Scattering from polymer-like micelles

Polymer-like micelles are analogs to polymer solutions and provide an exciting class of materials for both applications and fundamental understanding of polyelectrolyte systems. Small angle neutron and X-ray scattering have been key to the characterization of these materials from the first observations of linear micelle growth. As new materials are developed, these techniques continue to be utilized and combined with other analytical tools to characterize the length and time scales of polymer-like micelle behavior. Recent reports on the use of small-angle scattering to characterize polymer-like and wormlike micelles are reviewed, with focus on new materials, improvements in analytical approaches and anisotropic structures.     

新型Rh_2(esp)_2配体手性类似物的合成

以(R)-叔丁基亚磺酰胺为手性助剂,与1,3-苯二甲醛经缩合反应制得关键中间体——(Rs,Rs)-双叔丁基亚磺酰亚胺(7);锂化的羧酸酯与7经不对称加成反应合成了两个新型的Rh_2(esp)_2配体类似物——(Rs,Rs',R,R')-β-胺基羧酸酯和(Rs,Rs',R,R',R,R')-α,β-氮杂环丙烷羧酸酯,产率分别为96%和65%,非对映选择性均大于20∶1。化合物的结构经1H NMR和13C NMR表征。     

A molecular dynamics simulation study on resonance frequencies comparison of tunable carbon-nanotube resonators

We investigated tunable gigahertz-resonators, which is based on the application of a telescoped double-walled carbon-nanotube that can be used repeatedly and operate at a single frequency or have a relatively narrow frequency range, via classical molecular dynamics simulations of a double-walled carbon-nanotube. Two types of telescoped double-walled carbon-nanotube resonators were compared with each other; one was bridge-type and another was cantilever-type, and one side was connected to a position controller in order to achieve a telescoped carbon-nanotube. The frequency bandwidth of our cantilevered type design can exceed that of the bridged type. Our simulations showed that such a system can tune it up its resonance frequency by controlling the length of oscillating carbon-nanotube resonator.     

Second Order Nonlinear Evolution Inclusions Ⅱ： Structure of the Solution Set

We contimle the work initiated in [1] （Second order nonlinear evolution inclusions I： Existence and relaxation results. Acta Mathematics Science, English Series, 21（5）, 977-996 （2005）） and study the structural properties of the solution set of second order evolution inclusions which are defined in the analytic framework of the evolution triple. For the convex problem we show that the solution set is compact Rs, while for the nonconvex problem we show that it is path connected, Also we show that the solution set is closed only if the multivalued nonlinearity is convex valued. Finally we illustrate the results by considering a nonlinear hyperbolic problem with discontinuities.     

Copper nanocluster diffusion in carbon nanotube

The diffusion of copper nanocluster in carbon nanotube was investigated using a classical molecular dynamics simulation and three empirical potential functions. The results indicated a growth mechanism of the copper-filled ultra-thin carbon nanotubes: the copper nanoclusters inserted into carbon nanotubes swiftly migrate along the tube axis, and then the copper nanowires grow in the ultra-thin carbon nanotubes. Periodic energy barriers in the carbon nanotubes induced the directional movement of copper nanoclusters in the carbon nanotubes. The diffusion speeds of copper nanocluster in the carbon nanotube showed the Arrherius relation.     

Fabrication of freestanding GaN microstructures using AlN sacrificial layers

The fabrication of freestanding GaN microstructures using AlN sacrificial layers (SLs) is reported. GaN layers were grown by plasma assisted molecular beam epitaxy (PAMBE) on polycrystalline AlN sacrificial layers that have been deposited at 600 °C. Isotropic wet chemical etching of the AlN film released GaN microbridges and – cantilevers. The stress gradient and the compressive stress in the GaN‐film was extracted by analysis of the relation between beam geometry and displacement. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polyelectrolyte brushes

We survey recent progress made in the field of polyelectrolyte brushes. These systems consist of long polyelectrolyte chains that are grafted densely to planar or curved surfaces. The main feature of all polyelectrolyte brushes is the strong confinement of the counterions within the brush layer. The high osmotic pressure which is thus built up explains the unusual features of these systems. Here we focus on the most recent experimental developments which are rationalized on the basis of existing theoretical predictions and opens new challenging problems. In particular, we shall discuss briefly the experimental systems used for comparing theory and experiment lately. Moreover, we review various aspects related to the experimental analysis of polyelectrolyte brushes. As a final point, we survey trends in recent applications which demonstrate that polyelectrolyte brushes have an excellent prospect for future nanotechnology.     

