Coalescence or isolation: A coarse-grained molecular dynamics simulations of post-collision behavior of droplets in...

Amphiphilic natural polymers, as a biomass resource, have been widely utilized in stabilizing oil-water emulsions due to their numerous advantages. However, the mechanism by which they maintain emulsion stability during droplet dynamic equilibrium remains unclear. In this study, hydrophobically modified sodium alginate (HMSA) was used as a model to investigate the molecular dynamics behavior of droplet models constructed with varying amounts of HMSA through coarse-grained molecular dynamics simulations, with experimental validation providing additional support. Results show that increasing HMSA concentration leads to a progressively denser interfacial structure with soft particulate formation, consistent with experimental findings. Umbrella sampling reveals that the energy barrier for droplet coalescence rises with greater HMSA surface coverage. Additionally, soft particulate structures at collision interfaces create a cushioning effect, further increasing the energy barrier for droplet approach. Molecular dynamics simulations correlate well with QCM-D, interfacial tension, and morphological analyses. These findings elucidate the mechanistic divergence between amphiphilic macromolecules and small-molecule surfactants in stabilizing emulsions, highlighting the steric hindrance imparted by the unique architecture of amphiphilic macromolecules as a significant contribution to emulsion stability. This understanding provides molecular-level insights into the application of amphiphilic macromolecular surfactants in food science, agriculture, pharmaceuticals, and materials science.