Responsive core-shell nanoparticles at fluid interfaces offer great potential for realizing controllable self-assembly that can benefit various applications, ranging from 2D nanomaterials synthesis, switchable emulsions and microdroplet reactor. The intricate interplay of various forces acting on particles gives rise to interesting interfacial dynamics of these responsive and deformable core-shell particles. The responsive core-shell particles could not only change interparticle interactions at interfaces but also droplet-droplet interactions when adsorbed at water-oil interfaces in Pickering emulsions. Thus, a novel mechanism of achieving switchable emulsions can also be obtained.In this dissertation, the electrostatic dissipative particle dynamics (EDPD) was developed to model the interfacial dynamics of pH-responsive core-shell nanoparticles at water-oil interfaces and probe the direct interactions between emulsion droplets stabilized with these active nanoparticles. The model nanoparticle is functionalized with weak polyelectrolytes to render the pH-sensitivity. During changing the degree of ionization α (i.e., pH value in water), the adsorption of PGNPs was prohibited and the morphology of particles was spreading. The introduction of electrolytes can screen the image charge effect and mitigate the adsorption prohibition. Besides the study of adsorption behavior, qualitative and quantitative analysis of the monolayer microstructure showed a disorder-order phase transition, which is driven by the modulation of interparticle electrostatic interactions subject to pH changes. Different regimes of particle self-diffusion in the monolayer were identified and correlated with the structural transition. We further modeled the head-on collision and coalescence of two emulsion droplets covered by PGNPs. The maximal resistance forces were measured to quantitatively discriminate the efficacy of particles in stabilizing emulsions at different degrees of ionization. Moreover, the influence of ionization state was studied in various surface coverage regimes and shows two different mechanisms of preventing coalescence. The findings of these numerical simulations provide greater insights into the interfacial behavior of active polymer-grafted nanoparticles at water-oil interfaces and open a new avenue for achieving responsive emulsions by tuning direct interactions between emulsions.