A Summary of Synthetic Methods

In spite of the simplified description of particle synthesis given above, large particles from macroemulsions are indeed synthesized by several different methods, the main variation being in step (iii) mentioned in Section 4.1 above. Brief descriptions of these variations are provided below. 

A direct way of converting aqueous droplets of emulsions into solid particles is by removal of water. One example is dropwise addition of the emulsion into a hot oil phase of relatively high boiling point [164,18]. This causes evaporation of the water in the droplets and precipitation of the precursor solid for eventual calcination, i.e. step (iv) in Section 4.1 above. The oil can be petroleum, kerosene etc. [ 164,18] and the bath temperature can be in the range of 80 -180 C for kerosene and 200 -240 C for mineral oil [165]. Precipitation has also been obtained by stirring the emulsion under hot condition [166]. The water in the droplets can on 

In addition to the above, there is extensive documentation on the transformation of aqueous sol droplets into micrometer-sized solid particles by external or internal gelation [30]. In case of external gelation where a rise in basicity is required for precipitation of hydroxides, ammonia is usually bubbled through the emulsion, or added gradually in the form of ammonium hydroxide. Liquid amines, e.g. triethanolamine have also been added into emulsions for the same purpose [169]. Another gelling agent, utilized effectively for the purpose, is triethylamine, (C2H5)3N [170]. 

The precipitation through anions proceeds through three steps  

For internal gelation of sol droplets, in situ decomposition of urea or 

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A summary of synthetic methods for obtaining spiropyrans from benzo-dithioles, benzoxathioles, and 1,3-dithioles is given elsewhere.75... 

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