Stabilizing gyroid structures by blending or asymmetry of high-χ oligomers*

Molecular dynamics simulations of block oligomers containing polar CHxOH and nonpolar CHy repeat units are used to explore features that stabilize gyroid phases with domain pitches under 3 nm. In their pure form, AB diblock and AB₂ miktoarm triblock amphiphiles can self-assemble into ordered lamellar (LAM) and cylindrical (CYL) structures, respectively.   However, their AB -rich blend (0.2 ≤ x ≤ 0.4) forms a double gyroid (DG) network structure. Structural analyses reveal that the non-uniform interfacial curvature of the DG structure is supported by local composition variations of the LAM and CYL forming amphiphiles.  Interestingly, introducing large shape asymmetry into miktoarm multiblock amphiphiles by coupling of blocks of different length can also yield DG structures where the volume fraction of polar and nonpolar blocks can be varied over a wide range. This work provides molecular-level insights into how blending and asymmetry of shape-filling molecular architectures enables network phase formation with extremely small feature sizes over a wide composition and volume fraction ranges.