Core-shell approach

Use of Core-Shell Approach to Reduce Catalyst s Precious Metal Content and Cost... 

An alternative, but related, approach to reduce Ft content and yet increase catalytic activity is the nanostructured core-shell approach taken by Adzic and co-workers [41]. As an example, a cartoon of a core-shell structure is illustrated in Figure 14.5, in which a nanostructured catalyst particle is shown that has a Ft monolayer surface with a Fd sublayer on top of a core material of metal M. This core-shell nanostructure is architected to take into account the surface contraction effects that shift the d-band center and reduce the oxygen binding energy, the natural surface segregation effects, and the stability offered by a contiguous monolayer. Clearly, the amount of Ft is reduced because the core can be made of less costly materials. 

There is extensive Hterature on PC blends with ABS, and blends of PC with related materials such as SAN, methacrylate-butadiene—styrene (MBS) emulsion-made core-shell mbber modifiers (297—299), and other impact modifiers. One report reviews some of these approaches and compares PC blends based on emulsion vs bulk ABS (229). In PC—ABS blends, no additional compatihili er is used, because of the near-miscihility of the SAN matrix of ABS and PC. 

More recently Frechet and Gitsov [130] used a similar approach as above and synthesized a novel series of dendritic copolymers derived from a central penta-erythritol core unit. These hybrid star molecules behaved as unimolecular micelles with different core-shell conformational-structures as a response to the polarity of the solvent used. 

This strategy was first realized by Lozinsky et al., who studied the redox-initiated free-radical copolymerization of thermosensitive N-vinylcaprolactam with hydrophilic N-vinylimidazole at different temperatures, as well as by Chi Wu and coworkers. Lozinsky presents an extensive review of the experimental approaches, both already described in the literature and potential new ones, to chemical synthesis of protein-like copolymers capable of forming core-shell nanostructures in a solution. 

A method in which the precursor solutions are successively injected into a cell containing the substrate and rinsed in between has been used to analyze the morphology of SILAR-grown films by atomic force microscopy (AFM).10 Recently, this approach has been applied to the growth of core/shell nanocrystals by Li et al.12... 

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