SCFT-Guided Experimental Fabrication of Double-Diamond Structures in A₁B/A₂B Block Copolymer Binary Blends

It is well-known that neat AB linear diblock copolymers can form 3-fold double-gyroid (DG) bicontinuous tubular network nanostructures but cannot form thermodynamically stable 4-fold double-diamond (DD) structures. Although theoretical studies have suggested that blending homopolymers or homopolymer-like diblock copolymers into diblock copolymers can stabilize the DD structures in a wide region, experimentally achieving a stable DD structure in diblock copolymer systems still remains challenging. A series of previous studies has demonstrated that the binary blends composed of two A1B/A2B diblock copolymers with equal B-blocks but unequal A-blocks exhibit unique capability in stabilizing diverse nonclassical ordered structures by substantially shifting phase boundaries. In this work, we first employed self-consistent field theory (SCFT) to investigate the self-assembly behavior of the A1B/A2B blends and identified the parameters for stable DD structures. Our theoretical results reveal that the stability of DD structures is sensitive to the volume fraction of the AB diblock copolymers with shorter A-blocks, as well as sensitive to the length ratio of the two A-blocks. Guided by our theoretical predictions, we synthesized a number of polyisoprene-b-polystyrene (PI-b-PS) diblock copolymers. We subsequently blended diblock copolymers with varying polyisoprene (PI) lengths and investigated their self-assembled structures across various blending ratios. The DD structure was identified by small-angle X-ray scattering (SAXS) and confirmed by transmission electron microscopy (TEM). Our work demonstrates that experiments guided by reliable SCFT predictions can efficiently discover intriguing nonclassical nanostructures. In addition, our work confirms that this A1B/A2B binary blend possesses significant potential for stabilizing diverse novel structures.