Tracer Diffusion in Tightly-Meshed Homogeneous Polymer Networks: A Brownian Dynamics Simulation Study

Area of Science:

• Polymer Physics
• Soft Matter Science
• Computational Chemistry

Background:

• Understanding molecular and nanoparticle transport in polymer networks is crucial for various applications.
• Polymer network structure, including mesh size and crosslinking density, significantly influences diffusion dynamics.
• Tracer particle size relative to network mesh size affects confinement and transport mechanisms.

Purpose of the Study:

• To investigate the dynamics of tracer diffusion in regularly crosslinked polymer networks using Brownian dynamics simulations.
• To elucidate the role of average mesh size and mesh size fluctuations in controlling tracer transport.
• To understand the transition from subdiffusion to normal diffusion based on network properties.

Main Methods:

• Brownian dynamics simulations were employed to model tracer diffusion.
• The average mesh size of polymer networks was systematically varied by adjusting crosslinking density and swelling.
• Tracer particle size was kept comparable to the average mesh size of the network.

Main Results:

• Tracer particles exhibited subdiffusion at intermediate time scales and normal diffusion at long time scales.
• Subdiffusion duration increased with decreasing mesh size (higher crosslinking).
• Diffusion dynamics were influenced by rattling within cages and hopping between them, with mesh fluctuations playing a key role.

Conclusions:

• Both average mesh size and mesh size fluctuations are critical determinants of tracer dynamics in polymer networks.
• At higher polymer volume fractions, larger network fluctuations facilitate tracer escape from cages.
• At lower volume fractions, reduced fluctuations lead to prolonged trapping and infrequent hopping, highlighting the importance of network dynamics.