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Differential Scanning Calorimetry Measurements (differential + scanning_calorimetry_measurement)
Selected AbstractsProperties of a poly(acrylamide- co -diallyl dimethyl ammonium chloride) hydrogel synthesized in a water,ionic liquid binary systemJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Qian Zhao Abstract A novel copolymer hydrogel, poly(acrylamide- co -diallyl dimethyl ammonium chloride), was prepared by the radical copolymerization of acrylamide and diallyl dimethyl ammonium chloride in an ionic liquid (IL),water binary system in the presence of the crosslinker N,N,-methylene bisacrylamide. The equilibrium swelling ratios of the hydrogels synthesized in the IL,water binary system increased with the content of IL and were remarkably higher than that of the gel synthesized in water. Differential scanning calorimetry measurements showed that the glass-transition temperatures of the dry hydrogels that were synthesized in the IL,water binary system were remarkably lower than that of the gel synthesized in pure water. The mechanical properties of the gels synthesized in both water and the IL,water binary system were characterized with a universal material-testing machine. The results show that fracture toughness of the hydrogels was improved when they were synthesized in the IL,water binary system. The gel shrank under a direct-current electric field. The response rates of the gels that were synthesized with the IL,water binary system were faster than that of the gel synthesized in water. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] The influence of thermal treatment on the mechanical characteristics of a PLLA coiled stentJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2009Tré R. Welch Abstract We studied the effects of thermal treatment on the expansive characteristics of a coil-within-coil Poly(L -lactic acid) (PLLA) fiber stent developed at our institution to improve its mechanical performance and reproducibility. Following fabrication, furled stents were thermally treated at 62°C for 25 min. The mechanical characteristics were measured compared with those of untreated stents when both were expanded via sequential balloon catheter pressure loading up to 12 atm. Treated stents reached full diameter at 3 atm and maintained that diameter despite further pressure increases. Using measurements of pressure, diameter, and axial length, we calculated the sequential mechanical work required to unfurl the stent. The mechanical work for complete unfurling of treated stents was significantly less than that required for untreated controls. Little axial dimensional change was observed for treated stents. Treated stents exhibited higher stiffness than controls at all pressure levels and also demonstrated higher resistance to external pressure-induced collapse, as measured in a special apparatus developed in our laboratory. Differential scanning calorimetry measurements indicated higher crystallinity values for fibers used in treated stents compared with controls. SEM examination of striations revealed that treated stents underwent less twist than controls following balloon-induced unfurling. The results indicate that, thermal treatment improves the reorientation and realignment of fiber crystalline structure, and favorably influences on the fiber stress-strain behavior and the expansive mechanical characteristics of the PLLA fiber stents. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source] Synthesis and characterization of new polyamides based on DiphenylaminoisosorbideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2005Asmaa A. Caouthar Abstract New aromatic polyamides were synthesized by the microwave-assisted polycondensation of an optically active isosorbide-derived diamine with different diacyl chlorides in the presence of a small amount of N -methylpyrrolidinone. Polymers with inherent viscosities between 0.22 and 0.73 dL/g were obtained corresponding to molecular weights up to 140,000 g/mol. With interfacial polymerization or the Higashi method, lower molecular weight polymers were obtained with inherent viscosities in the range of 0.04,0.36 dL/g. Differential scanning calorimetry measurements clearly demonstrated the high thermal stability of these polymers (mp = 180,300 °C) and the absence of decomposition. