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131.
132.
133.
Fang‐Chyou Chiu Qiang Fu Ya Peng Hsi‐Hsin Shih 《Journal of Polymer Science.Polymer Physics》2002,40(4):325-337
Metallocene polyethylene (mPE) fractions are recognized as being more homogeneous with respect to short‐chain branch (SCB) distribution as compared with unfractionated mPEs. Differential scanning calorimetry and polarized optical microscopy (POM) were used to study the influences of SCB content on the crystallization kinetics, melting behavior, and crystal morphology of four butyl‐branched mPE fractions. The parent mPE of the studied fractions was also investigated for comparative purposes. mPE fractions showed a much simpler crystallization behavior as compared with their parent mPE during the cooling experiments. The Ozawa equation was successfully used to analyze the nonisothermal crystallization kinetics of the fractions. The Ozawa exponent n decreased from about 3.5 to 2 as the temperature declined for each fraction, indicating the crystal‐growth geometry changed from three‐dimensional to two‐dimensional. For isothermal crystallization, the fraction with a lesser SCB content exhibited a higher crystallization temperature (Tc) window. The results from the Avrami equation analysis showed the exponent n values were around 3 (with minor variation), which implied that the crystal‐growth geometry is pseudo‐three‐dimensional. Both of the activation energies for nonisothermal and isothermal crystallization were determined for each fraction with Kissinger and Arrhenius‐type equations, respectively. Double melting peaks were observed for both nonisothermally or isothermally crystallized specimens. The high‐melting peak was confirmed induced via the annealing effect during heating scans. The Hoffman–Weeks plot was inapplicable in obtaining the equilibrium melting temperature (Tm°) for each fraction. The relationship between Tc and Tm for the fractions is approximately Tm = Tc (°C) + 8.3. The POM results indicated that the crystals of parent or fractions formed under cooling conditions did not exhibit the typical spherulitic morphology as a result of the high SCB content. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 325–337, 2002 相似文献
134.
Chia‐Fen Lee Chia‐Jen Wen Chia‐Lung Lin Wen‐Yen Chiu 《Journal of polymer science. Part A, Polymer chemistry》2004,42(12):3029-3037
Poly [N‐isopropylacrylamide (NIPAAm)–chitosan] crosslinked copolymer particles were synthesized by soapless emulsion copolymerization of NIPAAm and chitosan. An anionic initiator [ammonium persulfate (APS)] and a cationic initiator [2,2′‐azobis(2‐methylpropionamidine)dihydrochloride (AIBA)] were used to initiate the reaction of copolymerization. The chitosan–NIPAAm copolymer synthesized by using APS as the initiator showed a homogeneous morphology and exhibited the characteristic of a lower critical solution temperature (LCST). The copolymer synthesized by using AIBA as an initiator showed a core–shell morphology, and the characteristic of LCST was insignificant. The LCST of the chitosan–NIPAAm copolymer depended on the morphology of the copolymer particles. In addition, the chitosan–NIPAAm copolymer particles were processed to form copolymer disks. Then, the effect of various variables such as the chitosan/NIPAAm weight ratio, the concentration of crosslinking agent, and the pH values on the swelling ratio of chitosan–NIPAAm copolymer disks were investigated. Furthermore, caffeine was used as the model drug to study the characteristics of drug loading of the chitosan–NIPAAm copolymer disks. Variables such as the chitosan/NIPAAm weight ratio and the concentration of the crosslinking agent significantly influenced the behavior of caffeine loading. Two factors (pore size and swelling ratio) affected the behavior of caffeine release from the chitosan–NIPAAm copolymer disks. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3029–3037, 2004 相似文献
135.
