Directing the self-assembly of nanocrystals beyond colloidal crystallization

This article gives an overview of recent progress in the self-assembly of nanocrystals. Classic self-assembly of nanocrystals, so-called colloidal crystallization driven by van der Waals interactions, is highlighted first with an emphasis on the recent realization of binary colloidal crystals. Next, new developments in the integration of nanocrystals into clusters based on electrostatic interactions, hydrogen bonding and dipole-dipole interactions are summarized, shedding light on the defined control of the interactions between the nanocrystals. Finally, the fabrication of heterogenous nanocrystals, obtained via either phase selective modification at the water/oil interface or facet-selective crystal growth on non-spherical nanocrystals is discussed. These last materials may provide significant building blocks for mimicking molecular self-assembly.     

Adsorption of amyloid beta-peptide at polymer surfaces: a neutron reflectivity study.

The adsorption of amyloid beta-peptide at hydrophilic and hydrophobic modified silicon-liquid interfaces was characterized by neutron reflectometry. Distinct polymeric films were used to obtain noncharged (Formvar), negatively (sodium poly(styrene sulfonate)) and positively charged (poly(allylamine hydrochloride)) hydrophilic as well as hydrophobic surfaces (polystyrene and a polysiloxane-dodecanoic acid complex). Amyloid beta-peptide was found to adsorb at positively charged hydrophilic and hydrophobic surfaces, whereas no adsorbed layer was detected on hydrophilic noncharged and negatively charged films. The peptide adsorbed at the positively charged film as patches, which were dispersed on the surface, whereas a uniform layer was observed at hydrophobic surfaces. The thickness of the adsorbed peptide layer was estimated to be approximately 20 A. The peptide formed a tightly packed layer, which did not contain water. These studies provide information about the affinity of the amyloid beta-peptide to different substrates in aqueous solution and suggest that the amyloid fibril formation may be driven by interactions with surfaces.     

Nanoengineering of iron oxide and iron oxide/silica hollow spheres by sequential layering combined with a sol-gel process

Fe2O3 and Fe2O3/SiO2 hollow spheres with tailored dimensions and compositions were created by consecutively coating polystyrene (PS) latices either with Fe3+ alternately adsorbed with Nafion or combining a sol-gel process based on the hydrolysis of tetraethoxysilane (TEOS), and subsequently removing the cores upon pyrolysis.     

Biquaternionic Integral Representations for Massive Dirac Spinors in a Magnetic Field and Generalized Biquaternionic Differentiability

The Dirac equation with a vector potential is considered using a biquaternionic formalism and boundary integral representations for its solutions are obtained. In order to characterize these solutions by a property of local approximability by linearization the corresponding notion of biquaternionic differentiability and its generalization in the sense of Bers (adapted to the spatial case) are given.