bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation and characterisation of polyamide–polyimide organoclay nanocomposites
Authors: Varley Russell J , Groth Andrew M , Leong KH 
Published: January 2008

AbstractBACKGROUND: Ternary nanocomposites containing an organomodified layered silicate polyimide additive within a polyamide matrix have been investigated to gain greater insight into structure–property relationships and potential high‐temperature automotive applications.RESULTS: Polyamide nanocomposite blends, containing 3 wt% of organoclay, were prepared and compared with organoclay‐reinforced polyamide and neat polyamide. Nanoclay addition significantly increased heat distortion temperature, as well as both the tensile and flexural moduli and strength. The addition of polyimide demonstrated further increases in heat distortion temperature, glass transition temperature and the flexural and tensile moduli by about 17, 21 and 40%, respectively. The tensile and flexural strengths were either unaffected or decreased modestly, although the strain‐to‐failure decreased substantially. Morphological studies using transmission electron microscopy (TEM) and X‐ray diffraction showed that the nanoclay was dispersed within the ternary blends forming highly intercalated nanocomposites, regardless of the presence and level of polyimide. However, TEM revealed clay agglomeration at the polyamide–polyimide interface which degraded the mechanical properties.CONCLUSIONS: A range of improvements in mechanical properties have been achieved through the addition of a polyimide additive to a polyamide nanocomposite. The decrease in ductility, arising from the poor polyamide–polyimide interface and nanoclay clustering, clearly requires improving for this deficiency to be overcome. Copyright © 2008 Society of Chemical Industry
Kinetics of isothermal and non‐isothermal degradation of cellulose: model‐based and model‐free methods
Authors: Dahiya Jai Bhagwan , Kumar Krishan , Muller‐Hagedorn Matthias , Bockhorn Henning 
Published: January 2008

AbstractBACKGROUND: The kinetics of the thermal decomposition of cellulosic materials is of interest from the viewpoint of flame retardancy for safety, optimization of incineration processes and reducing energy production from fossil sources and associated pollution. One essential step in these processes is the thermal degradation through mass and energy transport, which determines the rate of evolution of various types of products from cellulosic materials.RESULTS: Kinetic parameters have been determined using various model‐based and model‐free methods in the thermal degradation of cellulose up to 700 °C in helium atmosphere. The values of the activation energy obtained in isothermal processes and non‐isothermal processes have been found to be not far from each other. From the integral method, the random nucleation (F1)‐type mechanism has been found most probable for cellulose degradation having an activation energy, Ea, in the range 156.5–166.5 kJ mol−1, lnA = 20–23 min−1, for first‐order reaction during its decomposition process at heating rates of 2, 5 and 10 °C min−1. Based on the high correlation coefficient, many types of mechanisms seem equally good for non‐isothermal degradation of cellulose.CONCLUSION: The linear correlation coefficient has a limitation for verifying the correctness of a reaction mechanism in the study of degradation kinetics. Therefore, the correctness of a mechanism should be considered on the basis of comparing the kinetic parameters obtained from isothermal as well as non‐isothermal methods. Copyright © 2008 Society of Chemical Industry
Effect of Lewis acids on the Diels–Alder reaction in ionic liquids with different activation modes
Authors: Vidiš Ana , Küsters Ernst , Sedelmeier Gottfried , Dyson Paul J. 
Published: January 2008

AbstractThe Diels–Alder reaction has been examined in room temperature ionic liquids with high molar concentrations of Lewis acids under various conditions. A molar ratio of 10% catalyst gave a large increase in the selectivity and the yield of the reaction. The effect of catalysts on reaction rates was also examined under 100 MPa of pressure which leads to modest improvements in reaction rates. Ultrasound and microwave dielectric heating were also shown to improve the rate and, to a minor extent, selectivity of the examined reactions. Copyright © 2008 John Wiley & Sons, Ltd.
Kinetics and mechanism of the anilinolysis of dimethyl and diethyl chloro(thiono)phosphates
Authors: Kumar Dey Nilay , Hoque Md. Ehtesham Ul , Kim Chan Kyung , Lee Bon‐Su , Lee Hai Whang 
Published: January 2008

