Bulk synthesis of Janus objects and asymmetric patchy particles

This review article highlights the most recent advances with respect to the preparation of Janus objects by bulk phase processes. Historically most of the concepts developed for generating asymmetric particles have been based on the use of interfaces or surfaces, which are necessary to break the symmetry. This restricts in many cases the amount of produced particles, due to the two-dimensional nature of the approaches. Therefore the bulk synthesis of such asymmetric micro- and nanoobjects is of primary importance for their production at an industrial scale and helps to open up the field to commercial applications. We summarize here the different alternative concepts, spanning a wide range from sophisticated polymer chemistry to the use of external electromagnetic fields, that have been proposed in recent years in order to break the symmetry in true bulk processes.