Dynamic heterogeneity and collective motion in star polymer melts

Area of Science:

• Polymer Physics
• Materials Science
• Computational Chemistry

Background:

• Glass formation in linear polymer melts is well-understood.
• Limited knowledge exists regarding glass formation in star polymer melts.
• Star polymer architecture significantly influences material properties.

Purpose of the Study:

• Investigate segmental dynamics in star polymer melts.
• Examine the cooperative nature of segmental motion.
• Quantify the impact of star polymer architecture (arm number and length) on glass transition temperature (Tg), non-Gaussian displacements, and collective monomer motion.

Main Methods:

• Utilized molecular dynamics simulations to study star polymer melts.
• Analyzed segmental dynamics and cooperative motion.
• Quantified effects of varying arm number (f) and arm molecular mass (Ma).

Main Results:

• Demonstrated that varying star polymer architecture influences molecular shape, Tg, and dynamics.
• Showed that all relaxation data are quantitatively described by the string model of glass formation.
• Identified the average length of string-like particle exchange motions (L) as a key indicator of cooperative motion.

Conclusions:

• The string model provides a unified framework for understanding glass formation in star polymer melts.
• Cooperative motion in star polymer melts is directly related to the length of string-like movements.
• Findings extend the applicability of the string model to complex polymer architectures and systems with mobility gradients.