AbstractThe deuterium kinetic isotope effects (KIEs) involving deuterated aniline nucleophiles (XC6H4ND2) are reported for the reactions of dimethyl chlorophosphate (1), dimethyl chlorothionophosphate (2), diethyl chlorophosphate (3) and diethyl chlorothionophosphate (4) in acetonitrile at 55.0 °C. The obtained kH/kD values are 0.798–0.979, 0.945–1.06, 0.714–0.919 and 1.01–1.10 for 1, 2, 3 and 4, respectively. A concerted mechanism with dominant backside nucleophilic attack is proposed for the reactions of 1 and 3. A concerted mechanism involving partial frontside attack through a hydrogen‐bonded four‐centre‐type transition state (TS) is proposed for the reactions of 2 and 4. Copyright © 2008 John Wiley & Sons, Ltd.
Proteins multi‐funnel energy landscape and misfolding diseases
Authors: Cruzeiro L. 
Published: January 2008

AbstractThe problem of how a given α‐amino acid sequence, in cells, most of the times, assumes the native structure, is a fundamental problem in Biology, known as the protein folding problem. Here, evidence is presented that suggests that the same α‐amino acid sequence can assume several, very different, structures that have the same Gibbs energy as the native structure, in the same thermodynamic conditions. These results lend support to a multi‐funnel Gibbs energy landscape for proteins in which Anfinsen's thermodynamic hypothesis alone cannot explain protein folding. How then do proteins fold? In a multi‐funnel picture, transient deterministic forces are needed to select the native funnel from all other funnels that the protein can potentially fall into. The suggestion here is that such transient, deterministic forces arise from specific vibrational excited states (VES) that constitute the first step in protein folding and function (the VES hypothesis). An application of the VES hypothesis to calculate the energy absorbed, from water molecules, by a protein α‐helix with extensive glutamine (gln) repeats is made, which can explain the structural instability of these proteins and their association with many misfolding diseases. Copyright © 2008 John Wiley & Sons, Ltd.
Confined space regulated polymerization
Authors: You Ye‐Zi , Pan Cai‐Yuan 
Published: January 2008

AbstractThe confined space produced during the polymerization has access for all small organic molecules or oligomers with small size to enter this confined space; however, it can prevent the macromolecules with big size from entering. Therefore, the reaction between two branched macromolecules is excluded in A2+B3 polymerization system, resulting uncrosslinked branched polymers, and there was no gel point observed throughout the polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1730–1737, 2008
Permeability control in electro‐sensitive microcapsules with immobilized ferroelectric liquid crystalline segments
Authors: Yoshida Masahiro , Matsui Tsutomu , Hatate Yasuo , Takei Takayuki , Shiomori Koichiro , Kiyoyama Shiro 
Published: January 2008

AbstractNylon‐polystyrene microcapsules with immobilized ferroelectric liquid crystalline segments were prepared, and permeability control of an encapsulated core material was investigated under an external electric field. A ferroelectric liquid crystal monomer possessing both mesogenicity and chirality responded effectively to the external electrical field. Permeation of the material (oxprenolol) contained in the inner aqueous core of the microcapsules was enhanced under a weak electric field (2 V). Furthermore, the permeability of oxprenolol did not depend on the external electric field in the absence of the ferroelectric liquid crystal segments. To clarify the controlled‐release mechanism of the core material, the light transmittance of the polymer membranes was quantitatively evaluated under an external electric field using a handmade polarized light transmittance apparatus. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1749–1757, 2008
Synthesis and characterization of sulfonated poly(phthalazinone ether phosphine oxide)s by direct polycondensation for proton exchange membranes
Authors: Ma Xuhui , Zhang Chunjie , Xiao Guyu , Yan Deyue , Sun Guoming 
Published: January 2008