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6480,6491, 2005 [source] Vibrational 13C-cross-polarization/magic angle spinning NMR spectroscopic and thermal characterization of poly(alanine-glycine) as model for silk I Bombyx mori fibroinBIOPOLYMERS, Issue 5 2003Patrizia Monti Abstract This study focuses on the conformational characterization of poly(alanine-glycine) II (pAG II) as a model for a Bombyx mori fibroin silk I structure. Raman, IR, and 13C-cross-polarization/magic angle spinning NMR spectra of pAG II are discussed in comparison with those of the crystalline fraction of B. mori silk fibroin (chymotryptic precipitate, Cp) with a silk I (silk I-Cp) structure. The spectral data give evidence that silk I-Cp and the synthetic copolypeptide pAG II have similar conformations. Moreover, the spectral findings reveal that silk I-Cp is more crystalline than pAG II; consequently, the latter contains a larger amount of the random coil conformation. Differential scanning calorimetry measurements confirm this result. N-Deuteration experiments on pAG II allow us to attribute the Raman component at 1320 cm,1 to the amide III mode of a ,-turn type II conformation, thus confirming the results of those who propose a repeated ,-turn type II structure for silk I. The analysis of the Raman spectra in the ,NH region confirms that the silk I structure is characterized by the presence of different types of H-bonding arrangements, in agreement with the above model. © 2003 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 72: 329,338, 2003 [source] The Relevance of the Collaborative Effect in Determining the Performances of Photorefractive Polymer MaterialsCHEMPHYSCHEM, Issue 2 2010Rocco Angelone Dr. Abstract A derivative of 2-methylindole, 3-[2-(4-nitrophenyl)ethenyl]-1-allyl-2-methylindole, NPEMI-A, is studied for its photoconductivity and photorefractivity behaviour. Its blends with the organic polymer poly-(2,3-dimethyl- N -vinylindole), PVDMI, are also investigated. Due to the expected and devised mutual solubility of the two components of the blends, it is possible to carry out measurements with the weight percent of the chromophore NPEMI-A changing from zero to 100. Films were produced by a squeezing process between two ITO-covered glass sheets. No opacity phenomena, that are so common for many other organic blends due to the segregation of the dissolved chromophore, are observed. The photorefractive optical gain ,2 is obtained as a function of the chromophore content. Differential scanning calorimetry measurements (DSC) are also carried out to obtain the whole change of the glass transition temperature Tg as a function of the amount of chromophore contained in the blends. From the experimental trend of Tg a meaningful quantitative estimate of the value of the electrostatic interactions acting in the studied blends, is obtained. The importance of the value of Tg, and of the electrostatic interactions, in determining the extent of the photorefractivity is clearly evident. The results are compared for NPEMI-A (,2=210 cm,1) and for NPEMI-E (,2 , 2000 cm,1) that has a N-2-ethylhexyl group instead of a N-allyl group. The Pockels and Kerr contributions and,for the first time,a "collaborative effect" of the photorefractivity of NPEMI-A are distinguished and quantitatively evaluated. [source] Polarized Raman scattering and phase transition studies of n -diethylenediammonium monohydrogenmonophosphate dihydrateJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2006S. Elleuch Abstract Polarized Raman scattering studies at room temperature were carried out on N -diethylenediammonium monohydrogenmonophosphate dihydrate single crystal samples, abbreviated N -DDHP. An assignment of the normal modes is proposed based on group theory analysis and correlations with previous data reported for other homologous hydrogen-bonded systems. A careful analysis of the vibrational spectra shows that the assignment of the fundamental vibrational modes can be done based on phosphate, organic and water group vibrations. In addition, differential scanning calorimetry measurement and a Raman spectroscopic study at several temperatures in the range 100,300 K are presented. The occurrence of a low-temperature phase transition near 220 K is well evidenced. From the temperature-dependence behavior of some internal and external modes, this transition is interpreted by an order,disorder transition which involves the structural modifications of both anion and cation groups. Copyright © 2006 John Wiley & Sons, Ltd. [source] The conformational stability of the Streptomyces coelicolor histidine-phosphocarrier proteinFEBS JOURNAL, Issue 11 2004Characterization of cold denaturation, protein interactions Thermodynamic parameters describing the conformational stability of the histidine-containing phosphocarrier protein from Streptomyces coelicolor, scHPr, have been determined by steady-state fluorescence measurements of isothermal urea-denaturations, differential scanning calorimetry at different guanidinium hydrochloride concentrations and, independently, by far-UV circular dichroism measurements of isothermal urea-denaturations, and thermal denaturations at fixed urea concentrations. The equilibrium