DSC Traces Research Articles

Electrical conductivity and phase transformations in the composite ionic conductors AgI : α-Al 2O 3 prepared via a high-pressure route

Silver ion conducting composites of the general formula xAgI : (1 − x)α-Al 2O 3, where 0.2 ≤ x ≤ 0.8 (vol fraction) were prepared using a high-pressure synthesis route ( T = 400 °C, p = 7.5 GPa). The microstructure of as-received rigid, non-brittle and dense samples was investigated by SEM. Other studies — DSC, XRD and impedance spectroscopy, were done as a function of temperature in the 20–200 °C temperature range. Close correlations were observed between the temperature dependences of the XRD patterns, the electrical conductivity and events seen on DSC traces. It was found out that the electrical conductivity at room temperature of all as-received composite materials was higher (by a factor between 7 and 100, depending on composition) than that measured after the heating–cooling cycle. This effect and other observed correlations were explained referring to the residual stress concept.

Magnetic Properties, Nanostructure, and Ordering Kinetics of Nb Additive FePtCu Films

In this study,the (FePt)94-xCu6Nbx (x=0, 2.87, 4.52, 5.67) alloy films were prepared by co-sputtering. The effects of Nb addition content and heat treatment on the microstructure and magnetic properties of the polycrystalline FePtCu films are reported. Our previous experiments showed that the ordering temperature of the (FePt)94Cu6 films reduced to 320 °C, which is much lower than that of the FePt alloy. However, the grain growth after heat treatment limited the practical application in recording media. By adding the Nb content in the (FePt)94Cu6 film, the grain sizes of the films can be adjusted from 50 to 18nm, even for the films annealed at temperature as high as 600°C. DSC traces of as-deposited disorder films at different heating rates, to evaluate the crystallization of the order phase, revealed that the addition of Nb enhanced the activation energy of ordering from 87 kJ/mol to 288 kJ/mol for the (FePt)94-xCu6Nbx (x=0 and 2.87, respectively) films. The reduction of the grain size and the corresponding increase in the activation energy of the Fe-Pt-Cu-Nb films might result from the precipitation of the Nb atoms around the ordering FePt phase. The (FePt)94-xCu6Nbx (x=2.87) film showed a coercive force of 13.4 kOe and the magnetization of 687 emu/cc.

Isothiocyanate derivatives of soybean oil triglycerides: Synthesis, characterization, and polymerization with polyols and polyamines

AbstractIn this article, a novel two step synthesis of soy oil based isothiocyanate is described. Allylicaly brominated soybean oil (ABSO) was reacted first with ammonium thiocyanate in tetrahydro furan to form allylic thiocyanates. These compounds were then converted to isothiocyanated soybean oil (ITSO) by a thermal rearrangement. Conversion was found to be 70%. The structure of the ITSO was characterized by IR and 1 H‐NMR techniques. Then ITSO was reacted with ethylene glycol, glycerol, and castor oil to produce polythiourethanes and ethylene diamine and triethylene tetra amine to produce polythioureas. Thermal properties of the products were determined by DSC and TGA techniques. DSC traces showed Tg's for ethylene glycol polythiourethane at −39 and 58°C, for glycerol polythiourethane at −39 and 126°C, for castor oil polythiourethane at −38°C and −17°C, for ethylene diamine polythiourea at −45°C, and for triethylene tetra amine poly thiourea at −39°C. Additionally, DSC analysis of polythioureas showed an endotherm at around 100°C. All of the polymers started to decompose around 200°C. Tensile properties of the polymers were determined. Polythiourethanes showed higher tensile strength and lower elongation when compared with their urea analogs. Stress at break values of the polymers were 1.2 MPa for glycerol polythiourethane, 0.6 MPa for ethylene glycol polythiourethane, 0.5 MPa for ethylene diamine polythiourea, and 0.9 MPa for triethylene tetra amine polythiourea polymers. Unfortunately, polymers synthesized showed poor solvent resistance. All polymers swelled and disintegrated in CH2Cl2 in 5 h. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Relationship between free volume properties and structure of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) membranes via various crystallization conditions