AbstractA series of sulfonated poly(phthalazinone ether phosphine oxide)s (sPPEPO) were prepared via aromatic nucleophilic substitution polycondensation of 4‐(4‐hydroxyphenyl) phthalazinone (HPPZ) with sulfonated bis(4‐fluorophenyl)phenyl phosphine oxide (sBFPPO) and bis(4‐fluorophenyl)phenyl phosphine oxide (BFPPO) at various ratios. The properties such as molecular weight, ion exchange capacity (IEC), swelling, thermal stability, proton conductivity, and morphology were investigated. sPPEPO with high IEC exhibited high proton conductivity while they still showed low swelling. Typically, sPPEPO with IEC of 1.54 and 1.69 meq/g exhibited high conductivity of 0.091 and 0.19 S/cm, and low swelling ratios of 14.3% and 19.5% at 80 °C, respectively. The low swelling was attributed to the strong intermolecular interaction including the electrostatic force and hydrogen bond. sPPEPO would be promising candidates used as polyelectrolyte membranes for fuel cells. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1758–1769, 2008
Solvent and concentration effects on the properties of electrospun poly(ethylene terephthalate) nanofiber mats
Authors: Veleirinho Beatriz , Rei Manuel F. , Lopes‐DA‐Silva J. A. 
Published: January 2008

AbstractThis study describes the preparation and characterization of nanofibrous mats obtained by electrospinning poly(ethylene terephthalate) (PET) solutions in trifluoroacetic acid/dichloromethane (TFA/DCM). Special attention was paid to the effect of polymer concentration and solvent properties on the morphology, structure, and mechanical and thermal properties of the electrospun nonwovens. The results show that the spinnable concentration of PET solution in TFA/DCM solvents is above 10 wt %. Mats have nanofibrous morphology with fibers having an average diameter in the range of 200–700 nm (depending on polymer concentration and solvent composition) and an interconnected pore structure. Higher solution concentration favors the formation of uniform fibers without beads and with higher diameter. Morphology and fiber assembly changed with the solvent properties. Solvent mixtures rich in TFA, i.e., those with higher dielectric constant and lower surface tension, originated fibers with small diameter. However, due to the lower volatility, those solvent mixtures also produced more branched and crosslinking fibers, with less morphologic uniformity. Mechanical properties (Young's modulus, ultimate strength, and elongation at break) and thermal properties (glass transition, crystallization, and melting) have been studied for the PET electrospun nanomats and compared with those of the original polymer. Solvent effect on fiber crystallinity was not significant, but a complex effect was observed on the mechanical properties of the electrospun mats, as a consequence of the different structural organization of the fibers within the mat network. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 460–471, 2008
Molecular motion, morphology, and thermal properties of multiwall carbon nanotube/polysilsesquioxane composite
Authors: Yuen Siu‐Ming , Ma Chen‐Chi M. , Teng Chih‐Chun , Wu Hsin‐Ho , Kuan Hsu‐Chiang , Chiang Chin‐Lung 
Published: January 2008

AbstractDiglycidyl ether of bisphenol A (DGEBA)‐bridged polyorganosiloxane precursors have been prepared successfully by reacting diglycidyl ether of bisphenol A epoxy resin with 3‐aminopropyltriethoxysilane. Acid‐modified and unmodified multiwalled carbon nanotube (MWCNT) were dispersed in the diglycidyl ether of bisphenol A‐bridged polyorganosiloxane precursors and cured to prepare the carbon nanotube/diglycidyl ether of bisphenol A‐bridged polysilsesquioxane (MWCNT/DGEBA‐PSSQ) composites. The molecular motion of MWCNT/DGEBA‐PSSQ nanocomposites was studied by high‐resolution solid‐state 13C NMR. Acid‐modification can improve the affinity between MWCNT and the polymer matrix. The molecular motion of the DGEBA‐PSSQ decreased with acid‐modified MWCNT content. However, when unmodified MWCNT was used, the molecular motion of the DGEBA‐PSSQ was increased. SEM and TEM microphotographs confirm that acid‐modified MWCNT exhibits better dispersion than unmodified MWCNT in DGBEA‐PSSQ. The dynamic mechanical properties of acid‐modified MWCNT/DGBEA‐PSSQ composites are more favorable than those of unmodified MWCNT. Tg of the DGEBA‐PSSQ decreased from 174.0 °C (neat DGEBA‐PSSQ) to 159.0 °C (1 wt % unmodified MWCNT) and 156.0 °C (1 wt % acid‐modified MWCNT). The storage modulus (at 30 °C) of the DGEBA‐PSSQ increased from 1.23 × 109 Pa (neat DGEBA‐PSSQ) to 1.65 × 109 Pa (1 wt % acid‐modified MWCNT). However, when unmodified MWCNT was used, the storage modulus of the DGEBA‐PSSQ decreased to 6.88 × 108 Pa (1 wt % unmodified MWCNT). At high temperature, above 150 °C, storage modulus of nanocomposites was higher than that of neat polymer system. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 472–482, 2008
Experimental investigation into the cushioning properties of honeycomb paperboard
Authors: Wang Dong‐Mei , Wang Zhi‐Wei 
Published: January 2008

