Diguanidinium hydrogenarsenate monohydrate and its deuterated analogue vibrational, DSC and X-ray investigations

The crystal structure of diguanidinium hydrogenarsenate monohydrate has been found to belong to the P42(1)/c space group of the tetragonal system, with Z = 8, a = 17.114(2) A, c = 7.3500(10) A. In this complex, a network of hydrogen bonds links water molecules and hydrogenarsenate ions. The hydrogenarsenate ions form hydrogen-bonded chains along the crystallographic c-axis. Detailed vibrational studies have been carried out (FTIR and FT-Raman on powder samples, polarized FTIR microscope on a small single crystal at room temperature). The vibrational spectra are discussed in relation to the crystal structure. Calorimetric (DSC) studies have been performed, but no phase transition was found in the temperature range 100-350 K.     

Synthesis,crystal structure,vibrational spectra,optical properties and theoretical investigation of a two-dimensional self-assembled organic-inorganic hybrid material

Organic–inorganic hybrid material of formula (C₄H₃SC₂H₄NH₃)₂[PbI₄] was synthesized and studied by X-ray diffraction, Infrared absorption, Raman scattering, UV–Visible absorption and photoluminescence measurements. The molecule crystallizes as an organic–inorganic two-dimensional (2D) structure built up from infinite PbI₆ octahedra surrounded by organic cations. Such a structure may be regarded as quantum wells system in which the inorganic layers act as semiconductor wells and the organic cations act as insulator barriers. Room temperature IR and Raman spectra were recorded in the 520–3500 and 10–3500 cm⁻¹ frequency range, respectively. Optical absorption measurements performed on thin films of (C₄H₃SC₂H₄NH₃)₂[PbI₄] revealed three distinct bands at 2.4, 2.66 and 3.25 eV. We also report DFT calculations of the electric dipole moments (μ), polarizability (α), the static first hyperpolarizability (β) and HOMO–LUMO analysis of the title compound investigated by GAUSSIAN 09 package. The calculated static first Hyperpolarizability is equal to 11.46 × 10⁻³¹ esu.     

Effect of aromatic substitution in aniline on the properties of polyaniline

Substitution in aniline has tremendous effect in the synthesis of poly(substituted anilines) as well as in their properties. In this investigation polyaniline (PANI), poly(m-nitro aniline) (PMNA), poly(m-amino phenol) (PMAP) and poly(o-ethyl aniline) (POEA) were synthesized by oxidative polymerization under identical conditions. Different properties were measured and compared with PANI to find out the presence of electron donating -OH group, electron withdrawing -NO₂ group and less effecting ethyl group on the properties of poly(substituted anilines). It was found that presence of any type of substitution in the benzene ring of aniline increases the solubility of the resulted polymer but reduces the yield, degree of polymerization, thermal stability, electrical and thermal conductivity. The colors, bulk density, particle size, percentage of crystallinity vary considerably depending on the nature of substitution.     

Effect of the nucleating agent 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol on the γ phase content of propylene/ethylene copolymer

The influence of the concentration of a nucleating agent (NA), namely 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol (DMDBS), on the γ phase content in a propylene/ethylene copolymer was investigated by means of Differential Scanning Calorimetry (DSC), Wide-Angle X-ray Diffraction (WAXD), Small-Angle X-ray Scatter (SAXS) and Polarized Optical Microscopy (POM). It was found that the nucleated cPP showed two endothermic peaks, corresponding to the melt behaviors of α and γ crystal; both α and γ crystal forms were present in each lamella within the same spherulite; the γ phase developed on the edges of α phase lamellae rather than on the less favorable DMDBS nucleating agent; the γ content in the crystallized samples increased initially with increasing DMDBS concentration and reached a maximum, then decreased with further increment of NA concentration under the non-isothermal condition. We interpreted these results in terms of competition and deposition between α and γ crystals.     

Latent heat nano composite building materials

Heat storage for heating and cooling of buildings reduces the conventional energy consumption with a direct impact on CO₂ emissions. The goal of this study was to find the physico-chemical fundamentals for tailoring phase change material (PCM)-epoxy composites as building materials depending on phase change temperature and latent heat using the optimal geometry for each application. Thus, some nano-composite materials were prepared by mixing a PCM with large latent heats with epoxy resin and Al powder. Some polyethylene glycols of different molecular weights (1000, 1500, and 2000) were used as PCMs. Subsequently these PCM-epoxy composites were thermo-physically characterized by DSC measurements and found to be suitable for building applications due to their large latent heat, appropriate phase change temperature and good performance stability. Moreover these cross-linked three dimensional structures are able to reduce the space and costs for encapsulation.     

