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排序方式: 共有7717条查询结果,搜索用时 15 毫秒
981.
José A. Quintana José M. Villalvilla Pedro G. Boj Luis Martín‐Gomis Javier Ortiz Fernando Fernández‐Lázaro Ángela Sastre‐Santos María A. Díaz García 《Advanced functional materials》2009,19(3):428-437
It is shown that the photorefractive (PR) performance of polymer composites based on poly(N‐vinylcarbazole) can be improved when samples are subjected to an electric field for a certain time, i.e. conditioned, previous to the PR characterization. It is also found that for conditioned samples the addition of an organic ionic liquid to the PR composition allows to obtain PR effect without the need of using a sensitizer. The typical electric field treatment time at room temperature and at a field of 20 V µm?1 is 20 min. This procedure leads to a decrease of dark conductivity and an increase of photoconductivity, and consequently an increase of conductivity contrast. This results in higher PR two‐beam‐coupling gain coefficients and shorter response times, particularly at low fields. Dependencies of the process dynamics on impurities, applied field strength, temperature and the presence of an organic ionic liquid are examined in detail. It is remarkable the significant increase of the PR gain coefficients, and more drastically of the net gain coefficients, observed at low fields (<55 V µm?1), when an ionic organic liquid such as benzalkonium chloride is added to unsensitized conditioned PR composites. These findings open a new route to improve the PR performance, not only of PVK‐based composites, but also of other types of organic materials, the main advantage being that no sensitizer is needed. 相似文献
982.
Roberto Sastre Virginia Martín Leoncio Garrido José Luis Chiara Beatriz Trastoy Olga García Angel Costela Inmaculada García‐Moreno 《Advanced functional materials》2009,19(20):3307-3316
Here, the design, synthesis, and characterization of laser nanomaterials based on dye‐doped methyl methacrylate (MMA) crosslinked with octa(propyl‐methacrylate) polyhedral oligomeric silsesquioxane (8MMAPOSS) is reported in relation to their composition and structure. The influence of the silicon content on the laser action of the dye pyrromethene 567 (PM567) is analyzed in a systematic way by increasing the weight proportion of POSS from 1 to 50%. The influence of the inorganic network structure is studied by replacing the 8MMAPOSS comonomer by both the monofunctionalized heptaisobutyl‐methacryl‐POSS (1MMAPOSS), which defines the nanostructured linear network with the POSS cages appearing as pendant groups of the polymeric chains, and also by a new 8‐hydrogenated POSS incorporated as additive to the polymeric matrices. The new materials exhibit enhanced thermal, optical, and mechanical properties with respect to the pure organic polymers. The organization of the molecular units in these nanomaterials is studied through a structural analysis by solid‐state NMR. The domain size of the dispersed phase assures a homogeneous distribution of POSS into the polymer, thus, a continuous phase corresponding to the organic matrix incorporates these nanometer‐sized POSS crosslinkers at a molecular level, in agreement with the transparency of the samples. The silicon–oxygen core framework has to be covalently bonded into the polymer backbone instead of being a simple additive and both the silica content and crosslinked degree exhibit a critical influence on the laser action. 相似文献
983.
HPLC-DAD-ESI/MS identification of anthocyanins in Dioscorea trifida L. yam tubers (purple sachapapa) 总被引:1,自引:0,他引:1
Fernando Ramos-Escudero Celestino Santos-Buelga José Joaquín Pérez-Alonso Jaime A. Yáñez Montserrat Dueñas 《European Food Research and Technology》2010,230(5):745-752
The coloured tubers of purple sachapapa (Dioscorea trifida L.), a common crop in the subtropical and tropical regions, were analysed to characterise their anthocyanin composition.
High-performance liquid chromatography-diode array detection-mass spectrometry (HPLC-DAD-ESI/MS) allowed the detection of
12 anthocyanin pigments. The compounds identified were derived from peonidin (Pn), cyanidin (Cy), and pelargonidin (Pg) aglycones,
most of them showing the same substitution pattern, anthocyanin 3-acylglucoside-5-glucoside, where the acyl residue consisted
of a hydroxycinnamic acid (i.e., ferulic or p-coumaric acid). The main anthocyanin found was peonidin 3-O-p-coumaroylglucoside-5-O-glucoside. 相似文献
984.
