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Thermal Transitions (thermal + transition)
Selected AbstractsAbrupt Morphology Change upon Thermal Annealing in Poly(3-Hexylthiophene)/Soluble Fullerene Blend Films for Polymer Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Minjung Shin Abstract The in situ morphology change upon thermal annealing in bulk heterojunction blend films of regioregular poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) is measured by a grazing incidence X-ray diffraction (GIXD) method using a synchrotron radiation source. The results show that the film morphology,including the size and population of P3HT crystallites,abruptly changes at 140,°C between 5 and 30,min and is then stable up to 120,min. This trend is almost in good agreement with the performance change of polymer solar cells fabricated under the same conditions. The certain morphology change after 5,min annealing at 140,°C is assigned to the on-going thermal transition of P3HT molecules in the presence of PCBM transition. Field-emission scanning electron microscopy measurements show that the crack-like surface of blend films becomes smaller after a very short annealing time, but does not change further with increasing annealing time. These findings indicate that the stability of P3HT:PCBM solar cells cannot be secured by short-time annealing owing to the unsettled morphology, even though the resulting efficiency is high. [source] Production and physicochemical characterization of resistant starch type III derived from pea starchMOLECULAR NUTRITION & FOOD RESEARCH (FORMERLY NAHRUNG/FOOD), Issue 1 2003Undine Lehmann Abstract Smooth pea starch was used for the production of physiological important resistant starch type III. For reduction of the molecular weight of the starch, different strategies including enzymatic debranching and acid hydrolysis (lintnerization( were tested to obtain an optimal starting material for retrogradation. The resulting polymer chain lengths were analyzed by high-performance anion-exchange chromatography. Temperature regimes and starch concentrations in gel were optimized during the retrogradation with the aim to obtain a high yield of resistant starch. Optimal conditions led to resistant starch contents up to 74%. The products were thermostable and showed no loss of resistant structures after autoclaving. The peak temperatures of the thermal transition were at approximately 147°C. The resulting resistant starch products are suitable for the generation of functional foods. [source] Effect of eggshell powder as nucleating agent on the structure, morphology and functional properties of normal corn starch foams,PACKAGING TECHNOLOGY AND SCIENCE, Issue 3 2007Yixiang Xu Abstract Corn starch and eggshell powder (with particle sizes of 4,5µm and 8,10µm) composite foams were prepared by extrusion. Effects of eggshell on the structure, morphology, physical properties (unit density and expansion ratio), mechanical properties (spring index and compressibility) and thermal behaviour (thermal transition and stability) of the foams were investigated. Foam cell size decreased and cell population increased with addition of eggshell into starch matrix. The foam unit density, expansion ratio and compressibility decreased significantly (p < 0.05), while the spring index increased significantly (p < 0.05) as the eggshell content increased from 0 to 6wt%. Further increasing eggshell content to 10wt% increased the unit density and compressibility and decreased the expansion ratio and spring index. The thermal transition and stability increased with the addition of eggshell. The optimum eggshell content was 6wt% and the smaller-sized eggshell powder had a favourable effect on the functional properties of the foams. Copyright © 2006 John Wiley & Sons, Ltd. [source] Two modes of O,H...O hydrogen bonding utilized in dimorphs of racemic 6- O -acryloyl-2- O -benzoyl- myo -inositol 1,3,5-orthoformateACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Shobhana Krishnaswamy The title compound, C17H16O8, yields conformational dimorphs [forms (I) and (II)] at room temperature, separately or concomitantly, depending on the solvent of crystallization. The yield of crystals of form (I) is always much more than that of crystals of form (II). The molecule has one donor ,OH group that can make intermolecular O,H...O hydrogen bonds with one of the two acceptor C=O groups, as well as with the hydroxyl O atom; interestingly, each of the options is utilized separately in the dimorphs. The crystal structure of form (I) contains one molecule in the asymmetric unit and is organized as a planar sheet of centrosymmetric dimers via O,H...O hydrogen bonds involving the OH group and the carbonyl O atom of the acryloyl group. In the crystal structure of form (II), which contains two independent