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排序方式: 共有9723条查询结果,搜索用时 171 毫秒
41.
《International Journal of Hydrogen Energy》2022,47(7):4846-4853
One of the alternative types of proton-conducting membranes for a hydrogen-air solid polymer fuel cell is the type of hybrid membranes based on polyvinyl alcohol (PVA) crosslinked with aldehyde, modified by sulfonic acid. Earlier, for the first time, we obtained new ion – conducting membranes based on furfural-crosslinked PVA modified aminosulfonic acid (ASA) and tetraethoxysilane (TEOS), as well as membranes not crosslinked with furfural (FUR) or unmodified ASA and TEOS, by a liquid-phase synthesis method, in an organic medium-dimethyl sulfoxide. The values of their ionic conductivity and the degree of swelling in water are presented. In this work, the composition and structure of the obtained ion-conducting membranes are studied using liquid-phase nuclear magnetic resonance (NMR) spectroscopy on 1H nuclei. In the 1H NMR spectrum of an ion – conducting membrane not cross-linked with the «PVA/ASA», the signal of free OH groups of PVA is observed to disappear, but at the same time a characteristic triplet at 7.1 ppm. is preserved, having a constant of ~51 Hz and components of the same intensity (1:1:1), which corresponds to protons of 14NH4+ hydrolyzed ASA. The disappearance of the expanded signal at 9.6 m. d. of protons of the free sulfo group of ASA and a narrow singlet signal at 5.8 m. d. of free protons of the NH2 group of ASA indicates the interaction of ASA with OH groups of PVA. In the 1H NMR spectrum of an ion – conducting membrane crosslinked with FUR – «PVA/ASA/FUR», signals of protons of the furan ring of FUR and a signal of its aldehyde group are observed, which is shifted to a strong field, which is determined by the formation of a chemical bond between FUR and the polymer chain of PVA. In the 1H NMR spectra of all membranes modified by ASA, the appearance of a second weaker-field 14NH4+ triplet is observed, and in the spectra of a number of ion – conducting hybrid membranes modified by TEOS – «PVA/ASA/FUR/TEOS», signals of the third type of 14NH4+ triplets shifted in a strong field relative to the other two 14NH4+ triplets were detected. The appearance of additional 14NH4+ triplets indicates the formation of several bound forms of the ammonium ion. 相似文献
43.
Marc-Joseph Antonini Atharva Sahasrabudhe Anthony Tabet Miriam Schwalm Dekel Rosenfeld Indie Garwood Jimin Park Gabriel Loke Tural Khudiyev Mehmet Kanik Nathan Corbin Andres Canales Alan Jasanoff Yoel Fink Polina Anikeeva 《Advanced functional materials》2021,31(43):2104857
Fiber drawing enables scalable fabrication of multifunctional flexible fibers that integrate electrical, optical, and microfluidic modalities to record and modulate neural activity. Constraints on thermomechanical properties of materials, however, have prevented integrated drawing of metal electrodes with low-loss polymer waveguides for concurrent electrical recording and optical neuromodulation. Here, two fabrication approaches are introduced: 1) an iterative thermal drawing with a soft, low melting temperature (Tm) metal indium, and 2) a metal convergence drawing with traditionally non-drawable high Tm metal tungsten. Both approaches deliver multifunctional flexible neural interfaces with low-impedance metallic electrodes and low-loss waveguides, capable of recording optically-evoked and spontaneous neural activity in mice over several weeks. These fibers are coupled with a light-weight mechanical microdrive (1 g) that enables depth-specific interrogation of neural circuits in mice following chronic implantation. Finally, the compatibility of these fibers with magnetic resonance imaging is demonstrated and they are applied to visualize the delivery of chemical payloads through the integrated channels in real time. Together, these advances expand the domains of application of the fiber-based neural probes in neuroscience and neuroengineering. 相似文献
44.
《Ceramics International》2022,48(9):12209-12216
We report the structural, magnetic, electrical and broadband microwave absorption in La0.7Na0.3MnO3 sample synthesized by microwave (MW) irradiation (Na0.3LMO_MW) and compare them to the sample synthesized by solid-state (SS) reaction method (Na0.3LMO_SS). Single phase Na0.3LMO_MW was synthesized at 800 °C in 30 min, whereas, Na0.3LMO_SS sample was obtained by sintering at 1200 °C for 48 h. Although both these samples show ferromagnetic transition at TC ~324.8 K, the MW-synthesized sample shows distinct physical properties: broad ferromagnetic transition, smaller saturation magnetization, a large difference between the magnetic ordering and metal-insulator transition temperatures, a large high-field magnetoresistance, a table top-like magnetocaloric effect, and a large low-field microwave absorption compared to the solid state synthesized sample. These differences are suggested to arise from magnetic heterogeneity induced by smaller grain size and surface spin disorder in the MW synthesized La0.7Na0.3MnO3. 相似文献
45.
