Encapsulation of Clay by Mini emulsion Polymerization

In the past few years, many groups have tried to encapsulate clay platelets inside latex particles. This encapsulation poses some extra challenges because of the tendency of the clay platelets to form stacks and house-of-cards structures in an aqueous medium. Furthermore, the clay platelets also tend to reside at the water-polymer interface, as discussed previously in this chapter. This means that most efforts would lead to clay platelets situated mainly at the outside of the latex particles. In this section, a few examples are shown in which clay has been proven to be located inside the latex particles. Another challenge in this respect is to confirm where the clay platelets reside. It is very diffieult to visualize natural clay platelets when they do not form stacks. Individual clay platelets are too thin to see by TEM they only become visible when their basal planes are oriented more or less parallel to the eleetron beam. A (cryo)-TEM instrument with a stage that can rotate can help verify the location of an exfoliated clay platelet, i.e. whether it is inside or on the surface of a latex particle.  

Many of the papers described emulsion or miniemulsion polymerization in the presence of unmodified or modified clays (often MMT). The modifieation can be surface modification, edge modification or both. lanchis et al. claimed that they obtained both clay platelets (silylated MMT) inside the latex partieles and on the surface of latex particles. Although the elay was not easily visible in the TEM pictures presented, they indirectly inferred the presence of MMT platelets inside the latex particles by looking at the shape of the latex particles. Snowman morphologies were associated with the encapsulated clay. Recently, reversible addition-fragmentation chain transfer (RAFT)-mediated 

van Herk and A. L. German, in Microspheres, Microcapsules and Liposomes, Vol 1 Preparation and Chemical Applications, ed. R. Arshady, Citus Books, London, 1998 pp. 457-486. 

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