Simulation Studies of Dynamical Heterogeneity in a Dense Two-Dimensional Dimer-Solvent System with Obstacles

Area of Science:

• Soft Matter Physics
• Colloidal Science
• Computational Physics

Background:

• Understanding the dynamic properties of colloidal suspensions is crucial for materials science.
• Heterogeneity, introduced by obstacles, significantly influences particle diffusion.
• Distinguishing diffusion behaviors (normal vs. subdiffusion) is key to characterizing complex fluids.

Purpose of the Study:

• To develop and simulate a coarse-grained model of a 2D athermal colloidal suspension.
• To investigate the impact of immobile obstacles on the diffusion of solvent (monomer) and dimer molecules.
• To identify concentration regimes where solvent and dimer diffusion characteristics diverge.

Main Methods:

• Designed a coarse-grained, athermal lattice model incorporating solvent monomers, dimer molecules, and impenetrable obstacles.
• Employed Monte Carlo simulations utilizing the dynamic lattice liquid (DLL) algorithm to determine dynamic properties.
• Analyzed diffusion coefficients for solvent and dimer components across varying obstacle and dimer concentrations.

Main Results:

• Observed distinct diffusion characteristics for dimers and solvents within specific obstacle concentration ranges.
• Identified concentration windows where solvent and dimer movement transitions between normal diffusion and subdiffusion.
• Found that the ratio of diffusion coefficients is independent of obstacle concentration at short times but increases with obstacle concentration at long times, remaining independent of dimer concentration.

Conclusions:

• The presence and concentration of obstacles fundamentally alter the diffusion dynamics in 2D colloidal systems.
• Specific component concentration ranges allow for the differentiation of normal diffusion and subdiffusion behaviors for solvent and dimer particles.
• The model provides insights into how system heterogeneity dictates particle transport mechanisms in complex colloidal fluids.