Real time small‐angle x‐ray scattering during annealing of polymer single crystals

Experiments at the Cornell high energy synchrotron source (CHESS) have shown that it is possible to obtain 2‐D small‐angle x‐ray scattering patterns from single crystal mats of high density polyethylene with a time resolution of 0.3 s. However, it took up to 5 s to heat the 0.1‐mm‐thick specimen to the annealing temperature. A logarithmic increase of long spacing was quickly established, after an induction time of <2 s at the higher annealing temperatures. At lower temperatures the original reflection remains, weakening, while a continuous scatter to smaller angles builds up. At 10–20 s annealing time a new maximum becomes clear, and then the logarithmic increase of long spacing begins. The intensity of this reflection is intially low and increases with annealing time. On cooling it decreases again. It seems that here we can directly observe two mechanisms of lamellar thickening, melting then recrystallization at short times and diffusional thickening at long times.