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Beatriz Veleirinho Manuel F. Rei J. A. Lopes‐DA‐Silva 《Journal of Polymer Science.Polymer Physics》2008,46(5):460-471
This 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 相似文献
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We have examined the capacitance of Si inversion layers at kHz frequencies under strong inversion, low temperatures and modest magnetic fields. We find that the real and imaginary parts can be well described by a one dimensional diffusion equation providing that H is not too large. 相似文献
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龙爪芦荟和库拉索芦荟中微量锗的测定与红外光谱区别 总被引:1,自引:0,他引:1
采用吸光光度法对龙爪芦荟和库拉索芦荟中的微量锗进行了测定,并探讨了两种芦荟的红外光谱的区别。结果表明,龙爪芦荟中含锗量在26.1~28.6μg·g-1,回收率为91.6%~97 5%。库拉索芦荟中含锗量在16.8~20.0μg·g-1,回收率为87.1%~94.5%。两种芦荟的FT IR光谱图在2100cm-1处有明显差异,由此可区别两种芦荟。 相似文献
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C D Stiles W J Pledger R W Tucker R G Martin C D Scher 《Journal of supramolecular structure》1980,13(4):489-499
The platelet-derived growth factor (PDGF), which is found in serum but not in plasma, has been purified to homogeneity; it stimulates replication at a concentration of 10(-10) M. Brief treatment with PDGF causes density-inhibited Balb/c-3T3 cells to become competent to synthesize DNA; pituitary fibroblast growth factor (FGF) or precipitates of calcium phosphate also induce competence. Continuous treatment with plasma allows competent, but not incompetent, cells to synthesize DNA. A critical component of plasma is somatomedin, a group of hormones with insulin-like activity; multiplication-stimulating activity (MSA) or insulin replace plasma somatomedin in promoting DNA synthesis. We have studied the molecular correlates of competence and the role of SV40 gene A products in regulating DNA synthesis. Treatment of quiescent cells with pure PDGF or FGF causes the preferential synthesis of five cytoplasmic proteins (approximate molecular weight 29,000, 35,000, 45,000, 60,000, and 72,000 detected by SDS-PAGE under reducing conditions). Two of these competence-associated proteins (29,000 and 35,000 daltons) are insulin, or epidermal growth factor (EGF). PDGF, FGF, or calcium phosphate induce an ultrastructure change within the centriole of 3T3 cells; this ultrastructural modification of the centriole is detectable by immunofluorescence within 2 h or PDGF treatment. Plasma, EGF, or MSA do not modify the centriole. SV40 induces replicative DNA synthesis in growth-arrested 3T3 cells but does not cause this alteration in centriole structure. Gene A variants of SV40, including a mutant with temperature-sensitive (ts) T-antigen (ts A209), a deletion in t-antigen (dl 884), and several ts A209 strains containing t-antigen deletions were used to induce DNA synthesis in Balb/c-3T3 cells. Like wild type SV40, all strains induced DNA synthesis equally well under permissive or nonpermissive conditions. Addition of PDGF or plasma had little effect on SV40-induced DNA synthesis. Thus, the viral function that induces replicative DNA synthesis in Balb/c-3T3 cells. Like wild type SV40, all strains induced DNA synthesis equally well under permissive or nonpermissive conditions. Addition of PDGF or plasma had little effect on SV40-induced DNA synthesis. Thus, the viral function that induces replicative DNA synthesis in Balb/c-3T3 cells is not t and is not temperature sensitive. This SV40 gene function overrides the cellular requirement for hormonal growth factors. It does not induce transient centriole deciliation, a hormonally regulated event. 相似文献
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The determination of microgram quantities of chlorine in polychlorinated biphenyls and organochlorine insecticides by molecular emission cavity analysis is described. Samples either pure, in admixture or mixed with sand were decomposed at 900 ± 50°C in a quartz combustion tube in a humidified oxygen atmosphere. The products of decomposition were bubbled through water or 1% ammonia and 4-μl aliquots of the solution obtained were injected into a stainless steel indium-lined cavity and heated in a nitrogen/hydrogen flame. The chlorine was quantified by comparing the intensity of the InCl emission at 360 nm with that obtained from hydrochloric acid standards. The effect of potential interferences such as alkali and alkaline earth metals, nitrogen, phosphorus, sulphur, carbon aluminium and iron were studied. Except for the alkali and alkaline earth elements, the recoveries of the compounds burned were not affected. Where the elements interfered, methods for eliminating the interferences are described. The chlorine recovery was usually >90%. 相似文献