Encapsulation of Inorganic Materials

For many applications, the encapsulation of inorganic material is of high interest either the inorganic components should be protected from the environment (e.g., air-sensitive components) or the environment from potentially toxic components, or polymeric films with improved color, mechanical, or gas diffusion properties, having finely distributed (and protected) inorganic material for coating applications, are desired. Furthermore, UV-blocking applications are reported [81-83], 

Due to their often hydrophilic surfaces, inorganic components have to be hydrophobized in order to incorporate them in hydrophobic polymers. For the encapsulation in polystyrene shells, the surface of calcium carbonate was modified with stearic acid which allowed an encapsulation of about 5 wt% of the inorganic 

Titania nanoparticles were first surface-modified with polybutylene succinimide diethyl triamine (OLOA370) [87-91] and then 5wt% of the hydrophobized material was dispersed in styrene prior to a miniemulsification process. About 89% of the titania could be encapsulated in 73% of the PS, but pure polystyrene particles were still detected. Another efficient compatibilizer for titania is Solsperse 32000, a polyamine/polyester. By modifying titania with this polymer, hybrid nanoparticles with PS and PS-co-polybutylacrylate(PS-co-PBA) could be generated [92-95]. 

Silica nanoparticles are also hydrophilic and have therefore to be functionalized prior to encapsulation. Without functionalization, the negatively charged silica particles can be used as Pickering stabilizers, leading to hybrid nanoparticles with silica located on the surface of the nanoparticles (see Fig. 13a) [100]. 

Hydrophobized silica nanoparticles were obtained by adsorbing the cationic surfactant CTMA-Cl on the surface subsequently the silica particles could be incorporated in polymer nanoparticles (Fig. 13b). Depending on the reaction conditions 

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Some of the sugar- and peptide-based vesicles described in the previous chapter have been used for very few applications in the field of life science (as carriers for drug, genes, etc. or as bioreactors) and for the fabrication of organic/inorganic composite materials (encapsulation of inorganic nanoparticles). 

Besides inorganic pigment and filler partieles, there is also early work (from 1978) on encapsulation of organic pigments, e.g. eopper-phtaloeyanine and azo pigments [43]. For further reading on encapsulation of different materials see [44]. 

As the pH-stability of OIT is only guaranteed up to 10 in homogenous systems, the incorporation into an appropriate binder or encapsulation into inorganic materials can protect the molecule against hydrolysis even in... 

Inorganic Materials. Sol—gel chemistry involves first the formation of a sol, which is a suspension of soHd particles in a Hquid, then of a gel, which is a diphasic material with a soHd encapsulating a solvent. A detailed description of the fundamental chemistry is available in the Hterature (2—4). The chemistry involving the most commonly used precursors, the alkoxides (M(OR) ), can be described in terms of two classes of reactions ... 

Common to all encapsulation methods is the provision for the passage of reagents and products through or past the walls of the compartment. In zeolites and mesoporous materials, this is enabled by their open porous structure. It is not surprising, then, that porous silica has been used as a material for encapsulation processes, which has already been seen in LbL methods [43], Moreover, ship-in-a-bottle approaches have been well documented, whereby the encapsulation of individual molecules, molecular clusters, and small metal particles is achieved within zeolites [67]. There is a wealth of literature on the immobilization of catalysts on silica or other inorganic materials [68-72], but this is beyond the scope of this chapter. However, these methods potentially provide another method to avoid a situation where one catalyst interferes with another, or to allow the use of a catalyst in a system limited by the reaction conditions. For example, the increased stability of a catalyst may allow a reaction to run at a desired higher temperature, or allow for the use of an otherwise insoluble catalyst [73]. 

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