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A mobile and low-cost apparatus for dynamic nuclear polarization (DNP) hyperpolarization based on a Halbach magnet is presented and its performance is demonstrated at room temperature and with three different radical species dissolved in a glycerol-water mixture. DNP enhancement factors for a triarylmethyl-based radical, TEMPOL and a polyelectrolyte spin-labeled with nitroxide radicals are measured as a function of the microwave power, and the extrapolated maximum enhancement factors are compared. The spin-labeled polyelectrolyte shows the best DNP efficiency and 1H DNP enhancement factors up to −50 were observed and a maximum enhancement factor of −80 was projected. The results demonstrate that with the new mobile apparatus reliable DNP experiments can be performed with reasonably high 1H-DNP enhancements. [ABSTRACT FROM AUTHOR]

The discovery of electrically conducting organic crystals and polymers has widened the range of potential optoelectronic materials, provided these exhibit sufficiently high charge carrier mobilities and are easy to make and process. Organic single crystals have high charge carrier mobilities but are usually impractical, whereas polymers have good processability but low mobilities. Liquid crystals exhibit mobilities approaching those of single crystals and are suitable for applications, but demanding fabrication and processing methods limit their use. Here we show that the self-assembly of fluorinated tapered dendrons can drive the formation of supramolecular liquid crystals with promising optoelectronic properties from a wide range of organic materials. We find that attaching conducting organic donor or acceptor groups to the apex of the dendrons leads to supramolecular nanometre-scale columns that contain in their cores π-stacks of donors, acceptors or donor–acceptor complexes exhibiting high charge carrier mobilities. When we use functionalized dendrons and amorphous polymers carrying compatible side groups, these co-assemble so that the polymer is incorporated in the centre of the columns through donor–acceptor interactions and exhibits enhanced charge carrier mobilities. We anticipate that this simple and versatile strategy for producing conductive π-stacks of aromatic groups, surrounded by helical dendrons, will lead to a new class of supramolecular materials suitable for electronic and optoelectronic applications. [ABSTRACT FROM AUTHOR]

The use of NMR imaging techniques for the characterization of superabsorbing polymers is explored. Spatial differences in the cross-link densities of polyacrylate-based superabsorbing particles are investigated by parameter-selective 1H NMR imaging of samples swollen with water. Images of the transverse relaxation time and of the self-diffusion coefficient of the absorbed water provide valuable information on the local water mobility and, thus, indirectly also on the polymer. The time evolution of the swelling process was also studied by NMR images acquired after different swelling times. Moreover, using magic-angle-spinning imaging, the influence of mechanical load on the swollen particle was investigated by taking advantage of the centrifugal forces on the spinning sample. These experiments indicate the presence of two water components, one strongly adsorbed, while the other is relatively mobile. [ABSTRACT FROM AUTHOR]

The properties of polymer films prepared from latex dispersions are influenced by the drying or film formation process. In order to investigate this process, various systems of aqueous latex dispersions were dried until a specific solid content was reached. The samples investigated were based on vinyl acetate, vinyl acetate/ethylene and pure acrylics employing different surfactants and polyelectrolytes as stabilisers of the dispersions. The role of water in these partially dried films was investigated using 1H and 2H solid-state NMR spectroscopy. Different types of water could be distinguished in the spectra. The drying latex films were found to contain interfacial external water, water at ionic and nonionic groups at surfactants in the polymer/water interface and also water inside the swollen polymer. These different types of water were examined separately using various NMR techniques. [ABSTRACT FROM AUTHOR]

The on-line detection of emulsion polymerization processes by means of solid-state NMR spectroscopy is demonstrated for the first time using poly(butyl acrylate) as a model system. Relatively short time intervals are accessible via 1H detection while the use of 13C NMR spectroscopy results in an increased spectral resolution. Details of sample preparation and experimental techniques are given, while remaining artifacts of the preliminary results will be addressed in further investigations. [ABSTRACT FROM AUTHOR]

Oscillatory shear of polymeric liquids in the non-linear regime generates higher harmonic contributions in the shear stress response. These non-linear contributions are analyzed in Fourier space with respect to the different frequencies and intensities. Simulated and experimental Fourier rheology spectra for atactic poly(propylene) melts are shown. [ABSTRACT FROM AUTHOR]

Presents a correction to volume numbers that appeared incorrectly in the footer of pages 384, 385 and 386 in the article 'Self-organization of supramoleular helical dendrimers into complex electronic materials,' by V. Percec, M. Glodde, T.K. Bera, Y. Miura, I. Shiyaovskaya, K.D. Singer, V.S.K. Balagurusamy, P.A. Heiney, I. Schell, A. Rapp and H.-W. Spiess published in the October 2002 issue of the journal 'Nature.'