With the guidance of Prof. Li，the work titled “Stretch-Induced Reverse Brill Transition in Polyamide 46” studied by post doctor Minfang An et al. has been published in Macromolecules.

In this work, Structural transitions of polyamide 46 (PA46) films during the tensile stretch at temperatures from 37 to 249 °C were studied using in situ synchrotron radiation wide-angle X-ray diffraction (SR-WAXD) and Fourier transform infrared (FTIR) techniques. The structural evolution during the stretch at different temperatures can be roughly divided into three regions. In region I (37 ≤ T < 180 °C), stretch enlarges the d-spacing gap between the (100) and (010/110) planes of α phase (triclinic), which is opposite to that during heating. In region II (180 ≤ T < 230 °C), stretch induces a reverse Brill transition, which is characterized by the single diffraction of γ phase (pseudohexagonal) splitting into two diffractions of α phase, while further increasing the strain drives the two split diffractions to transform to a single broad diffraction. As in situ FTIR measurements reveal the continuously increasing content of trans conformation, we speculate that stretch may induce a new form, which is an intermediate structure close to both α and γ phases (named α′ phase) at large strain. In region III (230 ≤ T ≤ 249 °C), the γ phase may skip the α phase and directly transform into the α′ phase. The nonequilibrium crystal phase diagrams of PA46 were constructed in the strain−temperature space and true stress−temperature space. Current results demonstrate that stretch plays a countereffect of heating on the Brill transition of PA46.

This work is supported by the National Key Research and Development Program of China (2016YFB0302500) and the National Natural Science Foundation of China (51903230, 51903091, 51633009, and 51890872).

Related links: https://pubs.acs.org/doi/10.1021/acs.macromol.0c00542