MEASURING THE SPRING CONSTANT OF A SINGLE POLYMER CHAIN

We present a measurement of the mechanical properties of single polystyrene molecules of size (cid:82) (cid:248) (cid:53)(cid:48) nm. Using a micromechanical technique, we show directly that the polymer chain behaves like a spring, and we measure the spring constant. We examine both cross-linked and non-cross-linked polystyrene. The former forms a stiffer spring, and the value of the spring constant is in agreement with theory, while in the latter case the measured value is larger than expected. [S0031-9007(97)04848-5]