Poly(methyl methacrylate) (PMMA)/silica/titania ternary nanocomposites with covalent bonding interaction between polymer and inorganic phases have been prepared using a novel non-hydrolytic sol-gel method. Transmission electron microscope (TEM) image of silica/titania binary inorganic component indicates a core-shell-like structure. Scanning electron microscope (SEM) images suggest that the well dispersed silica/titania particles in the hybrid are on the nanometer-scale. The transparencies of nanocomposites are maintained in visible region while the absorption band in ultraviolet (UV) region is red shifted with increasing inorganic content. The thermogravimetric analysis (TGA) results show that the thermal stability of PMMA copolymer increases dramatically with the addition of silica/titania moieties both in nitrogen and in air. 相似文献
The secondary reduction in the direct and oxazaborolidine‐catalyzed asymmetric borane reduction of ketones was investigated by the use of GC/MS tracing titration and control experiments. The results indicate that the secondary reduction affects the enantioselectivity only in noncoordinated solvents at low temperature and not under the usual catalytic reduction conditions because the intermediate alkoxyborane is unstable and quickly converts to borane and dialkoxyborane. The function of an alcohol additive in the asymmetric borane reduction of ketones is to consume excess borane in the reduction system thus inhibiting noncatalytic reduction, which leads to increased enantioselectivity in the catalytic reduction. 相似文献
Rational manipulation of supramolecular structures on surfaces is of great importance and challenging. We show that imidazole-based hydrogen-bonded networks on a metal surface can transform into an isostructural coordination network for facile tuning of the pore size and guest recognition behaviours. Deposition of triangular-shaped benzotrisimidazole (H3btim) molecules on Au(111)/Ag(111) surfaces gives honeycomb networks linked by double N–H⋯N hydrogen bonds. While the H3btim hydrogen-bonded networks on Au(111) evaporate above 453 K, those on Ag(111) transform into isostructural [Ag3(btim)] coordination networks based on double N–Ag–N bonds at 423 K, by virtue of the unconventional metal–acid replacement reaction (Ag reduces H+). The transformation expands the pore diameter of the honeycomb networks from 3.8 Å to 6.9 Å, giving remarkably different host–guest recognition behaviours for fullerene and ferrocene molecules based on the size compatibility mechanism.A hydrogen-bonded network on a Ag(111) surface can transform into an isostructural Ag(i) coordination network, giving drastically different host–guest recognition behaviours.相似文献
Changeable size moving window partial least squares (CSMWPLS) and searching combination moving window partial least squares (SCMWPLS) are proposed to search for an optimized spectral interval and an optimized combination of spectral regions from informative regions obtained by a previously proposed spectral interval selection method, moving window partial least squares (MWPLSR) [Anal. Chem. 74 (2002) 3555]. The utilization of informative regions aims to construct better PLS models than those based on the whole spectral points. The purpose of CSMWPLS and SCMWPLS is to optimize the informative regions and their combination to further improve the prediction ability of the PLS models. The results of their application to an open-path (OP)/FT-IR spectra data set show that the proposed methods, especially SCMWPLS can find out an optimized combination, with which one can improve, often significantly, the performance of the corresponding PLS model, in terms of low prediction error, root mean square error of prediction (RMSEP) with the reasonable latent variable (LVs) number, comparing with the results obtained using whole spectra or direct combination of informative regions for a compound. Regions consisting of the combinations obtained can easily be explained by the existence of IR absorption bands in those spectral regions. 相似文献
The objective of the present article was to study the thermal degradation behavior and flame retardancy of flexible polyvinyl chloride (PVC) composites containing TiO2/SO2?4 solid superacid because of its strong catalytic ability for esterification and dehydration. The TiO2/SO2?4 solid superacid was synthesized by using precipitation immersion method, and its structure was investigated by X-ray diffraction. As expected, the value of limiting oxygen index for PVC/Sb2O3/(TiO2/SO2?4) composite was 32.5% and the char yield of PVC/Sb2O3/(TiO2/SO2?4) composite was significantly improved compared to neat PVC in thermogravimetry tests. In addition, the peak heat release rate and smoke production rate of PVC/Sb2O3/(TiO2/SO2?4) decreased by 14% and 42%, respectively, compared with neat PVC. Moreover, the results of cone calorimetry tests and electron micrograph of char residue showed that the char yield of TiO2/SO2?4 was enhanced, resulting in a strong char layer structure with outstanding fire retardance cone. In conclusion, the results of this work showed that the addition of solid superacid promoted the decomposition and dehydration of PVC, which formed a compact and continuous char layer on the surface of the material. Hence, the study provides a new perspective for producing composites with excellent flame retardancy and smoke suppression properties of PVC.