Stability and thermophysical properties of azithromycin dihydrate

The aim of this paper was to describe the temperature effect on the stability and the thermophysical properties of azithromycin (AZ). First, the density, the heat capacity and the solubility of original (commercial) AZ were determined. Second, the original samples were heated at 50 °C and 80 °C and their PLM, DSC, TGA and XRD data were compared to those of the original AZ. According to our results, the original AZ was a dihydrate which converted to anhydrate when heated up to 80 °C. The dehydration induced a change of crystal habit while the crystalline lattice remained unchanged.     

The crystal structure, thermal behaviour and ionic conductivity of a novel lithium gadolinium polyphosphate LiGd(PO3)4

Crystal structure and ionic conductivity of lithium gadolinium polyphosphate, LiGd(PO₃)₄, were investigated. Single crystals of the title compound have been grown by a flux technique. The structure of this novel phosphate was determined by single crystal X-ray diffraction techniques. LiGd(PO₃)₄ is isotypic with LiNd(PO₃)₄. It crystallizes in the monoclinic space group C2/c with the unit cell parameters a=16.386(2), b=7.059(3), c=9.677(2) Å, β=126.12(1)°, V=904.2(4) Å³ and Z=4. The structure refined from 967 independent reflections leads to R₁=0.0167 and wR₂=0.0458. The lattice of LiGd(PO₃)₄ is built of twisted zig-zag chains running along with the b direction and make up of PO₄ tetrahedra sharing two corners, connected to the GdO₈ and LiO₄ polyhedra by common oxygen atoms to form a three-dimensional framework. Differential and thermogravimetric thermal analysis are given. The thermal curve of this compound was recorded and interpreted in agreement with impedance measurements. The ionic conductivity has been measured on pellet of the polycrystalline powder and evaluated as a function of temperature. This phase showed the conductivity of 2×10⁻⁶ and 2×10⁻⁴ Ω⁻¹ cm⁻¹ at 682 and 951 K, respectively.     

Single crystal structure,vibrational study,and thermal behavior of a new rare earth diphosphate HYbP2O7·4H2O

A new ytterbium diphosphate: HYbP₂O₇·4H₂O was prepared via soft chemistry route from evaporation of aqueous solution. It was investigated by single crystal X-ray diffraction, vibrational spectroscopy, and thermal analysis.

The framework of the title compound consists in an assemblage of HP₂O₇ groups and [YbO₅(H₂O)₂] polyhedra, giving rise to corrugated layers stacked along the b axis at y = 1/4 and y = 3/4. Between these layers are located two uncoordinated water molecules. The cohesion of this arrangement is well ensured by a three-dimensional network of water-layer and inter-layer hydrogen bonds of different strengths. Non-coincidences are observed between the majority of the IR and Raman bands and confirm a centrosymetric structure for this compound. Thermal analysis reveals the elimination of 4.5 water molecules per formula unit in three stages between 310 K and 1100 K, which correspond to the departure of the four crystallization water molecules and the OH group. A comparative study among hydrated lanthanide monohydrogendiphosphates known in the literature is presented.     

Kinetics and hazards of thermal decomposition of methyl ethyl ketone peroxide by DSC

Differential scanning calorimetry (DSC) was applied to analyze thermal decomposition of methyl ethyl ketone peroxide (MEKPO). Thermokinetic parameters and thermal stability were evaluated. MEKPO decomposes in at least three exothermic decomposition reactions and begins to decompose at 30–32 °C. The total heat of decomposition is 1.26 ± 0.03 kJ g⁻¹. Thermal decomposition of MEKPO can be described by a model of two independent reactions: the first is decomposition of a less stable isomer of MEKPO, followed by decomposition of the main isomer, after which an exothermic reaction of the reaction products with the solvent, dimethyl phthalate. The results can be applied for emergency relief system design and for emergency rescue strategies during an upset or accident.     

High-temperature chiral nematic phase in naphthalene and cholesterol derivative liquid crystal: characterisation and dielectric relaxation study

In this article, we report the synthesis of the naphthalene and cholesterol derivative 2-(cholesterol-n-decanoate)-6-(heptyloxy benzoate) naphthalene (2CD6HBN) liquid crystal (LC) having chiral nematic (N*) mesophase. The synthesised mesophase has been characterised using polarising optical microscopy (POM) and differential scanning calorimetric (DSC) study. The presence of the rigid and less polarisable cores causes a higher N*-Iso transition temperature. The relaxation phenomenon of the present LC sample was analysed by the dielectric relaxation spectroscopic study. The dielectric properties, electrical conductivity and the relaxation time were observed as a function of the temperature. The relaxation time follows the first-order exponential decay–type equation. The properties of the LC sample have also been correlated with the structure of the compound.     