AbstractThe cushioning properties of honeycomb paperboards are studied by means of experimental analysis. Experimental results indicate that the cushioning behaviour of paper honeycombs with and without liners are similar, but the cushioning capability is significantly larger for the material with liners. Experiment and theory show that the relative density of paper honeycomb core has a significant effect on the cushioning properties of honeycomb paperboards; however, the basis weight of the liner has only little effect. Experimental results also show that the energy absorption properties of multilayer honeycomb paperboards are not always higher than those of monolayer honeycomb paperboards, and that the height of honeycomb paperboard has an effect on its cushioning properties. These results can be used to characterize and improve the cushioning properties of honeycomb paperboard pads efficiently. Copyright © 2008 John Wiley & Sons, Ltd.
Quantitative analysis of small molecules by desorption electrospray ionization mass spectrometry from polytetrafluoroethylene surfaces
Authors: Ifa Demian R. , Manicke Nicholas E. , Rusine Allison L. , Cooks R. Graham 
Published: January 2008

AbstractDesorption electrospray ionization mass spectrometry (DESI‐MS) is an emerging technique for ambient analysis. However, its application to routine quantitation has not been explored extensively and this is undertaken here. We present studies that utilize a particularly suitable surface, porous polytetrafluoroethylene (porous PTFE), which shows less cross contamination between samples and improved sensitivity and signal stability compared to other surfaces. Quantitative experiments for 1 µL spotted solutions of the β‐blocker propranolol, using isotopically labeled propranolol as internal standard, showed a good linear correlation (r2 > 0.996) over the range 0.01–100 µM. The inter‐day precision, based on the relative standard deviation, for replicates analyzed on three different days was 13% for 0.01 µM and better than 7% for the remainder of the calibration points. The inter‐day accuracy, expressed as relative error, was better than ±7% for all calibration points along the curve. These day‐to‐day measurements suggest that DESI‐MS can be successfully employed for routine quantitative analysis. The use of the analog atenolol as an internal standard and further considerations that should improve quantitation by DESI‐MS are also presented. Copyright © 2008 John Wiley & Sons, Ltd.
Determination of D/L‐amino acids by zero needle voltage electrospray ionisation
Authors: Sørensen Morten B. , Aaslo Per , Egsgaard Helge , Lund Torben 
Published: January 2008

AbstractIon formation may be made more efficient than in normal electrospray ionization (ESI) for certain classes of compounds, such as the polar amino acids Glu, Asn, His, Ser, Asp, Arg, Tyr and Lys, by adjusting the voltage of a normal ESI interface needle to zero voltage. For aspartic acid (Asp) the gain in signal‐to‐noise (S/N) ratio of the liquid chromatography/mass spectrometry (LC/MS) chromatograms obtained in the selective ion monitoring (SIM) mode (m/z 134) with zero needle potential was 40–50 times higher than detection at 4 kV. Ion formation at zero potential is likely to follow a mechanism related to sonic spray ionization. The utility of the zero needle voltage ESI was illustrated by determining the age of a human tooth by the aspartic acid epimerization method. The procedure involved separating the D‐ and L‐aspartic acid of a tooth extract on a chiral HPLC column and detection by zero voltage ESI‐MS3. Copyright © 2008 John Wiley & Sons, Ltd.
A novel ‘peak parking’ strategy for ultra‐performance liquid chromatography/tandem mass spectrometric detection for enhanced performance of bioanalytical assays
Authors: Li Fumin , Maguigad Jacob , Pelzer Mary , Jiang Xiangyu , Ji Qin C. 
Published: January 2008