The effect of different solid components of calcareous soil on the retention of Sr was investigated by using batch technique and selective extraction method. The sorption and desorption isotherms of Sr on the untreated calcareous soil and the three treated soils were determined at 20°C, pH 7.8±0.2 and in the presence of 0.001 M CaCl2. It was found that all isotherms are linear and that the sorption of Sr on the calcareous soil can be described by a reversible sorption process and the sorption mechanism is mainly ion exchange. 相似文献
With frontal analysis(FA),the dependence of adsorption isotherms of insulin on the composition of mobile phase in reversed phase liquid chromatography (RPLC) has been investigated,This is also a good example to employ the stoichiometric displacement theory (SDT) for ivestigating solute adsorption in physical chemistry.Six kinds of mobile phase in RPLC were employed to study the effects on the elution curves and adsorption isotherms of insulin.the key points of this paper are:(1) the stability of insulin due to delay time after preparing,the organic solvent concentration,the kind and the concentration of ion-pairing agent in mobile phase were found to affect both elution curve and adsorption isotherm very seriously.(2)To obtain a valid and comparable result,the composition of the mobile phase employed in FA must be as same as possible to that in usual RPLC of either analytical scale or preparative purpose.(3)Langmuir Equation and the SDT were employed to imitate these obtained adsorption isotherms.The expression for solute adsorption from solution of the SDT was found to have a better elucidation to the insulin adsorption from mobile phase in RPLC. 相似文献
Six novel inorganic-organic coordination supramolecular networks based on a versatile linking unit 4-pyridylthioacetate (pyta) and inorganic Co(II), Cu(II), Ag(I), Zn(II), Mn(II) and Pb(II) salts have been prepared in water medium and structurally characterized by single-crystal X-ray diffraction analysis. Reaction of CoCl(2).6H(2)O with Hpyta afforded a neutral mononuclear complex [Co(pyta)(2)(H(2)O)(4)](1), which exhibits a two-dimensional (2-D) layered architecture through intermolecular O-HO interactions. Reaction of CuCl(2.2H(2)O with Hpyta yielded a neutral one-dimensional (1-D) coordination polymer [[Cu(pyta)(2)(H(2)O].0.5H(2)O](n)(2) consisting of rectangle molecular square units, which show a three-dimensional (3-D) supramolecular network through S...S and O-H...O weak interactions. However, when AgNO(3), Zn(OAc)(2).2H(2)O or MnCl(2).4H(2)O salts were used in the above self-assembled processes, the neutral 2-D coordination polymers [Ag(pyta)](n)(3), [[Zn(pyta)(2)].4H(2)O](n)(4) or [[Mn(pyta)(2)(H(2)O)]](n)(5) with different topologies were obtained, respectively. While substituting the transition metal ions used in 1-5 with Pb(OAc)(2).3H(2)O, a one-dimensional coordination polymer [Pb(pyta)(2)](n)(6), which shows a novel 2-fold interpenetrating 2-D supramolecular architecture through weak SS interactions, was isolated. It is interesting to note that the building block pyta anion exhibits different configurations and coordination modes in the solid structures of complexes 1-6. These results indicate that the versatile nature of this flexible ligand, together with the coordination preferences of the metal centers, play a critical role in construction of these novel coordination polymers or supramolecules. The spectral and thermal properties of these new materials have also been investigated. 相似文献
Most magnetorheological materials, composed of magnetic microparticles in a liquid, require significant amounts of magnetic particles and a large magnetic field to achieve the desired effects. Here, we report on a new type of magnetorheological materials consisting of small amounts of magnetic nanoparticles (0.8 wt %) but exhibiting large rheological change (i.e., a gel-sol transition) upon the application of a small magnetic field. We use self-assembly to create hybrid nanofibers, which consist of supramolecular hydrogelators and magnetic nanoparticles, as the matrices of the hydrogel. Localized in the nanofibers at a distance of 1-2 nm, the magnetic nanoparticles occupy a small volume fraction of the hydrogel, significantly enhancing the magnetic dipole interactions between them, which results in the large magnetoresponse. This strategy generates a hierarchical nanostructure and eliminates several drawbacks of the simple mixture of polymers with nanoparticles, and thus provides a new methodology that uses magnetic force to control the nanostructures and properties of soft materials. 相似文献