Polymer crystallization under external flow

The general aspects of polymer crystallization under external flow, i.e., flow-induced crystallization (FIC) from fundamental theoretical background to multi-scale characterization and modeling results are presented. FIC is crucial for modern polymer processing, such as blowing, casting, and injection modeling, as two-third of daily-used polymers is crystalline, and nearly all of them need to be processed before final applications. For academics, the FIC is intrinsically far from equilibrium, where the polymer crystallization behavior is different from that in quiescent conditions. The continuous investigation of crystallization contributes to a better understanding on the general non-equilibrium ordering in condensed physics. In the current review, the general theories related to polymer nucleation under flow (FIN) were summarized first as a preliminary knowledge. Various theories and models, i.e., coil-stretch transition and entropy reduction model, are briefly presented together with the modified versions. Subsequently, the multi-step ordering process of FIC is discussed in detail, including chain extension, conformational ordering, density fluctuation, and final perfection of the polymer crystalline. These achievements for a thorough understanding of the fundamental basis of FIC benefit from the development of various hyphenated rheometer, i.e., rheo-optical spectroscopy, rheo-IR, and rheo-x-ray scattering. The selected experimental results are introduced to present efforts on elucidating the multi-step and hierarchical structure transition during FIC. Then, the multi-scale modeling methods are summarized, including micro/meso scale simulation and macroscopic continuum modeling. At last, we briefly describe our personal opinions related to the future directions of this field, aiming to ultimately establish the unified theory of FIC and promote building of the more applicable models in the polymer processing.

Automated summary

This paper presents the general aspects of polymer crystallization under external flow conditions, emphasizing the importance of flow-induced crystallization (FIC) in modern polymer processing. The paper summarizes the theoretical background of polymer nucleation under flow and discusses the multiple steps involved in FIC, including chain extension, conformational ordering, density fluctuation, and final perfection of the polymer crystalline structure. Experimental results and various hyphenated rheometer techniques are introduced to elucidate the hierarchical structure transition during FIC. The paper also summarizes the micro/meso scale simulations and macroscopic continuum modeling methods used in understanding and modeling FIC. Finally, the paper briefly describes future directions in the field, aiming to establish a unified theory of FIC and develop more applicable models for polymer processing.