Shao, Y.;^# Han, D.;^# Tao, Y.; Feng, F.; Han, G.; Hou, B.; Liu, H.; Yang, S.; Fu, Q.;* Zhang, W.-B.* Leveraging Macromolecular Isomerism for Phase Complexity in Janus Nanograins. ACS Cent. Sci. 2023, 9, 289-299. https://doi.org/10.1021/acscentsci.2c01405

It remains intriguing if macromolecular isomerism, along with competing molecular interactions, could be leveraged to create unconventional phase structures and generate considerable phase complexity in soft matter. Herein, we report the synthesis, assembly, and phase behaviors of a series of precisely defined regio-isomeric Janus nano-grains with distinct core symmetry. They are named B₂DB₂ where B stands for iso-butyl functionalized polyhedral oligomeric silsesquioxanes (POSS) and D stands for di-hydroxyl functionalized POSS. While BPOSS prefers crystallization with a flat interface, DPOSS prefers to phase-separate from BPOSS. In solution, they form 2D crystals owing to strong BPOSS crystallization. In bulk, the subtle competition between crystallization and phase separation is strongly influenced by the core symmetry, leading to distinct phase structures and transition behaviors. The phase complexity was understood based on their symmetry, molecular packing, and free energy profiles. The results demonstrate that regio-isomerism alone could lead to profound phase complexity.