Single-Chain Mechanics at Low Temperatures: A Study of Three Kinds of Polymers from 153 to 300 K

The single-chain mechanics of three kinds of polymers (i.e., polydimethylsiloxane, polyoxymethylene, and poly(methyl methacrylate)) has been investigated from room temperature to 153 K by atomic force microscopy-based single-molecule force spectroscopy in high vacuum and a theoretical model. The stretched part of the individual polymer chain can be regarded as an isolated chain. In the broad range of temperature, the isolated chain shows a gradual change in single-chain mechanics, which can be depicted nicely by an elastic model. Further analysis shows that with thermal fluctuation, the single bonds (e.g., Si–O or C–O) in the backbone of an isolated chain can rotate freely in the temperature range in the timescale of single-molecule manipulation. To our best knowledge, this is the first experimental study on the single-chain mechanics at cryogenic temperatures, which validates the theoretical prediction that the transition temperature of an isolated chain is much lower than that of the corresponding bulk polymer material.