Flow-induced density fluctuation assisted nucleation in polyethylene.

J Chem Phys

National Synchrotron Radiation Lab and CAS Key Laboratory of Soft Matter Chemistry, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, University of Science and Technology of China, Hefei, China.

Published: December 2018

The nucleation processes of polyethylene under quiescent and shear flow conditions are comparatively studied with all-atom molecular dynamics simulations. Under both conditions, nucleation is demonstrated to be a two-step process, which, however, proceeds via different intermediate orders. Quiescent nucleation is assisted by local order structures, while flow-induced nucleation is promoted by density fluctuation, which is a coupling effect of conformational and orientational orderings. Flow drives the transformation from flexible chains to conformational ordered segments and circumvents the entropic penalty, which is the most peculiar and rate-limited step in polymer crystallization. This work suggests that the acceleration of the nucleation rate in orders of magnitude by flow is mainly attributed to the different kinetics pathway via conformational/orientational ordering-density fluctuation-nucleation.

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http://dx.doi.org/10.1063/1.5054273DOI Listing

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