Tricontinuous Double Diamond Network Structure from Binary Blends of ABC Triblock Terpolymers

We report the tricontinuous double diamond (TDD) structure in binary blends of ABC triblock terpolymers with different chain lengths of the two end-blocks. Although, the TDD structure has been long considered as an unstable phase because of the high energetic barrier associated with stretching energy and interfacial energy due to wider interfacial area than those for known structures such as a lamellar structure or a tricontinuous double gyroid (TDG) structure. The different chain length possibly helps to alleviate the free energy penalty, which resulted in the occurrence of the TDD as a stable phase at wide range of compositions. Transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and TEM tomography (TEMT) results all corroborate the existence of TDD in the present blend system. We present the first solid evidence of the thermodynamically stable TDD structure.