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Deciphering the dynamics of star molecules in shear flow
Jurij Sablić1, Matej Praprotnik2, Rafael Delgado-Buscalioni3
1Department of Molecular Modeling, National Institute of Chemistry, Hajdrihova 19, SI-1001 Ljubljana, Slovenia. praprot@cmm.ki.si.
Soft Matter
|June 16, 2017
Summary
This study reveals essential tangential friction for star polymer melts under shear flow. It identifies three dynamic regimes and a general relation for star molecule rotation, challenging prior assumptions.
Area of Science:
- Polymer Physics
- Soft Matter Science
- Computational Materials Science
Background:
- Understanding polymer dynamics under flow is crucial for material properties.
- Star polymers exhibit complex behaviors influenced by molecular architecture and flow conditions.
- Previous models often overlooked tangential friction's role in polymer melts.
Purpose of the Study:
- To analyze the rotational dynamics of star polymers in melts and dilute solutions under shear flow.
- To investigate the impact of tangential friction on melt dynamics.
- To identify distinct dynamic regimes and universal scaling relations for star polymer rotation.
Main Methods:
- Simulations using single molecule Brownian hydrodynamics for dilute solutions.
- Non-equilibrium molecular dynamics (NEMD) for melts, including Dissipative Particle Dynamics (DPD) thermostat for friction.
- Analysis of molecular angular momentum and dynamic regimes across varying shear rates.
Main Results:
- Tangential friction is identified as critical for controlling hydrodynamic effects in star polymer melts.
- Three distinct dynamic regimes are observed with increasing shear rate, linked to relaxation mechanisms.
- A universal 'breathing' mode and a relation between oscillation frequency (Ω) and orientation angle are found.
- Tank-treading frequency increases with shear rate, contradicting previous studies.
Conclusions:
- Tangential friction must be included for accurate modeling of star polymer melts under shear.
- The identified dynamic regimes and rotational relations provide a more comprehensive understanding of star polymer hydrodynamics.
- This work corrects previous interpretations of tank-treading dynamics in star polymers.
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