Onion-structured nanoparticles

Scheme 10.3 Fabrication of drug-loaded pH-responsive three-layered onion-structured nanoparticles (3LNPs) via pH-controUed hierarchical self-assembly...

Zhan, Y Van Kirk, E. Xu, P Murdoch, W. J. Radosz, M. Shen, Y. pH-responsive three layer onion-structured nanoparticles for drug delivery. Polym. Mater. Sci. Eng. Prepr. 2006, 94, 139-140. 

Little is known so far about the chemical properties, yet first results suggest a reactivity similar to that of multiwalled carbon nanotubes. Furthermore, a transformation of nano-onions into other forms of carbon can be achieved by heating (equihbration as faceted nanoparticles) or electron bombardment. In large carbon onions, a formation of small diamond clusters due to internal self-compression has been observed. These grow up to be nanoscale diamond particles under complete consumption of the onion structure. 

The obtained structures can be isotropic, i.e. the metal nanoparticles segregate in one type of lamellae in onion-like nanoparticles [78-80], form isotropic surface structures [81, 82] (Fig. 6), or can be anisotropic with regard to the particle geometry. The latter case was based on metal nanoparticles/polymer assemblies [81] or similar assemblies but with a fluorescent dye instead of the metal nanoparticles [83]. 

The final section of the volume contains three complementary review articles on carbon nanoparticles. The first by Y. Saito reviews the state of knowledge about carbon cages encapsulating metal and carbide phases. The structure of onion-like graphite particles, the spherical analog of the cylindrical carbon nanotubes, is reviewed by D. Ugarte, the dominant researcher in this area. The volume concludes with a review of metal-coated fullerenes by T. P. Martin and co-workers, who pioneered studies on this topic. 

Figure 13. The TEM micrograph of two NbS2 nanoparticles with nested (onion) fullere-like structure. [Courtesy of M. Homyonfer, Weizmann Institute.]...

Figure 21.2 Assembly of mesosfructured hybrids, (a) Nanoparticles smaller than the darker gray block s R0 are miscible and assemble into a lamellar structure, (b) Nanoparticles larger than the darker gray block s R0 segregate, forming a nanoparticle-rich core around which lamellae assemble into an onion-type structure, (c) This can be used to generate compositionally heterogeneous nanostructures from tailored nanoparticle size distributions.10 (Reprinted with permission from S. C. Warren et al., Nature Mater. 2007, 6, 156-161. Copyright 2007 Macmillan Publishers Ltd.)...

Figure 21.4 Influence of nanoparticle size on silica-type mesostructuie. (a, b) TEM micrographs showing mesostructuies with a nanoparticle volume fraction

The preformed Pt core may be regarded as a living-metal polymer on which the Pd atoms are deposited to give onion-type bimetallic nanoparticles (5 nm), the structure of which has been characterized by a combination of analytical methods. 

It has been menhoned before (Section 4.2.1) that apart from the spherical carbon onions, there are also markedly faceted structures. Some of these exhibit a large central cavity (Figure 4.7a). They may be generated, for instance, by heating spherical nano-onions, or by direct methods like arc discharge or others. Structures of this kind are furthermore observed as faceted shells of metal nanoparticles that fill the void within the carbon structure. 

Owing to their curved and defective structure, carbon onions are quite easily converted into other forms of carbon. The transformation of spherical particles into faceted nanoparticles by heating to at least 1900 °C has already been described in Section 4.3.5.3 on the thermal produchon of nano-onions from diamond particles. 

Fig. 7 TEM micrograph of NbS2 nanoparticle with nested ( onion ) fullerene-like structure (courtesy of Dr. M. Homyonfer, Weizmann Institute). The layerto layer distance is 0.59 nm.

A nanoparticle is generally defined as a particle whose diameter is between 1 and 100 nm. No distinction is made according to the material nanoparticles can be metals, metal compounds, organic compounds, and polymers. A composite nanoparticle is a nanoparticle which has a composite stmcmre, including core-shell structure, onion-like structure, or gladiate composition. 

As an overview of rounded concentric structures, it can be said that they have been detected as wholly carbon nanoparticles like onions, with and without a hole in the center, or a kernel of other material inside. They are the consequence of successive elimination of pair of carbon atoms from... 

When two metals are combined within a nanoparticle, potentially they could mix in different patterns called as nanostructures. A few commonly nanostructures are (a) core-shell, (b) sub-cluster segregated, (c) homogeneous (ordered or random) alloy and (d) multi-shell or onion like structure. In the case of supported AuPd catalysts, homogeneous... 

The process of formation of complex block copolymer stmctures in 3D confinement has been elucidated for some selected PS-Z>-PMMA copolymers. Introduction of a nonsolvent into the spherical nanoparticles yielded hemispherical structures of onionlike morphology. Such structures may be viewed as a result of double confinement consisting of the outer surfactant double layer and the inner nanophase separation between the block copolymer and the nonsolvent for both blocks. This concept allows targeting the nanoparticle shape as well as the iiuier particle morphology (ranging from simple core-shell to onion-Uke to patched structures), which may find application for encapsulation of various substrates with predetermined release characteristics. 

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