Exploring water−macromolecule interactions at the single-molecule level: A comprehensive review

Water is ubiquitous and indispensable on the Earth. Its importance has long been recognized on a macroscopic scale. However, it took a long time to comprehend the impact of water molecules on the microscopic level. According to the hydrophilicity of matter, the impact of water can be divided into two categories: 1) intermolecular hydrogen bonds (H-bonds) and 2) hydrophobic interactions. In recent years, atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS) has been used to investigate the effect of water on the single-chain properties of macromolecules. Herein, we summarize recent advances in the AFM-SMFS study on the impact of water on some kinds of synthetic polymers, biomacromolecules, and molecules containing supramolecular interactions from the two aspects of H-bonds and hydrophobic interactions. It is expected that a deeper understanding of the interactions between water molecules and macromolecules will enable the design of polymer materials with specific functionalities and properties in a bottom-up way.