The effects of morphology on 1H NMR spectra and relaxation in semicrystalline polyolefins

A brief résumé is given of the role of structural heterogeneity, magnetic dipolar couplings, molecular structure, and molecular motion in determining the ¹H NMR spectra and relaxation properties of heterogeneous solids such as semicrystalline polymers. Measurements of ¹H spin-lattice relaxation in laboratory (T₁) and rotating frames (T) are reported for a number of solid polyolefin samples. These include solution-crystallized and melt-crystallized polyethylene, annealed and quenched isotactic polypropene, and isotactic polybut-1-ene. In addition, broad-line ¹H spectra, both normal and partially (T) relaxed, are reported for these materials as well as a number of pulsed NMR experiments having the philosophy of the so-called Goldman–Shen experiment. Spin-lattice relaxation (T₁) for all samples is a single exponential process, whereas rotating-frame relaxation comprises three exponential processes both on-resonance (θ = 90°) and off-resonance at the magic angle (θ = 54.7°), with the latter generally being much slower. The spectra show clearly the existence of components having differing degrees of mobility and, with the exception of the solution-crystallized polyethylene, the partially (T) relaxed spectra indicate a correlation between breadth of resonance line and magnitude of T_1ρ. The Goldman–Shen-type experiments indicate a spin-diffusional transport of magnetization between the different spectral and (T) components. A computer program has been used to simulate the NMR behavior of a three-region system comprising repeating units of infinite lamellae of different widths, each region having different intrinsic relaxation times and spin diffusion coefficients. The results demonstrate that the observed ¹H NMR behavior of these samples can be interpreted in terms of this model and that, inter alia, the long-time T behavior reflects, qualitatively, the time taken for magnetization to diffuse a distance of the order of the dimensions of the region to which it corresponds.     

Sol-gel optical nanocomposites: Design and applications

The history and method of producing gel-polymer composites is presented. Tailoring properties, such as density, refractive index, hardness, elastic modulus, compressive strength, abrasion resistance, and modulus of rupture is achieved through controlling the ratio of gel-derived silica to polymer phases. Several different applications of composite technology are presented. Solid-state lasing in dye-doped silica gel-PMMA composites has been recently achieved. The difficulties in generating stable photochromism in gels and gel-derived composites are discussed. Microlens arrays for data reading, employing large gel-polymer spheres, have been developed. In addition, a new flat-screen color display technology, based upon the periodic arrangement of dye-doped microsphere pixels, emitting blue, green and red light, is disclosed for the first time.     

Universal area product formulas for rotating and charged black holes in four and higher dimensions

We present explicit results for the product of all horizon areas for general rotating multicharge black holes, both in asymptotically flat and asymptotically anti-de Sitter spacetimes in four and higher dimensions. The expressions are universal, and depend only on the quantized charges, quantized angular momenta and the cosmological constant. If the latter is also quantized these universal results may provide a "looking glass" for probing the microscopics of general black holes.     

Temperature dependent structured absorption spectra of molecular chlorine

A dual wavelength range spectrometer system has been designed and constructed which can simultaneously perform single pass UV absorption spectroscopy and cavity enhanced absorption spectroscopy in the green region of the visible spectrum. Using the system the absorption spectrum of molecular chlorine has been measured, in the wavelength range 509-570 nm, using cavity enhanced absorption spectroscopy. Absolute absorption cross sections were obtained by simultaneous measurement of the UV spectrum to obtain the Cl(2) concentration. These are the first temperature dependent measurements of the Cl(2) absorption cross sections in this region which are vibronically resolved. Laboratory measurements were conducted at four temperatures (298, 273, 233, and 197 K). Spectral modelling of the Cl(2) B(3)Π(0(u)(+))-X(1)Σ(g)(+) electronic transition has been performed, the results of which are in good agreement with our measured spectra.     

Deep Red Emitting Heteroleptic Ir(III) Complexes that Incorporate Unsymmetrical 4-quinoline Carboxylic Acid Derived Ligands

Six disubstituted ligands based upon 2-(2′-pyridinyl/pyrazinyl)quinoline-4-carboxylic acids have been synthesised, solvent-free, in one step from a range of commercially available isatin derivatives. These species behave as ancillary chelating ligands for Ir(III) complexes of the form [Ir(C^N)₂(N^N)]PF₆ (where C^N=cyclometalating ligand; N^N=2-(2′-pyridinyl/pyrazinyl)quinoline-4-carboxylic acids). An X-ray crystallographic study on one complex shows a distorted octahedral geometry wherein a cis-C,C and trans-N,N coordination mode is observed for the cyclometalating ligands. DFT calculations predicted that variations in N^N ligand from 2,2′-bipyridine to L^{1 – 6} should localise the LUMO on to the Lⁿ ligand and that the complexes are predicted to display MLCT/LLCT character. All complexes displayed luminescence in the deep red part of the visible region (674–679 nm) and emit from triplet states, but with little apparent tuning as a function of L^{1 – 6} . Further time-resolved transient absorption spectroscopy supports the participation of these triplet states to the excited state character.