Poly(amidoamine) (PAMAM) dendrimers can be used as a polymeric template/stabilizer/ reservoir to prepare stable gold-dendrimer nanocomposites by reducing PAMAM-tetrachloroaurate polysalts using hydrazine. In the gold-dendrimer nanocomposite, the presence of elemental gold is indicated by its characteristic plasmon absorption peak at 529 nm in aqueous solution and is visualized by transmission electron microscopy (TEM) equipped with energy-dispersive X-ray spectroscopy (EDXS). Electrostatic layer-by-layer assembly of the gold-dendrimer nanocomposite using poly(sodium 4-styrenesulfonate) (PSS) as the oppositely charged polyelectrolyte leading to nanoscale uniform multilayers of gold-dendrimer nanoclusters is reported. UV-vis absorption spectra from the consecutive multilayers indicated that each bilayer growth is regular, even though a 20 nm absorption bathochromic shift takes place in the film. TEM of PSS/gold-dendrimer nanocomposite film demonstrates that gold nanoparticles (5-20 nm) appear as aggregates within a gold-dendrimer nanocomposite monolayer, an observation borne out by crystalline gold electron diffraction patterns obtained from PSS/gold-dendrimer nanocomposite. Atomic force microscopy (AFM) of PSS/gold-dendrimer nanocomposite film indicates that the nanoclusters are arrayed with high uniformity at the nanometer scale.
Summary: Electrospinning of polymer blends offers the potential to prepare functional nanofibers for use in a variety of applications. This work focused on control of the internal morphology of nanofibers prepared by electrospinning polymer blends to obtain core‐sheath structures. Polybutadiene/polystyrene, poly(methylmethacrylate)/polystyrene, polybutadiene/poly(methylmethacrylate), polybutadiene/polycarbonate, polyaniline/polycarbonate, and poly(methylmethacrylate)/polycarbonate blends were electrospun from polymer solutions. It was found that the formation of core‐sheath structures depends on both thermodynamic and kinetic factors. Incompatibility and large solubility parameter difference of the two polymers is helpful for good phase separation, but not sufficient for the formation of core‐sheath structures. Kinetic factors, however, play a much more important role in the development of the nanofiber morphology. During the electrospinning process, the rapid solvent evaporation requires systems with high molecular mobility for the formation of core‐sheath structures. It was found that polymer blends with lower molecular weight tend to form core‐sheath structures rather than co‐continuous structures, as a result of their higher molecular mobility. Rheological factors also affect the internal phase morphology of nanofibers. It was observed the composition with higher viscosity was always located at the center and the composition with lower viscosity located outside.TEM image of electrospun polybutadiene/polycarbonate nanofibers at 25/75 wt.‐% ratio after staining by osmium tetroxide. The dark regions are polybutadiene and the light region is polycarbonate.magnified imageTEM image of electrospun polybutadiene/polycarbonate nanofibers at 25/75 wt.‐% ratio after staining by osmium tetroxide. The dark regions are polybutadiene and the light region is polycarbonate.
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