Double Diamond of Self-Assembled Chiral Diblock Copolymers

Here, a double diamond (DD) phase was found in the self-assembly of chiral block copolymer, polystyrene-b-poly(L-lactide) (PS-PLLA). The tetrapod with four fold symmetry in the DD phase can be directly visualized by transmittance electron microscope tomography (i.e., 3D TEM) and further identified by small angle x-ray scattering with fitting of effective sphere model for two-node dihedral texture. In contrast to the double gyroid (DG) phase from achiral block copolymer, polystyrene-b- poly(D,L-lactide) (PS-PLA), the excessive frustration in the center of the node of the DD phase can be alleviated by the formation of helical polymer chain with higher persistent length (helical persistent length); the helical conformation with preferred handedness can be evidenced by the vibrational circular dichroism (VCD) at which the split-type Cotton effect can be clearly recognized. Moreover, interesting phase transitions among DD and DG as well as helical phase from the chiral PS-PLLA were systematically examined in comparison with the DG from achiral PS-PLA. The corresponding transition mechanisms were examined by the real-space imaging and the reciprocal scattering as well as the spectroscopic results of VCD for the metastability study of self-assembled phases from chiral block copolymers.