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排序方式: 共有1132条查询结果,搜索用时 16 毫秒
931.
932.
Sami Hietala Mikael Paronen Svante Holmberg Jan Nsman Jyrki Juhanoja Milja Karjalainen Ritva Serimaa Minna Toivola Tero Lehtinen Katri Parovuori Gran Sundholm Hanna Ericson Britta Mattsson Lena Torell Franciska Sundholm 《Journal of polymer science. Part A, Polymer chemistry》1999,37(12):1741-1753
A series of proton exchange membranes have been prepared by the preirradiation grafting method. Styrene was grafted onto a matrix of poly(vinylidene fluoride) (PVDF) after electron beam irradiation. Part of the samples was crosslinked with divinylbenzene (DVB) or bis(vinylphenyl)ethane (BVPE). Subsequent sulfonation gave membranes grafted with poly(styrene sulfonic acid) and marked PVDF‐g‐PSSA. It was found that the intrinsic crystallinity of the matrix decreased in both the grafting and the sulfonation reaction in all the membranes. The graft penetration and the ion conductivity are influenced strongly by the crosslinker. The ion conductivity is considerably lower in crosslinked membranes than in noncrosslinked ones. Generally, the mechanical strength decreases with crosslinking. The membranes show a regular phase separated structure in which the sulfonated grafts are incorporated in the amorphous parts of the matrix polymer. The phase separated domains are small, of the order of magnitude of 100–250 nm. These were resolved on transmission electron micrographs and on atomic force images but could not be resolved with microprobe Raman spectroscopy. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1741–1753, 1999 相似文献
933.
Aart Molenberg Daniela Michalke Martin Mller Thomas Pieper 《Journal of polymer science. Part A, Polymer chemistry》1998,36(1):169-177
Poly[(S)-(+)-2-methylbutyl]pentylsiloxane has been synthesized by anionic ring opening polymerization of the corresponding strained cyclic trisiloxane with cryptated lithium (Li+/[211]) as counterion. The polymer did not show the low and high temperature crystalline phases, that are generally found for poly(di-n-alkylsiloxane)s. Instead, the material formed a hexagonal columnar mesophase until it melted around 400°C. MAS and solution 13C- and 29Si-NMR, polarizing microscopy and WAXS indicated an unexpectedly regular chain structure. It was tentatively concluded that the steric interaction of the (S)-(+)-2-methylbutyl side chains introduces sufficient regularity of the tacticity and that the chains tend to adopt a defect helix conformation. On the other hand, DSC showed the presence of a glass transition at −113°C, indicating a high flexibility of the backbone. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 169–177, 1998 相似文献
934.
Uwe Beginn Elmar Fischer Thomas Pieper Felix Mellinger Rainer Kimmich Martin Mller 《Journal of polymer science. Part A, Polymer chemistry》2000,38(11):2041-2056
Semi‐interpenetrating networks of poly(ethylene oxide) (PEO) and highly crosslinked poly(methacrylate)s were generated from solutions of PEO in mixtures of methacrylate monomers and dimethacrylate crosslinkers. The deep quenching of the solutions into the unstable region resulted in microphase separation via a spinodal decomposition mechanism. Through the crystallization of the PEO inside the polymer‐rich phase, the domain size was reduced below the Cahn–Hilliard limit. The microstructure was permanently preserved by subsequent UV‐initiated polymerization of the monomers well below the PEO melting temperature. The semi‐interpenetrating networks were characterized by differential scanning calorimetry, small‐angle X‐ray scattering, NMR spin‐diffusion measurements, and electron microscopy. Morphologies based on networks of cylindrical PEO aggregates with diameters of 10 ± 2 nm were observed, nearly independent of the molecular weight of the used PEO. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2041–2056, 2000 相似文献
935.
