129Xe NMR study of Xe adsorption on multiwall carbon nanotubes

¹²⁹Xe NMR spectroscopy has been used to study the adsorption of Xe on multi-wall carbon nanotubes (MWCNT). The results obtained have shown the ¹²⁹Xe NMR ability to probe the intercrystalline (aggregate) and the inner porosity of CNT. In particular, the effects on porosity of tubes openings by hydrogen exposure and of ball milling were examined. Dramatic changes observed in the ¹²⁹Xe NMR spectra after moderate ball milling of MWCNTs were attributed to the destruction of the initial intercrystalline pore structure and to the Xe access inside the nanotubes. To examine the exchange dynamics the mixture of as-made and milled MWCNTs was studied with one- and two-dimensional (1D and 2D) ¹²⁹Xe NMR. The exchange between the interior of milled nanotubes and the aggregate pores of as-made MWCNTs was fast on the NMR acquisition time scale. The Xenon exchange between the interior of the as-made MWCNTs and the large aggregate pores occurred on a longer time scale of 10 ms, as was established by 2D ¹²⁹Xe NMR exchange spectroscopy. Variable temperature ¹²⁹Xe NMR data were also discussed and analyzed in terms of the fast exchange approximation.     

Comparison of Xe single bubble sonoluminescence in water and sulfuric acid

Using the equations of fluid mechanics with proper boundary conditions and taking account of the gas properties, we can numerically simulate the process of single bubble sonoluminescence, in which electron-neutral atom bremsstrahlung, electron-ion bremsstrahlung and recombination radiation, and the radiative attachment of electrons to atoms and molecules contribute to the light emission. The calculation can quantitatively or qualitatively interpret the experimental results. We find that the accumulated heat energy inside the compressed gas bubble is mostly consumed by the chemical reaction, therefore, the maximum degree of ionization inside Xe bubble in water is much lower than that in sulfuric acid, of which the vapour pressure is very low. In addition, in sulfuric acid much larger pa and R0 are allowed which makes the bubbles in it much brighter than that in water.     

Surface chemical modification of zeolites and their catalytic performance for naphthalene alkylation

Acid-catalyzed naphthalene alkylation products, such as 2,6-dialkylnaphthalenes (2,6-DAN), are industrially important compounds used to make monomers for advanced polymer materials [1]. Zeolite molecular sieves can be extensively used in many catalytic applications, specifically in naphthalene alkylations due to their high activity and stability as well as their high selectivity. The initial studies have mainly focused on gas phase alkylation of naphthalene with methanol, and only obtained th…     

129Xe NMR as a probe of polymer blends

The miscibility of two-component polymer blends has been investigated using xenon-129 (¹²⁹Xe) nuclear magnetic resonance (NMR) to probe the phase morphology. The chemical shift of ¹²⁹Xe dissolved in a given polymer is unique, thus heterogeneous blends with large domain sizes exhibit two ¹²⁹Xe NMR lines. When a single resonance is obtained, the data are consistent with miscibility, yielding an upper bound on the domain size. The temperature dependence of the relative solubilities and chemical shifts of ¹²⁹Xe dissolved in the pure components may allow a determination of the phase morphology in blends exhibiting a single resonance. The method is used to demonstrate that polychloroprene and 25% epoxidized 1,4-polyisoprene form a miscible blend.     

Interaction Study of Guest with Host in Clathrate Hydrate

Lattice dynamical simulations of noble gas hydrate structuresⅠandⅡhave been performed. Potential energies were investigated to study the influence of guest species on the stability of the hydrate structure.Results show that when the diameter of inclusion molecules is between 3(?)and 4.2(?),such as Ar and Kr,the critical role of the 5~(12)cage in the stabilization of hydrates becomes effective.For Xe hydrates SⅠand SⅡ,with the help of lattice dynamical calcnlations,the modes attributions are identified directly.We proposed the resonant effect of the fingerprint frequency at about 7 meV and 10 meV which arise from the coupling of Xe molecules in the 5~(12)cage with the host lattice.     

