Differential Calorimetry Research Articles

Thermotropic Liquid Crystalline Dimers with Varying Alkoxy Terminal Chain Length

We have design and synthesized of homologous Series I dimers and to study the effect of molecular structure variation and change in alkoxy terminal chain length (n = 6, 7, 8) on mesomorphic properties of liquid crystals. Explore further understanding of the structure-property relationship of liquid crystal homologous Seriesl dimers having varying alkoxy terminal chain length. It was found that the decrease in crystalline phase, smectic C and nematic phase transition temperatures with increasing terminal alkoxy chain length. The molecular structures of the Seriesl dimer were characterized by Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy. Their mesomorphic properties were investigated by differential scannning calorimetry (DSC) and on the hot-stage of a polarizing microscope (POM).

Spin crossover star-shaped metallomesogens of iron(II).

Three new types of spin crossover (SCO) metallomesogens of Fe(II) based on symmetric tripod ligands and their magnetic and structural properties are reported here. These were obtained by condensation of tris(2-aminoethyl)amin (tren) with the aldehyde derived from 3-alkoxy-6-methylpyridine (mpyN, N (number of carbon atoms in n-alkyl chains) = 8, 18), 1-alkyl-1H-imidazole (imN, N = 4, 16, 18, 20, 22), or 1-alkyl-1H-benzimidazole (bimN, N = 6, 14, 16, 18, 20). A complex derived from 1-octadecyl-1H-naphtho[2,3-d]imidazole (nim18) retains the high spin state at any temperature. Single crystals of the short-chain complexes were investigated by a combination of X-ray crystallography, magnetic measurements and Mössbauer spectroscopy. Generally, in comparison with the short-chain complexes the long-chain complexes display more gradual SCO and undergo a phase transition crystal-liquid crystal that is reflected in their magnetic properties. Characterization by X-ray powder diffractometry and differential calorimetry reveal formation of a smectic mesophase upon melting.

Influence of PVD Target Power on the Age Hardening Behaviour of Al-4Zr Micro Sheets

High strength aluminium alloys with improved stability at elevated temperatures for micro components, which are needed e.g. in the automotive or the micro electronics industry, require new alloys and advanced production processes regarding primary shaping, heat treatment and cold forming. Their development is part of the Collaborative Research Centre 747 Micro Cold Forming of the German Research Foundation. Especially heat treatment is a necessary step in the manufacturing process chain to adjust the mechanical properties of semi-finished micro components to cold forming and finally the usage properties of aluminium micro components by precipitation hardening to increase the strength above the strain hardened level. Conventional casting techniques limit the dissolvable zirconium content in alloys to 0.28 mass-% due to Al3Zr precipitation of higher contents during slow cooling. With physical vapour deposition (PVD) by magnetron sputtering at temperatures below 50 °C it is possible to achieve alloys with a highly oversaturated solid solution and up to 3.6 mass-% of zirconium. The target power of the plasma during the magnetron sputtering process has considerable impact on the mechanical properties of the deposited Al-Zr alloys. Therefore the age hardening response of different micro sheets is evaluated by ultra micro hardness measurements (UMH), transmission electron microscopy (TEM) and differential power scanning calorimetry (DPSC).

In-vitro anti-proliferative and anti-oxidant activity of galangin, fisetin and quercetin: Role of localization and intermolecular interaction in model membrane

Flavonols are an important class of naturally occurring molecules and are known for their pharmacological activity. The activity is associated with the ability of flavonols to influence membrane-dependent processes. We have investigated the in-vitro anti-proliferative and anti-oxidant activity of galangin (GLN), fisetin (FTN) and quercetin (QTN), which possess variable number of phenolic hydroxyl groups. An attempt has been made to correlate the biological activity of these molecules with their interaction and localization in dipalmitoyl phosphatidyl choline (DPPC) bilayers, using differential dcanning calorimetry (DSC) and nuclear magnetic resonance (NMR) methods. Results indicate that GLN interacts to the alkyl chains of the lipid bilayer involving hydrophobic interactions. FTN and QTN interact with head region and sn-1-glycero region involving hydrogen bonding. Ring current induced chemical shifts of lipid protons, due to intermolecular interaction indicate that GLN acquires a parallel orientation with respect to the bilayer normal whereas FTN and QTN resume a mixed orientation. The membrane binding constants of these molecules are in the order GLN > QTN > FTN. It has been shown that the number and position of hydroxyl groups in these molecules play an important role in membrane binding and thereby in biological activity.

