Nanosilica asymmetric

Synthesis of Symmetric and Asymmetric Nanosilica for Materials, Optical and Medical Applications... 

The benefit of this division can be illustrated from several perspectives. From a synthetic point of view, the division is significant as synthesis normally results in the production of symmetric materials. Hence, the synthesis of asymmetric nanosilica and molecular species are quite unique by themselves. The division can thus be viewed as a helpful hint to understanding the synthesis of helical materials and other asymmetric nanomaterials. The origin of the production of asymmetric nanosilica is believed to be the nature of the different catalysts or templates involved, while the exact growth mechanism depends on the structure of these catalysts or templates. To date, asymmetric nanosihca has not been prepared without these two assisting species. 

I 2 Sfnthesis of Symmetric and Asymmetric Nanosilica Table 2.1 Continued... 

The three phases refer to the feedstocks, the catalysts, and the form of the nanomaterials produced, respectively. As nanosilica are usually in a solid form at the growth temperatures, the final phase is almost always solid, while the catalysts may be either solid or liquid (see Figure 2.4). Solid-form catalysts may represent the key for producing asymmetric nanosilica such as nanocoils, where the phase of the feedstocks may be gas, liquid or solid. The three mechanisms are depicted diagrammatically in Figure 2.4 any variations to these methods usually focus on changes to the phase of the feedstock and the catalysts. 

The preparation of asymmetric nanosilica differs slightly from that of their symmetric counterparts, the main difference being an involvement of templates or anisotropic catalysts [28]. The addition of these materials initiates an asymmetric growth of nanomaterials, thus producing helical nano materials. In the template nanosiUca, a further treatment of as-made silica-like nanomaterials is required to convert them into real siUca nanomaterials. However, in the catalytic growth of heUcal nanomaterials such as nanocoils, no post-synthesis treatment is required. 

The thmst behind the advancement of any field depends on the appUcation potential or real benefits, much more so than the materials themselves, and the same rule appUes to nanosiUca-whether symmetric or asymmetric. In the following sections we will survey the appUcations of both symmetric and asymmetric nanosilica. It will become clear that asymmetric nanosiUca, at present, have far fewer applications than their symmetric counterparts, although several excellent obvious... 

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