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排序方式: 共有309条查询结果,搜索用时 77 毫秒
1.
Jigneshkumar P. Patel Zou Guo Xiang Shaw Ling Hsu Andrew B. Schoch Sena Ada Carleen Dean Matsumoto 《Journal of Polymer Science.Polymer Physics》2015,53(21):1519-1526
A uniform dispersion of reactants is necessary to achieve a complete reaction involving multicomponents. In this study, we have examined the role of plasticizer in the reaction of two seemingly unlikely reactants: a highly crystalline hexamethylenetetramine (HMTA) and a strongly hydrogen bonded phenol formaldehyde resin. By combining information from NMR, infrared spectroscopy and differential scanning calorimetry, we were able to determine the role of specific intermolecular interactions necessary for the plasticizer to dissolve the highly crystalline HMTA and to plasticize the phenol formaldehyde resin in this crosslinking reaction. The presence of the plasticizer increased the segmental mobility, disrupted the hydrogen bonded matrix, and freed the hydroxyl units, which further increased the solubility of the HMTA. Both the endothermic and exothermic transitions are accounted for in the calorimetric data obtained. For the first time, it is possible to obtain the effective molar ratio of each component needed to complete the crosslinking reaction efficiently. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1519–1526 相似文献
2.
E. R. Hensema M. E. R. Sena M. H. V. Mulder C. A. Smolders 《Journal of polymer science. Part A, Polymer chemistry》1994,32(3):527-537
New aromatic poly-1,2,4-triazoles and poly-1,3,4-oxadiazoles are studied as thermally stable membrane materials. Various groups were introduced onto the pendant phenyl groups of poly-1,2,4-triazoles. Glass transition temperature, degradation temperature, and cold crystallization behavior were studied as a function of these groups. Cold crystallization appeared to be highly sensitive to macromolecular regularity. The solubility of poly-1,3,4-oxadiazoles was highly improved upon incorporation of 5-t-butylisophthalic, 1,1,3-trimethyl-3-phenylindane, 4,4′-(2,2′-diphenyl) hexafluoro propane, and diphenyl ether groups into the polymeric main chain, whereas the high glass transition temperatures and degradation temperatures typical for aromatic poly-1,3,4-oxadiazoles were maintained. © 1994 John Wiley & Sons, Inc. 相似文献
3.
[reaction, structure: see text] We report a unimolecular system functioning as a combinatorial logic circuit for half-subtractor. The emission characteristics can be modulated by chemical inputs, and when followed at two different wavelengths, two functionally integrated logic gates XOR and INHIBIT are obtained. Both logic gates function in the emission mode, and with very large differences in the signal intensity allowing unequivocal assignment of logic-0 and logic-1. 相似文献
4.
We report a novel dimeric boradiazaindacene dye which can be converted in one step to an efficient resonance energy transfer (RET) dyad. In addition, if this modification is done with appropriate ligands, RET can be coupled to ion sensing. The utility of this approach is demonstrated in a highly selective, emission ratiometric chemosensor for Ag(I). 相似文献
5.
The reactions of the polymethylmethacrylate anion have been investigated at 200 K and 250 K in both THF and 9/1 toluene/THF. Sodium-α methyl styrene tetramer and fluorenyl sodium were used as initiators. Only ion pair reactions were investigated. The rate constant of monomer addition to the ion pair at 200 K was determined to be 80 ± 6 M?1 sec?1. At 250 K in the presence of excess monomer, the poly MMA anion reacts with the monomer vinyl function and the monomer ester function at comparable rates. Once fully reacted, the poly MMA anion terminates very slowly in THF at 250 K by an intermolecular mechanism. This rate of termination is enhanced in the toluene/THF system. No evidence was found for different reaction mechanisms for the two initiators. 相似文献
6.
L. A. Sena A. Ya. Barskaya S. P. Varshavskii O. L. Ryazantseva 《Russian Physics Journal》1984,27(7):590-593
The sputtering characteristics of KCl and NaCl alkali halide single crystals by bombardment with argon and mercury atoms are investigated. The sputtering coefficients are measured in the energy range 0.5–3 keV. Anisotropy is found in sputtering at various incident angles of the beam. The yield of charged particles during bombardment of thin specimens (of the order of 8–20 m) of KCl single crystals is investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 55–59, July, 1984. 相似文献
7.
