Tuning the Complex Spherical Phase of Sugar-Based Block Co-Oligomer via Single-Monomer-Mediated Composition Variation

• Published in: Macromolecules Vol. 57; no. 13; pp. 6076 - 6089
• Main Authors: Chiu, Wei-Chi, Cheng, Yu-Hung, Lin, Jin-Hao, Tung, Chi-Huan, Nishimura, Taiki, Chen, Chun-Yu, Isono, Takuya, Satoh, Toshifumi, Chen, Hsin-Lung
• Format: Journal Article
• Language: English
• Published: American Chemical Society 09.07.2024
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.4c00439

We show that a full spectrum of Frank–Kasper (FK) phase and dodecagonal quasicrystal (DDQC) having been discovered among different block copolymers (BCPs) can be accessed in a single sugar-based AB2 star block co-oligomer (BCO) system composed of an oligosaccharide (Glcn) block attached with two solanesol (Sol) blocks (denoted as Glcn-(Sol)2). A discrete increase of the number of glucose monomer (n) in the Glcn block with a single-monomer resolution led to the transition of the micelle packing from DDQC/body centered cubic (BCC) (n = 1) to FK σ (n = 2) and then to FK A15 (n = 3) phase. The observed transformation of packing lattice along the oligosaccharide composition coordinate aligned with the lyotropic transition sequence predicted by the self-consistent field theory of conformationally asymmetric coil–coil block copolymer, despite the fact that the conformation of the sugar block deviated from a linear coil and the molecular weight of the BCO was low. Notably, Laves C15/C14 phase was found to develop from the high-temperature σ phase in Glc2-(Sol)2 upon stepwise cooling, which expanded the phase spectrum of the BCO to cover all the soft FK phases having been found in BCPs. The strong propensity of the sugar-based BCO to form the FK phase is ascribed to its high-χ/low-N characteristic, which leads to the formation of micelles with significant surface free energy at the core–corona interface and a large surface area per unit volume. These attributes collectively amplify the significance of the interfacial free energy in the selection of packing lattice, making FK phase the favored packing symmetry over BCC.