Magdalena Krupka Dariusz J. Michalczyk Jrat
altauskait Gintar Sujetovien Katarzyna Gowacka Hanna Grajek Marta Wierzbicka Agnieszka I. Piotrowicz-Cielak 《Molecules (Basel, Switzerland)》2021,26(22)
In this study, the ability of Lemna minor L. to recover to normal growth, after being degraded in a tetracycline-containing medium, was extensively investigated. The plants were exposed to tetracycline (TC) at concentrations of 1, 2.5, and 10 mM. Subsequently, their physiological status was analysed against the following criteria: rate of plant growth; free radical accumulation; antioxidant enzyme activity; chlorophyll content; HSP70 protein content; cell membrane permeability, and mitochondrial activity. The study showed that duckweed can considerably recover from the damage caused by antibiotics, within a week of cessation of stress. Of the plant properties analysed, mitochondrial activity was the most sensitive to antibiotic-induced disturbances. After transferring the plants to a tetracycline-free medium, all plant parameters improved significantly, except for the mitochondrial activity in the plants grown on the medium containing the highest dose of tetracycline. In the plants treated with this antibiotic at the concentration of 10 mM, the proportion of dead mitochondria increased and was as high as 93% after one week from the beginning of the recovery phase, even after the transfer to the tetracycline-free medium. 相似文献
936.
Jianhui Zhang Guanjun Dong Aaron Thurber Yayi Hou Dmitri A. Tenne Charles B. Hanna Min Gu Zhongda Pan Kaiyu Wang Youwei Du Alex Punnoose 《Particle & Particle Systems Characterization》2015,32(5):596-603
Tuning the bandgap and cytotoxicity of ZnO nanoparticles (NPs) is very important, not only for customizing their optoelectronic and biomedical applications, but also for their cytotoxicity assay and safe usage. A unique soft‐template of polyvinylpyrrolidone has been developed here to realize a rapid room‐temperature neutral synthesis of ZnO with controlled nanostructures for tuning the bandgap and cytotoxicity of ZnO. By simply changing the reagent stoichiometry and the soft‐template shape, high‐purity ZnO rods, tripods, tubes, and unique T‐like tubes with tunable size, surface composition/charge, bandgap, and cytotoxicity are obtained. It has been revealed that the ZnO bandgap can be remarkably reduced by introducing the surface nonstoichiometry; and the ZnO‐induced cytotoxicity can be tuned by the size, shape, surface charge/composition, and bandgap of ZnO NPs at different degrees. Significantly, both the photochemistry reaction and the reactive oxygen species induced by ZnO NPs are not necessary for the ZnO‐induced cytotoxicity. 相似文献
937.
Some aspects of weak sufficiency of quantum statistics are investigated. In particular, we give necessary and sufficient conditions
for the existence of a weakly sufficient statistic for a given family of vector states, investigate the problem of its minimality,
and find the relation between weak sufficiency and other notions of sufficiency employed so far. 相似文献
938.
939.
Frontispiece: Ordered Layered Dendrimers Constructed from Two Known Dendrimer Families: Inheritance and Emergence of Properties
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940.
Kristoffer Lund Hanna de la Motte Harald Brelid Gunnar Westman Charlotta Hanson 《Cellulose (London, England)》2011,18(5):1365-1375
Many different approaches to the introduction of intra-fibre cross-links in fibres for use in absorption products are described
in the patent literature, but relatively little has been done in terms of academic research. In this study, the long fibre
fraction of a Scandinavian softwood kraft pulp has been cross-linked with the diepoxide 1,4-butanediol diglycidyl ether (BDDE).
The fibre properties and the performance of the pulp in low density fibre networks were analyzed. In experiments, the cross-linking
agent (BDDE) was dissolved in acetone and then mixed with the pulp. It was shown that a prior wash with NaOH (0.1 M) activates
the polysaccharides and increases the extent of cross-linking, detected as a decrease in the water retention value. Chemical
analysis of modified fibres also gave a clear indication of that cross-linking reactions actually occurred. The pulp properties
could furthermore be influenced by varying time, temperature and the amount of BDDE in the reaction. It was also shown that
it is possible to use water as a solvent for the cross-linking agent, even though the reactivity of water towards diepoxide
must be considered to be high. The cross-linked pulps showed wet bulk under load comparable to that of the mechanical pulps
and enhanced properties than unmodified Scandinavian softwood kraft pulp. It was also observed that fibre network test pads
of the cross-linked pulp fibres, after being tested in the wet state, regained a substantially large part of their low-density
structure when air-dried. 相似文献