Thermal, mechanical and electrical properties of copper powder filled low-density and linear low-density polyethylene composites

Low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) with different copper contents were prepared by melt mixing. The copper powder particle distributions were found to be relatively uniform at both low and high copper contents. There was cluster formation of copper particles at higher Cu contents, as well as the formation of percolation paths of copper in the PE matrices. The DSC results show that Cu content has little influence on the melting temperatures of LDPE and LLDPE in these composites. From melting enthalpy results it seems as if copper particles act as nucleating agents, giving rise to increased crystallinities of the polyethylene. The thermal stability of the LDPE filled with Cu powder is better than that for the unfilled polymer. The LLDPE composites show better stability only at lower Cu contents. Generally, the composites show poorer mechanical properties (except Young's modulus) compared to the unfilled polymers. The thermal and electrical conductivities of the composites were higher than that of the pure polyethylene matrix for both the LDPE and LLDPE. From these results the percolation concentration was determined as 18.7 vol.% copper for both polymers.     

Synthesis and characterization of polyamides and poly(amide-imide)s derived from 2,2-bis(4-aminophenoxy) benzonitrile

A series of polyamides and poly(amide-imide)s were prepared by the direct poly-condensation of 2,2-bis(4-aminophenoxy) benzonitrile [4-APBN] with aromatic dicarboxylic acids and bis(carboxyphthalimide)s in N-methyl-2-pyrrolidone [NMP] with triphenyl phosphite and pyridine as condensing agents. The synthesis of 4-APBN involves a nucleophilic displacement reaction in dipolar aprotic solvent with the alkali metal salt of p-aminophenol and an activated aromatic dichloro compound. Bis(carboxyphthalimide)s were prepared by condensation of 4,4^′-diaminodiphenylsulfone, 3,3^′-diaminodiphenylsulfone, 4,4^′-diaminodiphenylether, 4,4^′-diaminodiphenylmethane, 3,3^′-diaminobenzophenone, and trimellitic anhydride at a 1:2 molar ratio. The inherent viscosities of the resulting polymers were found to be in the range of 0.31-0.93 dl/g and glass transition temperatures between 235 and 298 °C. All polymers were soluble in aprotic polar solvents such as dimethylsulfoxide and NMP. The results of thermogravimetry revealed that all the polymers showed no significant weight loss before 400 °C. Wide-angle X-ray diffractograms revealed that all polymers were found to be amorphous except for the polyamide derived from isophthalic acid and polyamide-imides derived from diaminodiphenylether and diaminobenzophenone based bis(carboxyphthalimide)s.     

Synthesis and properties of fluorosilicone with perfluorooctylundecyl side chains

A series of fluorosilicone (FLS) homopolymers with 4,4,5,5,6,6,7,7,8,8, 9,9,10,10,11,11,11‐heptadecafluoroundecylmethylsiloxane [? C₈F₁₇CH₂CH₂CH₂(CH₃) SiO? ; HDFUSiO] and copolymers based on dimethylsiloxane [? (CH₃)₂SiO? ] were prepared by the hydrosilylation of 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11‐heptadecafluoro‐1‐undecene (C₈F₁₇CH₂CH?CH₂) with poly(hydromethylsiloxane)s. Thermal characterization showed that the decomposition of fluoroalkyl side chains occurred at about 245 °C. Side‐chain crystallization was observed for FLSs with more than 30 mol % HDFUSiO. The refractive index decreased with increasing HDFUSiO content. The dielectric constant increased with increasing HDFUSiO content. The liquid surface tension of the FLS containing 10 mol % HDFUSiO was as low as that of the highly fluorinated FLSs. FLSs with HDFUSiO and trichlorosilylethyl side chains (Cl₃SiCH₂CH₂? ) were also prepared so that their solid surface tension (surface free energy) could be measured. The surface free energy of these FLSs decreased with increasing Cl₃SiCH₂CH₂? content, but the sliding angle of a water droplet and the contact‐angle hysteresis adversely increased. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2704–2714, 2003     

Synthesis,Structural Study and Phase Transitions Characterization by Thermal Analysis and Vibrational Spectroscopy of an Ammonium Rubidium Arsenate Tellurate

The Rb_2.42(NH₄)_0.58(HAsO₄)(H₂AsO4)·Te(OH)₆ crystals(denoted by RbNAsTe) crystallize in the monoclinic system, space group P2₁/n with the following parameters:a=1.3059(5) nm, b=0.6755(3) nm, c=1.6675(6) nm, β=94.126(4)°, Z=4 and V=1.46733(10) nm³. Thermal analyses(DSC, DTA and TG) confirm the presence of the phase transition and the temperature of the decomposition. The vibrational spectroscopy study at room temperature show the presence and the independence of anionic groups, cationic groups, and give more importance to the hydrogen bonds. Raman spectra were recorded in the temperature range of 298-503 K. The temperature dependence of the Raman line shift, intensity reduction and the half width detects the phase transitions and confirms their nature. So, the phase transition at 453 K corresponds to the superprotonic-ionic conduction phase transition, and those at 483 and 491 K correspond to the decomposition of our material.     

