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Large-scale simulations reveal that ring melts dynamics depend on macromolecular caging, not linear chain entanglement. A crossover degree of polymerization (ND) successfully organizes dynamic scaling exponents and diffusion constants.

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Area of Science:

  • Polymer Physics
  • Soft Matter Physics
  • Computational Biophysics

Background:

  • Dynamics of non-concatenated ring melts are crucial for soft materials and cellular biophysics.
  • Understanding their slow dynamics is a key challenge in polymer science.

Purpose of the Study:

  • Investigate monomer and center-of-mass (CM) mean square displacements (MSD) and stress relaxation in model ring melts.
  • Analyze dynamical slowing down using sub-diffusive fractional time scaling exponents.
  • Explore the influence of polymerization degree and stiffness on dynamics.

Main Methods:

  • Large-scale molecular dynamics simulations of model ring melts.
  • Analysis of monomer and CM MSD, and stress relaxation functions.
  • Characterization of dynamical slowing down via fractional time scaling exponents.

Main Results:

  • Dynamics are not organized by linear chain entanglement (N/Ne).
  • A crossover degree of polymerization (ND), based on macromolecular caging, successfully collapses dynamic scaling exponents and organizes long-time CM self-diffusion.
  • Different properties exhibit distinct exponents with one or two regimes of linear variation with log(ND/N).
  • A crossover in CM-MSD and stress relaxation exponents at high N or stiffness indicates dynamic decoupling and activated transport.

Conclusions:

  • Macromolecular caging, quantified by ND, is a more effective measure than N/Ne for organizing ring melt dynamics.
  • A novel dynamic decoupling and transition to activated transport are observed at high N or stiffness.
  • Results suggest potential intermolecular collective contributions to stress, analogous to soft colloidal matter.