The relationship between the crystalline structure and the free volume properties within the amorphous phase of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) membranes, which were prepared via isothermal crystallization processes at various crystallization temperatures, was investigated. From the data of positron annihilation lifetime (PAL) spectroscopy over a temperature range of 25–90°C, the temperature dependence of free volume size, amount, distribution, and relative fractional free volume and thermal expansion behaviors of free volume were discussed. The existence of a rigid-amorphous fraction (RAF) which constrained long-range motions in the semi-crystalline polymer was demonstrated by DSC trace and considered to interpret the temperature dependence of those free volume properties. Based on the crystallization conditions, the effect of the crystallization rate of PHBV polymer was proposed to explain the thermal expansion coefficients of free volume size. The membranes crystallized at faster crystallization rate would accompany higher thermal expansion coefficients of free volume size and the larger free volume size at higher temperatures. Larger distribution of the free volume size and higher thermal expansivity of o-Ps lifetime dispersion (dσ/dt) of isothermally melt-crystallized membranes were observed as a result of the bimodal distribution of the lamellar periodicity, which was obtained by small-angle X-ray scattering (SAXS), and less amount of RAF than that of a cold-crystallized membrane. Conclusively, free volume size and thermal expansion of the free volume in PHBV membranes were affected by the kinetics of crystallization; comparatively, the total amount of free volume and fractional free volume were determined by the final crystallinity. The size distribution of free volume was associated with the crystalline lamellar structure which was dominated by the crystallization conditions.

Synthesis of Photoisomerizable Block Copolymers by Atom Transfer Radical Polymerization

AbstractA series of polystyrene‐block‐poly(n‐butyl methacrylate) (PS‐b‐PnBMA) diblock copolymers (di‐BCPs) with an azobenzene moiety [trans‐4‐methacryloyloxyazobenzene (MOAB)] in the PnBMA segment was prepared by atom transfer radical polymerization (ATRP). P(nBMA‐co‐MOAB) macroinitiators were prepared by activators regenerated by electron transfer (ARGET) ATRP. The MOAB was slightly more reactive than nBMA, resulting in a weak gradient fashion of copolymer. The macroinitiators were subsequently chain‐extended with styrene. Acceleration of the ATRP rate was observed in the presence of a reducing agent. P(nBMA‐co‐MOAB)‐b‐PS di‐BCPs were obtained with relatively narrow molecular weight distributions ($\overline M _{\rm w}$/$\overline M _{\rm n}$ = 1.16–1.49) and the molecular weights were in good agreement with the theoretical values. The efficiency of photoisomerization of the MOAB units was above 80%. DSC traces showed a single Tg suggesting the block copolymers were miscible before UV irradiation. After UV irradiation, the X‐ray reflectivity measurements showed the beating of two frequencies, indicating the formation of island‐hole structure.magnified image

DSC, ESR AND IR SPECTRAL STUDIES ON Li2O–WO3–B2O3 GLASS SYSTEM DOPED WITH VANADIUM IONS

With in glass forming region of Li2O–WO3–B2O3 glass system, a particular composition 40Li2O–5WO3–(55 –x) B2O3 : x V2O5 (with x ranging from 0.2 to 0.8, all are in mol.%) is chosen. The DSC traces are obtained to identify the glass transition temperature ( Tg ) and the glass forming ability of all the glass samples. The ESR and IR spectra portray the local structure of the glass system and valance states of the vanadium ions in the glass matrix. As the content of V2O5 increases up to 0.6 mol.% in the glass system, a gradual conversion of vanadium ions from V5+ state to V4+ state is observed, causing the depolymerization in the glass matrix by the transformation of several glass forming units BO4 → BO3 and WO4 → WO6 .

