Organic–inorganic tandem route to polymer nanocomposites: kinetic products versus thermodynamic products

We report a facile single-step photochemical methodology to afford alkylsiloxane-polymer hybrid films which relies on the tandem photoacid-catalyzed polymerization of n-alkyltrimethoxysilane precursors and a diglycidyl ether organic monomer. Photoacids liberated by the UV decomposition of iodonium salt triggers simultaneously the sol–gel process and epoxy cationic polymerization. Such conditions are intended to favour the formation of kinetic products trapped by cross-linking reactions instead of the thermodynamically most stable structures, whose preference would be for macrophase segregation. Organosilane precursor exhibiting different structures and chain lengths (n-butyl, n-octyl, n-dodecyl, n-hexadecyl, isobutyl and isooctyl) were systematically investigated to afford a range of transparent alkylsiloxane-polyether hybrids. The competitive organic–inorganic reaction kinetics were investigated using in situ real-time Fourier transform infrared spectroscopy. A main emphasis has been on discussing the effect of the alkyl substituent structure on the photoinduced polymerization kinetics and the silicate networks characterized by ²⁹Si solid-state NMR. To avoid phase separation, the rate of formation of the two phases was tailored to favour concomitancy upon modulating several experimental parameters: film thickness, alkyl structure, photoacid generator concentration. Finally, the viscoelastic and surface properties were also assessed by dynamic mechanical analysis and water contact angle measurements, respectively.     

Reactions of Organic Ions at Ambient Surfaces in a Solvent-Free Environment

Solvent-free ion/surface chemistry is studied at atmospheric pressure, specifically pyrylium cations, are reacted at ambient surfaces with organic amines to generate pyridinium ions. The dry reagent ions were generated by electrospraying a solution of the organic salt and passing the resulting electrosprayed droplets pneumatically through a heated metal drying tube. The dry ions were then passed through an electric field in air to separate the cations from anions and direct the cations onto a gold substrate coated with an amine. This nontraditional way of manipulating polyatomic ions has provided new chemical insights, for example, the surface reaction involving dry isolated 2,4,6-triphenylpyrylium cations and condensed solid-phase ethanolamine was found to produce the expected N-substituted pyridinium product ion via a pseudobase intermediate in a regiospecific fashion. In solution however, ethanolamine was observed to react through its N-centered and O-centered nucleophilic groups to generate two isomeric products via 2H-pyran intermediates. The O-centered nucleophile reacted less rapidly to give the minor product. The surface reaction product was characterized in situ by surface enhanced Raman spectroscopy, and ex situ using mass spectrometry and H/D exchange, and found to be chemically the same as the major pyridinium solution-phase reaction product.     

Thermal studies on Zirconium hydroxide gel formed by aqueous gelation

Zirconium hydroxide gel has been prepared by a novel aqueous gelation process by the controlled hydrolysis of zirconium oxychloride in the presence of sodium acetate. The gel thus formed has been subjected to thermal analysis: TG, DTG, and DSC. Thermal analysis shows that the gel is continuously dehydrated in the temperature range between room temperature and 500?°C. The total mass loss relative to the initial mass is about 44.1%. Thermal analysis shows that the decomposition takes place in three stages. The gel contains absorbed and coordinated water. In the second stage of dehydration, dehydration of the Zr(OH)₄ gel also takes place along with the removal of the coordinated water. The DSC analysis coupled with TG and structural information, indicate that the exothermic processes between 349 and 460?°C can be attributed to the nucleation process of the formation of tetragonal zirconia, with phase transformation at 460?°C.     

Pore size distributions of ion exchangers and relation to protein binding capacity

The pore structure of chromatographic media directly influences macromolecular transport and adsorption, and consequently separation resolution and loading capacity in chromatographic separations. The pore size distribution (PSD) is therefore a central structural characteristic of chromatographic materials and a critical determinant of chromatographic behavior. In this work the PSDs of a set of commercial anion exchangers were determined by inverse size-exclusion chromatography (ISEC). The PSDs were further utilized to develop relations to functional properties of adsorbents, such as intraparticle diffusivity, and static and dynamic binding capacities. We find that the detailed PSD is useful in semi-quantitative understanding of chromatographic behavior. However, more accurate prediction of column behavior requires more thorough knowledge of the pore structure, specifically the connectivity of the pore network, as well as improved understanding of the function of grafted resins.     

An exactly solved model with a wetting transition

A model of a binary mixture, showing a wetting transition, is examined. No prewetting phenomena are found. The scaling functions are obtained for the film thickness and for the correlation lengths.     

Bottonium production at LEP

We investigate the production of Υ(³ S ₁) and η _b (¹ S ₀) with two gluons from Z decay. We find that at LEP luminosities experimental detection will hardly be feasible.     

Bose–Einstein condensation transition studies for atoms confined in Laguerre–Gaussian laser modes

Multiply-connected traps for cold, neutral atoms fix vortex cores of quantum gases. Laguerre–Gaussian laser modes are ideal for such traps due to their phase stability. We report theoretical calculations of the Bose–Einstein condensation transition properties and thermal characteristics of neutral atoms trapped in multiply connected geometries formed by Laguerre–Gaussian (LG_p^l) beams. Specifically, we consider atoms confined to the anti-node of a LG₀¹ laser mode detuned to the red of an atomic resonance frequency, and those confined in the node of a blue-detuned LG₁¹ beam. We compare the results of using the full potential to those approximating the potential minimum with a simple harmonic oscillator potential. We find that deviations between calculations of the full potential and the simple harmonic oscillator can be up to 3%–8% for trap parameters consistent with typical experiments.