A high temperature superionic phase of CsSn2F5

The compound CsSn₂F₅ has been investigated over the temperature range from ambient to 545 K using differential scanning calorimetry, impedance spectroscopy and neutron powder diffraction methods. A first-order phase transition is observed from DSC measurements at 510(2) K, to a phase possessing a high ionic conductivity (σ∼2.5×10⁻² Ω⁻¹ cm⁻¹ at 520 K). The crystal structure of the high temperature superionic phase (labelled α) has been determined to be tetragonal (space group I4/mmm, a=4.2606(10) Å, c=19.739(5) Å and Z=2) in which the cations form layers perpendicular to the [001] direction, with a stacking sequence CsSnSnCsSnSn… All the anions are located in two partially occupied sites in the gap between the Cs and Sn layers, whilst the space between the Sn cations is empty, due to the orientation of the lone-pair electrons associated with the Sn²⁺. The structure of α-CsSn₂F₅ is discussed in relation to two other layered F⁻ conducting superionic phases containing Sn²⁺ cations, α-RbSn₂F₅ and α-PbSnF₄ and, to facilitate this comparison, an improved structural characterisation of the former is also presented. The wider issue of the role of lone-pair cations such as Sn²⁺ in promoting dynamic disorder within an anion substructure is also briefly addressed.     

Total luminescence intensity (TLI) offers superior early oxidation detection in unstabilised polyethylene but is no better than FT-IR for stabilised polyolefins

In an earlier study, we have shown that chemiluminescence (CL) and the total luminescence intensity (TLI) method are highly sensitive to oxidation in degradable PE. In this study, stabilised PE and PP were characterised with CL in an inert (TLI) and in an oxygen atmosphere (CL-OIT) and the results were compared to those obtained by the commonly used techniques, FT-IR (carbonyl index (CI)) and thermal analysis (DSC-OIT). PE was aged at a low temperature (80 °C) and PP was aged at temperatures between 60 and 120 °C. Non-Arrhenius behaviour was observed in the oxidation of PP. This showed the importance of aging at a low temperature to obtain realistic results. TLI and CI of stabilised PP and most of the stabilised PE gave comparable results with the same sensitivity for oxidation detection. This was in contrast to our previous results for degradable PE. However, TLI of unstabilised PE showed earlier oxidation detection than CI, which agreed with our earlier results. TLI of PE had a higher sensitivity than CL-OIT, and both TLI and CI of PP were sufficiently sensitive to detect the effect of aging at different temperatures, whereas DSC-OIT was not.     

The effect of the linear charge density of carrageenan on the ion binding investigated by differential scanning calorimetry, dc conductivity, and kHz dielectric relaxation

The effect of the linear charge density of natural polyelectrolyte, carrageenan, on the ion binding to carrageenan molecules in relation to the gelation was investigated by using the dielectric relaxation spectroscopy, dc conductivity, optical rotation, and differential scanning calorimetry (DSC). Although carrageenan is an anionic polysaccharide, carrageenan molecules in the helix state at low temperatures can bind not only cation, such as potassium and cesium, but also anion, such as iodide. The dc conductivity steeply decreases just below the coil–helix transition temperature, which indicates the binding of ion to the carrageenan molecules in the helix state due to the increase of the linear charge density compared with that in the coil state. The addition of NaI promotes the helix formation, and prevents from aggregation of helices, which was suggested by the results of the dynamic shear modulus and the DSC, and resulted in an increase of the relaxation amplitude of the lowest frequency relaxation (kHz) attributed to the fluctuation of the tightly bound counter ions along the high charge density region (helix). It is concluded that binding of iodide induces (1) the increase in the amount of tightly bound counterions to carrageenan molecules and (2) the formation of non-aggregated helix.     

Non-isothermal crystallization kinetics of exfoliated and intercalated polyethylene/montmorillonite nanocomposites prepared by in situ polymerization

Polyethylene/montmorillonite (PE/MMT) nanocomposites, one intercalated sample with higher MMT content and one exfoliated sample with lower MMT content, were prepared by in situ polymerization using MMT-supported metallocene as catalyst. Non-isothermal crystallization behaviors of these two nanocomposites were investigated and compared. The exfoliated sample exhibits higher crystallization temperature (T_c) than the neat PE, showing nucleation effect of MMT. The intercalated sample has lower T_c than the neat PE due to the confinement of MMT. It is observed that the intercalated sample has longer induction period and faster overall crystallization rate, indicating co-existence of suppression and nucleation effects in this sample. The Avrami plots show that the crystal growth of PE in the intercalated sample is two-dimensional, while it is three-dimensional in the exfoliated sample. The crystallization activation energy of the intercalated sample is slightly smaller than that of the exfoliated sample.