Mesochiral Phases from Self-Assembly of Chiral Block Copolymers

Herein, we aim to create new phases with chiral sense from the self-assembly of block copolymers (BCPs). The main idea is to create a BCP with a chiral block, giving the BCP with helical polymer chain for self-assembly in bulk; this BCP system is denoted as chiral BCP (BCP*). With the introduction of the chirality effects on BCP self-assembly, a helical phase (H*) with hexagonally packed twisted cylinders can be obtained. By taking advantage of homochiral evolution from monomer to polymer chain and further extended to hierarchical superstructures, controlled chirality of the H* can be achieved; this phase is thus referred as one of the mesochiral phases from the self-assembly of BCPs*. A methodology to scrutinize the chirality transfers at different length scales for BCP* self-assembly was thus developed by using electronic circular dichroism, vibrational circular dichroism and electron microscopy tomography for examination of monomer chirality (optical activity of molecule), polymer chain chirality (intra-chain chiral interactions) and hierarchical chirality (twisting of multi-chain mesodomain attributed to inter-chain chiral interactions), respectively. The chirality effects and the corresponding homochiral evolution on BCP self-assembly have been proved to be generic experimentally and supported by tilted chiral lipid bilayer model and orientational self-consistent field theory. Most interestingly, the forming helical cylinder can be served as a stepping stone for the formation of a network phase, gyroid, through twisting to give a wide region for forming network phase. With the easy development of the gyroid phase, a platform technology, referred as templated syntheses, for the fabrication of nanonetwork-structured materials was thus developed. Consequently, various gyroid-structured materials can be fabricated by templated atomic layer deposition, electroplating, electroless plating, sol-gel reaction and polymerization to give well-ordered nanonetwork semi-conductive, metallic, ceramic and polymeric materials after removal of the template. Note that, the hidden chirality of the gyroid can be defined by using the dihedral (torsion) angle concept from the simplified building unit with a tripod texture. With the controlled chirality of the helical cylinder and chiral network, it is appealing and promising to fabricate chiral materials by combining the mesochiral self-assembly and the platform technology of templated syntheses, giving well-ordered nanohybrids and nanoporous materials with helical sense. By taking the advantage of the deliberate structuring, the fabrication of chiral metamaterials with appealing applications such as negative refractive index materials, devices with giant optical activity and beam splitters can be expected.