The spontaneous organization of two types of nanoparticles (NPs) with different shapes or properties into binary nanoparticle superlattices (BNSLs) with different configurations has recently attracted significant attention due to the coupling or synergistic effect of the two types of NPs, providing an efficient and general route for designing new functional materials and devices. Here, this work reports the co-assembly of polystyrene (PS) tethered anisotropic gold nanocubes (AuNCs@PS) and isotropic gold NPs (AuNPs@PS) via an emulsion-interface self-assembly strategy. The distributions and arrangements of the AuNCs and spherical AuNPs in the BNSLs can be precisely controlled by adjusting the effective size ratio (λeff ) of the effective diameter (deff ) of the embedded spherical AuNPs to the polymer gap size (L) between the neighboring AuNCs. λeff determines not only the change of the conformational entropy of the grafted polymer chains (∆Scon ) but also the mixing entropy (∆Smix ) of the two types of NPs. During the co-assembly process, ∆Smix tends to be as high as possible, and the -∆Scon tends to be as low as possible, leading to free energy minimization. As a result, well-defined BNSLs with controllable distributions of spherical and cubic NPs can be obtained by tuning λeff . This strategy can also be applied for other NPs with different shapes and atomic properties, thus largely enriching the BNSL library and enabling the fabrication of multifunctional BNSLs, which have potential applications in photothermal therapy, surface-enhanced Raman scattering, and catalysis.
Keywords: anisotropic gold nanocubes; binary superlattices; effective size ratio; entropic interaction; isotropic gold nanoparticles.
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