molecules in the asymmetric unit, two different O,H...O hydrogen bonds, viz. hydroxyl,hydroxyl and hydroxyl,carbonyl (benzoyl), connect the molecules in a layered arrangement. Another notable feature is the transformation of form (II) to form (I) via melt crystallization upon heating to 411,K. The higher yield of form (I) during crystallization and the thermal transition of form (II) to form (I) suggest that the association in form (I) is more highly favoured than that in form (II), which is valuable in understanding the priorities of molecular aggregation during nucleation of various polymorphs. [source] Structural and thermodynamic encoding in the sequence of rat microsomal cytochrome b5,BIOPOLYMERS, Issue 5 2008Juliette T. J. Lecomte Abstract The water-soluble domain of rat microsomal cytochrome b5 is a convenient protein with which to inspect the connection between amino acid sequence and thermodynamic properties. In the absence of its single heme cofactor, cytochrome b5 contains a partially folded stretch of ,30 residues. This region is recognized as prone to disorder by programs that analyze primary structures for such intrinsic features. The cytochrome was subjected to amino acid replacements in the folded core (I12A), in the portion that refolds only when in contact with the heme group (N57P), and in both (F35H/H39A/L46Y). Despite the difficulties associated with measuring thermodynamic quantities for the heme-bound species, it was possible to rationalize the energetic consequences of both types of replacements and test a simple equation relating apoprotein and holoprotein stability. In addition, a phenomenological relationship between the change in Tm (the temperature at the midpoint of the thermal transition) and the change in thermodynamic stability determined by chemical denaturation was observed that could be used to extend the interpretation of incomplete holoprotein stability data. Structural information was obtained by nuclear magnetic resonance spectroscopy toward an atomic-level analysis of the effects. © 2007 Wiley Periodicals, Inc. Biopolymers 89: 428,442, 2008. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Ferrocenyl-Ended Thieno,Vinylene Oligomers: Donor,Acceptor Polarization and Mixed-Valence Properties with Emphasis on the Raman Mapping of Localized-to-Delocalized TransitionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2009Juan Casado Dr. Abstract What's your role? New oligothiophene,vinylene compounds have been synthesized to study the role of the conjugated chain in two different cases (see scheme; MV=mixed valence). The electronic and molecular structures were analyzed by means of electronic, X-ray photoelectron, and Raman spectroscopy, together with thermo spectroscopy, electrochemistry, and DFT calculations. New oligothiophene,vinylene compounds have been synthesized in order to study the role of the conjugated chain in two different cases: 1),when push,pull action operates between an electron-donor and an electron-acceptor group at the ends of the thiophene,vinylene conjugated chain, and 2),when mixed-valence action is induced by single oxidation of the same chain functionalized at both terminal positions with ferrocene groups leading to competition between the donor groups. The electronic and molecular structures are analyzed by means of electronic, X-ray photoelectron and Raman spectroscopies, together with thermospectroscopy, electrochemistry and density functional theory calculations. The cyclic voltammetry processes have been followed by spectrochemistry. It is shown that the radical cation of the diferrocenyl derivative is a class,III mixed-valence system (i.e., fully delocalized) according to its Raman spectrum. Moreover, by Raman thermo-spectroscopy the thermal transition of this radical cation from a delocalized (class,III, room temperature) to a localized (class,II, ,160,°C) state is scanned. In all cases the Raman study is paralleled by an electronic absorption spectroscopic analysis. Structure,property relationships are proposed for molecules of two important fields of very active research as that of the non-linear optics (i.e., organic optoelectronic) and that of the mixed-valence systems (i.e., charge-transfer processes). [source] Effect of polymer size and cosolutes on phase separation of poly(vinylpyrrolidone) (PVP) and dextran in frozen solutionsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2005Ken-ichi Izutsu Abstract The aim of this study was to elucidate the effect of the molecular weight of polymers on their miscibility in frozen solutions to model the physical properties of freeze-dried pharmaceutical formulations. Thermal analysis of frozen solutions containing poly(vinylpyrrolidone) (PVP) and dextran of various molecular weights was performed at polymer concentrations below the binodal curve at room