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

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.