Closed-shell colloids

The unique selling proposition of the tandem-assembly process is its contribution to the field of green chemistry in obtaining closed-shell colloidal structures through an environmentally friendly route, as the entire synthesis is carried out in water, at near neutral pH, and at room temperature. Further, the size of the colloidal template can be controlled by the charge ratios of reactants, which results in structures with sizes ranging from 100nm to 2p,m [32-35,80,81]. 

Colloidosomes are a recent class of microcapsules and thus far have only been applied to catalysis and drug delivery in a few cases. The term colloidosomes was coined by Anthony Dinsmore and colleagues in 2002 to refer to capsules where the shells are composed of close-packed layers of monodisperse colloidal particles (usually micron-sized polymer beads) that have been linked together by sintering. 

Fig. 4 Comparison of FEM results (filled circles connected by solid lines) for the deformation of a spherical shell with a ratio thickness to radius as in the experiment by a rigid spherical colloid. Dotted and broken lines are the analytical results from Reissner (Eq. 1) and Pogorelov (Eq. 2). In the FEM, R = 10 xm, It = 50 nm, E = 250 MPa und v = 1 /3 were used which is close to the experimental situation...

To create particles with a hydrophobic core and a hydrophilic shell, preformed hydrophobic polymer particles can be used as substrate for the covalent grafting of hydrophilic polymer chains. Aqueous emulsion polymerization is thus the method of choice for synthesis of core particles with submicrometric diameter (due to the scope of this review article, discussion will be restricted to aqueous emulsion polymerization, although some examples of particle substrates created via suspension polymerization exist however, with much larger diameters). The grafting methods are very close to those used for the surface modification of inorganic materials, such as for instance silicon wafers or colloidal silica particles [46,48-52], Various strategies can be employed such as ... 

Above we described the possibilities how to introduce the macromolecules into the hollow capsules by regulation of shell permeability. Pores in the polyelectrolyte shell can be opened and closed by variation of pH, salt and/or solvent exchange. The main drawback if this approach is low encapsulation efficiency for macromolecules. Indeed, one could capture in the hollow capsules only the macromolecules, which are floating in the capsule interior when pores are closed. In following we propose another approach to encapsulate macromolecules and nanoparticles which could provide rather high encapsulation efficiency. This approach consists in combination of layer-by-layer approach and controlled precipitation of polymers on surface of colloidal particles. 

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