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In this work, Aratsu et. al., used two artificial supramolecular polymers as a model system to investigate molecular recognition-controlled assembly/disassembly processes, which is critical for the functions of complex polymer systems. The two artificial supramolecular polymers possess almost identical molecular structures, and the only mutation is to add a carbonyl group next to the naphthalene moiety so that one molecule is electron-rich (molecule 1), and the other is electron-poor (molecule 2 with the carbonyl group).
They noted that molecule 1 usually forms uniform toroidal fibers, while molecule 2 usually forms linear fibrils; however, mixing of molecules 1 and 2 can form amorphous coaggregates as a kinetic coassembly, and then they are gradually (several days) transformed to helicoidal structures. In addition, the research found that molecule 1 plays a structure-directing role in the formation of helicoidal structures, whereas molecule 2 only plays an auxiliary role. Furthermore, the authors found the supramolecular structures experienced significant transition from helicoid to amorphous coaggregates when the temperature rose from 20°C to 65°C because of the large entropic penalty.
All these supramolecular structures have sizes of tens of nanometers to a couple of nanometers and can be easily visualized by the AFM. In this research, all AFM images of the various supramolecular structures have been collected by Bruker's Multimode 8 using PeakForce mode in air. High-resolution AFM images showing the clear molecular structures provide solid evidence for their conclusions.