Unusual Endotaxy Growth of Hexagonal Nanosheets by the Self-Assembly of a Homopolymer

A classical crystallization usually grows epitaxially from a crystal nucleus. Presented in this study is an unusual endotaxy growth manner of a crystalline homopolymer to form hexagonal nanosheets. The amphiphilic homopolymer, poly(3-(4-(phenyldiazenyl)phenoxy)propyl methacrylate) (PAzoPMA), is first annealed in isopropanol to afford a hexagonal nut-like structure. Then, the PAzoPMA crystallizes from the inner wall to the center to form a thin bottom, which grows upwards along the bottom, leading to the formation of the evenly hexagonal nanosheets. The energy fluctuation by molecular dynamics (MD) simulation during self-assembly confirms the packing state of PAzoPMA chains in different solvents. In isopropanol, the total energy is the lowest, demonstrating the tight regular arrangement of polymer chains. In addition, the non-bonding interaction energy is also the lowest, leading to the favorable contact with solvent molecules and the formation of hexagonal nanosheets. Otherwise, nanowires and giant large compound micelles are formed in ethanol and n-butanol, respectively. Overall, an unusual endotaxy crystallization manner of an amphiphilic homopolymer is observed during the preparation of hexagonal nanosheets, which brings fresh insight for understanding the crystallization behavior of polymers and preparing functional soft nanomaterials.