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排序方式: 共有86条查询结果,搜索用时 15 毫秒
1.
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Liu J Lin Y Liang L Voigt JA Huber DL Tian ZR Coker E McKenzie B McDermott MJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(3):604-611
Although oriented carbon nanotubes, oriented nanowires of metals, semiconductors and oxides have attracted wide attention, there have been few reports on oriented polymer nanostructures such as nanowires. In this paper we report the assembly of large arrays of oriented nanowires containing molecularly aligned conducting polymers (polyaniline) without using a porous membrane template to support the polymer. The uniform oriented nanowires were prepared through controlled nucleation and growth during a stepwise electrochemical deposition process in which a large number of nuclei were first deposited on the substrate using a large current density. After the initial nucleation, the current density was reduced stepwise in order to grow the oriented nanowires from the nucleation sites created in the first step. The usefulness of these new polymer structures is demonstrated with a chemical sensor device for H(2)O(2), the detection of which is widely investigated for biosensors. Finally, we demonstrated that controlled nucleation and growth is a general approach and has potential for growing oriented nanostructures of other materials. 相似文献
3.
ABSTRACT Copolymers of 1,5-dioxepan-2-one (DXO) and e-caprolactone (?-CL), δ-valerolactone (δ-VL) or L-lactide (LLA) have been synthesized and characterized. High molecular weight copolymers were obtained using stannous-2-ethyl hexanoate as catalyst in bulk. Reactivity ratios for the copolymerization of DXO and δ-VL were determined at 110°C as rVL=0.5 and rDXO=2.3. At high conversion, depolymerization of δ-VL occurred, resulting in lower molecular weight and variations in the copolymer composition. Physical properties, such as crystallinity and melting temperature of the DXO-copolymers proved to be strongly dependent on the choice of comonomer and on the molar composition of the copolymers. DXO appears to be incorporated into the poly-?-caprolactone (PCL) crystals and to some extent into the poly-δ-valerolactone (PVL) crystals, resulting in a more gradual decrease in crystallinity with increasing amount of DXO. 相似文献
4.
Diode laser spectroscopy has been employed to monitor the formation of chlorine nitrate (ClONO2) in the association reaction of ClO with NO2. Chlorine nitrate is the only stable end-product of this reaction at room temperature. Time-resolved measurements of ClONO2 formation using molecular modulation showed no evidence for any involvement of unstable isomers of ClNO3 in the reaction. These measurements gave a value of k1 = (1.8 ± 0.4) × 10?31 cm6/molecule2 · s for the reaction at 295 K and an upper limit of 5 ms for the lifetime of any isomeric products at this temperature. 相似文献
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James N. Coker 《Journal of polymer science. Part A, Polymer chemistry》1975,13(11):2473-2489
Interpolymers of tetrafluoroethylene and isobutylene containing approximately equimolar amounts of each monomer have been prepared by emulsion polymerization. Also prepared were compositions containing small amounts of other monomers such as acrylic acid. The characterization of these products is discussed, as is the preparation of both “ionomer” and iminated derivatives of the carboxylated terpolymers. 相似文献
8.
Causo MS Ciccotti G Montemayor D Bonella S Coker DF 《The journal of physical chemistry. B》2005,109(14):6855-6865
We generalize the linearized path integral approach to evaluate quantum time correlation functions for systems best described by a set of nuclear and electronic degrees of freedom, restricting ourselves to the adiabatic approximation. If the operators in the correlation function are nondiagonal in the electronic states, then this adiabatic linearized path integral approximation for the thermal averaged quantum dynamics presents interesting and distinctive features, which we derive and explore in this paper. The capability of these approximations to accurately reproduce the behavior of physical systems is demonstrated by calculating the diffusion constant for an excess electron in a metal-molten salt solution. 相似文献
9.
The electric field gradients at27Al and63Cu nuclei which are nearest neighbors to the muon in the face-centered cubic metals aluminum and copper, with muon at an octahedral
interstitial site, are studied. The electron density fluctuations needed for the evaluation of the electronic, or valence,
contributions to field gradients are taken from earlier investigations involving the spherical solid approximation. The enhancement
factors a that have to be applied to the electric field-gradients obtained from these approximations, due to the departures
of the electronic wave-functions from plane-wave character, and the incorporation of antishielding effects, have been obtained
for both APW and OPW approaches to the conduction electron wave-functions and good agreement is found between the results
by the two approaches. Size effects due to the lattice distortion associated with the presence of the muon are included through
actual point ion summations using available calculated displacements of the ions surrounding the muon. The valence contributions
are the dominant ones but the size effect contributions are also significant. The net field-gradient obtained for the27Al site is significantly smaller than experiment while that for63Cu is substantially larger than experiment. Possible sources that could lead to better agreement with experiment are discussed
and it is concluded that major improvement is needed in the valence effect contributions in both metals. 相似文献
10.
Dynamic crack growth along the interface of a fiber-reinforced polymer composite-Homalite bimaterial subjected to impact shear loading is investigated experimentally and numerically. In the experiments, the polymer composite-Homalite specimens are impacted with a projectile causing shear dominated interfacial cracks to initiate and subsequently grow along the interface at speeds faster than the shear wave speed of Homalite. Crack growth is observed using dynamic photoelasticity in conjunction with high-speed photography. The calculations are carried out for a plane stress model of the experimental configuration and are based on a cohesive surface formulation that allows crack growth, when it occurs, to emerge as a natural outcome of the deformation history. The effect of impact velocity and loading rate is explored numerically. The experiments and calculations are consistent in identifying discrete crack speed regimes within which crack growth at sustained crack speeds is possible. We present the first conclusive experimental evidence of interfacial crack speeds faster than any characteristic elastic wave speed of the more compliant material. The occurrence of this crack speed was predicted numerically and the calculations were used to design the experiments. In addition, the first experimental observation of a mother-daughter crack mechanism allowing a subsonic crack to evolve into an intersonic crack is documented. The calculations exhibit all the crack growth regimes seen in the experiments and, in addition, predict a regime with a pulse-like traction distribution along the bond line. 相似文献