Experimental study of crystallization of PolyEtherEtherKetone (PEEK) over a large temperature range using a nano-calorimeter

The recently developed fast scanning differential calorimetry is used for the first time to determine the crystallization kinetics of Poly(EtherEtherKetone) (PEEK). In our experiments, crystallization is studied in isothermal conditions over a large temperature range from 170 °C to 310 °C. Two different measurement protocols were employed. Between 200 °C and 300 °C the heat flow was directly measured during isothermal crystallization. Outside this temperature range we measured the heat of fusion on heating after interrupted isothermal crystallization. We show that data can be analyzed with the Avrami approach incorporating a term describing secondary crystallization. The crystallization half-times are measured. The Avrami kinetic coefficient KAv associated with primary crystallization is evaluated from isothermal crystallization between 170 °C and 310 °C where data were not previously available. The kinetics of crystallization of PEEK has only one maximum located around 230 °C and its Avrami exponent is close to 3, suggesting instantaneous nucleation with subsequent spherical growth. The whole isothermal crystallization process is modeled in terms of Hillier's model since it takes secondary crystallization kinetics into account. Finally, it is shown that the double melting peak behavior observed after isothermal crystallization (below 260 °C) is a consequence of the reorganization process during heating.

Adsorption of Procion Blue MX-R dye from aqueous solutions by lignin chemically modified with aluminium and manganese

A macromolecule, CML, was obtained by purifying and carboxy-methylating the lignin generated from acid hydrolysis of sugarcane bagasse during bioethanol production from biomass. The CMLs complexed with Al3+ (CML-Al) and Mn2+ (CML-Mn) were utilised for the removal of a textile dye, Procion Blue MX-R (PB), from aqueous solutions. CML-Al and CML-Mn were characterised using Fourier transform infrared spectroscopy (FTIR), scanning differential calorimetry (SDC), scanning electron microscopy (SEM) and pHPZC. The established optimum pH and contact time were 2.0 and 5h, respectively. The kinetic and equilibrium data fit into the general order kinetic model and Liu isotherm model, respectively. The CML-Al and CML-Mn have respective values of maximum adsorption capacities of 73.52 and 55.16mgg−1 at 298K. Four cycles of adsorption/desorption experiments were performed attaining regenerations of up to 98.33% (CML-Al) and 98.08% (CML-Mn) from dye-loaded adsorbents, using 50% acetone+50% of 0.05molL−1 NaOH. The CML-Al removed ca. 93.97% while CML-Mn removed ca. 75.91% of simulated dye house effluents.

LOW-POWER LASER IGNITION OF ALUMINUM/METAL OXIDE NANOTHERMITES

Abstract : In this study, three different types of nanothermites, i.e., Al/CuO, MoO3, and Al/Bi2O3, were produced using the widely spread wet (i.e., isopropanol based) method. In addition to the above method, the three nanothermites were also produced using a Resodyn LabRAM mixer. A paraffin-coated spherical Al nanopowder (100 nm) was used as the fuel source, while the oxidizers were nanometric powders of CuO (40 nm), MoO3 (100 nm), and Bi2O3 (200 nm). The effect of nanothermite composition on the sensitivity for the tests of electrostatic discharge (ESD), impact, and friction was investigated. Scanning electron microscopy (SEM) was used to analyze the morphology and homogeneity of the nanothermites. Next, the nanothermites were thermally analyzed in terms of energy release, ignition temperature, and flame temperature using a thermogravimetric analysis differential and scanning calorimetry (TGA/DSC) technique. A low-power diode laser was used to evaluate the ability of different laser wavelengths (661, 532, and 445 nm) to produce the ignition energy needed for a specific thermite reaction. Low ignition delays (less than 15 ms) were obtained at approximately 300 mW laser power output for both Al/MoO3 and Al/Bi2O3 thermites. Finally, a forward-looking infrared camera was used to estimate the ignition and burning temperatures of the Al/MoO3 nanothermite.

