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Flow-induced density fluctuation assisted nucleation in polyethylene.

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Area of Science:

  • Polymer Science
  • Materials Science
  • Computational Chemistry

Background:

  • Polymer crystallization is crucial for material properties.
  • Understanding nucleation mechanisms is key to controlling polymer structure.
  • Shear flow is known to influence polymer crystallization kinetics.

Purpose of the Study:

  • To comparatively study polyethylene nucleation under quiescent and shear flow conditions.
  • To elucidate the distinct intermediate orders and kinetic pathways involved.
  • To explain the significant acceleration of nucleation rates by shear flow.

Main Methods:

  • All-atom molecular dynamics simulations were employed.
  • Polyethylene nucleation was simulated under both quiescent and shear flow.
  • Intermediate ordering and density fluctuations were analyzed.

Main Results:

  • Nucleation is a two-step process under both conditions, but with different intermediate orders.
  • Quiescent nucleation involves local order structures.
  • Flow-induced nucleation is driven by density fluctuations from conformational and orientational ordering.

Conclusions:

  • Shear flow promotes nucleation by facilitating conformational ordering and density fluctuations.
  • Flow circumvents the entropic penalty, a rate-limiting step in quiescent crystallization.
  • The accelerated nucleation rate under flow is attributed to a distinct kinetic pathway.