Formation of Pickering Emulsions Using Nanodiamonds

Pickering emulsions are used over surfactant stabilized emulsions in a wide range of applications including personal care products, pharmaceuticals, and oil recovery because of their enhanced stability and lower toxicity. We examine here the use of nanodiamonds (ND), a relatively novel carbonaceous filler with high adsorption activity, small size, and large surface area to create solid stabilized emulsions. Using a system consisting of isopropyl palmitate and water, stabilized by hydroxylated NDs, we investigate the stability, rheology and frictional behavior of these emulsions as a function of ND concentration. Optical microscopy reveals increasing ND concentration results in smaller droplet sizes, due to the greater availability of particles that can be adsorbed on the oil-water interface. This behavior is consistent with our rheological results of higher G’ and yield stress with increased ND, as the presence of smaller droplets facilitate the formation of a densely packed network. Microstructure recovery after breakdown at different stress levels correlate with the ratio of applied stress to the yield stress for each ND concentration. Tribological behavior of ND emulsions was also investigated using a soft model contact and the data related to the rheological characteristics.