The effects of multiparticle interactions on the aggregation of asphaltenes

In this paper, we analyze aggregation in a systems of spherical primary particles in a liquid solvent with implicitly modeled polymer molecules that are not grafted to the particle surface, but rather are adsorbed by one end; the sorption is too strong for a chain to desorb and diffuse into the solution, but weak enough so that the polymer heads can move along the surface. The potential between the particles includes short-range core attraction and a longer range steric repulsion between the polymer chains. Upon contact, the particles form a permanent bond; the contact area becomes unavailable to the polymers which redistribute along the surface and strengthen the steric repulsion. Thus, the particle-particle interaction depends on the number of bonds each particle has already made. We call this type of multiparticle interactions neighbor-dependent potentials and analyze their behavior with Brownian Dynamics simulations, comparing it to that of particles with reversible pairwise potentials. The neighbor-dependent systems agglomerated into stable fractal structures with the dimensions between 1.7 and 2.0 (seemingly diffusion or reaction limited, depending on the parameters) and showed almost no tendency to restructuring of fractal aggregates into droplets, while pairwise interactions with similar parameters showed restructuring into droplets undergoing concurrently to the cluster-cluster aggregation. The neighbor-dependent systems also showed a different, more ramified cluster structure with multiple internal loops. The main limitation of the modeling approach is related to the arbitrary criteria of the bond formation and call for a fully ergodic Monte Carlo modeling of systems with neighbor-dependent interactions.

Automated summary

In this study, aggregation behavior in a system of spherical primary particles in a liquid solvent was analyzed. It was found that systems with neighbor-dependent interactions formed stable fractal structures, showing different behavior compared to systems with reversible pairwise potentials.