We show that polymer‒polymer attraction actively recruits free chains in solution to adsorb onto the surface regions of NPs already partially occupied by other polymers, overcoming competing energetic costs such as polymer-solvent attraction and steric hinderance 23. Here we report an approach to engineer patches on anisotropic NPs through the grafting of polymers onto curved NP surfaces. However, such patch formations are governed by NP geometry, making it difficult to target specific surface facets/locations. Previous synthetic efforts to induce polymeric patch formation on anisotropic nanoparticles (NPs) rely on NP shape variations to drive post-synthesis segregation of uniformly adsorbed polymers 15, 16, 17, spontaneous phase separation of ligand mixtures 18, partial ligand exchange 19, or curvature-induced selective adsorption of polymers 20, 21, 22. Patchy particles 1, 2, 3, 4 have attracted increasing synthetic attention for applications in directed assembly 5, 6, 7, 8, 9, plasmonics 10, catalysis 11, and targeted delivery 12 thanks to their directional interaction 1, 2, hybrid composition 13, and force imbalance under external fields 14. Our work provides an approach to leverage polymer interactions with nanoscale curved surfaces for asymmetric grafting in nanomaterials engineering. Both the experimental strategy and theoretical prediction extend to nanoparticles of other shapes such as octahedra and bipyramids. To unveil the mechanism of symmetry-breaking patch formation, we develop a theory that accurately predicts our experimental observations at all scales-from patch patterning on nanoparticles, to the size/shape of the patches, to the particle assemblies driven by patch‒patch interactions. These asymmetric single-patch nanoparticles are shown to assemble into self-limited patch‒patch connected bowties exhibiting intriguing plasmonic properties. In our model system of triangular gold nanoparticles and polystyrene- b-polyacrylic acid patch, single- and double-patch nanoparticles are produced at high yield. Here we show that polymers can be designed to selectively adsorb onto nanoparticle surfaces already partially coated by other chains to drive the formation of patchy nanoparticles with broken symmetry. Synthesizing patchy particles with predictive control over patch size, shape, placement and number has been highly sought-after for nanoparticle assembly research, but is fraught with challenges.
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