Core excitons in solid rare gases: Kr-3d and Xe-4d transitions

Core excitons from 3d levels of Kr and 4d levels of Xe are examined within the integral equation formalism both in the isolated atoms and in the crystals. Earlier interpretation that resonances at the interband edge Kr-3d and Xe-4d are due to 1s, 2p, 3p excitons is well supported by the present calculation.     

Determination of tellurium in geochemical materials by flameless atomic-absorption spectroscopy

A method is described for the determination of tellurium at nanogram levels in rocks and in other complex materials by the use of flameless atomic-absorption spectroscopy. A very selective organic extraction procedure is applied to avoid matrix interference effects during extraction of Te and the atomization stage in the graphite furnace. Prior separation of iron and other interfering elements is achieved by a combined cupferron-ethyl acetate extraction. Tellerium is extracted from 6M hydrochloric acid with MIBK and stripped into aqueous medium. Pipetting of the aqueous extract into the graphite furnace gives fairly good instrumental reproducibility (2-3% error). Detection limits of about 10 ppM Te for a 0.5-g sample have been achieved with the medium-performance apparatus used. Results for Te in some geochemical reference materials are reported. Indications are given for the determination of Sb and Mo in the same solutions.     

A new technique for studying gelation in polyesters

A new method for studying polymer network formation has been devised. Crosslinking reactions are carried out in a recording viscometer, which provides accurate determination of incipient gel points and also serves as a high-speed stirrer. The molten, nonstoichiometric mixtures are reacted to completion to eliminate the inaccuracies inherent in the determination of reaction extent and this, together with the use of esterification reactions with minimal side reactions, reduces many of the problems of previous methods. The experimental results for the reactions of simple model compounds are in very close agreement with Flory's network theory. A system containing crosslinking reagents with unequally reactive groups has also been considered and the accuracy of the method enables the reactivity ratios of the different groups to be calculated.     

Some New Results on the Kinetic Ising Model in a Pure Phase

We consider a general class of Glauber dynamics reversible with respect to the standard Ising model in ^d with zero external field and inverse temperature strictly larger than the critical value _c in dimension 2 or the so called slab threshold in dimension d 3. We first prove that the inverse spectral gap in a large cube of side N with plus boundary conditions is, apart from logarithmic corrections, larger than N in d = 2 while the logarithmic Sobolev constant is instead larger than N ² in any dimension. Such a result substantially improves over all the previous existing bounds and agrees with a similar computations obtained in the framework of a one dimensional toy model based on mean curvature motion. The proof, based on a suggestion made by H. T. Yau some years ago, explicitly constructs a subtle test function which forces a large droplet of the minus phase inside the plus phase. The relevant bounds for general d 2 are then obtained via a careful use of the recent –approach to the Wulff construction. Finally we prove that in d = 2 the probability that two independent initial configurations, distributed according to the infinite volume plus phase and evolving under any coupling, agree at the origin at time t is bounded from below by a stretched exponential , again apart from logarithmic corrections. Such a result should be considered as a first step toward a rigorous proof that, as conjectured by Fisher and Huse some years ago, the equilibrium time auto-correlation of the spin at the origin decays as a stretched exponential in d = 2.     

Effect of Free Trimethylaluminum Content in Methylaluminoxane on Performances of Bis(salicylaldiminate)nickel(II)‐Based Catalysts for Ethylene Polymerization

Summary: The performances of ethylene polymerization catalysts based on III and commercial methylaluminoxane were investigated by reducing the content of free trimethylaluminum in methylaluminoxane by its reaction with 2,6‐di‐tert‐butylphenol. This allowed optimization of the formulation of the catalyst, affording a high‐molecular‐weight linear polyethylene (PE) with a productivity [(1 900 kg of PE/(mol of Ni × h)], ten‐fold higher than that previously achieved for the same system adopting commercial methylaluminoxane not pre‐treated with the above phenol derivative.

     

On the Bulk Properties of a Poly(Bicycloacrylate) Carrying Semifluorinated Side Groups

We prepared a novel fluorinated polymer from a bicycloacrylate monomer, (1H,1H,2H,2H)-perfluorododecyl 2-(bicyclo[3.1.0]hex-1-yl)acrylate, by radical ring opening polymerization. The bulk properties of the polymer were investigated by thermal analysis and X-ray diffraction, which proved the existence of a smectic mesophase up to the isotropization temperature of 74 °C. Furthermore, a solid state NMR study was started to characterize domains with different mobility mainly by ¹³C cross-polarization magic angle spinning and T₂ selective experiments. We found that the polymer is a homogeneous sample with the presence of dynamic motions in the kHz regime below the glass transition temperature.     

PDMS network blends of amphiphilic acrylic copolymers with poly(ethylene glycol)‐fluoroalkyl side chains for fouling‐release coatings. I. Chemistry and stability of the film surface

Amphiphilic copolymers of a methacrylic monomer (SiMA) carrying a polysiloxane side chain and an acrylic monomer (ZA) with a mixed poly(ethylene glycol) (PEG)‐fluoroalkyl side chain (10–85 mol % ZA) were incorporated as the surface‐active components into poly(dimethylsiloxane) (PDMS) network blends at different loadings (1 and 4 wt % with respect to PDMS). Wettability of the coating surfaces was investigated by contact angle measurements, and their surface chemical composition was determined by angle‐resolved X‐ray photoelectron spectroscopy. It was found that the surface segregation of the fluoroalkyl segments of the amphiphilic copolymers was responsible for the high enrichment in fluorine concentration within 10 nm of the coating surface. The PEG segments were also concentrated at the polymer?air interface. The chemical composition of the films was proven to be relatively little affected by immersion in water. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012