Abstract
Understanding the flow induced crystallisation process is necessary due to its technological relevance to polymer processing. Polymer crystallisation controls the morphology of semi-crystalline polymers and hence the properties of the end product. We perform molecular dynamics simulations of polymer melts consisting of sufficiently entangled linear chains under shear flow. We determine the Rouse relaxation time (τR) for linear polymer chains using an established rheological model at different temperatures and fit the simulation data with the Arrhenius and Williams-Landel-Ferry equations. We simulate the crystallisation induction times for different values of the Rouse-Weissenberg number (WiR=γ̇τR) at different temperatures. We observe that the level of strain and stretch required to induce crystallisation increases with temperature. We find that the induction times follow a power law in shear rate and observe a more pronounced effect of flow rate for higher temperatures than at lower temperatures. Moreover, we determine that nucleation events occur relatively early in the shear transient and at a stretch value that is smaller than its steady state value. We also report the values of strain at which the occurrence of a nucleation event is most likely to happen.
Highlights
The commercial importance of polymer processing means that polymer crystallisation remains an active and vital field even after extensive efforts over several decades from various fields of science, engineering and technology
Shear flow is expected to significantly change the nucleation rate above a shear rate that corresponds to a Rouse Weissenberg number of order 1
In order to determine the spread of the induction time and its corresponding stress and strain values, we show histograms of the observed induction times and stress with red bars and blue lines respectively in FIG. 6 at two different temperatures and different values of the Rouse Weissenberg number (WiR) (Further simulation data for three different temperatures and at two different values of the Rouse Weissenberg number can be seen in appendix A)
Summary
The commercial importance of polymer processing means that polymer crystallisation remains an active and vital field even after extensive efforts over several decades from various fields of science, engineering and technology. Intensive efforts have been made to understand the crystallisation process under quiescent conditions[1,2,3,4,5,6,7,8,9,10] and under the influence of external flow[11,12,13,14,15,16,17,18,19,20,21,22,23] In these studies, the flow affects the nucleation and growth rates and morphological features including single and multiple shish. There are coarse grained semi-empirical models available,[15,24,25,26,27,28,29,30,31,32]
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