Amphiphilic Janus particles are mixed with homogeneous binder particles with strong adhesion to create robust hydrophobic coatings through a unique “active self-stratification” process. Contrasting with homogeneous particle mixtures where stratification is driven passively by evaporation, Janus particles vigorously accumulate at the interface due to strong adsorption, with their hydrophobic sides orienting towards air. They form a complete and densely packed monolayer that effectively increases the water contact angle. Since the hydrophilic side of Janus particles adheres strongly to the binder particles, this new system addresses the weak adhesion issue of conventional hydrophobic coatings. The coating maintains its high contact angle even after solvent rinsing, whereas conventional coating completely breaks down. Remarkably, simply adding Janus particles renders a hydrophilic commercial primer coating surface hydrophobic and drastically reduces the surface tackiness. These results suggest that Janus particles can be used as a novel additive to provide cost-effective and commercially scalable solutions to many long-standing challenges in waterborne emulsion coatings, including water resistance, adhesion, surface hardness and film formation. The study also opens new front for Janus particle research and provides a novel strategy to self-assemble and fabricate hierarchical structures, which may find broad applications beyond coating materials, including cosmetics, adhesives, drug formulations and 3d printing.

Apply Janus particles as an effective coating additive through self-stratification

ACS Fall 2021

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