《Journal of the European Ceramic Society》2014,34(10):2217-2227
The point defects and the structural and dielectric properties of Dy-doped BaTiO3 ceramics prepared at 1400 °C were investigated. The solubility of Dy in the self-compensation mode was determined to be x = 0.07 for (Ba1−xDyx)(Ti1−xDyx)O3, and no EPR signals associated with the Dy3+ Kramers ion or the Ba and Ti vacancies were detected using the electron paramagnetic resonance (EPR) technique. As x increases, the dielectric behavior changed from a first-order phase transition to a diffuse phase transition to a Y7R dielectric-temperature stability. A strong EPR signal at g = 1.974, which is rare among rare-earth-doped BaTiO3 ceramics appeared unexpectedly in the single-phase (Ba1−xDyx)Ti1−x/4O3 ceramics with deliberately designed Ti vacancies. This signal was attributed to ionized Ba vacancy defects. A preference for the self-compensation mode of Dy3+ ions is responsible for the appearance of Ba vacancies. The real formula of the nominal (Ba1−xDyx)Ti1−x/4O3 is expressed as (Ba1−xDy3x/4)(Ti1−x/4Dyx/4)O3. In addition, the defect chemistry is discussed. 相似文献
46.
Dendrimers are novel three dimensional, hyperbranched globular nanopolymeric architectures. Attractive features like nanoscopic size, narrow polydispersity index, excellent control over molecular structure, availability of multiple functional groups at the periphery and cavities in the interior distinguish them amongst the available polymers. Applications of dendrimers in a large variety of fields have been explored. Drug delivery scientists are especially enthusiastic about possible utility of dendrimers as drug delivery tool. Terminal functionalities provide a platform for conjugation of the drug and targeting moieties. In addition, these peripheral functional groups can be employed to tailor-make the properties of dendrimers, enhancing their versatility. The present review highlights the contribution of dendrimers in the field of nanotechnology with intent to aid the researchers in exploring dendrimers in the field of drug delivery. 相似文献
47.
Three-dimensional flower-like Bi2WO6 microspheres with the diameter of about 4 μm were prepared by a facile hydrothermal method using bismuth nitrate pentahydrate and sodium tungstate dihydrate as raw materials. A novel Ag-modified Bi2WO6 was synthesized through a simple and practical photoreduction process. The UV–vis diffuse reflectance spectra indicate that the Ag/Bi2WO6 samples have a significantly enhanced optical absorption in the visible light region than that of pure Bi2WO6 microspheres due to the surface plasmon resonance (SPR) of Ag nanoparticles on the surface of pure Bi2WO6. The photocatalytic activities of the as-prepared samples were evaluated by the decolorization of rhodamine B under simulated sun-light irradiation. The results reveal that the photocatalytic activities of the Ag/Bi2WO6 samples increase first and then decrease with increasing amount of loading Ag and the 1.0 wt% Ag-loaded Bi2WO6 sample exhibits the best photocatalytic activity compared with the other samples. The enhanced photocatalytic activity could be attributed to the synergistic effect of the strong SPR and the effective separation of photogenerated electrons and holes caused by Ag nanoparticles. 相似文献
48.
49.
Hongxia Chen Feng Liu Fangjie Qi Kwangnak Koh Keming Wang 《International journal of molecular sciences》2014,15(4):5496-5507
Three calix[4]arene (Cal-4) derivatives which separately contain ethylester (1), carboxylic acid (2), and crownether (3) at the lower rim with a common reactive thiol at the upper rim were synthesized and constructed to self-assembled monolayers (SAMs) on Au films. After spectroscopic characterization of the monolayers, surface coverage and orientation of antibody immobilized on the Cal-4 derivative SAMs were studied by surface plasmon resonance (SPR) technique. Experimental results revealed that the antibody could be immobilized on the Cal-4 derivatives spontaneously. The orientation of absorbed antibody on the Cal-4 derivative SAMs is related to the SAM’s dipole moment. The possible orientations of the antibody immobilized on the Cal-4 derivative 1 SAM are lying-on or side-on, while on the Cal-4 derivative 2 and Cal-4 derivative 3 head-on and end-on respectively. These experimental results demonstrate the surface dipole moment of Cal-4 derivative appears to be an important factor to antibody orientation. Cal-4 derivatives are useful in developing site direct protein chips. 相似文献
50.
Siamak Shoravi Gustaf D. Olsson Bj?rn C. G. Karlsson Ian A. Nicholls 《International journal of molecular sciences》2014,15(6):10622-10634
Aspects of the molecular-level basis for the function of ethylene glycol dimethacrylate and trimethylolproprane trimethacrylate crosslinked methacrylic acid copolymers molecularly imprinted with (S)-propranolol have been studied using a series of all-component and all-atom molecular dynamics studies of the corresponding prepolymerization systems. The crosslinking agents were observed to contribute to template complexation, and the results were contrasted with previously reported template-recognition behavior of the corresponding polymers. Differences in the extent to which the two crosslinkers interacted with the functional monomer were identified, and correlations were made to polymer-ligand recognition behavior and the results of nuclear magnetic resonance spectroscopic studies studies. This study demonstrates the importance of considering the functional monomer–crosslinker interaction when designing molecularly imprinted polymers, and highlights the often neglected general contribution of crosslinker to determining the nature of molecularly imprinted polymer-template selectivity. 相似文献