Force-induced hydrogen bonding between single polyformaldehyde chain and water

To explore the nature of water insolubility of polyformaldehyde (POM), we utilize single-molecule atomic force microscopy (AFM) and molecular dynamics (MD) simulations to study the possible interactions between POM and water at the single-chain level. Single-molecule force-extension curves of POM obtained in nonane and deionized water showed a marked deviation in the middle force region, which is similar to that observed in polyethylene glycol (PEG). The results indicate that force-induced hydrogen bonding between POM and water occurs upon initial stretching, followed by a dehydration process upon high force stretching. MD simulations show that POM chain itself is able to form H-bonds with water, but this potential is heavily hindered by the native conformation in the crystal. This finding not only provides new insight into the understanding of water insolubility of POM, but also helps the rational design of advanced polymer materials in the future.