Density fluctuations as precursors of crystallization in polyamide 6,6 using time-resolved X-ray scattering techniques

In the present study, attempts are made to throw light on the mechanisms leading to primary nucleation in polymer crystallization. Previous studies in this field are not conclusive. Aiming to investigate the induction period prior to crystallization, time-resolved simultaneous small- and wide-angle X-ray scattering (SAXS and WAXS) measurements have been made in situ for polyamide 6,6, while it was crystallized from the melt. For this polymer, it is confirmed that at a low supercooling (DeltaT approximate to 28degreesC), during the induction period, a well-resolved SAXS pattern appears. The time evolution of this scattering pattern can be described by the kinetics of spinodal decomposition, as previously reported for the glass crystallization of PEKK and TPI. According to this analysis, a value for the most probable scattering vector q of density fluctuations at around 0.43 nm(-1) is found. It corresponds to a characteristic wavelength of 14.7 nm of long-range density fluctuations growing with time.