Five-line model for the description of radial x-ray diffractometer scans of nylon 6 yarns

Types of nylon 6 yarn which contain large γ crystals cannot be described by a model comprising three Pearson VII curves, as we formerly proposed. Hence, a new extended computer program has been developed containing five Pearson VII lines. Two lines are related to the α phase, two to γ-phase crystals, and the fifth describes the amorphous contribution. Some physical relations between parameters could be derived and were incorporated into the computer program. This program provides extremely good fits to all equatorial diffractometer scans which can be obtained from nylon 6 yarns, including those containing large γ crystals. The parameter accuracy is quite satisfactory for diffractometer traces with well-resolved peaks from both α and γ crystals. However, if the traces are poorly resolved or the samples do not contain a sufficient amount of the γ modification, resulting in a lack of detailed information, the parameter accuracy can be rather poor. For those cases special versions of the computer program were developed which contain further empirical interrelations between parameters. With these programs crystal sizes and molecular distances within the crystals of both the α and β modifications can be determined. The method has also been applied to radial scans at various small azimuthal angles with respect to the equator. In that way the relative amounts of the α and γ crystals as well as their orientation factors could be determined. Various aspects of this investigation are illustrated by some examples.     

Surface-Confined Metallodendrimers: Isolated Nanosize Molecules

The incorporation of dialkyl sulfide side chains in metallodendrimers is a simple method for their insertion into a monolayer of decanethiol formed by self-assembly on a gold surface. The dendrimer binds through the sulfide group to a defect in the monolayer on the gold surface (see picture). The surface concentration of the isolated dendrimer adsorbate can be regulated by the adsorption time (for example, 55 adsorbates on a surface of 200×200 nm² after 20 h).     

On the origin of slow processes of charge transport in porous media

Dielectric relaxation spectra in porous media reveal the importance of slow processes of charge transport with polarisation currents down at least to mHz. The spatial scale of the relaxation is frequency-dependent, potentially allowing information about the structure of the medium to be obtained from the AC conductivity. Many mechanisms of relaxation have been proposed, but we review only two in any depth. These two approaches relate long relaxation times on the one hand to diffusion limited relaxation, on the other, to geometrical limitations on conduction pathways. For equidimensional non-fractal particles, the first (second) generates a quadratic (linear) dependence of relaxation time on particle (or pore) size. In each a fractal model of the pore space generates a power-law AC conductivity with the power of the frequency a function of the fractal dimensionality, but the powers have different relationships with system parameters. Comparison with data does not support either interpretation generally, though some data sets agree with each. Since surface conduction yields a quadratic dependence for particles elongated in one dimension, but more complex dependences for fractal interfaces, it seems easier and more productive to start from the perspective that surface conduction processes are the basis for the relaxation.