crystals of6 are triclinic, space groupP¯1. Both structures were solved by direct methods, and refined by a full-matrix, least-squares procedure giving for3 R=0.045 and for 6R=0.056 (R _w =0.065). From the NMR investigations in solution a twofold symmetry of both molecules (probably in intermediate conformations) is suggested; no such symmetry was found in crystalline state. The structure of6 exhibits a positional disorder of one O-heteroatoms with the population ratio 0.510.49. The arrangement of the macroring with respect to the carbonyl groups was found to betransoid in3 andcisoid in6.     

Physical Properties of Vanadium Oxide Bronzes β-A0.33V2O5 (A = Ca and Sr)

Abstract

The vanadium bronzes.β-A_0.33V₂O₅(A= Ca and Sr) have been synthesized, and their electromagnetic properties investigated. They show phase transitions at 150K and 170K, respectively, accompanying with anomalies in the magnetic susceptibility and resistivity curves. These transitions are of charge order type. Below the transition temperature the magnetic susceptibility showed low dimensional behavior in both compounds, especially spin gap behavior in Sr_0.33V₂O₅. Such behavior is closely related to the crystal structure characteristic of the vanadium β-bronzes and a manner of ordering for magnetic V⁴⁺ ions at the transition.     

Synthesis,structure, and mesomorphism of novel liquid crystalline acrylate monomers and polymers

A series of novel liquid crystalline monomers (M₁?M₈) and side chain polymers base polyacrylate backbone were synthesized. The chemical structures were characterized by FT-IR and ¹H-NMR spectra. The mesomorphism and thermal behavior was investigated by polarizing optical microscopy, differential scanning calorimetry, and thermogravimetric analysis. The relationships of structure and mesomorphism are discussed in detail. The eight monomers and their corresponding polymers all show enantiotropic nematic phase. With increasing the spacer length or flexibility of the terminal group, the melting temperature (T_m) and isotropic temperature (T_i) of the corresponding monomers and polymers all decreased. However, with increasing the rigidity of the mesogenic core, T_m and T_i of the corresponding monomers and polymers all increased. TGA showed that all the polymers obtained in this study had excellent thermal stability.     

Lithium Transport Through Sputter Deposited Lithium Cobalt Dioxide Thin Film Electrode

Abstract

Lithium transport through lithium cobalt dioxide thin film electrode prepared by rf-magnetron sputtering was investigated in IM solution of LiClO₄ in propylene carbonate using cyclic voltammetry, galvanostatic intermittent titration technique (GITT) and potentiostatic current transient technique. The cathodic and anodic current transients exhibited the non-Fickian behaviour of lithium transport when the applied potential steps encountered potential plateaus near 3.91 V _Li/Li+' determined from GITT. It is suggested that the occurrence of this abnormal behaviour during lithium intercalation and deintercalation is accompanied by a ‘diffusion-controlled’ α/β phase transformation and ‘cell-impedance-controlled’ phase transformation, respectively. Lithium transport through the electrode comprising two phases of α and β has been theoretically considered by a numerical analysis of the phase transformation.     

High resolution neutron and X‐ray diffraction studies as a function of temperature and electric field of the ferroelectric phase transition of RDP

Neutron and high resolution X‐ray diffraction investigations on perfect single crystals of RbH₂PO₄ (RDP), a hydrogen bonded ferroelectric of KDP type are reported. The results of crystal structure analysis from diffraction data, below and above the paraelectric ‐ ferroelectric phase transition, support a disorder ‐ order character of [PO₄H₂]^‐‐groups. The tetragonal symmetry of the paraelectric phase with the double well potential of the hydrogen atoms obtained by diffraction, results simply from a time‐space average of orthorhombic symmetry. According to the group ‐ subgroup relation between the tetragonal space group I42d and the orthorhombic Fdd2 a short range order of ferroelectric clusters in the tetragonal phase is observed. With decreasing temperature the ferroelectric clusters increase and the long range interaction between their local polarisation vectors leads to the formation of lamellar ferroelectric domains with alternating polarisation directions at T_C = 147 K. From the high resolution X‐ray data it is concluded that below T_C the ferroelastic strain in the (a,b)‐plane leads to micro‐angle grain boundaries at the domain walls. The tilt angle is enhanced by an applied electric field parallel to the ferroelectric axis. The resulting dislocations at the domain walls persist in the paraelectric phase leading to a memory effect for the arrangement of twin lamellae. With increased electric field the phase transition temperature T_C is decreased. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

ELECTRIC FIELD-INDUCED DIRECTOR ORIENTATION OF SMECTIC-A DOMAINS IN AN ISOTROPIC PHASE

Abstract

Electric field-induced director orientation of smeetic-A phase in an isotropic phase has been studied with a polarizing microscope using the binary mixture of octyloxycyanobiphenyl and dodecyl alcohol. Electric field is applied to the samples in which spherical smectic-A domains with and without defects in an isotropic phase are observed. Field-induced orientation of smectic-A director is observed for spherical smectic-A domains with defects but not observed for those without defects below electric field strength of 1.0 V/μm, indicating that the presence of defects facilitates the director orientation. The threshold field for the smectic-A director orientation varies from smectic-A domain to domain, suggesting that the threshold field is dependent on the structure of defects.     

Influence of the temperature and the oxygen partial pressure on the phase formation in the system Cu – Fe – O

Copper iron oxides, Cu_1‐xFe_2+xO₄ (0 ≤ x ≤ 0.5), have been synthesized by thermal oxidation of copper ‐ iron mixtures. In this process, the phase formation and the phase stability were investigated as function of the temperature (800°C – 1200°C) and the oxygen partial pressure (1.013 x 10¹ – 1.013 x 10⁵ Pa). The phase formation starts with the reaction of the metallic components to simple oxides (Fe₃O₄, Fe₂O₃, CuO). From these simple oxides, the formation of complex oxides requires a minimum temperature of 800°C. The synthesis of single phase spinel compounds Cu²⁺_1‐2x Cu¹⁺_xFe_2+xO_4±δ is realized for 0.1 ≤ x ≤ 0.5, using specific temperature – p(O₂) – conditions for a given value of x. Remarkably, to achieve our goal, we found that the increase of x implies that of the reaction temperature and/or a decrease of the p(O₂) in the reaction gas stream. Besides, a single phase spinel CuFe₂O₄ does not exist in the temperature / p(O₂)‐field investigated. Using the results of XRD ‐ phase analysis, T ‐ p(O₂) – x – diagrams were constructed. These diagrams allow the prediction of phase compositions expected for different synthesis conditions. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)