Structural, optical and thermal studies of Eu 3+ ions in lithium fluoroborate glasses

Borate glasses doped with trivalent europium were prepared by the conventional melt quenching technique, in the chemical composition of (49.99- x)B 2O 3 + 25Li 2O + 25LiF+ xEu 2O 3 by varying the concentration of the rare earth ion in the order 0.01, 0.1, 1, 2 and 3 wt% and their structural, luminescence and thermal behavior have been reported. The XRD and FTIR spectra reveal the glass structure and the functional groups. The UV–VIS, luminescence spectra and lifetime of the Eu 3+ ions were measured. The local site symmetry around the Eu 3+ ions were evaluated through the luminescence intensity ratio (R) of the 5D 0 → 7F 2 to 5D 0 → 7F 1 transitions. Optical measurements have been carried out to explore the optical properties such as bonding parameters, Judd–Ofelt parameters, stimulated emission cross-section, transition probability, branching ratio, radiative lifetime, etc. The lifetime measurements of the 5D 0 level as a function of the concentration of Eu 3+ ion have been found and is comparable to other reported for Eu 3+ doped borate, phosphate glasses and higher than that for the tellurite glasses. The thermal properties such as glass transition, crystallization and melting temperatures of the Eu 3+ glasses were studied through the DSC traces in the temperature range of 30−1200 °C at a heating rate of 10 °C per minute. The change in optical properties with the variation of Eu 3+ ion concentration have been discussed and compared with similar results.

Crystalline Gaq3Nanostructures: Preparation, Thermal Property and Spectroscopy Characterization

Crystalline Gaq31-D nanostructures and nanospheres could be fabricated by thermal evaporation under cold trap. The influences of the key process parameters on formation of the nanostructures were also investigated. It has been demonstrated that the morphology and dimension of the nanostructures were mainly controlled by working temperature and working pressure. One-dimensional nanostructures were fabricated at a lower working temperature, whereas nanospheres were formed at a higher working temperature. Larger nanospheres could be obtained when a higher working pressure was applied. The XRD, FTIR, and NMR analyses evidenced that the nanostructures mainly consisted of δ-phase Gaq3. Their DSC trace revealed two small exothermic peaks in addition to the melting endotherm. The one in lower temperature region was ascribed to a transition from δ to β phase, while another in higher temperature region could be identified as a transition from β to δ phase. All the crystalline nanostructures show similar PL spectra due to absence of quantum confinement effect. They also exhibited a spectral blue shift because of a looser interligand spacing and reduced orbital overlap in their δ-phase molecular structures.

MAGNETIC PROPERTIES, NANOSTRUCTURE AND ORDERING KINETICS OF FePtCu THIN FILMS

In this study, the ( FePt )100- x Cu x ( x =0, 4.6, 6.7, 8.8, 10.9) ( FePtCu ) alloy films were prepared by co-sputtering. The effects of Cu addition content and heat treatment on the nanostructure and magnetic properties of the polycrystalline ( FePt )100- x Cu x films are reported. The experimental results show that the ordering temperature of the ( FePt )100- x Cu x ( x =6.7) films reduced to 320°C, which is much lower than that of the FePt alloy. After heat treatment at 600°C for 1 hour, the ( FePt )100- x Cu x ( x =6.7) film shows a coercive force of 15 kOe and the magnetization of 576 emu/cc. The magnetic properties of the FePtCu films can be adjusted by varying the Cu content in the films. The enhancement of the magnetic properties of the FePtCu films mainly resulted from the formation of the order L 10 phase. DSC traces of as-deposited disorder films at different heating rates, to evaluate the crystallization of the order phase, showed that the addition of Cu atoms reduced the activation energy of ordering from 217 kJ/mol to 87 kJ/mol for the ( FePt )100- x Cu x films ( x = 0 and 6.7, respectively). The reduction of the ordering temperature and corresponding activation energy might due to the solid solution of the Cu atoms in the FePt films.

Interpretation of partial thermal decomposition mechanism of Dy2(SO4)3·8H2O

Partial dehydration of Dy2(SO4)3·8H2O was studied employing TG, DSC, D.C. electrical conductivity and spectroscopic techniques. The possible mechanism for the loss of water molecules (partial dehydration) was found to be random nucleation obeying Mapel equation based on TG trace. The DSC traces are supports the results of TG traces and are also utilized to understand the enthalpy changes accompanying the partial dehydration and phase transition accompanying the dehydrated samples. D.C. electrical conductivity studies are attempted to supplement these TG studies. Attempts are made to explain the structural changes accompanying dehydration on the basis of infrared spectra and X-ray diffraction and scanning electron microscopic studies.

