Emergence and Stability of Distinct Hierarchical Single-Network Structures in ABC Star Triblock Copolymers

Based on the formation mechanism of stable hierarchical network structures composed of binary A/C-spheres in close contact in the AB2C quadruple-arm star copolymer, we propose that the ABC star triblock copolymer could also self-assemble into this kind of unusual network structures under the condition of χAC > χAB ∼ χBC. Accordingly, we first construct the phase diagram of the ABC star copolymer with respect to fB and χACN for χABN = χBCN = χN = 40 and fA = fC. It is observed that the usual polygonal phases transfer to the hierarchical network phases in the region of relatively large fB when χACN is increased to be significantly higher than χN, including hierarchical single-diamond (hSD0) and single-gyroid (hSG0). Moreover, another stable single-diamond phase (hSD1) is also predicted, all nodes of which are formed by A- or C-blocks and are separated by a “strut” domain composed of C- or A-blocks. It is revealed that the polygonal phase has more favorable interaction energy than the corresponding hierarchical network phase but unfavorable entropic contribution. More critically, the disadvantage of the interaction energy of the hierarchical network phase diminishes as χACN increases, improving its stability relative to that of the polygonal phase. By considering a special ratio of χAC/χAB = χAC/χBC to mimic an experimentally accessible ABC star copolymer, PI-b-PS-b-PEO (ISO), we confirm that these hierarchical single-network phases remain considerably stable in parameter regions. Our work is expected to promote relevant experimental research for the fabrication of these astonishing hierarchical single-network structures.