Depletion from a hard wall induced by aggregation and gelation

Area of Science:

• Colloid Science
• Statistical Mechanics
• Computational Physics

Background:

• Understanding particle interactions and system structure is crucial in colloid science.
• Diffusion-limited cluster aggregation (DLCA) and gelation are key phenomena in colloidal systems.
• Wall-particle interactions influence macroscopic properties of confined colloidal fluids.

Purpose of the Study:

• To investigate the influence of gelation on the structure of hard sphere systems.
• To compare wall-particle and particle-particle correlations in aggregated and non-aggregated states.
• To analyze the behavior of correlation functions at varying volume fractions and proximity to walls.

Main Methods:

• Off-lattice Monte Carlo simulations were employed to model diffusion-limited cluster aggregation and gelation.
• Wall-particle and particle-particle correlation functions were calculated.
• Theoretical models, including Ornstein-Zernike equation and Percus-Yevick closure, were used for comparison.

Main Results:

• At high volume fractions (>40%), gelation minimally affects correlation functions.
• At low volume fractions (<10%), gelation results in a universal correlation function dependent on the correlation length (xi).
• A depletion layer of approximately 0.5xi width was observed, with concentration increasing as a power law towards the wall.

Conclusions:

• Gelation significantly alters the structure of dilute hard sphere systems.
• The correlation length (xi) is a key parameter governing the structure of gelled colloidal systems near walls.
• The study provides insights into the spatial organization of particles in aggregated colloidal fluids.