(742f) Heterogeneous Nanoparticles Simulated At Water-Oil Interfaces: Implications for the Stability of Pickering Emulsions

Pickering emulsions find many applications, including some in food processing, personal care products, and drug delivery devices. Because Pickering emulsions are stabilized by nanoparticles adsorbed at oil-water interfaces, the emulsions stability is naturally related to the structural and dynamical properties of the interfacial nanoparticles. Such properties are investigated here by means of dissipative particle dynamics simulations. The force field parameters have been derived to reproduce atomistic simulation results for silica-based nanoparticles at water-decane interfaces (Langmuir 2011, 27, (9), 5264-5274). Several nanoparticles are considered, including Janus or homogeneous ones with different amounts of hydrophilic/hydrophobic surface groups (e.g., 25% hydrophilic – 75% hydrophobic surface groups). We focus on systems of different composition. For example, systems containing both homogeneous and Janus nanoparticles are investigated. For a given composition, simulations are conducted at increasing nanoparticle density. The results are quantified in terms of radial distribution function, hexagonal order parameter, contact angle, and self-diffusion coefficient. We sometimes find unexpected behavior. For example, at high surface density ‘caging’ phenomena are observed, where the diffusion of a nanoparticle is hindered by the rigid structure (i.e., cage) formed by surrounding nanoparticles. Cage relaxation and rearrangement are discussed. Radial distribution functions, and even the contact angle of a given nanoparticle are found to strongly depend on the system composition. Implications of such observations on macroscopic observables are discussed.