A novel dilution strategy for tuning Janus particle morphology

Morphology plays a critical role in determining the properties of colloidal particles. To better understand the morphological evolution of Janus particles formed via seeded emulsion polymerization, we constructed a phase diagram based on the seed-to-monomer ratio and cross-linking density. We found that systematically diluting swollen seed particles before polymerization induces distinct morphological transitions. Quantitative analysis of monomer uptake in seed particles revealed that these transitions are primarily driven by monomer diffusion during dilution. Computational simulations supported our experimental findings, demonstrating a sphere-to-dumbbell transition as seed cross-linking density increased. Simulations also captured changes in the interfacial curvature between the seed and monomer lobes, which were further validated through particle etching experiments. Using this new dilution strategy, we successfully synthesized amphiphilic Janus particles with fluorinated monomers. When combined with homogeneous binder particles, these Janus particles formed stratified coatings that significantly improved water resistance. Notably, the water contact angle remained stable even after repeated solvent rinsing and mechanical abrasion. This dilution approach provides a simple yet effective method for controlling Janus particle morphology and optimizing their functional properties.