Raspberry-like morphology

Li et al. [51] prepared monodisperse microspheres by distillation precipitation polymerization of DVB and NIPAM with 2,2-azobisisobutyronitrile (AIBN) as initiator in acetonitrile, in the absence of any surfactant. Next, latex particles of poly(EGDMA-co-AA) were assembled onto the microspheres to afford a corecorona composite polymer particle with a raspberry-like morphology, strengthened by hydrogen-bonding interaction. 

Apart from the nse of a polymerizable alkoxysilane, silica/polystyrene composite particles with a raspberry-like morphology have been elaborated in the presence of a methyl methacrylate-terminated polyethylene glycol macromonomer. This macromonomer is mainly hydrophilic due to the presence of ethylene oxide repeat units (n 23), which are able to form hydrogen bonds with the silanol groups of silica and adsorb on its snrface. In addition, this molecnle contains a methacrylate functionality able to copoljmerize with styrene thus... 

Of relevance to this section, Reculusa et al. also recently demonstrated that the addition of a small amount (only 1.5 pmole/m ) of a monomethylether mono methylmethacrylate poly(ethylene oxide) macromonomer (structure 9, Table 4.5) allowed the direct self-assembly of nanometric polystyrene latex particles on the surface of submicronic sihca particles through an in-situ nucleation and growth process (Fig. 4.12) [102]. The two sets of particles were assembled in a raspberry-like morphology via the formation of hydrogen bonds at the interface of the inorganic and organic coUoids. The size and shape of the assembly can be easily controlled by varying the sizes and stoichiometries of the colloidal components (Fig. 4.13). 

Inverted raspberry-like morphologies (the mineral particles being located at the surface of the latex spheres) have also been discussed in Sections 4.4.2.2 and 4.4.2.4 about colloidal silica and layered silicates, respectively. These are mainly a consequence of the surfactant-like behavior of the inorganic particles in specific situations. This was clearly illustrated in a recent report by Landfester, who showed that silica or clays can be used as pickering stabilizers of miniemulsion jxjlymer-izations, resulting therefore in the formation of armored latexes, the surface of which was recovered by the small inorganic particles [99,131]. 

The above computations for the fiee energy changes for composite latex particles have shown that only core-shell, inverted core-shell and hemispherical particles are stable in a thermodynamic sense. All of the other reported morphologies (e.g. sandwich-like , raspberry or confetti-like particles or occluded domains) are non-equilibrium, kinetically controlled structures, prepared... 

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