Reprecipitation-microwave irradiation

Techniques such as vacuum evaporation method, melting process in a glass matrix, and so on [88], basically fundamental fabrication techniques for inorganic NPs and semiconductor quantum dots, would not be expected to be applied to organic and polymer compounds and materials because of their thermal instability [89, 90]. In contrast, the so-called reprecipitation method [1-4] is a useful and convenient procedure to prepare organic and polymer NCs. This method has been further improved as the supercritical reprecipitation method [1-3,28,29], reprecipitation-microwave irradiation method [1-3, 30-34], and inverse-reprecipitation method [1-3, 27, 42, 43], being closely related to the physicochemical properties of the target compound and materials. 

Microwave irradiation (2.45 GHz, 500 W, for a given time) after injection in the reprecipitation-microwave irradiation method could greatly promote rapidly nanocrystallization [1-3, 30-34] due to quick removal of the used organic solvent... 

The improved co-reprecipitation and microwave-irradiation method is an effective process to fabricate Ag core/poly(ADA)-shell hybridized NCs [30,45, 50], Ag NPs in an aqueous dispersion liquid were prepared by reducing silver nitrate (AgN03) with trisodium citrate [106], The size of the resulting Ag NPs was ca. 45-50 nm, which is larger than that in Sect. 3.2. 

Figure 5 displays the SEM and TEM images of Ag core/poly(ADA)-shell hybridized NCs [50], Actually, Ag core was clearly covered with almost uniform poly(ADA) shell. The thickness of the shell was about 5 nm, and the morphology of the core/shell nanostructure in the present hybridized NCs was dependent remarkably on microwave irradiation conditions [50], For example, the above-mentioned microwave irradiation condition is the most desirable, and the core/shell nanostructure could not be formed successfully when the irradiation condition was 500 W, 20 s or 200 W, 40 s. After co-reprecipitation, the dispersion liquid is considered to be a mixture of Ag NPs and ADA NCs. The heated ADA NCs were probably partially melted by microwave irradiation, and may easily collide and fuse with Ag NPs at the elevated temperature. As a result, molten ADA monomer could adsorb effectively on the surface of Ag core, and was then recrystallized to form solid-state polymerizable ADA shell during the cooling process after microwave irradiation [50]. The present co-reprecipitation and microwave-irradiation method is available for the fabrication of another type of metal-core/ji-conjugated polymer-shell hybridized NCs [107]. 

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