Experimental Evaluation of Effect of Oxidative Degradation of Aqueous Monoethanolamine on Heat of CO2 Absorption, Vapor Liquid Equilibrium and CO2 Absorption Rate

Oxidative degradation produces carboxylic acids which are one of the undesirable degradation products and may have a negative impact on the CO2 separation energy of post combustion capture system. 30wt% MEA solutions mixed with carboxylic acids were regarded as a simulated solution for degraded MEA and effect of the additives on heat of CO2 absorption, equilibrium CO2 loading and CO2 absorption rate were experimentally evaluated by using a differential reaction calorimetry (DRC) apparatus, a pressurized vessel to obtain vapor liquid equilibrium (VLE) data and a gas-liquid contactor, respectively. At the range of CO2 loading from 0.0 to 0.3 mol-CO2/mol-amine, the heat of CO2 absorption of the simulated solution increased by around 10% compared to the normal MEA solution. Moreover, the changing-point of the heat of CO2 absorption of the simulated solution moved to a leaner CO2 loading compared to the normal solution. Result of a 13C-NMR analysis also indicated the change in reaction mechanism. At the absorber condition, the equilibrium CO2 loading of the simulated solution decreased by 20% in comparison with the normal solution, where it decreased by 10% at the stripper condition and therefore the cyclic CO2 loading also decreased. Both CO2 absorption rates decreased linearly but in different gradients with increasing CO2 loading. Higher pH in the simulated solution kept higher CO2 absorption rate, which is consistent with the result of pH measurement.

Nanocomposites Obtained by Montmorilonite Clay Additivation in P3 (HB-8%HV)

Modified montmorilonite additivated films of poly 3 (hydroxybutyrateco-8%-hydroxyvalerate) were formulated by solvent evaporation technique and then characterized by means of X-ray diffraction, scanning electron microscopy, atomic force microscopy and scanning differential calorimetry. A preliminary characterization using these analyses revealed the formation of nanocomposites with partially exfoliated and interlayered structures. These nanocamposites display changes in the crystalline structure of the precursor biodegradable polymer.

Confinement of Water in Hydrophobic Nanopores: Effect of the Geometry on the Energy of Intrusion

Water confinement in the hydrophobic nanopores of highly siliceous zeolite having MFI and CHA topology is investigated by high pressure manometry coupled to differential calorimetry. Surprisingly, the intrusion of water is endothermic for MFI but exothermic for CHA. This phase transition depends on the geometry of the environment in which water is confined: channels (MFI) or cavities (CHA). The energy of intrusion is mainly governed by the change in the coordination of water molecules when they are forced to enter the nanopores and to adopt a weaker, hydrogen-bonded structure. At such a nanoscale, the properties of the molecules are governed strongly by geometrical restraints. This implies that the use of classical macroscopic equations such as Laplace-Washburn will have limitations at the molecular level.

