G1 dendrimers-mediated evolution of silver nanostructures from nanoparticles to solid spheres.
With the control of G1 poly(amidoamine) (PAMAM), an evolutionary course of stable colloidal silver from discrete nanoparticles to solid spheres through ultraviolet irradiation reduction of silver nitrate solutions was observed by transmission electron microscopy (TEM). The morphologies of the products depend on the Ag+ concentration. A mechanism of globular assembly was put forward to interpret the evolution of the nanostructures. Powder X-ray diffraction (XRD), electron diffraction (ED) patterns, and X-ray photoelectron spectroscopy (XPS) indicate the presence of cubic symmetry silver. XPS and Fourier transform infrared (FT-IR) spectroscopy confirm that dendrimers have participated in the stabilization and control of Ag nanostructures. In the UV-vis spectra, the intense surface plasmons are centered at 425 and 430 nm corresponding to the shapes of dots and solid spheres, respectively. The solid spheres exhibit excellent catalytic efficiency on the reduction of 2,7-dicholoroflurescein (DCF).
Role of functionalized terminal groups in formation of nanofibrillar morphology of hyperbranched polyesters
Abstract A series of amphiphilic hyperbranched polymers with a polyester–polyol core and 64 terminal hydroxyl groups were modified by substituting various terminal groups: alkyl tails, amino, and carboxyl groups. The effect of the pendant groups' chemical composition on the resulting surface morphology within Langmuir–Blodgett monolayers with respect to their ability to form nanofibrillar surface structures was investigated. We demonstrated that the amphiphilicity of the polyester core with 64 hydroxyl groups can be achieved if a fraction of alkyl tails (C15) is higher than 1/4. Nanofibrillar morphology was consistently formed as the highly polar functional groups were added to the polyester cores in combination with a significant (>30%) fraction of alkyl terminal groups. Addition of amino end groups was observed to be much more effective in promoting the nanofibrillar assembly than the addition of carboxyl end groups.
SR topography of plastically deformed Fe-Si bicrystals - observation in situ and post mortem
SR reflection topography was applied to study the interaction of slip dislocations with the grain boundaries in Fe-4at%Si bicrystals deformed by compression. Three experimental settings with either a white or monochromatic beam were used and the corresponding orientation contrast analysed. Dislocation transmission through the grain boundary was observed in bicrystals with favourable geometry of the slip systems.