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排序方式: 共有75条查询结果,搜索用时 9 毫秒
1.
Aqueous dispersions of single-wall and multiwall carbon nanotubes with designed amphiphilic polycations 总被引:1,自引:0,他引:1
Sinani VA Gheith MK Yaroslavov AA Rakhnyanskaya AA Sun K Mamedov AA Wicksted JP Kotov NA 《Journal of the American Chemical Society》2005,127(10):3463-3472
Poor solubility of single-walled and multiwalled carbon nanotubes (NTs) in water and organic solvents presents a considerable challenge for their purification and applications. Macromolecules can be convenient solubilizing agents for NTs and a structural element of composite materials for them. Several block copolymers with different chemical functionalities of the side groups were tested for the preparation of aqueous NT dispersions. Poly(N-cetyl-4-vinylpyridinium bromide-co-N-ethyl-4-vinylpyridinium bromide-co-4-vinylpyridine) was found to form exceptionally stable NT dispersions. It is suggested that the efficiency of macromolecular dispersion agents for NT solubilization correlates with the topological and electronic similarity of polymer-NT and NT-NT interactions in the nanotube bundles. Raman spectroscopy and atomic force and transmission electron microcopies data indicate that the polycations are wrapped around NTs forming a uniform coating 1.0-1.5 nm thick. The ability to wind around the NT originates in the hydrophobic attraction of the polymer backbone to the graphene surface and topological matching. Tetraalkylammonium functional groups in the side chains of the macromolecule create a cloud of positive charge around NTs, which makes them hydrophilic. The prepared dispersions could facilitate the processing of the nanotubes into composites with high nanotube loading for electronic materials and sensing. Positive charge on their surface is particularly important for biological and biomedical applications because it strengthens interactions with negatively charged cell membranes. A high degree of spontaneous bundle separation afforded by the polymer coating can also be beneficial for NT sorting. 相似文献
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We discuss the notion of spin squeezing considering two mutually exclusive classes of spin-s states, namely, oriented and non-oriented states. Our analysis shows that the oriented states are not squeezed while non-oriented
states exhibit squeezing. We also present a new scheme for construction of spin-s states using 2s spinors oriented along different axes. Taking the case of s=1, we show that the ‘non-oriented’ nature and hence squeezing arise from the intrinsic quantum correlations that exist among
the spinors in the coupled state. 相似文献
4.
AA Yan LI Kai CAO ZhongHua & HU WenRui Key Laboratory of Microgravity 《中国科学:物理学 力学 天文学(英文版)》2011,(2)
The dependency of the critical Marangoni number on the geometrical aspect ratio of the floating half zone is essential to predict the onset of oscillatory thermocapillary convection.The experimental studies in the microgravity conditions on floating half zones of several centimeters in diameter have predicted that the critical Marangoni number increases with the increasing aspect ratio,and the terrestrial experimental studies have predicted the contradictory conclusion for floating half zones of several mil... 相似文献
5.
Non-Gravitational Effects with Density-Matching in Evaluating the Influence of Sedimentation on Colloidal Coagulation 下载免费PDF全文
The method of density matching between the solid and liquid phases is often adopted to effectively eliminate the effect of sedimentation of suspensions in studies on dynamic behaviour of a colloidal system. However, the associated changes in the solvent composition may bring side effects to the properties investigated and therefore might lead to a faulty conclusion if the relevant correction is not made. To illustrate the importance of this side effect, we present an example of the sedimentation influence on the coagulation rate of suspensions of 2μm (diameter) polystyrene. The liquid mixtures, in the proper proportions of water (H2O), deuterium oxide (D2O) and methanol (MeOH) as the liquid phase, density-matched and unmatched experiments are performed. Besides the influence of viscosity, the presence of methanol in solvent media, used to enhance the sedimentation effect, causes significant changes (reduction) in rapid coagulation rates compared to that in pure water. Without the relevant corrections for those non-gravitational factors it seems that gravitational sedimentation would retard the coagulation. The magnitude of the contribution from the non-gravitational factor is quantitatively determined, making the relevant correction possible. After necessary the influence of the sedimentation on coagulation rates at corrections for all factors, our experiments show that the initial stage of the coagulation is not observable. 相似文献
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D. A. Davydov A. A. Rakhnyanskaya V. N. Orlov A. V. Bychkova A. L. Kovarskii A. A. Yaroslavov 《Polymer Science Series A》2010,52(7):693-703
Adsorption of the synthetic polycation poly-N-ethyl-4-vinylpyridinium bromide (PEP) on the surface of bilayered lipid vesicles (liposomes) is studied. Two types of liposomes
are used: (i) traditional two-component liposomes formed from neutral phosphatidylcholine (PC) and anionic diphosphatidylglycerol
(cardiolipin, CL2−) and (ii) PC/CL2− anionic liposomes with the built-in nonionogenic surfactant poly(ethyleneglycol) cetyl ether with a degree of polymerization
of 20 (Brij-58). PEP is quantitatively linked with both types of liposomes; this process is electrostatic in character and
fully reversible. The formation of a poly(ethylene glycol) layer on liposomal membrane decreases the stability of polycation-liposome
complexes in aqueous salt solutions. Adsorption of PEP on the surface of PC/CL2− liposomes is accompanied by their aggregation; PC/CL2−/Brij liposomes do not aggregates, even during complete neutralization of their charge by the adsorbed PEP. DSC measurements
showed that the adsorption of the polycation is accompanied by microphase separation in the liposomal membrane: formation
of domains, which are composed primarily of CL2− molecules and linked to the complex with PEP, and regions, where electroneutral lipids are primarily concentrated. With the
use of a spin probe, the packing density of bilayers (their microviscosity) is estimated, and a preferential localization
of the probe at the boundaries of lipid domains in the membrane based on PC/CL2−/Brij liposomes is proposed. The causes of the aggregative stability of three-component PC/CL2−/Brij liposomes are described, and the structure of the prepared polymer-liposome complexes is discussed. 相似文献
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