Comparison of poly(ethylene-co-acrylic acid) loaded Zn2+–montmorillonite nanocomposites and poly(ethylene-co-acrylic acid) zinc salt

Novel nanocomposite films based on poly(ethylene-co-acrylic acid) (PEAA) and zinc montmorillonite (Zn2+–MMT) were fabricated using a solution casting method with water as the solvent. Transmission electron microscopy indicated that Zn2+–MMT was distributed finely in the PEAA matrix. X-ray diffraction indicated that an ion exchange process occurs between Zn2+–MMT and PEAA. The nanocomposites filled with a low Zn2+–MMT loading increased the tensile strength and elongation at break. The significant improvements in these mechanical properties were attributed to the fine dispersion of Zn2+–MMT in the polymer and the covalent interaction between the polymer chains and Zn2+ cations. Thermogravimetric analysis and differential thermal calorimetry confirmed that PEAA formed a network through the presence of Zn2+ cations. A poly(ethylene-co-acrylic acid) zinc salt (PEAAZn) film by hot pressing was introduced for comparison. Zn2+–MMT improved the mechanical properties of the PEAA significantly compared to that of PEAAZn.

Experimental investigation and thermodynamic assessment of the Hf–Ge system

The Hf–Ge system has been studied via experiment, first-principles calculations and thermodynamic modeling. 15 annealed Hf–Ge alloys were analyzed by means of X-ray diffraction, scanning electron microscope with energy dispersive X-ray analysis, differential thermal analysis and high temperature reaction calorimetry. The major experimental results are as follows: (I) the heat contents of the Hf3Ge and HfGe2 phases were measured from 400 to 1050 °C; (II) the enthalpy of formation at 298 K for the HfGe2 phase (−67 ± 4 kJ/mol atoms) was measured; (III) the invariant reaction temperature of Liquid ↔ (Ge) + HfGe2 was determined to be at 932.6 ± 2.3 °C; and (IV) the previously reported phases HfGe and Hf3Ge2 were not found in the present experiment. In addition, the enthalpies of formation at 0 K for the Hf3Ge, Hf2Ge, Hf5Ge3, Hf5Ge4, Hf3Ge2, and HfGe2 phases were computed from first-principles calculations in order to provide the necessary energy levels for the thermodynamic properties of the binary compounds. Based on the present experimental results and first-principles calculations as well as the reliable literature data, the Hf–Ge system was modeled by using a CALPHAD approach.

Characterization of Biocatalysts Prepared with Thermomyces lanuginosus Lipase and Different Silica Precursors, Dried using Aerogel and Xerogel Techniques

The use of lipases in industrial processes can result in products with high levels of purity and at the same time reduce pollutant generation and improve both selectivity and yields. In this work, lipase from Thermomyces lanuginosus was immobilized using two different techniques. The first involves the hydrolysis/polycondensation of a silica precursor (tetramethoxysilane (TMOS)) at neutral pH and ambient temperature, and the second one uses tetraethoxysilane (TEOS) as the silica precursor, involving the hydrolysis and polycondensation of the alkoxide in appropriate solvents. After immobilization, the enzymatic preparations were dried using the aerogel and xerogel techniques and then characterized in terms of their hydrolytic activities using a titrimetric method with olive oil and by the formation of 2-phenylethyl acetate in a transesterification reaction. The morphological properties of the materials were characterized using scanning electron microscopy, measurements of the surface area and pore size and volume, thermogravimetric analysis, and exploratory differential calorimetry. The results of the work indicate that the use of different silica precursors (TEOS or TMOS) and different drying techniques (aerogel or xerogel) can significantly affect the properties of the resulting biocatalyst. Drying with supercritical CO2 provided higher enzymatic activities and pore sizes and was therefore preferable to drying, using the xerogel technique. Thermogravimetric analysis and differential scanning calorimetry analyses revealed differences in behavior between the two biocatalyst preparations due to the compounds present.

The effect of Mo6S3I6 nanowires on the thermal and mechanical properties of polyamide 12

Nanocomposites consisting of PA12 and Mo6S3I6 nanowires at concentrations of 0.5, 1.0 and 2.0wt.% were prepared by extrusion and characterised. Using electron microscopy it was confirmed that bundles of nanowires were present, whose size increases with increasing concentrations. Differential dynamic calorimetry showed that the nanowires act as a nucleating agent, increasing the crystallization rate and the overall degree of crystallinity, but at the same time the size of the crystals is decreased. As a result, Young’s modulus was increased by 15% with the addition of only 0.5wt.% of Mo6S3I6. The improved mechanical properties are attributed to changes in the polymer morphology and crystallinity.