Fulgencio Saura‐Calixto Jara Pérez‐Jiménez Sonia Touriño José Serrano Elisabet Fuguet Josep Lluis Torres Isabel Goñi 《Molecular nutrition & food research》2010,54(7):939-946
Proanthocyanidins (PAs) or condensed tannins, a major group of dietary polyphenols, are oligomers and polymers of flavan‐3‐ol and flavan‐3, 4‐diols widely distributed in plant foods. Most literature data on PAs' metabolic fate deal with PAs that can be extracted from the food matrix by aqueous‐organic solvents ( extractable proanthocyanidins). However, there are no data on colonic fermentation of non‐extractable proanthocyanidins (NEPAs), which arrive almost intact to the colon, mostly associated to dietary fibre (DF). The aim of the present work was to examine colonic fermentation of NEPAs associated with DF, using a model of in vitro small intestine digestion and colonic fermentation. Two NEPA‐rich materials obtained from carob pod (Ceratonia siliqua L. proanthocyanidin) and red grapes (grape antioxidant dietary fibre) were used as test samples. The colonic fermentation of these two products released hydroxyphenylacetic acid, hydroxyphenylvaleric acid and two isomers of hydroxyphenylpropionic acid, detected by HPLC‐ESI‐MS/MS. Differences between the two products indicate that DF may enhance the yield of metabolites. In addition, the main NEPA metabolite in human plasma was 3,4‐dihydroxyphenyl acetic acid. The presence in human plasma of the same metabolites as were detected after in vitro colonic fermentation of NEPAs suggests that dietary NEPAs would undergo colonic fermentation releasing absorbable metabolites with potential healthy effects. 相似文献
985.
Raúl Avila-Sosa María Guadalupe Gastélum-Franco Alejandro Camacho-Dávila José Vinicio Torres-Muñoz Guadalupe Virginia Nevárez-Moorillón 《Food and Bioprocess Technology》2010,3(3):434-440
Antimicrobial activity of fractions obtained from Mexican oregano (Lippia berlandieri Schauer) chloroform extract was tested by growth inhibition against Escherichia coli, Staphylococcus aureus and Bacillus cereus, and antioxidant capacity was tested by inhibition of linoleic acid oxidation. Fractions were obtained by differences in
polarity or structure (phenolic and non-phenolic fraction). Gram-positive organisms were more susceptible to Mexican oregano
extracts. Fraction 3 (by polarity) and phenolic fractions I, II, III, IV and V were the extracts with higher antimicrobial
activity. The non-phenolic fraction had effect against B. cereus. Polarity fraction 5 and phenolic Fraction II had a high antioxidant capacity; a 0.08% concentration of fraction 5 had a
similar effect as butylated hydroxytoluene at 0.01% concentration. Fractions of Mexican oregano with different polarity and
functional groups had antioxidant and antimicrobial activity and can be used in a variety of applications. 相似文献
986.
José Antonio Gárate María de los Ángeles Valenzuela María Pilar Gárate Andrés F. Olea 《Journal of surfactants and detergents》2009,12(3):231-236
The solubility and aggregation process of polyethoxylated non-ionic surfactants, of general formula C
i
H2i+1–(O–CH2–CH2)
j
–OH with i = 6, 8, 10 and j = 3–6 (C
i
EO
j
), in heptane were studied. The aggregation of C
i
EO
j
surfactants in heptane was investigated by using methylene blue (MB) as an absorption probe. In solutions of MB in the presence
of these surfactants in heptane, at concentrations larger than the re-dissolution concentration, the UV bands associated to
free MB (A
1) and MB–EO complex (A
2) were detected. The ratio of these intensities A
2/A
1, was used to study the kinetics of the complex formation in pure surfactant. The value of A
2/A
1 depends on the surfactant structure and the media wherein MB is dissolved, being larger in the pure surfactant than in heptane
solutions. These results are explained in terms of solvent effect and aggregate structures on the complex formation.
相似文献
Andrés F. Olea (Corresponding author)Email: |
987.
