Cluster formation of Janus polymer microgels

Spherical particles whose surfaces are divided into two distinct chemical regions are termed Janus particles. The anisotropic architecture of Janus particles allows their directed assembly into multiple-particle structures. Here, a heteroaggregation technique between positively charged poly(2-vinylpyridine) microgel particles and much larger, negatively charged poly(2-vinylpyridine-co-styrene) latex particles was used to mask one face of the microgel particles. On the exposed face, atom transfer radical polymerisation was used to graft poly(N-isopropylacrylamide). The resultant pH- and temperature-responsive Janus microgels were isolated through dissolution of the latex particles, and characterised by transmission and scanning electron microscopy. The Janus microgel particles form spherical clusters in solution. The clusters can be formed reversibly by changing the solution temperature, or irreversibly through the addition of an electrolyte. The ability to control the flocculation of particles into small defined clusters may lead to advances in separation processes, optical sensing, and their use as delivery vehicles.