Preparation Methods of Uniform Solid Nanoparticles

Several preparation methods of uniform solid nanoparticles have been proposed in the literature. Generally, they can be classified as belonging to one of two groups the first one is a group of methods in which the nanoparticle synthesis requires the presence of a surfactant, while in the second one the preparation procedure takes place in the absence of surfactant. Surfactant-free methods include Stober synthesis [5] and solidification in spontaneously formed emulsions (the Ouzo effect) [6]. When surfactant is used during the synthesis the solidification occurs within the emulsion droplets. 

A variant of the Stober synthesis, in which the only reaction medium used was water, was presented by Miller et al. [12]. The surfactant-free synthetic route for the fabrication of silicone nanospheres via a two-step process was developed (1) acid-catalyzed hydrolysis and condensation of 3-mercap-topropyltrimethoxysilane, followed by (2) base-catalyzed condensation [12]. This procedure resulted in a rapid formation of emulsion droplets with a narrow size distribution, which undergo further condensation with the formation of soUd spheres with an equcdly narrow size distribution. By Vcuying the total monomer concentration the control over the pcuTicle size in the rjuige of 50 nm - 3 pm cm be achieved [13]. 

The preparation of functionahzed silicone nanoparticles using this approach was reported in the literature [14, 15]. Several compounds of chemical structure X-Si(OCHj)j, where X=H, CH3, CH=CH3, CH2-CH=CH2, (CH )3SH, (0113)3000011=0113 were used as precursors. The homo-and co-condensation was carried out in the aqueous phase in the presence of a cationic surfactant, benzethonium chloride. The process resulted in the formation of spherical particles with the size in a range of 3-20 nm. It was shown that they can be dispersed as individual particles in common organic solvents such as tetrahydrofuran, toluene or dichlorometh-ane. However, due to their high crosslinking density (T-units 

The nanoparticles obtained in this surfactant-aided synthesis in the aqueous phase are stabilized by the surfactant. Usually, the removal of the surfactant leads to the formation of an insoluble precipitate due to the interparticle condensation. To avoid the occurrence of this process, the Si-OH groups at the particle surface are reacted with an end-cap-ping agent such as trimethylmethoxysilane (MCjSiOMe) or hexamethyldisilazane ((MCjSiljNH). After the end-capping procedure the aqueous dispersion is destabilized by the addition of methanol. The precipitate is filtered off and washed several times with methanol to remove the traces 

2 Preparation Methods of the Core-Shell Silicone Nanopartides 

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