The Vaporization Enthalpies and Vapor Pressures of Some Primary Amines of Pharmaceutical Importance by Correlation Gas Chromatography

Vapor pressures, vaporization, and sublimation enthalpies of several pharmaceuticals have been evaluated by a combination of correlation chromatography experiments, differential calorimetry measurements with existing literature values. The compounds investigated and their properties include 1-adamantylamine [ΔcrlHm(Tfus)/kJ·mol–1 = (7.3 ± 0.2); Tfus/K = (477.4 ± 0.9); ΔlgHm(298.15 K)/kJ·mol–1 = (59.9 ± 2.5); ΔcrgHm(298.15 K)/kJ·mol–1 = (∼59.9 ± 3.5); p(l)/Pa = (21 ± 1); p(cr)/Pa = (11.5 ± 2.1)]; 1-adamantyl-ethanamine, [ΔlgHm(298.15 K)/kJ·mol–1 = (68.7 ± 3.7); p(l)/Pa = (3 ± 1)]; α,α-dimethylphenethylamine [ΔlgHm(298.15 K)/kJ·mol–1 = (60.2 ± 2.6); p(l)/Pa = (35 ± 4)]; trans 2-phenylcyclopropylamine [ΔlgHm(298.15 K)/kJ·mol–1 = (60.3 ± 2.1), p(l)/Pa = (28 ± 5)]; 1-dodecanamine [ΔcrgHm(298.15 K)/kJ·mol–1 = (118.3 ± 1.8); p(cr)/Pa = 1.6 ± 0.1]; and 1-tetradecanamine [ΔcrgHm(298.15 K)/kJ·mol–1 = (134.5 ± 2.1); p(cr)/Pa = 0.12 ± 0.04]. Vapor pressure equations also derived from vapor pressure—retention time correlations as a function of temperature are reported for both standards and targets. The equations appear applicable from T/K = 298.15 to each compound’s respective boiling temperature.

Microindentation and differential scanning calorimetry of “liquid wood”

Lignin was used only as a fuel until not so long ago, but the research done in the last few years has shown that it is a substance that confers wood its strength and takes the form of granules that may be melted. Thus, lignin was used to produce a material out of which almost anything can be manufactured, from furniture, accessories, toys, plastic cases for electronic devices, and food containers of any shape, to car bodies, and which is known as “liquid wood”. Its properties recommend “liquid wood” as an alternative to all plastic products in the near future, as it is biodegradable and reusable several times, and its properties remain intact. Three types of “liquid wood” are known: Arbofill, Arboblend and Arboform. Whereas Arboform is 100% biodegradable, the other two materials are only partially biodegradable. The following types of “liquid wood” were used: Arbofill Fitchie, Arboblend V2 Nature and Arboform L, V3 Nature. The research described in this paper focuses on the study of microindentation and differential calorimetry. Also, the software package we used enabled us to read both the microhardness values, and the reduced indentation modulus and Young’s modulus.The studied test samples showed the following mean recovery values: 45.9170μm for Arbofill Fitchie, 22.2783μm for Arboblend V2 Nature and 17.7430μm for Arboform L, V3 Nature. These values are in agreement with the microhardness and modulus of elasticity values. Differential calorimetry research has shown that Arboblend V2 Nature and Arboform L, V3 Nature suffered two transformations each, one endothermal and the other exothermal, during which we measured the transformation onset and completion temperatures, as well as the temperature in the middle of the transformation process. We also measured the amount of absorbed and dissipated heat, respectively. As far as Arbofill Fitchie is concerned, the DSC diagram showed no temperature-dependent heat flow variation that could suggest a solid state transformation. We could safely state that the Arbofill Fitchie sample is thermally stable up to a temperature of 423K.

