Double-Gyroid Network Morphologies Formed by Asymmetric AB₁B₂ Triblock Amphiphiles over Wide Volume Fraction Range

Molecular dynamics simulations are used to investigate the phase behavior of asymmetric AB₁B₂-type miktoarm triblock amphiphiles, composed of a sugar-based acyclic headgroup (A) and two hydrocarbon tails (B₁ and B₂). AB₁B₂ amphiphiles with significantly shorter B₂ tails (f _B1 /F _B2 ≫ 1, where f _i is the volume fraction) form lamellar (LAM) and perforated lamellae (PL) structures, whereas those with nearly equal tail lengths (f _B2 ≈ F _B1 ) assemble into hexagonally packed cylinders (CYL). Amphiphiles with a B₁/B₂ length ratio near 2:1 (2f _B2 ≈ F _B1 ) stabilize double gyroid (DG) networks, where the headgroups form the interconnected channels and the tails constitute the matrix, displaying feature sizes from 1.7 to 3.3 nm across a broad volume fraction range with $0.22\le f_A\le 0.40$ . For potential applications in membrane separation at infinite dilution, these networks significantly hinder the diffusion of polar molecules, while nonpolar molecules diffuse relatively unimpeded. Diffusion selectivities near 3 are found for 1-butanol versus water and n-hexane versus methanol. Self-consistent field theory (SCFT) calculations corroborate the presence of DG networks at intermediate compositions for AB₁B₂ miktoarm triblock polymers, although no specific B₁/B₂ ratio is predicted to significantly broaden the network phase window. This study highlights the role of asymmetry in the molecular design of amphiphilic block oligomers, which enables the stabilization of network morphologies with ultrasmall feature sizes over a wide composition range.