High-χ Block Copolymer Nanoreactors for the Confined Synthesis of Size-Controlled Nanoclusters

Metallic nanoclusters exhibit distinct optical, catalytic, and magnetic properties that depend strongly on size, shape, and composition. However, synthesizing these structures with precise control and in high yield remains challenging. Scanning probe block copolymer lithography (SPBCL) enables spatially defined synthesis of multimetallic nanostructures within block copolymer nanoreactors. Conventional aqueous SPBCL employs poly(ethylene oxide)-block-poly(2-vinylpyridine) (PEO-b-P2VP), which has a low Flory–Huggins interaction parameter (χ) and low degree of polymerization (N) that prevent ordered microphase separation. As a result, metal precursors are uniformly dispersed within the disordered polymer matrix, causing the entire patterned feature to act as a single nanoreactor. Consequently, both precursor loading and feature size dictate the final particle dimensions, and decreasing either parameter often produces nonuniform products and inconsistent nanocluster formation. To overcome these limitations, a nonaqueous SPBCL ink based on high-χ polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) is introduced. The high χ drives ordered microphase separation that tightly confines the metal-rich P4VP domains, generating exceptionally small nanoreactors (down to ∼13 nm diameter) within the larger lithographic feature. This decoupling of nanoreactor and feature dimensions enables the reproducible synthesis of sub-5 nm multimetallic nanoclusters, including alloyed structures composed of bulk-immiscible elements, and reveals nonspherical morphologies inaccessible through conventional SPBCL.