Recently, a feature article “Influence of inter-chain interactions on the tumbling of chains in a polymer melt during shear flow” was published in Journal of Rheology. Doctor Tingyu Xu is the first author.

Polymer chains in both dilute solutions and melts undergo cyclic rotation and retraction, which is known as tumbling, under steady shear flow. However, it is still not known how the individual molecules in melts rotate freely under the constraints caused by surrounding chains. In this work, Brownian dynamics simulation is used to investigate the influences of the inter-chain interactions on the polymer chain motions in both dilute solutions and melts under steady shear flow. Compared with previous simulation studies, a greater number of similarities and differences between tumbling in dilute solutions and melts are addressed, and results explicitly suggest the critical role of the entanglements in melts during shear flow. Three components of the gyration radius in different directions flow direction, gradient direction  vorticity direction are shown to exhibit different dependencies on the shear rate depending on whether dilute solutions or melts are being examined. However, the characteristic tumbling times in both cases are proportional to . The distributions  of time  that the chains spend in each tumbling cycle show that both states exhibit an exponential decay of  in the high- region. In the low- region,  in the melts with variable shear rates are coincident with each other, while  in dilute solutions show different shapes. With respect to the distributions of chain orientation, both cases show the same scaling relationships for shear rates and chain lengths. Based on these findings, main conclusions are as follows. The entanglements still restrict the evolutions of polymer chain configurations despite the number of entanglements decreasing with increased flow strength. The tumbling motion in melts can occur inside the tube, and the chain behaviors inside the confining tubes are rather similar to those in dilute solutions.

    Current work was supported by the National Key Research and Development Program of China (Grants 2016YFB0302500 and 2018YFB0704200), and the National Natural Science Foundation of China (Grants 51633009). The authors are grateful for the help from the employees and the support of the Z1 algorithm from Prof. Martin Kröger (Eidgenössische Technische Hochschule Zürich).

Figure 1. (a) and (b) The variations of the configurations of the polymer chains (N = 400) with time from bottom to top, for dilute solutions and melts, respectively. The color gradation denotes different positions of the beads in the polymer chains.

Related links: https://sor.scitation.org/doi/10.1122/8.0000013