Encapsulation of Pigments by Direct Miniemulsification

For the encapsulation of pigments by miniemulsification, two different approaches can be used. In both cases, the pigment-polymer interface as well as the polymer-water interface must be carefully adjusted chemically in order to obtain encapsulation as a thermodynamically favored system. The design of the interfaces is mainly dictated by the use of two surfactant systems, which govern the interfadal tensions, as well as by the use of appropriate functional comonomers, initiators, or termination agents. The sum of all the interface energies must be minimized. 

For the successful incorporation of a pigment into the latex particles, both type and amount of surfactant systems must be adjusted to yield monomer particles, which have the appropriate size and chemistry to incorporate the pigment by its lat- 

Nanoparticulate hydrophilic CaCOj was effectively coated with a layer of stearic add as surfactant system I prior to dispersing the pigments into the oil phase [95]. The COOH groups act as good linker groups to the CaCOj, and the tendency of the stearic add to pass to the second polymer-water interface was found to be low. A CaCOj level of 5 wt.%, based on monomer, could be completely encapsulated into polystyrene particles (95). The weight limit was limited due to the fact that, at this concentration, each polymer particle already contained one CaCOj colloid, which was encapsulated in the middle of the latex particle (Fig. 2.10). 

Silica nanoparticles could also be encapsulated with an epoxy resin to produce water-borne nanocomposite dispersions by using the phase-inversion emulsification technique [98]. Microscopy results indicated that all the siHca nanoparticles were encapsulated within the composites and uniformly dispersed therein. 

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