In situ atomic force microscopy observation of self-assembly process of diphenylalanine-based polymer/monomer

Diphenylalanine-based functional molecules and polymers are ideal motifs for the construction of dipeptide nanomaterials with sophisticated three-dimensional architectures via self-assembly involving non-covalent interactions. Despite various studies investigating the self-assemblies derived from diphenylalanine derivatives, direct in situ visualization of the assembly process has proven challenging. Herein, we describe the in situ atomic force microscopy (AFM) visualization of the fiber and fractal structure formation of a self-assembled diphenylalanine-based polymer, PAPhePheOH, originating from N-acryloyl-L,L-diphenylalanine (APhePheOH). In situ visualization of the PAPhePheOH chain and the corresponding monomer (APhePheOH) prepared under various conditions allowed for monitoring of the formation process of fibers and fractal structures with chain movements. This work provides a deeper understanding of the time-dependent morphological change to form complex structures with two different mechanisms; the specific interaction between the polymer and substrate and the interactions between two or more PAPhePheOH chains, depending on the conditions. Studies of the APhePheOH monomer have revealed faster self-assembling process including transformation of isolated spherical aggregates into fibers and prompt formation of fractal structures, allowing the feasibility to tune self-assembled structures of diphenylalanine-based materials.