Matrix isolation ESR and theoretical studies of metal phosphides

The ZnP, (67)ZnP, CdP, (111)CdP, and (113)CdP radicals have been formed by laser ablation of the metal with GaP pressed into the metal surface, isolated in an inert neon matrix at 4.3 K and their electronic structure was established using electron spin resonance spectroscopy. The following magnetic parameters were determined experimentally for ZnP/(67)ZnP, g(⊥)=1.9982(2), A(⊥)(P)=111(6)?MHz, A(⊥)((67)Zn)=160(2)?MHz, and D=-29?988(3)?MHz and estimates were made for the following ZnP/(67)ZnP magnetic parameters: g(∥)=1.9941(2), A(∥)(P)=-5(6)?MHz, and A(∥)((67)Zn)=180(50)?MHz. The following magnetic parameters for CdP/(111)CdP/(113)CdP were determined experimentally: g(⊥)=1.9963(2), A(⊥)(P)=97(3)?MHz, A(⊥)((111)Cd)=862(3)?MHz, and A(⊥)((113)Cd)=902(3)?MHz. Evidence for the formation of the MgP radical was also obtained and an approximate hyperfine coupling constant of A(⊥)(P)=157(6)?MHz was determined. The low-lying electronic states of ZnP and MgP were also investigated using the multiconfigurational self-consistent field technique. Potential energy surfaces, binding energies, optimized bond lengths, energy separations, and dissociation energies have been determined. Both radicals are found to have (4)Σ(-) ground states with a leading configuration at r(e) of 10σ(2)11σ(2)5π(1)5π(1)12σ(1) for ZnP and 7σ(2)8σ(2)3π(1)3π(1)9σ(1) for MgP. Significant mixing to this state is calculated for MgP.     

Synthetic and Structural Studies of 1,8‐Chalcogen Naphthalene Derivatives

Four novel 1,8‐disubstituted naphthalene derivatives 4 – 7 that contain chalcogen atoms occupying the peri positions have been prepared and fully characterised by using X‐ray crystallography, multinuclear NMR spectroscopy, IR spectroscopy and MS. Molecular distortion due to noncovalent substituent interactions was studied as a function of the bulk of the interacting chalcogen atoms and the size and nature of the alkyl group attached to them. X‐ray data for 4 – 7 was compared to the series of known 1,8‐bis(phenylchalcogeno)naphthalenes 1 – 3 , which were themselves prepared from novel synthetic routes. A general increase in the E???E′ distance was observed for molecules containing bulkier atoms at the peri positions. The decreased S???S distance from phenyl‐ 1 and ethyl‐ 4 analogues is ascribed to a weaker chalcogen lone pair–lone pair repulsion acting in the ethyl analogue due to the presence of two equatorial S(naphthyl) ring conformations. Two novel peri‐substituted naphthalene sulfoxides of 1 , Nap(O?SPh)(SPh) 8 and Nap(O?SPh)₂ 9 , which contain different valence states of sulfur, were prepared and fully characterised by using X‐ray crystallography and multinuclear NMR spectroscopy, IR spectroscopy and MS. Molecular structures were analysed by using naphthalene ring torsions, peri‐atom displacement, splay angle magnitude, S???S interactions, aromatic ring orientations and quasi‐linear O?S???S arrangements. The axial S(naphthyl) rings in 8 and 9 are unfavourable for S???S contacts due to stronger chalcogen lone pair–lone pair repulsion. Although quasi‐linear O?S???S alignments suggest attractive interaction is conceivable, analysis of the B3LYP wavefunctions affords no evidence for direct bonding interactions between the S atoms.     

