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.