Kinetically Controlled Synthesis of Nonspherical Polystyrene Nanoparticles with Manipulatable Morphologies

The morphology of nanoparticles plays a critical role in determining their properties and applications. Herein, we report a versatile approach to the fabrication of nonspherical polystyrene (PS) nanoparticles with controlled morphologies on the basis of kinetically controlled seed-mediated polymerization. By manipulating parameters related to the reaction kinetics including the concentration of monomers, injection rate of reactants, and reaction temperature, the monomers could be directed to polymerize on the selective sites of PS seeds, and after the removal of the second polymer, nonspherical nanoparticles with a variety of thermodynamically unfavored morphologies could be synthesized. We systematically investigated the formation mechanism of these nonspherical nanoparticles by monitoring the evolution of seeds during the reaction. Moreover, we have also successfully extended this strategy to reaction systems containing monomers with different combinations and seeds with different sizes. We believe this work will provide a promising route to the fabrication of nonspherical polymer nanoparticles with controlled morphologies for various applications

Facile Synthesis of Gold Wavy Nanowires and Investigation of Their Growth Mechanism

We describe a synthesis of Au wavy nanowires in an aqueous solution in the presence of cetyltrimethylammonium bromide (CTAB). The resultant Au nanowires automatically separated from the solution and floated at the air/water interface. We investigated the formation mechanism by characterizing the samples obtained at different stages of the synthesis. Both particle attachment and cold welding were found to be involved in the formation of such nanowires. Based on X-ray photoelectron spectroscopy and thermogravimetric analysis, the CTAB molecules adsorbed on the surface of a Au nanostructure went through a change in structure from a bilayer to a monolayer, converting the Au surface from hydrophilic to hydrophobic. As a result, the Au wavy nanowires were driven to the air/water interface during the synthesis. This growth mechanism is potentially extendable to many other systems involving small surfactant molecules

New Strategy for Surface Functionalization of Periodic Mesoporous Silica Based on meso-HSiO_1.5

Organic functionalization of periodic mesoporous silicas (PMSs) offers a way to improve their excellent properties and wide applications owing to their structural superiority. In this study, a new strategy for organic functionalization of PMSs is demonstrated by hydrosilylation of the recently discovered “impossible” periodic mesoporous hydridosilica, meso-HSiO_1.5. This method overcomes the disadvantages of present pathways for organic functionalization of PMSs with organosilica. Moreover, compared to the traditional functionalization on the surface of porous silicon by hydrosilylation, the template-synthesized meso-HSiO_1.5 is more flexible to access functional-groups-loaded PMSs with adjustable microstructures. The new method and materials will have wider applications based on both the structure and surface superiorities

Structural Color Patterns by Electrohydrodynamic Jet Printed Photonic Crystals

In this work, we demonstrate the fabrication of photonic crystal patterns with controllable morphologies and structural colors utilizing electrohydrodynamic jet (E-jet) printing with colloidal crystal inks. The final shape of photonic crystal units is controlled by the applied voltage signal and wettability of the substrate. Optical properties of the structural color patterns are tuned by the self-assembly of the silica nanoparticle building blocks. Using this direct printing technique, it is feasible to print customized functional patterns composed of photonic crystal dots or photonic crystal lines according to relevant printing mode and predesigned tracks. This is the first report for E-jet printing with colloidal crystal inks. Our results exhibit promising applications in displays, biosensors, and other functional devices

Kinetically Controlled Overgrowth of Ag or Au on Pd Nanocrystal Seeds: From Hybrid Dimers to Nonconcentric and Concentric Bimetallic Nanocrystals

This article describes a systematic study of the nucleation and growth of Ag (and Au) on Pd nanocrystal seeds. By carefully controlling the reaction kinetics, the newly formed Ag atoms could be directed to selectively nucleate and then epitaxially grow on a specific number (ranging from one to six) of the six faces on a cubic Pd seed, leading to the formation of bimetallic nanocrystals with a variety of different structures. In addition to changing the injection rate of precursor, we also systematically investigated other reaction parameters including the capping agent, reductant, and reaction temperature. Our results suggest that the site-selective growth of Ag on cubic Pd seeds could be readily realized by optimizing these reaction parameters. On the basis of the positions of Pd seeds inside the bimetallic nanocrystals as revealed by TEM imaging and elemental mapping, we could identify the exact growth pathways and achieve a clear and thorough understanding of the mechanisms. We have successfully applied the same strategy based on kinetic control to cubic Pd seeds with different sizes and octahedral Pd seeds of one size to generate an array of novel bimetallic nanocrystals with well-controlled structures. With cubic Pd seeds as an example, we have also extended this strategy to the Pd–Au system. We believe this work will provide a promising route to the fabrication of bimetallic nanocrystals with novel structures and properties for applications in plasmonics, catalysis, and other areas