Jiunn‐Hung Pan Yu‐Ma Chou Houn‐Lin Chiu Bo‐Cheng Wang 《Journal of Physical Organic Chemistry》2007,20(10):743-753
Recently, organic diamine compounds have been widely used as hole‐transporting materials. In this work, DFT B3LYP method with the 6‐31G* basis set was performed to investigate the influence of molecular conformation on the reorganization energy of a series of tetra(aryl)benzidine‐based hole‐transport materials. The results indicate that there are two types (i.e., ISB and BD/TPD) of geometric differences of the organic diamines with the relaxation processes. The reorganization energy of the ISB type is lower than that of the BD/TPD type. For the ISB type, the terminal phenyl moiety of the molecular framework plays an important role in determining the Marcus‐type reorganization energy and the central biphenyl moiety does not. A methyl group attached to a terminal phenyl can be used to tune the reorganization energy. According to the statistical analysis, four geometric parameters could affect the reorganization energy of the BD/TPD type. The conformation of either the central biphenyl or the terminal phenyl moiety of the BD/TPD type determines the Marcus‐type reorganization energy associated with the charge transport process at the molecular level. Presumably, this calculation can be employed to predict the electroluminescence (EL) character of the other organic diamines and to improve the design of new hole‐transporting materials in organic light‐emitting devices (OLEDs). Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
136.
Chuang-Hsiung Chiu 《Journal of Mathematical Analysis and Applications》2009,349(1):272-279
A coupled model for three-level food chain is considered, the coupling rule is discretized Laplacian diffusion type. The focus of this paper is on the global behavior of solutions. We will show that the differences of the same level population density approach zero as t→∞, provided that the coupling strength is sufficiently large. 相似文献
137.
Dr. Elizabeth H. Krenske Sarah Lam Jerome P. L. Ng Brian Lo Dr. Sze Kui Lam Prof. Dr. Pauline Chiu Prof. Dr. Kendall N. Houk 《Angewandte Chemie (International ed. in English)》2015,54(25):7422-7425
Silyl‐triflate‐catalyzed (4+3) cycloadditions of epoxy enolsilanes with dienes provide a mild and chemoselective synthetic route to seven‐membered carbocycles. Epoxy enolsilanes containing a terminal enolsilane and a single stereocenter undergo cycloaddition with almost complete conservation of enantiomeric purity, a finding that argues against the involvement of oxyallyl cation intermediates which have been previously proposed for these types of reactions. Reported are theoretical and experimental investigations of the cycloaddition mechanism. The major enantiomers of the cycloadducts are derived from SN2‐like reactions of the silylated epoxide with the diene, in which stereospecific ring opening and formation of the two new C? C bonds occur in a single step. Calculations predict, and experiments confirm, that the observed small losses of enantiomeric purity are traced to a triflate‐mediated double SN2 cycloaddition pathway. 相似文献
138.
139.
F. J. Garcia‐Garcia T. Y. Chiu P. Skeldon G. E. Thompson 《Surface and interface analysis : SIA》2015,47(1):30-36
Cathodic polarization of aluminium and Al–0.18 wt.% Mg and Al–0.08 wt.% Ti alloys in 0.24 mol dm?3 nitric acid solution at 38 °C has been employed to assist understanding of the roles of alloying elements in electrograining. The findings indicate that additions of magnesium and titanium to aluminium accelerate the corrosion of the substrate under the alkalization caused by the cathodic reactions. The accelerated dissolution and the consequent formation of hydrated alumina result in a decreased net cathodic current density in potentiostatic and potentiodynamic polarization conditions relative to the behaviour of aluminium. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
140.
An approach combining least squares methods and finite element methods (FEM) is presented for subsequent photoelastic stress
analysis of orthogonal 3D textile composites withR and α obtained in Part 1. Through this approach, these photoelastic stresses are obtained over a region of interest as if
the composites were homogeneous materials. The least squares method is used for requiring the solution strain fields to best
correlate with the distribution of the two photoelastic strain data of ɛ
x
− ɛ
y
and γ
xy
calculated directly from the measuredR and α. The FEM uses the homogenized composite properties to construct the nodal force equilibrium equations as constraints
in the least squares formulation. As a result of combining this least squares method and FEM with lagrange multipliers, a
linear system of equations is formulated with the unknown nodal displacements. Once these nodal displacements are solved,
the strains and stresses can be calculated through FEM formulations. This approach is tested with the two experimental results
completed in Part 1 for the aluminum and composite plates. The stresses obtained for the aluminum plate show close agreement
with those obtained with the plain FEM computation. In the case of the orthogonal 3D composite plate, the local variations
as observed inR and α are already necessarily eliminated from these solved photoelastic stresses. Furthermore, these stresses also match
well with those computed with the plain FEM from the homogenized composite properties. 相似文献