Crystallization kinetics and phase transformation in superionic lithium metaphosphate(Li2O–P2O5) glass system

The ionic conductivity of mol%50Li2O–50P2O5 melt quenched glass shows an anomalous increase after its glass transition temperature(Tg) around590 K. On further increasing the temperature gradually, the conductivity decreases owing to the devitrificationof Li2O–P2O5 glass. The evolution of devitrified crystallites was evidenced by XRD patterns. To understand thedevitrification process, isothermal and non-isothermal DSC studies have been carried out on mol%50Li2O–50P2O5 glass.Tg aswell as Tc values are found to increase monotonically with increasing heating rates. Variation ofTg as a function of heating rates has been investigated to evaluate the lower limiting temperature ofTg and the activation energy for structural relaxation. Results of the DSC studies indicate(i) single-stage bulk crystallization of the glass, with DSC traces exhibiting a single transition, (ii) an order parameter (Avrami constant) of2.8 ± 0.1,suggesting internal (bulk) crystallization of the glass, (iii) an activation energy for crystallization equalto 121.7 kJ mol−1 and (iv) the activation energy for structural relaxation,Eg, tobe 558.8 kJ mol−1. The crystallization mechanism is closely associated with the JMA model and theexperimental dataset have been fitted to a non-isothermal Avrami expression and theobtained parameters confirm the experimental results.

Dynamic mechanical behavior of a Zr-based bulk metallic glass during glass transition and crystallization

The dynamic mechanical behaviors of the Zr41Ti14Cu12.5Ni8Be22.5Fe2 bulk metallic glass (BMG) during continuous heating at a constant rate were investigated. The glass transition and crystallization of the Zr-based BMG were thus characterized by the measurements of storage modulus E′ and internal friction Q−1. It was found that the variations of these dynamic mechanical quantities with temperature were interrelated and were well in agreement with the DSC trace obtained at the same heating rate. The origin of the first peak in the internal friction curve was closely related to the dynamic glass transition and subsequent primary crystallization. Moreover, it can be well described by a physical model, which can characterize atomic mobility and mechanical response of disordered condense materials. In comparison with the DSC trace, the relative position of the first internal friction peak of the BMG was found to be dependent on its thermal stability against crystallization.

Short-Time Glycolysis of Post-Consumer Pet Catalyzed by Different Metal Complexes

Oligomers of bis(2-hydroxyethyl terephthalate) (BHET) was obtained by glycolysis of PET applying a simplified method. PET glycolysis was carried out in presence of ethylene glycol (EG) at reflux temperature, PET:EG molar ratio of 1:3 and 0.1 wt.% of catalyst. Metal compounds based on acetates and acetylacetonates of Zn, Mn, Pb, Co, Cu and Sm were used as catalyst. Molecular weights (MW) of these oligomers were determined by size exclusion chromatography (SEC). Gaussian deconvolution of SEC curves used to evaluate the oligomers composition generated with each catalyst showed that reactions carried out in presence of zinc acetate, lead acetate and manganese acetylacetonate lead to oligomers with the lowest molecular weights, predominating monomer and dimer of BHET. DSC traces showed that the melting behavior of these oligomers are highly dependent on the MW composition and in all cases multimodal profiles with melting peaks ranging from 80 to 155 °C were obtained.

Role of Superheated Water in the Dissolution and Perturbation of Hydrogen Bonding in the Crystalline Lattice of Polyamide 4,6