AbstractSensitive and high‐throughput bioanalytical assays are of vital importance to drug discovery and development. Ultra‐performance liquid chromatography (UPLC), utilizing sub‐2‐µm particles, greatly increases the separation throughput and efficiency, resulting in LC peaks as narrow as or less than 1 s (full width at half maxima, FWHM). This, however, could pose practical challenges for bioanalytical applications using quadrupole mass spectrometry (MS) to acquire sufficient data points to ensure accurate and reliable quantitation. Here, we present a novel ‘peak parking’ strategy to reduce the flow rate during UPLC peak elution, therefore extending the useful MS acquisition window. The high‐throughput advantage of UPLC is maintained since no significant increase of the overall UPLC run time is needed. This strategy was demonstrated in an assay development for lansoprazole, a gastric proton‐pump inhibitor, in human plasma employing liquid‐liquid extraction. The method was validated from 50.0 to 50 000 pg/mL. Copyright © 2008 John Wiley & Sons, Ltd.
Recognizing mechanistic reasoning in student scientific inquiry: A framework for discourse analysis developed from philosophy of science
Authors: Russ Rosemary S. , Scherr Rachel E. , Hammer David , Mikeska Jamie 
Published: January 2008

AbstractScience education reform has long focused on assessing student inquiry, and there has been progress in developing tools specifically with respect to experimentation and argumentation. We suggest the need for attention to another aspect of inquiry, namelymechanistic reasoning. Scientific inquiry focuses largely on understanding causal mechanisms that underlie natural phenomena. We have adapted an account of mechanism from philosophy of science studies in professional science [Machamer, P., Darden, D., & Craver, C. F., (2000). Thinking about mechanisms. Philosophy of Science, 67, 1–25] to develop a framework for discourse analysis that aids in identifying and analyzing students' mechanistic reasoning. We analyze a discussion among first‐grade students about falling objects (1) to illustrate the generativity of the framework, (2) to demonstrate that mechanistic reasoning is abundantly present even in these young students, and (3) to show that mechanistic reasoning is episodic in their discourse. © 2008 Wiley Periodicals, Inc.Sci Ed92:499–525, 2008
Preservice elementary teachers' views of their students' prior knowledge of science
Authors: Otero Valerie K. , Nathan Mitchell J. 
Published: January 2008

AbstractPre‐service teachers face many challenges as they learn to teach in ways that are different from their own educational experiences. Pre‐service teachers often enter teacher education courses with pre‐conceptions about teaching and learning that may or may not be consistent with contemporary learning theory. To build on preservice teachers' prior knowledge, we need to identify the types of views they have when entering teacher education courses and the views they develop throughout these courses. The study reported here focuses specifically on preservice teachers' views of their own students' prior knowledge and the implications these views have on their understanding of the formative assessment process. Sixty‐one preservice teachers were studied from three sections of a science methods course. Results indicate that preservice teachers exhibited a limited number of views about students' prior knowledge. These views tended to privilege either academic or experience‐based concepts for different aspects of formative assessment, in contrast to contemporary perspectives on teaching for understanding. Rather than considering these views as misconceptions, it is argued that it is more useful to consider them as resources for further development of a more flexible concept of formative assessment. Four common views are discussed in detail and applied to science teacher education. © 2008 Wiley Periodicals, Inc. J Res Sci Teach 45: 497–523, 2008
Ethnic identity, externalizing problem behaviour and the mediating role of self‐esteem among Dutch, Turkish‐Dutch and Moroccan‐Dutch adolescents
Authors: Wissink Inge B. , Deković Maja , Yağmur Şengül , Stams Geert Jan , de Haan Mariëtte 
Published: January 2008

ABSTRACTThe present study examined whether self‐esteem mediates the relationship between two aspects of ethnic identity (i.e. ethnic identity exploration and ethnic identity commitment–affirmation) and externalizing problem behaviour in Dutch, Turkish‐Dutch and Moroccan‐Dutch adolescents living in the Netherlands. A total number of 345 adolescents (115 Dutch, 115 Turkish‐Dutch, 115 Moroccan‐Dutch) with a mean age of 14.5 filled in questionnaires at school. Turkish‐Dutch and Moroccan‐Dutch adolescents reported higher levels of both aspects of ethnic identity than their native Dutch counterparts, but there were no ethnic differences in self‐esteem and externalizing problem behaviour. Only in the Moroccan‐Dutch group was support found for the mediational model: stronger ethnic identity commitment–affirmation was related to a higher level of self‐esteem, which, in turn, was related to a lower level of externalizing problem behaviour.