temperature. Frozen solutions containing PVP 29,000 and dextran 10,200 showed two thermal transitions (glass transition temperature of maximally freeze-concentrated solution: Tg,) representing two freeze-concentrated amorphous phases, each containing predominantly one of the polymers. A combination of smaller polymers (PVP 10,000 and dextran 1,060) was freeze-concentrated into an amorphous mixture phase across a wide range of concentration ratios. Combinations of intermediate size polymers separated into two freeze-concentrated phases only at certain concentration ratios. Addition of NaCl prevented the phase separation of PVP and dextran in the aqueous and frozen solutions. Higher concentrations of NaCl were required to retain the miscibility of larger polymer combinations in the freeze-concentrate. The molecular weights of the component polymers, polymer concentration ratio, and cosolute composition are the important factors that determine component miscibility in frozen solutions. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:709,717, 2005 [source] Novel tricomponent membranes containing poly(ethylene glycol)/poly(pentamethylcyclopentasiloxane)/poly(dimethylsiloxane) domains,JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2002Pious Kurian Abstract The synthesis and characterization of novel tricomponent networks consisting of well-defined poly(ethylene glycol) (PEG) and poly(dimethylsiloxane) (PDMS) strands crosslinked and reinforced by poly(pentamethylcyclopentasiloxane) (PD5) domains are described. Network synthesis occurred by dissolving ,,,-diallyl PEG and ,,,-divinyl PDMS prepolymers in a common solvent (toluene), introducing a stoichiometric excess of pentamethylcyclopentasiloxane (D5H) to the charge, inducing the cohydrosilation of the prepolymers by Karstedt's catalyst and completing network formation by the addition of water. Water in the presence of the Pt-based catalyst oxidizes the SiH groups of D5H to SiOH functions that immediately polycondense and bring about crosslinking. The progress of cohydrosilation and polycondensation was followed by monitoring the disappearance of the SiH and SiOH functions by Fourier transform infrared spectroscopy. Because cohydrosilation and polycondensation are essentially quantitative, overall network composition can be controlled by calculating the stoichiometry of the three network constituents. The very low quantities of extractable (sol) fractions corroborate efficient crosslinking. The networks swell in both water and hexanes. Differential scanning calorimetry showed three thermal transitions assigned, respectively, to PEG (melting temperature: 46,60 °C depending on composition), PDMS [glass-transition temperature (Tg) = ,,121 °C], and PD5 (Tg = ,,159 °C) and indicated a phase-separated tricomponent nanoarchitecture. The low Tg of the PD5 phase is unprecedented. The strength and elongation of PEG/PD5/PDMS networks can be controlled by overall network composition. The synthesis of networks exhibiting sufficient mechanical properties (tensile stress: 2,5 MPa, elongation: 100,800%) for various possible applications has been demonstrated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3093,3102, 2002 [source] Synthesis of Poly(ester-anhydrides) Based on Different Polyester PrecursorsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 7 2004Harri Korhonen Abstract Summary: Poly(ester-anhydrides) were synthesised from poly(L -lactide), poly(D,L -lactide), and poly(, -caprolactone) prepolymers prepared by ring-opening polymerisation of cyclic esters in the presence of 1,4-butanediol or ricinoleic acid as co-initiator. The hydroxyl group end functionality of the prepolymers was converted to carboxylic acid functionality by reaction with succinic anhydride, and the polyester precursors were coupled by melt polycondensation to give poly(ester-anhydrides). 1,4-Butanediol was used as co-initiator to study the properties of poly(ester-anhydrides) prepared from different monomers, whereas ricinoleic acid was used as co-initiator to introduce a hydrophobic fatty acid moiety to the polyester precursor. In hydrolysis tests, the poly(ester-anhydrides) showed a two-stage degradation comprising a rapid hydrolysis of anhydride linkages within three days, followed by the slower hydrolysis of the remaining polyester oligomer. Weight loss of the poly(ester-anhydrides) depended most importantly on molecular weight and thermal properties of the polyester precursors; thus, poly(ester-anhydrides) prepared from low molecular weight prepolymers having thermal transitions below 37,°C showed very fast weight loss. [source] A combined imaging, microthermal and spectroscopic study of a multilayer packaging systemPACKAGING TECHNOLOGY AND SCIENCE, Issue 3 2004I. Woodward Abstract The effectiveness of a packaging solution for the pharmaceutical and food