Synthesis and Photostructuring of Hybrid Photopolymers with Cinnamate and Anil Moieties by using UV Light and Femtosecond Laser Pulses

Two photosensitive methacrylates containing urea and two cinnamates (N,N–di(cinnamoyloxyethyl) N'-methacryloyloxyethyl urea, DC-MA), or urethane and saliciliden-aniline (anil) groups (methacryloyloxyethyl-2-carbamoyloxy(m-methyl, o-hydroxybenziliden)-aniline, UAn-MA) were synthesized and used besides N,N'-(methacryloxyethyldietoxy-methylsilylpropyl)-urea (UH-MA) in the preparation and photostructuring of hybrid photopolymers. Polymerization of the monomers was investigated by differential scanning photo calorimetry (photo-DSC), Fourier transform infrared (FTIR) and near-infrared (NIR) spectroscopies. The rate of photopolymerization increased upon adding UH-MA in formulation (DC-MA/UH-MA, Rp = 9.1 × 10−2 s−1; UAn-MA/UH-MA, Rp = 2.32 × 10−2 s−1), the degree of conversion being between 33 and 76%. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and optical microscopy confirmed the formation of bidimensional hybrid microstructures by using two-photon polymerization (2PP).

Improvement of the resistance to oxidation of the ecological greases by the additives

This article presents the results of research aimed at improving the oxidation stability of the ecological greases addressed toward application in machines working in the food industry. In order to improve the functional properties of grease, additives that modify the thermal stability have been added. Then, the influence of the additive on the grease resistance to the oxidation was examined. The results of tests of lubricants containing different types of additives are presented. The thermal examinations of the greases were carried out with the use of scanning differential calorimetry techniques. The lubricated properties of greases were investigated with the use of a four-ball tribotester. Based on the results, the relationships between the kind of additive, the resistance to oxidation and the lubricated properties of the grease were analysed, and the relationships between thermal and antiwear properties of grease were identified. Based on the results of this research, a new formulation of grease was proposed, which meets both the ecological needs and the working conditions in the food industry.

Influence of drying conditions on the gelling properties of the 7S and 11S soy protein fractions

Soy protein fractions rich in β-conglycinin (7S) or glycinin (11S) were freeze dried or spray dried at temperatures of 120, 150 or 180°C. The fractions were characterized for their particle size distribution, sorption isotherms and by scanning differential calorimetry. The gelling capacity of the protein fractions was studied at pH values of 3 and 7 using oscillatory measurements, mechanical properties and water holding capacity. The rheological measurements showed that viscous modulus (G″) predominated at low temperatures and the elastic modulus (G′) at high temperatures. At pH 3, the G′–G″ crossover occurred at lower temperatures when compared to pH 7. This behaviour was more accentuated for the 11S fractions due to its capacity to form stronger gels. An increase of drying temperature led to a displacement of the gel point to higher temperatures and decreased the elasticity modulus or gelling capacity of protein fractions. These results were confirmed by the mechanical properties, since at higher temperatures the gels were more fragile and brittle, especially when formed at pH 7.

Preparation of Anhydrous Magnesium Chloride from Ammonium Carnallite

High-purity anhydrous magnesium chloride was prepared by using ammonium carnallite as starting material and alumina as covering agent. X-ray diffraction (XRD) analysis and thermogravimetric analysis and differential calorimetry analysis (TG-DSC) analysis were employed to characterize the process. The mechanism involved in the process was proposed and discussed. The factors affecting the purity of anhydrous magnesium chloride were investigated. The results reveal that the mass fraction of magnesia in anhydrous magnesium chloride could reach 0.08% under the optimum conditions: alumina with the thickness of 1.3 cm was put on top of dehydrated ammonium chloride (NH4Cl · MgCl2 · 1.2H2O), and then the sample was maintained at 450°C for 1.5 h. After that, the sample was calcined at 700°C for 1 h.