G. Barone S. Capasso P. Del Vecchio C. De Sena D. Fessas C. Giancola G. Graziano P. Tramonti 《Journal of Thermal Analysis and Calorimetry》1995,45(6):1255-1264
In a previous paper, we report a preliminary DSC study on bovine (BSA) and human (HSA) serum albumins. However, at accurate HPLC analysis the commercial proteins show three peaks: Fraction V-I, probably globulins (as declared by the producers), Fraction V-II (about 15–18% of the product) and Fraction V-III that represents pure BSA or HSA. A hypothesis is that the Fraction II is a covalent dimer, or trimer or a mixture of both, generated during the scalf-life of the commercial product. Denaturation enthalpies of the purified Fraction V-III and Fraction V-II of BSA, have been determined calorimetrically, at changing thepH, and the results of both compared with those obtained on the untreated protein. Few calorimetric experiments have been also carried on a BSA monomer derivative with sulphidril group protected. Computer program have been developed for the deconvolution of exo- and endothermic effects and for the analysis of thermal denaturation profiles. 相似文献
8.
Mrcia Sousa Bispo Maria das Graas Andrade Korn Elane Santos da Boa Morte Leonardo Sena Gomes Teixeira 《Spectrochimica Acta Part B: Atomic Spectroscopy》2002,57(12):2175-2180
An analytical method for separation and pre-concentration of lead in seawater for determination by inductively coupled plasma optical emission spectrometry has been investigated. Lead was retained in the solid phase (0.5 g) composed of co-precipitated naphthalene and alizarin red. The solid phase quantitatively sorbs Pb(II) at pH 8–9, and the metal was eluted using 5.0 ml of 2 mol l−1 nitric acid. The effect of NaCl, KCl, BaCl2, CaCl2, Na2SO4, MgCl2 and Na3PO4 on the sorption of Pb(II) in the solid phase was studied. A set of solutions containing varying amounts of electrolytes (0.5; 1.0; 3.0 and 5.0% m/v) with Pb (50 μg) was prepared and the recommended procedure applied. The Na3PO4 was found to interfere; the other electrolytes did not interfere up to 5% m/v. A pre-concentration factor of 40 was obtained in this analytical procedure. The limit of detection and limit of quantification for Pb(II) were 53 and 176 μg l−1, respectively. Lead was determined in seawater samples collected in Salvador city, Bahia, Brazil. The precision, expressed as R.S.D., was 1.8–4.6%, and the recovery of lead added to seawater samples was 95–97%. 相似文献
9.
The effect of the addition of n-butanol (BuOH) and n-hexanol (HexOH) on the micellization of sodium dodecylsulfate (SDS) has been investigated using fluorescence quenching methods.
The binding constants were calculated using an expression which relates the total concentration of alcohols and the micelle
concentration. The values of K were 4.67 and 17.6 M-1 for BuOH/SDS and HexOH/SDS, similar to values obtained by other methods. The cmc of SDS decreases on addition of alcohols
and goes through a minimum for the BuOH/SDS system. Micellar aggregation numbers (N) were determined from linear plots of Ln (I
0/I) against [Quencher] at low alcohol concentrations. For 15 mM SDS, in the presence of BuOH the N values decrease on addition of alcohol up to 0.2 M. For HexOH, N can be assumed to be constant up to 4.8 mM, after which N decreases. The polarity of the micellar core containing alcohol was evaluated from the I
1/I
3 ratio of monomeric pyrene. The effect of addition of the alcohol causes a decrease in the I
1/I
3, which corresponds to a decrease in the polarity of the pyrene solubilization site.
Received: 28 October 1996 Accepted: 10 January 1997 相似文献
10.
Tufan Kumbasar Ibrahim Eksin Mujde Guzelkaya Engin Yesil 《International Journal of Approximate Reasoning》2013,54(2):253-272
It has been demonstrated that type-2 fuzzy logic systems are much more powerful tools than ordinary (type-1) fuzzy logic systems to represent highly nonlinear and/or uncertain systems. As a consequence, type-2 fuzzy logic systems have been applied in various areas especially in control system design and modelling. In this study, an exact inversion methodology is developed for decomposable interval type-2 fuzzy logic system. In this context, the decomposition property is extended and generalized to interval type-2 fuzzy logic sets. Based on this property, the interval type-2 fuzzy logic system is decomposed into several interval type-2 fuzzy logic subsystems under a certain condition on the input space of the fuzzy logic system. Then, the analytical formulation of the inverse interval type-2 fuzzy logic subsystem output is explicitly driven for certain switching points of the Karnik–Mendel type reduction method. The proposed exact inversion methodology driven for the interval type-2 fuzzy logic subsystem is generalized to the overall interval type-2 fuzzy logic system via the decomposition property. In order to demonstrate the feasibility of the proposed methodology, a simulation study is given where the beneficial sides of the proposed exact inversion methodology are shown clearly. 相似文献