Analyzing the Role of Surfactants in the Colloidal Stability of Nanoparticles in Oil through Coarse-Grained Molecular Dynamics Simulations

The mechanism by which surfactants stabilize nanoparticles in oil is not yet fully understood. There are numerous factors at play, and the conditions under which a nanoparticle is stabilized in oil cannot always be predicted with certainty. In this study, the SPICA coarse-grained force field was used to observe the molecular-level details of nanoparticle aggregation through simulation. Using SPICA, a free-energy pathway of aggregation is determined for different surfactant types and system configurations. The deformation of the surfactant layer surrounding the nanoparticle was shown to be the major source of colloid stabilization. This is further proven by the surprising result where decreasing the packing density of the surfactants in the layer actually reverses the role of the surfactants, from stabilizing to nucleating agents.