Reprecipitation method

Keywords Aggregation-induced enhanced emission (AIEE) Fluorescent organic nanoparticles Ion-association method Organic dye nanoparticles Reprecipitation method Restriction of intramolecular rotation Size-dependent optical properties... 

Organic dye nanoparticles of DHIA and DHBIA (the chemical structures are shown in Fig. 1) have been synthesized in THF/water mixed solvent by a reprecipitation method [32]. These dye molecules possess a 2-(2-hydroxyphenyl) benzothiazole (HBT) unit, which is known to be more stable as an enol imine form in the ground state and as a keto amine form in the excited state [32, 33] (Fig. 6). The nanoparticles exhibited the AIEE phenomenon mainly due to a restricted intramolecular motion, that is, impediment to free rotation of two end-substituted HBT units around single bonds. It is interesting to note that the... 

Another reprecipitation method commonly used is applicable to compounds which are difficultly soluble in water, but which form easily soluble salts. These include bases which dissolve in dilute acids and which are thrown out of solution by the addition of alkalis, as well as acidic substances, such as carboxylic acids, sulfonic acids, and phenols, which are dissolved in alkalis and thrown out by the addition of acids. This type of reprecipitation is effective in removing only those impurities which have no basic or acidic properties, and which, therefore, are not dissolved by the acid or alkali and are removed by filtration. Impurities having the same chemical properties as the main product are not removed to any extent by such a process. The effectiveness of the method is greatly increased, however, by two modifications. 

Microcrystals of some diacetylenes, prepared by the reprecipitation method, have been studied as dispersions in liquid media. Interesting behavior has been observed in the solid-state polymerization of diacetylene monomers and with the optical properties of polydiacetylene (PDA) microcrystals. First, the polymerization perfectly proceeded from one end to the other end of the diacetylene microcrystals. Next, the excitonic absorption peak position was found to shift to higher energy side with decreasing size of the PDA microcrystals. The size effect was observed even for crystals as large as 100 nm or more in contrast to conventional quantum effect of inorganic semiconductors where size effect is observed only for microciystals of less than about 10 nm size. In addition, since the microcrystal dispersions in water have low optical loss, the c tical Kerr shutter response of PDA microciystals could be measured, and the non-resonant value was estimated to be on the order of 10 to 10" esu in very low concentrations (ca. 10 M). 

Their microcrystal dispersions in water were prepared by the simple and easy reprecipitation method developed and established by our group(24). For example, in the case of 14-8ADA, 250 i of 1.0 x 10" M acetone solution was injected into 10 ml of water with 20 mg of poly(vinly alcohol) at room temperature. PDA microcrystals were obtained by UV irradiation of the microcrystal dispersions of the corresponding monomers. 

In this chapter, we represent fabrication of PI NPs and morphological controlled PI NPs, i.e., variously-sized NPs [13], soccer-ball-like NPs [14], cage-like microparticles [14], golf-balllike NPs [15-17] and hollow NPs [18], using our technique, the reprecipitation method [19]. Furthermore, fabrication of multilayered films of porous PI NPs and their dielectric property are described [18,20]. 

Figure 4. Schematic representation of PI nanoparticles via the reprecipitation method.

Zhao G, Ishizaka T, Kasai H, Oikawa H, Nakanishi H (2007) Fabrication of Unique Porous Polyimide Nanoparticles Using Reprecipitation Method. Chem. Mater. 19 1901-1905. 

PDLLA (NatureWorks, PLA 2002D, D-content 4.25%, p= 2A g/cm ) nanoparticles can be prepared either by the miniemulsion method or the reprecipitation method. In the present case, for the miniemulsion method PDLLA was dissolved in chloroform (CHCI3), at a 0.2 wt% concentration. The polymer solution was added to a 1 wt% aqueous surfactant solution of sodium dodecyl sulfate (SDS). Pre-emulsification was obtained by stirring at room temperature for... 

PDLLA nanoparticles were also prepared by the reprecipitation method. Specifically, 15 mg of PDLLA were dissolved in 5 mL of tetrahydrofuran (THE). The solution was left under stirring at room temperature for 30 min. Afterwards, in order to remove any macroscopic residues, the solution was filtered. Finally, the polymer solution was rapidly injected into a beaker filled with distilled water. This emulsion was left under stirring at room temperature for 90 min and then for 120 min at 66 °C to allow complete removal of the solvent. Figure 6.6 shows AFM topography images of the prepared PDLLA nanoparticles. 

Figure 6.6a, b show AFM topography images of the PDLLA nanoparticles prepared by the miniemulsion and reprecipitation method, respectively. In both cases, the nanoparticles consist of polymer nanospheres, without signs of... 

Fig. 6.6 AFM topography images and size distribution of PDLLA nanoparticles prepared by the miniemulsion method (a, c) and reprecipitation method (b, d). Size distribution was quantified on the AFM images by measuring the nanoparticles diameters. Continuous black line represents a Gaussian fit to the distribution...

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