Flow-Induced Crystallization Starting from Self-Nucleated Precursors

Flow-induced crystallization is a multistep process, in which precursors are often generated as a crucial ordering state intermediate between the initial amorphous state and the ultimate crystallite. In this work, the self-nucleation effect of isotactic polybutene-1 was employed to obtain the ordering precursors and to study flow-induced crystallization that started from both the self-nucleated precursors and the completely relaxed amorphous phase. This could answer the long-standing question whether the additional self-nucleated precursors behave as the flow-induced ordering structures to facilitate crystallization or are erased back to the completely relaxed melt under the action of flow. The results showed that for quiescent crystallization, the self-nucleated precursors effectively accelerated kinetics and exhibited a monotonously increasing dependence with decreasing self-nucleation temperatures over a broad range of 117–180 °C. Interestingly, with flow, the self-nucleated precursors were able to accelerate crystallization significantly by facilitating the initial step of generating local ordering precursors. In addition, it was unexpected to find a type of unique precursor through self-nucleation at 137 and 138 °C. Such self-nucleated precursors remained unavailable for quiescent crystallization but could be activated by flow, referred to as dormant self-nucleated precursors in this work. To the best of our knowledge, the dormant self-nucleated precursors, which have nonfunctionality under the quiescent condition but can be visualized by flow, were reported for the first time. Moreover, the flow-induced evolution of various self-nucleated precursors was investigated by controlling the shearing duration. It was found that the self-nucleated precursors can develop into oriented nuclei, accelerating crystallization kinetics and increasing the crystallite orientation.