Flammability studies of impregnated paper sheets

Paper sheets impregnated with flame retardants made from agricultural residues and other additives were studied with the cone calorimeter. The use of sugar beet ethanol eluent (SBE), CaCl₂, and ZnCl₂ lowered the peak rate of heat release (PRHR) the most in comparison to water treated material. The average effective heat of combustion (AEHC) was lowered by most of our treatments with the exception of BMIC (butylmethylimidazolium chloride)/starch (BMS). The average mass loss rate was lowered by all the treatments, but the most by the use of ZnCl₂ and CaCl₂ treatments. Mass losses were the least with SBE, CaCl₂/NaOH/starch, and CaCl₂/NaOH treatments. The BMS sample exhibited the greatest total heat release while SBE samples gave the smallest value of the parameter. The flame retarding effect of SBE was ascribed to the presence of ferulates which prevented the formation of volatile products by condensing into polycyclic aromatic residue.     

Apparate

Ohne Zusammenfassung     

On -reflexive representations of algebras

Module theoretic methods are employed to obtain simple proofs of extensions of two theorems of E. A. Azoff regarding the reflexivity of direct sums of copies of an algebra of operators on a finite dimensional Hilbert space.

     

The effect of low-temperature crystallization on the mechanical behavior of rubber

In cold climates the correct performance of rubber components such as seismic isolators depends on them maintaining their elastic properties when exposed to prolonged periods at low temperatures. The high damping compounds developed for seismic isolation are normally especially prone to crystallization when exposed to subzero temperatures for periods of a few weeks. The effect of low-temperature crystallization on the mechanical stiffening of natural rubber is evaluated. The relationship between the shear modulus and amount of crystallization is measured using a technique in which the dimensional change and stiffness are monitored simultaneously. The relationship is found to be approximately independent of the crosslink density and the temperature of crystallization. It appears not to be realistically modeled by considering the crystals to behave as rigid filler particles but good qualitative agreement with experiment was obtained by modeling the crystals as a network of threads. Partially crystalline rubbers are found to yield under the application of a large stress like other partially crystalline polymers. Mechanisms for suppressing crystallization in rubber are discussed and the low-temperature stiffening of specially formulated rubber compounds for seismic isolation is presented. These results show that carefully formulated high damping natural rubber compounds can give adequate performance at low temperatures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2181–2190, 2004     

Shear-banding structure orientated in the vorticity direction observed for equimolar micellar solution

 The non-monotonic shear flow of a viscoelastic equimolar aqueous surfactant solution (cetylpyridinium chloride-sodium salicylate) is investigated rheologically and optically in a transparent strain-controlled Taylor Couette flow cell. As reported before, this particular wormlike micellar solution exhibits first a shear thinning and then a pronounced shear-thickening behavior. Once this shear-thickening regime is reached, a transient phase separation/shear banding of the solution into turbid and clear ring-like patterns orientated perpendicular to the vorticity axis, i.e., stacked like pancakes, is observed (Wheeler et al. 1998; Fischer 2000). The solution exhibit several unique features as no induction period of the shear induced phase, no structural build-up at the inner rotating cylinder, jumping pancake structure of clear and turbid ringlike phases, and oscillating shear stresses appear once the pancake structure is present. According to our analysis this flow phenomenon is not purely a mechanical or rheological driven hydrodynamic instability but one has to take into account structural changes of the oriented micellar aggregates (flow induced non-equilibrium phase transition) as proposed by several authors. Although this particular flow behavior and the underlying mixture of shear induced phases and mechanical instabilities is not fully understood yet, some classification characteristics based on a recent theoretical approach by Schmitt et al. (1995) and Porte et al. (1997) where a strong coupling between the flow instability (non-homogeneous flow profile due to the bands) and the structural changes causes the observed transient phenomena can be derived. In reference to the presented model the observed orientation of the rings is typical for complex fluids that undergo a spinodal phase separation coupled with a thermodynamic flow instability. In contrast to other shear banding phenomena, this one is observed in parallel plate, cone-plate, and Couette flow cell as well as under controlled stress and controlled rate conditions. Therefore, it adds an additional aspect to the present discussion on shear banding phenomena, i.e., the coupling of hydrodynamics and phase transition of rheological complex fluids. Received: 8 January 2001 Accepted: 15 May 2001