Ultrathin gold nanoframes (up to 1.6 nm) were prepared via templating upon well-defined faceted silver morphologies. Starting with silver decahedra, small quantities of gold (1-10 mol% relative to the amount of silver) were selectively deposited on the nanoparticle edges under optimized reducing conditions. Silver dissolution in hydrogen peroxide yielded well-defined gold frames that retained their structural integrity in the ultrathin nanowire regime below 2 nm. The frame formation protocol was also successfully applied to other silver nanoparticle shapes featuring pentagonal twinning and (111) facets (e.g., pentagonal faceted rods and icosahedra). The demonstrated approach can be applied in the controlled preparation of ultrathin metal nanowires complementary to lithography and in the production of ultrafine noble-metal nanostructures for catalytic applications.
A new class of materials for optical data storage and security data encryption is reported. Multidye colloid particles comprising different dyes in different phases are employed as the building blocks to produce a multicolored multiphase polymeric material. The incorporation of dyes in different phases minimizes energy transfer, provides selective dye photobleaching, and allows storage of different data on a single spot (see Figure and also cover).
Macroporous copolymer particles have a broad range of applications such as ion exchange resins and sorbents, catalyst supports, and carriers of biologically active species. Many of these applications require precise control of the dimensions of microbeads in the range from 50 to 100 µm and predetermined size of pores. This paper reports semicontinuous photoinitiated microfluidic synthesis of macroporous polymer particles with the designated dimensions and a range of internal structures. Comparison with microspheres synthesized by conventional suspension polymerization shows that microfluidic synthesis provides better control over the porous structure of the microbeads.
Advances in nanotechnology depend upon expanding the ability to create new and complex materials with well-defined multidimensional mesoscale structures. The creation of hybrid hierarchical structures by combining colloidal organic and inorganic building blocks remains a challenge due to the difficulty in preparing organic structural units of precise size and shape. Here we describe a design strategy to generate controlled hierarchical organic-inorganic hybrid architectures by multistep bottom-up self-assembly. Starting with a suspension of large inorganic nanoparticles, we anchor uniform block copolymer crystallites onto the nanoparticle surface. These colloidally stable multi-component particles can initiate the living growth of uniform cylindrical micelles from their surface, leading to three-dimensional architectures. Structures of greater complexity can be obtained by extending the micelles via addition of a second core-crystalline block copolymer. This controlled growth of polymer micelles from the surface of inorganic particles opens the door to the construction of previously inaccessible colloidal organic-inorganic hybrid structures.
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