Surface Effect on the Self-Assembly of Nanofibers Revealed by in Situ AFM Imaging and Molecular Simulation

Conventional imaging techniques, such as scanning electron microscopy, transmission electron microscopy, and atomic force microscopy (AFM), have the same sample preparation, that samples are added dropwise on the substrate. It is not known whether the observed assemblies are formed exclusively in solution or subsequently assembled on the substrate surface. In this work, with an amino acid-containing silole molecule (silole-leu) as the ideal model system, we demonstrated that the assembly can be directly formed on the surface of mica. Real time and influence AFM imaging revealed the epitaxial growth of nanofibers during the evaporation of solvent. The highly oriented nanofibers intercrossed with each other at the angle of 60 or 120°, matching well with the underlying crystal lattice of mica. Prolonged evaporation of samples in the microchannel resulted in the formation of more aligned fibers. Molecular simulations showed that Coulomb interactions between the substrate and sample stretched silole-leu into an extensively expanded conformation. The joint effort from hydrogen bonding, π–π interactions between silole-leu molecules, and Coulomb interactions guided the nucleation and propagation of nanofibers. Our study revealed that the surface effect was nontrivial even for the samples in the evaporation state, which deserved more attention for understanding the morphologies of samples and revealing the principles of assemblies.