Janus particles with two hemispheres having different stabilizers, a polystyrene (PS) phase stabilized by poly(acrylic acid) (PAA) (PS(PAA)) and a poly(methyl methacrylate) (PMMA) phase stabilized by poly(vinylpyrrolidone) (PVP) (PMMA(PVP)), were synthesized by the solvent-absorbing/releasing method of PS(PAA)/PMMA(PVP) composite particles with a core-shell structure. The PS(PAA)/PMMA(PVP) composite particles were prepared by seeded dispersion polymerization of MMA using PVP as stabilizer in the presence of PS seed particles stabilized by PAA. We also demonstrated the facile formation of the colloidal chains via hydrogen bonding interaction between different stabilizers.

Emulsion polymerization of styrene was conducted using a biosurfactant (i.e., sodium surfactin, hereinafter called just "surfactin") having very low critical micelle concentration (CMC, 2.9 × 10 mmol/L) and biodegradability characteristics. The nucleation mechanism was investigated by comparing with a conventional surfactant (i.e., sodium dodecyl sulfate) system. Unlike the emulsion polymerization systems using conventional surfactants, nucleation mechanisms changed above CMC in the presence of a biosurfactant. At low concentrations of surfactin (above CMC), the polystyrene (PS) particles are likely generated via a soap-free emulsion polymerization mechanism. In contrast, at high surfactin concentrations, the PS particles would be synthesized by following a micellar nucleation mechanism. However, the slope (0.23) of the log N versus log C plot (N: number of particles; C: concentration of surfactin) did not obey the Smith-Ewart theory (0.6), this probably being produced by the high adsorbability of surfactin.