Simple models of complex aggregation: vesicle formation by soft repulsive spheres with dipolelike interactions

Area of Science:

• Statistical Mechanics
• Soft Matter Physics
• Computational Physics

Background:

• Investigating the behavior of systems with both structural and spin interactions is crucial for understanding complex materials.
• Classical spin systems provide a simplified yet insightful model for exploring emergent phenomena in condensed matter.

Purpose of the Study:

• To investigate the structural and thermodynamic properties of spherical particles with classical spins.
• To model the condensation behavior and aggregate formation under varying temperature and density conditions.
• To explore the potential for equilibrium polymerization and membrane properties in such systems.

Main Methods:

• Utilized Monte Carlo simulations to study systems of spherical particles with repulsive pair contributions and modified dipole-dipole spin interactions.
• Analyzed the system's behavior across a range of temperatures and densities to observe phase transitions and aggregate structures.

Main Results:

• At high temperatures and low densities, the system behaves as a homogeneous fluid with short-range spin correlations.
• Upon decreasing temperature, particles condense into equilibrium populations of free-floating vesicles, forming predominantly two-dimensional aggregates.
• Condensation is a continuous transformation when the isotropic part of the interatomic potential is purely repulsive.

Conclusions:

• The model successfully demonstrates particle condensation into vesicles and provides a framework for studying membrane properties at low temperatures.
• The system serves as a simplified model for equilibrium polymerization, particularly for systems forming two-dimensional aggregates at intermediate temperatures.
• Comparison with electrostatic systems highlights differences in aggregate dimensionality (1D vs. 2D) under similar conditions.