Interactions of quinine with polyacrylic and poly-L-glutamic acids in aqueous solutions

Drug-loaded polymers provide an attractive form for controlled drug delivery systems. A proper knowledge of polymer-drug interactions can aid in the designing of polymers for various drug-delivery applications. In this paper we have investigated the interaction of a drug such as quinine, with synthetic macromolecules such as poly(acrylic acid), PAA, and poly(L-glutamic acid), PGA, at pH 7 and 37 °C by fluorescence spectroscopy and viscometry. The analysis of the binding isotherms revealed that the association process is positive cooperative up to a threshold concentration and then it is negative. In addition, the thermodynamic parameters vary along the isotherm. Results also suggest that there is an optimum polymer to quinine ratio. Based on the viscometry results a mechanism of the interaction in which the polymer conformation plays a determinant role is proposed. Since the conformation depends on the molecular size, the architecture of the macromolecule, the effective charge and ergo the ionic strength, all these variables have been taken into account and their effect on the binding discussed.     

Phase transition in swollen gels 31. Swelling and mechanical behaviour of interpenetrating networks composed of poly(1-vinyl-2-pyrrolidone) and polyacrylamide in water/acetone mixtures

Swelling and mechanical behaviour of interpenetrating positively charged polymer networks (IPNs), composed of poly(1-vinyl-2-pyrrolidone) (PVP) networks and polyacrylamide (PAAm) networks, was investigated in water/acetone mixtures. The first PVP networks were prepared by radiation polymerization at room temperature; after that the PVP networks were swollen in PAAm aqueous solutions and the networks were prepared by thermal copolymerization at 65 °C. The IPNs were prepared with various amounts of the two charged comonomers (quaternary ammonium salts) in the presence of crosslinkers. Two transition regions, detected in the dependence of swelling ratio X on acetone concentration a, suggest that a two-phase structure was formed. The first transition, located between 44 and 60 vol% of acetone, corresponds to PAAm networks, while the second transition, located at 75 vol% of acetone, corresponds to PVP networks. Depending on the amount of positive charges bound to chains, both transitions exhibit continuous or discontinuous character; this fact indicates that intermolecular interactions between the two components occur with the formation of IPNs (e.g., more polar, charged PVP component increases the extent of hydrogen bonding and makes acetone less effective solvent for IPNs at the PAAm transition). The dependences of log G on log X are roughly the same regardless of charge concentrations; this means that the mechanical behaviour is predominantly determined by the degree of swelling for all gels.     

Effect of surface cationization on the conformal deposition of polyelectrolytes over cotton fibers

The effect of surface cationization on the conformal deposition of alternating nanolayers of poly(sodium styrene sulfonate) (PSS) [Kleinfeld E, Ferguson G (1996) Chem Mater 8:1575–1578] and poly(allylamine hydrochloride) (PAH) over cotton fibers is reported. Three different levels of cotton cationization were evaluated. Variations in the cationization degree were achieved by manipulating the ratio of 3-chloro-2-hydroxy propyl trimethyl ammonium to NaOH. Experimental results obtained via Carbon–Hydrogen–Nitrogen–Sulfur (CHNS) elemental analysis and X-ray Photoelectron Spectroscopy (XPS) indicated that the deposition process was not significantly influenced by the degree of cotton cationization. The build up of further polyelectrolyte layers was found to be less sensitive to variations in the cationic character of the substrates once a critical number of alternating layers was deposited.