The outcome of a coarse-grained simulation within the Dissipative Particle Dynamics framework strongly depends on the choice of the repulsive parameter between different species. Different methodologies have been used in the literature to determine these parameters towards reproducing selected experimental system properties. In this work, a systematic investigation on possible procedures for estimating the simulation parameters is conducted. We compare methods based on the Hildebrand and the Hansen solubility parameter theories, mapped into the Flory-Huggins model. We find that using the Hansen solubility parameters it is possible to achieve a high degree of coarse graining, with parameters that yield realistic values for the interfacial tension. The procedure was first applied to the water/benzene system, and then validated for water/n-octane, water/1,1dichloroethane, water/methyl cyclohexane, and water/isobutyl acetate. In all these cases, the experimental interfacial tension could be reproduced by adjusting a single correction factor. In the case of the water-benzene system, the Dissipative Particle Dynamics parameters derived using our approach were able to simultaneously describe both the interfacial tension and micellar properties of aqueous non-ionic surfactants representative of the octyl polyethylene oxide C 8 H 17 O(C 2 H 4 O) m H family. We show how the parameters can be used, within the Dissipative Particle Dynamics framework, to simulate the water/oil interface in presence of surfactants at varying concentrations. The results show, as expected, that as the surfactant concentration increases, the interfacial tension decreases and micelles form in bulk water.

Ostwald ripening is a diffusional mass transfer process that occurs in polydisperse emulsions, often with the result of threatening the emulsion stability. In this work, we design a simulation protocol that is capable of quantifying the process of Ostwald ripening at the molecular level.To achieve experimentally relevant time scales, the Dissipative Particle Dynamics (DPD) simulation protocol is implemented. The simulation parameters are tuned to represent two benzene droplets dispersed in water. The coalescence between the two droplets is prevented via the introduction of membranes, which allow diffusion of benzene from one droplet to the other. The simulation results are quantified in terms of the changes of the droplets volume as a function of time. The results are in qualitative agreement with experiments. The agreement with the Lifshitz-Slyozov-Wagner theory becomes quantitative when the simulated solubility and diffusion coefficient of benzene in water are considered. The effect of two different surfactants was also investigated. In agreement with both experimental observations and theory, the addition of surfactants at moderate concentrations decreased the Ostwald ripening rate because of the reduction in the interfacial tension between benzene and water; as the surfactant film becomes dense, other phenomena are likely to further delay Ostwald ripening.In fact, the results suggest that the surfactant that yields higher density at the benzene-water interface delayed more effectively Ostwald ripening. The formation of micelles can also affect the ripening rate, in qualitative agreement with experiments, although our simulations are not conclusive on such effects. Our simulations show that the coarse-grained DPD formalism is able to capture the molecular phenomena related to Ostwald ripening, and reveal molecularlevel features that could help to understand experimental observations. The results could be useful for predicting, and eventually controlling the long-term stability of emulsions.

In this work, using Dissipative Particle Dynamics simulations, we provide fundamental insights into the self-assembly of nanoparticles (NPs) on droplet surfaces in an oil-in-water emulsion. We highlight the effect of...