Phase behavior and particle size cutoff effects in polydisperse fluids.

Area of Science:

• Statistical Mechanics
• Physical Chemistry
• Soft Matter Physics

Background:

• Understanding fluid phase behavior is crucial in physical chemistry.
• Polydispersity, or variation in particle size, can significantly alter thermodynamic properties.
• Coupling particle size polydispersity with interaction strength presents a complex challenge in fluid modeling.

Purpose of the Study:

• To investigate the liquid-vapor phase behavior of a fluid with coupled particle size and interaction strength polydispersity.
• To analyze the influence of a specific Schulz distribution (delta = 14%) on phase coexistence.
• To compare the phase behavior of this polydisperse system with a monodisperse counterpart.

Main Methods:

• Grand Canonical Ensemble Monte Carlo (GCMC) simulations were employed to model the fluid.
• Moment free energy calculations were utilized for theoretical analysis.
• Cloud and shadow curves, density distributions, and fractional volumes were computed.

Main Results:

• Cloud and shadow curves are significantly separated, differing from monodisperse systems.
• The critical point is located substantially below the maximum of the cloud curve.
• Phase behavior is highly sensitive to the upper cutoff of the particle size distribution, especially below the critical density.

Conclusions:

• Coupled size and interaction polydispersity leads to distinct liquid-vapor phase behavior.
• Fractionation effects are pronounced and significantly influence phase separation.
• The upper cutoff of the particle size distribution plays a critical role, suggesting potential for new phase formation with wider distributions.