Insights into Spatiotemporal Polymeric Assembly of Semicrystalline Block Molecules by LP-TEM

Abstract

Molecular self-assembly is a fundamental process underlying the formation of both living and synthetic materials. Insights gained from studies of self-assembly have driven advances across the biological, chemical, and materials sciences. Among various molecular architectures, rigid–flexible block molecules offer unique opportunities to form diverse, well-defined nanostructures with controlled size and shape in selective solvents. Self-assembly occurs over broad spatial and temporal scales and often involves complex, non-intuitive pathways. Investigating these processes requires a combination of analytical and computational tools. Among them, transmission electron microscopy (TEM) is particularly powerful due to its ability to directly visualize and quantify self-assembled structures and their dynamic behavior. Recent advances in TEM have enabled three-dimensional (3D) structural characterization at nanometer resolution via electron tomography, providing detailed reconstructed volume images. This technique has proven highly effective for elucidating the morphology of polymeric materials. In parallel, liquid-phase (LP) TEM has revolutionized our ability to directly observe the physical and chemical processes that govern material formation in synthetic, biological, and geochemical environments. It has been widely applied to investigate dynamic phenomena such as nucleation, self-assembly, crystal growth, and coarsening across diverse systems, including metallic and semiconductor nanoparticles, biominerals, electrochemical interfaces, macromolecular complexes, and both organic and inorganic self-assembling materials. In this thesis, the self-assembly behavior of semicrystalline amphiphilic block molecules was directly visualized using in-situ LP-TEM, enabling quantitative analysis of their dynamic structural transition. By integrating LP- TEM with 3D electron tomography, this study aims to spatiotemporally resolve the self-assembly pathways and kinetics of semicrystalline amphiphilic block molecules. In Chapter 1, outlines the fundamentals of crystalline block molecules and crystallization-driven solution-state assembly, and introduces analytical approaches for investigating polymer self-assembly, including 3D structural analysis via electron tomography and real-time visualization using LP-TEM. In Chapter 2, the coupling modes (end-to-end or side-by-side) of quantum rods (QRs) of CdSe confined within nanowires (NWs) formed by CDSA of conjugated polymer (CP) were precisely controlled by changing the solution process. During this process, the competition between CP crystallization and QR dipole- dipole interactions influenced the QR orientation within the coaxial hybrid NWs. This work provides a deeper understanding of the mutual self-assembly between CP and QR and introduces a fabrication strategy for p-n heterojunction hybrid NWs with tailored performance in solution-processable optoelectronic devices. In Chapter 3, structural transformations from unimers to spherical micelles, cylindrical micelles, and toroidal micelles of semicrystalline amphiphilic block copolymers (BCPs) were achieved by varying the relative ratios of the components, and LP-TEM analyzed the self-assembly process. All the resulting nanostructures showed structural evolution by long-range attractive hydrophobic interactions from initially formed elemental micelles in anomalous diffusion motions, and in particular, the formation of toroids revealed that they follow a distinct morphological transition path compared to conventional BCPs due to the preference of semicrystalline BCPs for micellization with low curvature at the core-corona interface. In Chapter 4, based on the design and synthesis of semicrystalline rod–flexible coil organic molecules capable of precisely controlling the size, shape, and molecular arrangement of self-assembled aqueous nanostructures at the molecular level, and utilizing LP-TEM, a strategy is proposed to synthesize hierarchical and complex nanoparticles with morphological uniformity. It also provides a spatiotemporal imaging platform for real- time, multidimensional visualization of dynamic self-assembly processes and electron beam-induced chemical reactions, especially polymerization.