Here, we demonstrate that water, in the superheated state, is a solvent for polyamide 4,6 (PA4,6) and that the water molecules can strongly influence hydrogen bonding. In the presence of superheated water, the melting temperature of PA4,6 can be suppressed by nearly 100 degrees C. The depression in the melting temperature follows the Flory-Huggins principle. The instantaneous dissolution of the polymer hardly influences the molar mass of the polymer. However, if the polymer is retained in solution above the dissolution temperature for more than 10 min, hydrolysis occurs. These findings suggest that the dissolution of the aliphatic polymer in superheated water is mainly a physical process as opposed to a chemical process. Time resolved X-ray studies show that the dissolution occurs prior to the Brill transition temperature, as reported earlier. Crystals grown from the water solution show a lath-like morphology with interchain and intersheet distances that are similar to the distances obtained for crystals grown from other known solvents. Electron diffraction further confirmed that the crystals grown from superheated water are single crystals, where the chains are perpendicular to the ab-plane. SAXS performed on dried sedimented water grown single crystals showed a lamellar thickness of 6 nm. The lamellar thickness is in accordance with other reported studies on PA4,6, confirming that the single crystals incorporate four repeat units between re-entrant folds with an amide group incorporated in the tight fold. Solid state NMR studies performed on mats of these single crystals showed two different mobilities of the proton associated with the amide groups: a higher mobility linked to the amide protons in the fold and a reduced mobility of the hydrogen bonded amide protons within the crystal. Additionally, the solid state NMR studies on the dried water crystallized single crystals show the presence of water molecule(s) in the vicinity of the amide groups. This was confirmed by infrared studies that conclusively demonstrated the appearance of two new bands arising due to the binding of a water molecule in the vicinity of the amide group (i.e., NH3(+) and COO(-) bands that disappear upon heating at approximately 200 degrees C). Additionally, DSC traces of the water crystallized PA4,6 show an exothermic event in the same temperature region (i.e., in the vicinity of the Brill transition temperature, where the bound water exits from the lattice). Furthermore, this event was corroborated by TGA data.

Atom Transfer Radical Graft Copolymerization on a Poly(Epichlorohydrin-CO-Ethylene Oxide) (ECO) Elastomer

Abstract Graft copolymerization by conventional radical polymerization leads to poor control in molecular weight and quite often gel formation because of several side reactions. In this investigation, PMMA was grafted on poly(epichlorohydrine-co-ethylene oxide) (ECO) elastomer by using ‘grafting from’ technique via atom transfer radical polymerization (ATRP), a very recently developed method of controlled radical polymerization. The pendant —Cl group in ECO rubber was activated by using CuBr catalyst and thus macromolecular chain in ECO rubber acted as macroinitiator. Grafting of PMMA on ECO was confirmed by FT-IR and NMR analyses. DSC traces showed two Tgs in PMMA grafted ECO rubbers indicating microphase separation of hard and glassy PMMA microdomains in the flexible elastomeric ECO matrix. Interestingly, there was large increase in tensile strength and tension set in the ECO-grafted-PMMA materials.

Side Chain Disorder and Phase Transitions in Alkyl-Substituted, Conjugated Oligomers. Relation to Side-Chain Melting in P3ATs

Certain 4,4'-alkyl substituted 2,2'-bithiazole and bithiazole-thiophene oligomers display an endothermic transition in their DSC trace below their respective melting points. Variable-temperature FTIR, MAS-1H NMR, UV-vis spectra, and XRD all indicate that the thermal transition is due to a crystal-crystal phase transition that we have labeled alpha --> beta. FTIR shows a stepwise increase in the concentration of gauche defects at the alpha --> beta transition temperature, but MAS NMR spectra show little increase in the side chain motion until the mp is reached. UV-vis spectra demonstrate that the conjugated main chains remain essentially planar through the alpha --> beta transition, and significant deviations from planarity occur only at higher temperatures, but well below the mp. The close similarity of this behavior to the phase transitions in long chain n-paraffins and the "side-chain melting" phenomenon in poly(3-alkylthiophenes), P3ATs, suggests that the latter may actually be more accurately described as a crystal-crystal phase transition of the crystalline fraction, driven by side chain disorder.

Phase separation and crystallization in a melt-spun Ti 45Zr 35Ni 17Cu 3 alloy

Structure and crystallization behavior of amorphous and quasicrystalline Ti 45Zr 35Ni 17Cu 3 alloy have been studied. DSC trace of the amorphous alloy obtained during continuous heating to 1300 K shows distinctly an exothermic peak and two endothermic peaks. The amorphous alloy has different structures depending on annealing temperature. The first exothermic reaction at low temperature region from 400 K to 900 K is due to the precipitation of an icosahedral quasicrystalline phase, and the second endothermic reaction at higher temperature region from 950 K to 990 K results from the transformation of the I-phase to C14 Laves and α-(Ti, Zr) phases.

