Morphology manipulation in block copolymer films by reversible metal infiltration*

Block copolymers (BCPs) are enablers of nanofabrication and pattern transfer processes owing to the ordered nanoscale structures that they form by self-assembly. We show that the self-assembled structures of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) BCPs can be locked by infiltrating [PtCl₄]²⁻ from a HCl solution. Pt infiltrates the P2VP block, limiting chain mobility and therefore locking the microdomain structure against reorganization during a successive annealing process. The amount of Pt introduced into the P2VP increases with both metal precursor concentration and acid concentration, reaching 0.83 Pt atom per pyridine group. A reverse exfiltration process using a KOH + ethylenediaminetetraacetic acid disodium salt dihydrate (Na₂EDTA) complexing solution unlocks the structure and allows the microdomains to reorganize in a subsequent annealing step, for example, annealing in a different solvent vapor to change the morphology. The reversibility of metal infiltration and the corresponding morphology locking and unlocking effect is validated by characterizing the morphological evolution during multi-step annealing, infiltration and exfiltration steps, and in a 3D structural design process in which multiple layers of PS-b-P2VP are assembled with different morphologies. Structural locking and unlocking via infiltrated metal diversifies the toolkit for BCP-enabled nanofabrication.