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We report that organic semiconductors such as -sexithiophene (-6T) have magnetoresistance (MR) with unexpected sign changes; depending on applied voltage, temperature, and layer thickness, the resistance may either increase or decrease upon application of a small magnetic field (<100 mT). We propose that MR and the inversion of MR are due to the role of hyperfine interaction in a magnetic field, as illustrated by the recombination-limited regime.

The isothermal crystallization of in-situ-polymerized and melt-processed nylon-6/montmorillonite nanocomposites was studied by simultaneous small- and wide-angle X-ray scattering using synchrotron radiation. The isothermal crystallization rates, in the nucleation-controlled regime, for the nanocomposites are significantly faster than that for the pristine nylon-6 and suggest that the layered silicates act as nucleating centers. Within the experimental resolution, the initial crystal phase formed between 185 and 205 °C in the presence of the layered silicate is the metastable γ-phase, whereas the α-phase develops in the pristine nylon-6 at comparable temperatures. Additionally, the strong silicate−polymer interactions present in the in-situ-polymerized nanocomposites alter the crystallization process, creating a much weaker temperature dependence for the crystallization kinetics. Finally, the presence of well-dispersed layered silicates significantly disrupts the development of lamellar structure but does not alter the overall amounts of crystallinity.