Crystallization of chiral compounds 4. Simple physical model for reconstruction of post-eutectic DSC traces for melting of binary enantiomeric mixtures

A theoretical model reproducing qualitative and quantitative characteristics of DSC traces for melting of eutectic enantiomeric mixtures was proposed. The method for reconstruction of an idealized trace from a fragment of the real experimental melting curve was developed. When studying a sample of intermediate enantiomeric composition, the reconstruction of the trace makes it possible to avoid ambiguity in determination of the liquidus temperature, determine the melting temperature for an enantiopure compound, and estimate the composition of the sample.

Synthesis and properties of ortho-linked aromatic poly(ester-amide)s and poly(ester-imide)s bearing 2,3-bis(benzoyloxy)naphthalene units

Two new naphthalene-ring-containing bis(ester-amine)s, 2,3-bis(4-aminobenzoyloxy)naphthalene (p-2) and 2,3-bis(3-aminobenzoyloxy)naphthalene (m-2), were prepared from the condensation of 2,3-dihydroxynaphthalene with 4-nitrobenzoyl chloride and 3-nitrobenzoyl chloride, respectively, followed by catalytic hydrogenation. The novel aromatic poly(ester-amide)s and poly(ester-imide)s having 2,3-linked bis(benzoyloxy)naphthalene units have been synthesized from the polycondensation reactions of bis(ester-amine)s (p-2 and m-2) or an equimolar mixture of 4,4′-oxydianiline and p-2 or m-2 with various aromatic dicarboxylic acids and dianhydrides. The synthesis of the poly(ester-amide)s was achieved by the phosphorylation polyamidation reaction by means of triphenyl phosphate, and the synthesis of the poly(ester-imide)s included ring-opening polyaddition to give poly(amic acid)s followed by chemical imidization to polyimides. Most of the poly(ester-amide)s were readily soluble in various organic solvents. Six poly(ester-amide)s and two poly(ester-imide)s derived from less rigid diacids and dianhydrides, respectively, were amorphous and could be solution-cast into transparent and tough films with good mechanical properties. Most of the poly(ester-amide)s displayed discernible glass-transition temperatures (Tgs) between 192 and 223 °C in the DSC traces. All of the poly(ester-imide)s, except for one sample, showed clear Tg values between 225 and 265 °C by DSC. These poly(ester-imide)s showed excellent thermal stability with 10 wt% loss temperatures above 460 °C in nitrogen or air.

Thermal and Electrical Properties of PEO<sub>9</sub> CuCNS : Al<sub>2</sub>O<sub>3</sub> Nano-Composite Polymer Electrolyte

Nano-composite polymer electrolyte films of composition PE0 9 CuCNS + 10 wt% Al 2 0 3 were prepared by solvent casting technique. DSC traces show that the composite electrolyte exhibits a pronounced crystalline to amorphous phase transition around - 60°C similar to the filler-free electrolyte. The conductivity variation with temperature for both the filler free (PEO) 9 CuCNS material and composite polymer electrolyte (PEO) 9 CuCNS + 10 wt% Al 2 0 3 shows Arrhenius behaviour exhibiting two distinctive regions below and above - 60°C. There is about two-fold increase in the overall electrical conductivity of the composite polymer electrolyte compared to the filler free polymer electrolyte. DC Polarization measurements indicate that the charge transport in this electrolyte is predominantly due to ions, both systems exhibiting high anionic transference numbers: t = 0.86 for (PEO) 9 CuCNS, and t = 0.98 for (PEO) 9 CuCNS + 10 wt %, Al 2 O 3 . The observed conductivity enhancement is very likely to be due to the creation of additional transient sites and conducting pathways for the migrating anions caused by Lewis acid-base type H-bonding with OH surface groups on filler grains.