Molecular Dynamics Investigation of the Effect of Droplet Size on Dynamic Arrest and the Sol–Gel Transition in PEO-2D Microemulsion Systems

Abstract

Abstract In the present study, molecular dynamics simulations are employed to investigate a mixed system consisting of a microemulsion and PEO-2D polymers, with the aim of examining the effects of three principal parameters, namely, the reduced number density ρ*, the droplet radius R, and the number of polymers grafted per microemulsion droplet, n(PEO-2D), on dynamic properties and their relation with the sol–gel transition. The microemulsion is a direct cationic system composed of decane, cetylpyridinium chloride (CpCl), octanol, and saline water. The pair interaction potential is described within the framework of Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, comprising hard-sphere, van der Waals, and Coulombic contributions. Upon incorporation of PEO-2D polymers, two additional Yukawa-type contributions are introduced, corresponding to steric repulsion and polymer bridging attraction. The results show that the dynamics of the microemulsion droplets is strongly sensitive to ρ*, R, and n(PEO-2D). Increasing these parameters leads to increasingly complex dynamics and progressively anomalous droplet diffusion. Increasing the droplet radius slows droplet diffusion and promotes the onset of anomalous dynamics. Beyond a critical radius Rc, the droplets become trapped within cages, indicating the formation of a gel state. Similar behavior is observed when the reduced number density or the number of polymers per droplet is increased. Furthermore, a gel state can be reached at a lower critical reduced number density ρc* when the droplets are larger or when the average number of polymers per droplet is higher. The critical radius Rc associated with the sol–gel transition also decreases with increasing polymer grafting. Overall, these results demonstrate that the sol–gel transition can be controlled through the droplet radius, reduced number density, and polymer grafting density, providing useful insight into the dynamic behavior of polymer–microemulsion systems and their potential applications in biomedical drug delivery.