The non-equilibrium phase diagrams of flow-induced crystallization and melting of polymer

Zhen Wang, Youxin Ji, Jianzhu Ju, Xiaoliang Tang, Liangbin Li

National Synchrotron Radiation Lab and CAS Key Laboratory of Soft Matter Chemistry, University of Science and Technology of China, Hefei, China

With a combination of extensional rheology and in-situ synchrotron ultrafast x-ray scattering measurements, we have studied the flow-induced phase behaviors of polyethylene (PE) [1], isotactic polypropylene (iPP) [2] and Poly(1-butene) (PB-1) [3] over a wide temperature and flow strength range. Non-equilibrium phase diagrams are constructed in temperature-stress space for PE, and in temperature-strain rate space for iPP and PB-1, which reflect the non-equilibrium natures of flow-induced crystallization (FIC). Applying flow is recognized to favor the formation of structure with high entropy and low conformational order. The interplay of kinetic competitions and thermodynamic stabilities between different phases leads to rich kinetic pathways for FIC and diverse final structures. The non-equilibrium flow diagrams provide a detailed roadmap for precisely processing of polymers with designed structures and properties. It demonstrates that the non-equilibrium process stimulated by flow is fundamentally different from the equilibrium phase behaviors, where a rich source of physics is still waiting for us to dig out.

[1] Z. Wang, J. Ju, J. Yang, Z. Ma, D. Liu, K. Cui, H. Yang, J. Chang, N. Huang, and L. Li, Scientific Reports 6, 32968 (2016). (link)
[2] J. Ju, Z. Wang, F. Su, Y. Ji, H. Yang, J. Chang, S. Ali, X. Li, and L. Li, Macromolecular Rapid Communications 37, 1441 (2016). (link)
[3] Z. Wang, J. Ju, L. Meng, N. Tian, J. Chang, H. Yang, Y. Ji, F. Su, L. Li, and L. Li, Soft Matter 13, 3639 (2017). (link)