Engineering Three-Dimensional\nMorphologies in a Block\nCopolymer by Reversible Metal Infiltration

A range of three-dimensional (3D)\nmorphologies is established\nin\nlayered thin films of a block copolymer, polystyrene-<i>block</i>-poly(2-vinylpyridine) (PS-<i>b</i>-P2VP) (115 kg/mol,\nP2VP volume fraction 31.6%), by combinations of spin coating, solvent\nannealing, reversible metal infiltration, and surface modification\nby oxygen etching. Pt infiltrated into the cylindrical-morphology\nP2VP blocks from an acid solution containing [PtCl<sub>4</sub>]<sup>2–</sup> locks the morphology of the bottom layer during the\ncoating and annealing of a second layer, leading to a range of bilayered\nand trilayered 3D structures, including in-plane orthogonal meshes\nand layered I-shape and inverted T-shape P2VP microdomains. In contrast,\nunloading the metal by a KOH plus ethylenediamine­tetraacetic\nacid disodium salt dihydrate (Na<sub>2</sub>EDTA) solution allows\nchain reorganization during subsequent layer coating and annealing,\nproducing morphologies characteristic of a single layer of the PS-<i>b</i>-P2VP. However, a short oxygen etch modifies the surface,\nimpedes chain reorganization, and yields multilayer structures even\nwhen the metal unloading process is performed. Metal infiltration\nand exfiltration combined with layering, annealing, and oxygen etching\ndiversify the morphologies available from the block copolymer and\nprovide a path to localized morphology control, expanding the toolkit\nfor 3D nanofabrication.