It remains intriguing whether 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 regioisomeric Janus nanograins with
distinct core symmetry. They are named B2DB2 where B stands for iso-butyl-functionalized polyhedral
oligomeric silsesquioxanes (POSS) and D stands for dihydroxyl-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 regioisomerism could indeed generate profound phase complexity.
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