Supercooled melt structure and dynamics of single-chain nanoparticles: A computer simulation study.

Area of Science:

• Polymer Physics
• Materials Science
• Computational Chemistry

Background:

• Single-chain cross-linked nanoparticles (SCNPs) are novel polymer architectures with tunable properties.
• Understanding the relationship between cross-linking degree and thermophysical properties is crucial for material design.

Purpose of the Study:

• To investigate the impact of varying cross-linking degrees (ϕ) on the structure and dynamics of SCNP melts.
• To correlate simulation findings with experimental data for polystyrene-based SCNPs.

Main Methods:

• Coarse-grained molecular dynamics simulations were employed to model SCNP melts.
• Experimental synthesis of polystyrene-based SCNPs followed by differential scanning calorimetry (DSC) to measure glass-transition temperature (Tg).

Main Results:

• A nearly linear increase in Tg with increasing cross-linking degree (ϕ) was observed in simulations.
• Experimental Tg measurements qualitatively agreed with simulation trends, showing a significant Tg increase (up to 61 K) for higher ϕ.
• Simulations revealed that cross-linking increases effective hard-core volume, reduces free volume, and enhances dynamical heterogeneity (DH).

Conclusions:

• Intra-molecular cross-linking significantly influences segmental dynamics and glass-transition temperature in polymer melts.
• Increased cross-linking leads to slower structural relaxation, enhanced local cooperative motion, and more pronounced dynamical heterogeneity.
• Topological constraints imposed by cross-links play a key role in frustrating local packing and altering polymer dynamics.