Multifunctional core–shell particles composed of magnetic particles covered with a gold nanoshell can be induced to align into conducting lines upon application of a magnetic field (see Figure). The formation of Au clusters and “streaky” gold nanoparticles on the surface of the PS beads is demonstrated and the preparation, characterization, and applications of magnetic and polystyrene beads featuring a gold shell are addressed.
SynopsisThe feasibility of incorporating amine groups into the surface of polyester (PET) fibers by reaction with multifunctional amines was investigated. Reactions of diethylenetriamine (DETA), triethylenetetramine (TETTA), and tetraethylenepentamine (TTEPA) with PET monofilaments and with a multifilament yarn were studied. Microspectrophotometric examination of aminated fibers stained with an acid dye a t low pH revealed the location and concentration of amine groups. Amination could be confined to the periphery and was found to be uniform on the fiber surface. The rate of the reaction, as revealed by acid dye staining, was characterized by an induction period followed by an autoaccelerated stage. Extent of incorporation of amine groups was found to be similar for the three amines. There is a significant improvement in water wettability due to surface amination, and the interfacial shear strength of TTEPAtreated PET monofilaments embedded in an epoxy resin matrix was almost doubled. As the amination reaction proceeds, there is a weakening of the reacted zone in the PET due to chain scission leading to a decrease in the interfacial shear strength. Scanning electron microscopy (SEMI studies revealed that failure occurred within the filament most probably between the reacted and unreacted zones. The tensile properties of the TTEPA-treated PET filaments were hardly affected at the investigated extents of amination.
Neutron and x-ray reflectivity studies of modulated heterostructures consisting of alternate layers of conjugated and nonconjugated polymers is described. Such heterostructures are currently being used to fabricate polymer-based light emitting diodes. The heterostructures were prepared by the layer-by-layer self-assembly technique using the precursor of the conjugated polymer, deuterated poly(phenylenevinylene) (D-PPV), and other polyelectrolyte spacers. Heat treatment after the layer assembly converted the pre-D-PPV to a conjugated semiconducting polymer. For the first time in such heterostructures, we were able to observe quasi-Bragg reflections (up to the third order) due to the formation of ordered modulated structures. Both the neutron and the x-ray data were analyzed using the same layer-by-layer model and the same fitting procedure with consistent results. Most importantly, the model and the fitting procedure yield the buried interlayer roughness at the D-PPV/spacer interface. This roughness parameter, of the order of 12±3 Å, was found to be smaller than the thickness of the D-PPV and the spacer layers, suggesting that the length over which interdigitation between neighboring polymer layers occurs is significantly smaller than the spacer layer. We demonstrate that the conversion to conjugated polymer by the heat treatment leads to ∼7% reduction of the repeat unit and the film thickness without significant changes of other structural properties; in fact, the interfacial roughness was somewhat improved. The fabrication of high quality modulated structures with controlled layer thickness and relatively small interfacial roughness may be a first step towards polymer-based multiquantum wells analogous to such devices in inorganic heterostructures.
High‐qality self‐assembled heterostructures for polymer LEDs have been fabricated from PPV and newly synthesized copolymers of PPV and naphthalene. It is shown that the layer‐by‐layer self‐assembly of multilayer structures has advantages with respect to control of the thickness and homogeneity of the polymer films compared to the conventional spin coating technique. The fabrication and characterization of the heterostructures are detailed and features of the electroluminescence and photoluminescence discussed.
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