Carlos Alonso-Moreno José Sancho Fernando Carrillo-Hermosilla Antonio Otero Antonio Antiñolo Isabel López-Solera 《Inorganic chemistry communications》2009,12(2):184-186
Rac and meso ansa-zirconocenes [Zr{1-Me2Si(3-R-(η5-C9H5))(3-R′-(η5-C9H5))}Cl2] (R = Et, R′ = H; R = Pr, R′ = H; and R = Et, R′ = Pr) 4–9 have been prepared by the reaction of ZrCl4 with the corresponding dilithiated derivatives from the ligands {1-Me2Si(3-R-(η5-C9H5))(3-R′-(η5-C9H5))} (R = Et, R′ = H 1; R = Pr, R′ = H 2; and R = Et, R′ = Pr 3) in diethyl ether/toluene at ?78 °C. The molecular structure of rac [Zr{1-Me2Si(3-Et-(η5-C9H5))(3-Pr-(η5-C9H5))}Cl2] 8 has been determined by single crystal X-ray diffraction studies, which show a pseudotetrahedral environment formed by the two chlorine ligands and two η5-coordinated indenyl ligands. The activity in homogeneous and heterogeneous polymerization is compared and discussed. 相似文献
988.
Fernando G. Souza Jr Geiza E. Oliveira Cezar H. M. Rodrigues Bluma G. Soares Márcio Nele José Carlos Pinto 《大分子材料与工程》2009,294(8):484-491
The surface of natural Brazilian amazonic fibers (curauá, Ananas erectifolius) was modified with polyaniline nanoparticles, through in situ preparation of polyaniline nanoparticles in presence of the curauá fibers. This allowed for a significant increase in the electrical conductivity of the fibers (≈2 500 times). As the electrical resistivity of the modified fibers is a function of the applied external pressure, the produced composites can be used as a cheap pressure‐sensing material. The modified materials were also characterized by FT‐IR, XPS and SAXS, and the obtained results were used to explain some of the observed characteristics of the materials.
989.
Rebeca Bouza María José Abad Luis Barral Marcelino Ladra 《Polymer Engineering and Science》2009,49(2):324-332
The effects of composition and interface modification on the tensile properties and the impact resistance of different woodflour/polypropylene composites (WPC) were studied. The woodflour was treated with vinyltrimethoxy silane as a coupling agent, and its effect on the WPC properties was examined. In addition, the tensile data were fitted with several semiempirical models to clarify the mechanical behavior of the composites. The Pukánszky parameters obtained from the fit of the tensile strength data revealed that the distribution of the filler was more homogeneous in the composites containing silane and that interaction between components was improved. The impact strength was maximal for the composites containing 30% of silane‐treated woodflour. Morphological analysis by SEM revealed that the woodflour tended to form agglomerates when present in relatively high amounts in the formulations. For the silane‐treated composites, the dispersion of the filler into the polypropylene (PP) matrix improved, although surface treatment blocked the inclusion of PP into the wood cells. This probably decreased the elastic moduli, even when the filler‐matrix interaction was improved. The beneficial effects of the coupling agent on the WPC properties were greater in the materials containing a relatively low amount of filler (up to 30%); the effectiveness of 0.5% and 1% organosilane were very similar, demonstrating the effectiveness of the coupling agent. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers 相似文献
990.
Luiz K.C. de Souza José R. Zamian Geraldo N. da Rocha Filho Luiz E.B. Soledade Ieda M.G. dos Santos Antonio G. Souza Thomas Scheller Rômulo S. Angélica Carlos E.F. da Costa 《Dyes and Pigments》2009,81(3):187-192
The CoxZn1?xAl2O4 system (x = 0; 0.1; 0.3; 0.5; 0.7; 0.9 and 1) was synthesized by the polymeric precursor method and characterized by the techniques XRD, TG-DTA, IR, UV–vis and colorimetry. The XRD patterns displayed the characteristic peaks of the spinel structure and a good crystallinity. The DTA curves showed an exothermic peak corresponding to the enthalpy of the transition taking place at about 700 °C. The infrared spectra displayed vibrations at about 650, 550, 540, 520, 500, 490 cm?1, which were ascribed to the spinel structure. The UV–vis spectra presented three bands at 550, 580 and 620 nm attributed to the Co2+ spin transitions in tetrahedral sites. The colorimetric data point out the formation of blue pigments, corresponding to highly negative values of b1. The lightness, coordinate L1, increases with the heat treatment temperature. These facts reveal that CoxZn1?xAl2O4 is a promising system that can be employed to obtain ceramic blue pigments. 相似文献