Synthesis of "hard-soft" janus particles by seeded dispersion polymerization.

The majority of studies on Janus particles focus on those that show amphiphilicity, with distinct hydrophilic and hydrophobic domains. Here, we demonstrate the synthesis of a different class of Janus particles: "hard-soft" biphasic dumbbell- or peanut-shaped particles with distinct lobes of "soft" poly(n-butyl acrylate) and "hard" poly(styrene). The particles are made by seeded dispersion polymerization of butyl acrylate in the presence of poly(styrene) seed particles. Surface nucleation by capture of the oligoradicals onto the surface of the seed particles thereby forming a distinct new polymer phase is found to be the formation mechanism of these particles. The total available poly(styrene) seed surface area plays a significant role in the size and number of poly(butyl acrylate) lobes grown off a single particle. At particularly low values of the surface area, we observe the formation of multilobe particles. We further demonstrate that our synthesis method is versatile and can be extended to the submicrometer domains by using seed particles of 200 nm in diameter.