129Xe NMR法研究醇二元混合溶液

129Xe NMR可以作为研究液体结构状态的探针．甲醇是一个与水结构差别最小的有机溶剂．本文研究了129Xe在甲醇-丁醇,甲醇-戊醇,甲醇-辛醇,甲醇-癸醇混合溶剂中化学位移随组成的变化,并测定了混合溶剂的密度和折射率．129Xe化学位移随混合溶剂的摩尔分数的变化为四条曲率很近的曲线,而化学位移随混合溶剂的体积分数的变化为斜率随多碳醇碳原子数增加的直线．这表明甲醇-多碳醇二元混合溶剂中不存在疏溶剂作用,而构成分子均匀分布的体系．129Xe在甲醇-丁醇,甲醇-癸醇中的化学位移与混合溶剂折射率的一种函数的关系为两条斜率很接近的直线,表明Xe在溶液中主要受范德华力作用．     

Vacuum ultraviolet irradiation on siliceous coatings on polycarbonate substrates

We studied the effect of vacuum ultraviolet (vuv) irradiation on siliceous coatings of polycarbonate (PC) substrates derived by the sol–gel method, with the aim of improving the abrasion resistance of the substrate surface. Methyltriethoxysilane with colloidal silica was used to prepare the sol solution. The sol solution was spin-coated on PC and this was followed by vuv irradiation with a Xe excimer lamp at 172 nm under N₂ atmosphere. The PC substrate with vuv irradiated coating retained its high transmittance in the visible region for about 3 or more times of scraping turns by a steel wool tester on the surface, compared with the non-irradiated or mercury lamp-irradiated coatings, which demonstrated the remarkable improvement of the abrasion resistance by the vuv irradiation. The chemical changes under the vuv irradiation were also investigated by FTIR–ATR spectroscopy, composition analysis conducted with X-ray photoelectron spectroscopy and hardness measurements. It was concluded that the vuv light irradiation resulted in degrading the Si–CH₃ bond in sol–gel derived siliceous coatings to yield hardening of the coatings. The transmittance of the coating in vuv region also increased with the Xe lamp irradiation.     

ChemInform Abstract: XeNO3+: A Gaseous Cation Characterized by a Remarkably Strong Xe—O Bond.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Photolysis of a fluorinated polymer film by vacuum ultraviolet radiation

We studied the photolysis of a fluoroethylene–fluoropropylene copolymer (FEP) film by vacuum ultraviolet (VUV) radiation from a resonance Xe lamp at a wavelength of 147 nm and air pressures of 0.05 and 2.5 Torr. The chemical changes in the FEP surface layer were investigated by Fourier-transform infrared spectroscopy with attenuated total reflection attachment and X-ray photoelectron spectroscopy. Double bonds were found to be the main product in the case of VUV treatment at 0.05 Torr, while photo-oxidation of FEP occurred predominantly by VUV treatment at 2.5 Torr under formation of the —CF₂C(O)F group. This oxygen-containing group was more effectively formed in the FEP surface layer by VUV photo-oxidation than by conventional surface oxidation techniques such as treatments by plasma and corona discharge and ozone. Storage of the VUV-treated polymers in air at 50% relative humidity resulted in hydrolysis of —CF₂C(O)F to the —CF₂COOH group. Substantial improvement of the film wettability was noticed after VUV photo-oxidation. These findings suggest that VUV irradiation provides a high potential for surface modification of fluorinated polymers which are known to be particularly resistant against functionalization by conventional surface modification techniques such as plasma treatment. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2215–2222, 1998     

Resonance-Enhanced Photon Excitation Spectroscopy of the Even-Parity Autoionizing Rydberg States of Xe

Xenon atoms were produced in their metastable states 5p56s3/22 and 5p56s′1/20 in a pulsed DC discharge in beam,and subsequently excited to the even-parity autoionizing Rydberg states 5p5np′3/21,1/21,and 5p5nf′ 5/23 using single photon excitation. The excitation spectra of the even-parity autoionizing resonance series from the metastable 129Xe were obtained by recording the autoionized Xe+ with time-of-flight ion detection in the photon energy range of 28000-42000cm-1 .A wealth of autoionizing resonances were newly observed, from which more precise and systematic spectroscopic data of the level energies and quantum defects were derived.