Hybrid Janus particles based on polymer-modified kaolinite

Abstract

Janus particles are superior to ordinary Pickering emulsifiers. Widespread industrial usage is however hampered by the restricted accessibility of these polar colloids. Whereas established synthesis protocols that allow for breaking the symmetry of colloid surfaces are laborious and expensive, here we use Janus particles that are based on the ubiquitous layered silicate kaolinite. As a consequence of its crystal structure, the two opposing basal planes, the tetrahedral (TS) and the octahedral (OS) surface, are capped by distinct functional groups. We show that these chemically different basal surfaces allow for facile selective modification making them compatible with e.g. polystyrene (PS) and poly(methyl methacrylate) (PMMA), respectively. The TS was selectively modified by simple cation exchange with poly(2-(dimethylamino)ethyl methacrylate) polycations attached to a polystyrene block while on the OS PMMA chains were covalently anchored via statistically distributed catechol groups. Solid-state NMR proved successful modification, while TGA was provided the amount of polymer bound to both external basal surfaces of kaolinite. Moreover, the selective nature of the modification was proven indirectly by qualitatively comparing the sedimentation stability of suspensions of differently modified samples. These Janus particles with fine-tuned surface tension of the opposing hemispheres were tested on their interfacial activity in solvent-cast films of PS–PMMA blends. The assembly of the Janus particles at the interfaces of the blend was proven by transmission electron microscopy.