Macroscopic order in block copolymer gyroid films by solvent evaporation annealing

Abstract

Block copolymer (BCP) self-assembly is a versatile approach for fabricating advanced nanostructured materials with unique properties. Among various nanostructures, gyroid morphologies have attracted attention due to their unique periodic architectures, optical properties, and applications as optical metamaterials. However, the fabrication of these intricate morphologies in large domains with uniform ordering remains challenging, especially in thick films. Here, we present a solvent evaporation annealing (SEA) method to produce homogeneously ordered BCP morphologies in thick films. Established to generate order in films with 2D BCP morphologies, SEA employs a two-step evaporation process: rapid evaporation of a volatile solvent to initiate BCP self-assembly, followed by slow evaporation of a non-volatile additive to minimise nucleation rates and promote domain growth. Here, we extend SEA to 3D gyroid-forming systems using a polyisoprene-b-polystyrene-b-poly(ethylene oxide) (ISO) triblock copolymer, producing large, well-ordered domains up to nearly 2 mm2. Structural analysis of BCP films using cross-polarised light microscopy, small-angle X-ray scattering (SAXS), and focused ion beam (FIB) cross-sectional scanning electron microscopy (SEM) confirms their ordering both in-plane and out-of-plane. Our results highlight the efficiency of SEA in generating macroscopically ordered gyroid morphologies and underline its potential as a scalable approach to synthesise ordered functional materials from BCP templates, e.g. optical metamaterials.