Effect of nanoscale diamondoids on the thermomechanical and morphological behaviors of polypropylene and polycarbonate

Nanoscale MolecularDiamond products (various diamondoid materials), obtained from petrochemical feedstocks, have been investigated as additives for polypropylene and polycarbonate. Three of the homologues of this family (diamantane, triamantane, and the [121]tetramantane isomer) have marginal effects on the thermal and mechanical properties of nonpolar/semicrystalline polypropylene. Mixtures of methylated tetramantane nanofillers also increase the stress–strain behavior of polypropylene composites without significantly impacting their glass transition temperatures. The addition of the selected diamondoids to amorphous/moderately polar polycarbonate increases the polymer tensile modulus significantly with marginal increases in the yield stress. The effects of the selected diamondoids on the thermal stability, crystallinity, and optical properties of polypropylene and polycarbonate are also reported. The results for the mechanical properties show that the selected diamondoids behave as plasticizers in polypropylene, whereas in polycarbonate, they act as antiplasticizers without adversely affecting the optical clarity. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1077–1089, 2007     

Prescribing eigenvalues of the Dirac operator

In this note we show that every compact spin manifold of dimension ≥3 can be given a Riemannian metric for which a finite part of the spectrum of the Dirac operator consists of arbitrarily prescribed eigenvalues with multiplicity 1.     

Oxygen non-stoichiometry, redox thermodynamics, and structure of LaFe1 − x Co x O3 − δ

The oxygen non-stoichiometry and redox thermodynamic properties of the LaFe_{1 ? x} Co _x O_{3 ? δ} system (x?=?0.25 and 0.75) are studied. At low temperatures, the LaCoO₃ and LaFeO₃ systems show partial solid solubility. At 1,273 K (in air), both compounds are single phases and are orthorhombic and rhombohedral for x?=?0.25 and 0.75, respectively. Thermogravimetry has been used to measure the oxygen non-stoichiometry versus oxygen partial pressure at three temperatures, 1,223, 1,273, and 1,323 K. Redox thermodynamic quantities are extracted directly from the oxygen non-stoichiometry curves. The extracted enthalpies of oxidation do not vary significantly with stoichiometry, and for x?=?0.25 and 0.75, they are ?640?±?60 and ?440?±?60 kJ (mol O₂)^?1, respectively. Ideal solid solution thermodynamic models are used to analyze the redox mechanisms.     

Magnetic splitting of optical phonons in cubic dysprosium aluminum garnet

The magnetic splitting of triply degenerate (T _2g )-phonons in the cubic Rare Earth compound dysprosium-aluminum-garnet could be observed making use of the polarization properties of the Raman-effect.The theoretical predictions of a phenomenological symmetry analysis are compared to a more detailed microscopic treatment of the observations in terms of the magnetoelastic interaction.     

Biorthonormal electronic basis sets in the theory of electron transfer reactions

We have used the quantum-chemical concept of biorthonormal electronic basis functions to derive the two-centre electron exchange integrals in non-diabatic electron transfer reactions. It is shown that only non-diagonal parts induce the transfer corresponding to inclusion of the diagonal parts in the zero-order hamiltonians. This result coincides with the result derived previously by means of scattering theory.     

Stereochemistry of substitution at tricovalent phosphorus

Reactions of one diasteveomer of a XP-NMe₂ compound ($\text{1a}$) with alcohols, phenol and amines have been shown by NMR to proceed uith initial inversion at phosphorus, but the overall reactions are not stereoselective.