unfolding transitions are described adequately by the two-state model and they validate the linear free-energy extrapolation model, over the large temperature range explored, and the urea concentrations used. At moderate urea concentrations (from 2 to 3 m), scHPr undergoes both high- and low-temperature unfolding. The free-energy stability curves have been obtained for the whole temperature range and values of the thermodynamic parameters governing the heat- and cold-denaturation processes have been obtained. Cold-denaturation of the protein is the result of the combination of an unusually high heat capacity change (1.4 ± 0.3 kcal·mol,1·K,1, at 0 m urea, being the average of the fluorescence, circular dichroism and differential scanning calorimetry measurements) and a fairly low enthalpy change upon unfolding at the midpoint temperature of heat-denaturation (59 ± 4 kcal·mol,1, the average of the fluorescence, circular dichroism and differential scanning calorimetry measurements). The changes in enthalpy (m,Hi), entropy (m,Si) and heat capacity (m,Cpi), which occur upon preferential urea binding to the unfolded state vs. the folded state of the protein, have also been determined. The m,Hi and the m,Si are negative at low temperatures, but as the temperature is increased, m,Hi makes a less favourable contribution than m,Si to the change in free energy upon urea binding. The m,Cpi is larger than those observed for other proteins; however, its contribution to the global heat capacity change upon unfolding is small. [source] Simulation of heat transfer during rotational moldingADVANCES IN POLYMER TECHNOLOGY, Issue 4 2003A. Greco Abstract In rotational molding, polymer powders are subjected to heating, melting, cooling, and subsequent solidification in biaxially rotating molds. Heat transfer phenomena during rotational molding are significantly affected by the presence of endothermic and exothermic transitions. In this paper instead of using the traditional moving interface method, a new approach is presented which is applicable to semicrystalline materials like linear low-density polyethylene. Melting is described by a statistical model and crystallization by a kinetic model. The model parameters are determined from differential scanning calorimetry measurements. The one-dimensional unsteady heat conduction equation is solved by a finite difference method. The numerical predictions are in good agreement with experimental data. The overall heat transfer model can be used for process optimization purposes. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 271,279, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10055 [source] Synthesis and characterization of a cured epoxy resin with a benzoxazine monomer containing allyl groupsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Shiao-Wei Kuo Abstract Vinyl-terminated benzoxazine (VB-a), which can be polymerized through ring-opening polymerization, was synthesized through the Mannich condensation of bisphenol A, formaldehyde, and allylamine. This VB-a monomer was then blended with epoxy resin and then concurrently thermally cured to form an epoxy/VB-a copolymer network. To understand the curing kinetics of this epoxy/VB-a copolymer, dynamic differential scanning calorimetry measurements were performed by the Kissinger and Flynn,Wall,Ozawa methods. Fourier transform infrared (FTIR) analyses revealed the presence of thermal curing reactions and hydrogen-bonding interactions of the epoxy/VB-a copolymers. Meanwhile, a significant enhancement of the ring-opening and allyl polymerizations of the epoxy was observed. For these interpenetrating polymer networks, dynamic mechanical analysis and thermogravimetric analysis results indicate that the thermal properties increased with increasing VB-a content in the epoxy/VB-a copolymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Thermally curable benzoxazine monomer with a photodimerizable coumarin groupJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2007Baris Kiskan Abstract A new monomer, 4-methyl-9- p -tolyl-9,10-dihydrochromeno[8,7-e][1,3]oxazin-2(8H)-one, possessing both benzoxazine and coumarin rings in its structure was synthesized by the reaction of 4-methyl-7-hydroxycoumarin, paraformaldehyde, and p -toluidine in methanol at 40 °C and characterized with spectral analysis. Upon photolysis around 300 nm, this monomer underwent dimerization via the [2,s+2,s] cycloaddition reaction. Photodimerization reactions were investigated with UV and 1H NMR spectroscopy measurements. The thermal ring-opening reaction of the benzoxazine ring was demonstrated with differential scanning calorimetry measurements. The thermal behavior of the cured product was also investigated with thermogravimetric analysis. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1670,1676, 2007 [source] Synthesis of soluble branched polyimides derived from an ABB, monomerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2004Kun-Li Wang Abstract A novel ABB, monomer, an isomeric mixture of 4-[4-(2,4-diaminophenoxy)phenoxy]phthalic acid 2-methyl ester, was successfully prepared. The direct polycondensation of the ABB, monomer was carried out to form polyamic acid monomethyl ester as a precursor with an inherent viscosity of 0.30 dL/g and a number-average molecular weight of 12,000. The degree of branching of the precursor, determined by 1H NMR, was 0.07. The low degree of branching was caused by the differences in the reactivities of the amino groups. The shape factor was calculated to be 0.72. End-modified reactions with acetyl chloride, benzoyl chloride, and phthalic anhydride were carried out. After the chemical imidization of the end-modified precursors, end-modified polyimides were successfully prepared. The end-modified polyimides were soluble in dimethyl sulfoxide, dimethylformamide (DMF), and N -methyl-2-pyrrolidinone. On the basis of thermogravimetry and differential scanning calorimetry measurements of the polyimides, the 5 wt % thermal loss temperatures were determined to be 400,520 °C, and the glass-transition temperatures were determined to be 200,258 °C. According to the X-ray diffraction measurements, the end-modified polyimides were amorphous. A strong but brittle film was prepared from an acetamide end-modified polyimide solution, via casting from a DMF solution, with a tensile strength of 46 MPa, an elongation at break of 4%, and a modulus of 1.3 GPa. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3200,3211, 2004 [source] Crystallization of the , form in random propylene-ethylene copolymersPOLYMER INTERNATIONAL, Issue 12 2004Antonio Marigo Abstract Wide-angle X-ray scattering and differential scanning calorimetry measurements have been conducted on seven random copolymers of propylene with ethylene in order to study the , phase formation as a function of the comonomer content. The lamellar morphology of the samples was also investigated by small-angle X-ray scattering. The content of the , phase was found to go through a maximum with crystallization temperature and to increase with comonomer concentration, up to a point (ethylene ,6.5 wt%) where the latter parameter became less influential. The multiple melting endotherms behaviour of the samples was studied by DSC and temperature-controlled diffractometric techniques. The attribution of the DSC peaks to the different isotactic polypropylene polymorphs that form in these conditions was confirmed. The results obtained permitted us to ascertain that, in the experimental conditions chosen, some further formation of crystallites takes place during the quenching to room temperature after the crystallization isotherm. In this phase, the chains organize themselves in stacks with thin lamellae, forming a distinct population with respect to those formed on isothermal crystallization. The melting of the thinner lamellae determines a convergence of the two populations into just one, still retaining an organization in stacks, that gradually disappears until complete melting of the material. Copyright © 2004 Society of Chemical Industry [source] The first structure of a cold-adapted superoxide dismutase (SOD): biochemical and structural characterization of iron SOD from Aliivibrio salmonicidaACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 2 2009Hege Lynum Pedersen Superoxide dismutases (SODs) are metalloenzymes that catalyse the dismutation of the superoxide radical anion into O2 and H2O2 in a two-step reaction. The crystal structure of the iron superoxide dismutase from the cold-adapted and fish-pathogenic bacterium Aliivibrio salmonicida (asFeSOD) has been determined and refined to 1.7,Ĺ resolution. The protein has been characterized and compared with the closely related homologous iron superoxide dismutase from the mesophilic Escherichia coli (ecFeSOD) in an attempt to rationalize its environmental adaptation. ecFeSOD shares 75% identity with asFeSOD. Compared with the mesophilic FeSOD, the psychrophilic FeSOD has distinct temperature differences in residual activity and thermostability that do not seem to be related to structural differences such as intramolecular or intermolecular ion bonds, hydrogen bonds or cavity sizes. However, an increased net negative charge on the surface of asFeSOD may explain its lower thermostability compared with ecFeSOD. Activity measurements and differential scanning calorimetry measurements revealed that the psychrophilic asFeSOD had a thermostability that was significantly higher than the optimal growth temperature of the host organism. [source] | |||||||||||||