Yale University implements a manageable hierarchical nanostructure

On November 10, 2022, Professor Zhong Mingjiang’s research group at Yale University, together with Professor Jeremiah Johnson of the Massachusetts Institute of Technology, Professor Weihua Li of Fudan University, and Professor Chinedum Osuji of the University of Pennsylvania, published a paper entitled “Hierarchically engineered nanostructures from” in the journal Nature Materials compositionally anisotropic molecular building blocks”.

In this study, through the anisotropic molecular construction module self-assembly strategy, a tunable “phase-in-phase” hierarchical nanostructure is realized, which provides a simple and efficient new synthesis method for nanomaterials with complex hierarchical phase structures.

The corresponding authors are Zhong Mingjiang and Jeremiah A. Johnson; The three co-first authors, Liang Ruiqi, Xue Yazhen and Fu Xiaowei (now assistant researchers at Sichuan University), are all doctoral students from Zhong Mingjiang’s research group.

Biological systems can achieve diverse, complex and precise functions through the self-assembly process of biomolecules, and can be regulated at atomic, nano, mesoscopic and macroscopic scales. Inspired by this, researchers have been hoping to prepare multifunctional materials in biosystems through hierarchical self-assembly of molecular building blocks. However, the preparation of hierarchical structured phase materials combining nano- and mesoscopic scales in a manageable and scalable manner has always faced great challenges.

Based on previous explorations, the authors developed a simple and accurate synthesis method to prepare anisotropic molecular building blocks (CAMBB), relying on CAMBB self-assembly to form ordered hierarchical nanostructures, and simulated this self-assembly process by using dissipative particle dynamics, which provided strong theoretical support for the experimental results. CAMBB is based on a structure of grafted block copolymers (GBCPs) with well-designed side chains (Figure 1). Firstly, the macromolecular monomer Nb- (A-branch-B) homopolymerization prepared Janus polymer (A-alt-B) with mixed grafted side chains, and the A phase and B phase formed the phase interface in the direction of the main chain. Then, the macromolecular monomer Nb-C was introduced for block copolymerization, and a two-block copolymer (A-alt-B)-b-C with a set side chain sequence was prepared, and component C and components A and B formed a phase interface perpendicular to the direction of the main chain.

Figure 1: Schematic diagram of building hierarchical nanostructures based on GBCP-derived CAMBB.

In (A-ALT-B)-B-C, the A-alt-B block is separated by intramolecular phase separation to form a subphase structure, the A-alt-B block is separated from the C block to further form a large phase structure, and (A-alt-B)-b-C thus self-assembles to form a “phase in phase” hierarchical structure. Regulating the length of the main and side chains (Figure 2) and the chemical composition (Figure 3a, b) allows flexible regulation of the phase structure at all levels in the hierarchical phase topography. (A-ALT-B)-B-C can self-assemble to form hierarchical facies such as “layered phase in lamellar phase”, “lamellar phase in columnar phase”, “columnar phase in columnar phase”, and “columnar phase in columnar phase”.

Figure 2: Hierarchical nanostructures constructed based on (A-ALT-B)-B-C TYPE GBCP.

(A-ALT-B)-B-C self-assembled hierarchical phase structures with independently adjustable lattice sizes (Figure 3c). As the degree of polymerization of the main chain increases, the lattice size of the macrophase structure increases almost linearly, while the lattice size of the subphase structure remains unchanged because it is completely controlled by the A and B side chain lengths.

The hierarchical phase topography formed by (A-ALT-B)-B-C self-assembly has independent response to temperature, thanks to the fact that the two-stage phase structure has different order-disordered transition temperatures (TODT) (Figure 3d). When the test temperature increases from 70°C to 130°C, the subphase structure changes from ordered to disordered under the condition that the macrophase structure remains ordered. As the test temperature drops to 70°C, it changes from disordered to ordered. The above results show the independent temperature response capability of the (A-alt-B)-b-C hierarchical phase structure.

Figure 3: Diversity of GBCP side chain structures based on (A-ALT-B)-B-C type and independent regulation of nanostructures.

Based on the structural design of molecular building blocks, the (A-ALT-B)-B-(C-ALT-D) and (A-alt-C)-b-(B-alt-C) types GBCP can be self-assembled to form a hierarchical phase structure with hybrid subphase structure (Figure 4). (A-ALT-B)-B-(C-ALT-D) can self-assemble to form a hierarchical phase structure of “lamellar phase and columnar phase in lamellar phase”; (A-ALT-C)-B-(B-ALT-C) can form a hierarchical phase structure of “layered phase and columnar phase in the layered phase” and “layered phase and layered phase in the layered phase”.

Figure 4: Beyond (A-ALT-B)-B-C type GBCP hierarchy.(Source: Science Network)

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