Relaxation propelled long period change in the extension induced crystallization of polyethylene oxide

Abstract

The time evolution of the long period in the extension-induced crystallization of polyethylene oxide (PEO) is investigated with a combination of rheological measurement and in situ small angle X-ray scattering (SAXS), aiming to show the dynamic change in the spatial arrangement of nuclei in terms of both the chain stretching and orientation. The main findings are summarized as follows. (i) Strain hardening is observed when the strain is larger than 3.0, indicating a transition from chain orientation to chain stretching. (ii) The time evolution of the long period differs before and after strain hardening, reflecting changes in the evolution of nuclei arrangement. The full strain range is thus divided into two regions, namely the large strain region and the small strain region. In the large strain region the long period exhibits a two-step monotonic decrease. For the small strain region, an increase-plateau-decrease behavior is observed. (iii) A large gap exists between the initial values of the long period in each of the two strain regions. (iv) The crystallization kinetics shows no secondary acceleration after strain hardening. Based on these results, a qualitative model emphasizing the chain relaxation propelled rearrangement of nuclei is proposed to explain the structural evolution.