industry is dependent on the integrity of the constituent layers and the interfaces formed between them. The deconvolution and analysis of the many intimate layers found in packaging is analytically challenging, requiring techniques capable of identifying sub-micron regions. Here we have characterized the chemical and physical nature of the layers in a multilayer packaging system along with the interfaces, using a combination of high-resolution atomic force microscopy (AFM), microthermal analysis using scanning thermal microscopy (SThM), and Fourier transform infrared (FT-IR) spectroscopy. In particular, localized thermal analysis is shown to reveal the thermal transitions of the individual layers, but it was found that care must be exercised when melting through one layer to the next, as this can result in overestimates of melting temperatures of the underlying layer due to excess power loss from the SThM probe to the already molten top layer surrounding the probe. Copyright © 2004 John Wiley & Sons, Ltd. [source] Synthesis and characterization of Cu3TaIn3Se7 and CuTa2InTe4PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2008P. Grima-Gallardo Abstract Polycrystalline samples of Cu3TaIn3Se7 and CuTa2InTe4 were synthesized by the usual melt and anneal technique. X-ray powder diffraction showed a single phase behavior for both samples with tetragonal symmetry and unit cell parameter values a = 5.794 ± 0.002 Å, c = 11.66 ± 0.01 Å, c /a = 2.01, V = 391 ± 1 Å3 and a = 6.193 ± 0.001 Å, c = 12.400 ± 0.002 Å, c /a = 2.00, V = 475 ± 1 Å3, respectively. Differential thermal analysis (DTA) measurements suggested a complicated behavior near the melting point with several thermal transitions observed in the heating and cooling runs. From the shape of the DTA peaks it was deduced that the melting is incongruent for both materials. Magnetic susceptibility measurements (zero-field cooling and field cooling) indicated an antiferromagnetic character with transition temperatures of T = 70 K (Cu3TaIn3Se7) and 42 K (CuTa2InTe4). A spin,glass transition was observed in Cu3TaIn3Se7 with Tf , 50 K. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electrical study of InAs/GaAs quantum dots with two different environmentsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008M. Kaniewska Abstract Unusually complex spectra have been obtained for InAs/GaAs quantum dot (QD) structures when studied as a function of applied bias by deep level transient spectroscopy (DLTS). In spite of their complexity, basic processes for electron escape from the QDs have been recognized. We show that due to the variety of transitions involving direct tunneling and more complex thermal transitions, due to QD size fluctuations, and environmental dependent QD carrier population, measurement conditions have to be carefully suited for characterizing transport properties of the QDs. Additionally, on the basis of results of a comparative study under chosen measurement conditions, we conclude that the states of the InAs QDs shift towards the middle of the energy gap if the QDs are capped with a Ga-rich InGaAs insertion. It explains a red-shift of the emission wavelength that was found by photoluminescence measurements (PL). (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Does the anesthetic 2,2,2-trifluoroethanol interact with bovine serum albumin by direct binding or by solvent-mediated effects?BIOPOLYMERS, Issue 2 2005A calorimetric, spectroscopic investigation Abstract Thermal unfolding of bovine serum albumin (BSA) has been studied in the presence of 2,2,2-trifluoroethanol (TFE) using high-sensitivity microdifferential scanning calorimetry. Quantitative thermodynamic parameters accompanying the thermal transitions have been evaluated. TFE is observed to be a stabilizer or a destabilizer of the folded state of BSA depending on the pH. CD spectroscopy revealed an increase in the ,-helical content of BSA and a decrease in the tertiary structure in the presence of increasing molalities of TFE. Isothermal titration calorimetric results do not indicate appreciable binding of the TFE molecules to BSA. TFE quenches the steady-state tryptophan fluorescence of BSA only at higher molalities and there is no effect on the tryptophan fluorescence at lower molalities. The calorimetric and spectroscopic results obtained in this work suggest that solvent-mediated effects dominate the interaction of TFE with BSA and the binding component may be very weak. Since the binding component is very weak, one of the possibilities of anesthetic action of TFE molecules on the actual targets may be through perturbation of the structural and dynamic properties of the lipid bilayer so that the function of crucial but unspecified membrane proteins is affected. © 2005 Wiley Periodicals, Inc. Biopolymers 78: 78,86, 2005 [source] | ||||||||||||||||