Abstract
1 figure.-- Talk delivered at the "Designed Assembly of Colloids at Interfaces - Fundamentals to Applications. Online event", organised by the Liquids and Complex Fluids Group, Institute of Physics (Great Britain), 14th-16th June 2021.
In biomedical or pharmaceutical applications, surfactants in conventional emulsions can cause tissue irritation or cell damage. In this work, biocompatible nanoparticles of sp3 carbon, called nanodiamond (ND), with a carboxylated surface, were used to prepare mono-sized Pickering emulsions of sunflower oil in water. Emulsification of the oil in acidic ND dispersions was achieved via two different techniques: membrane emulsification and probe sonication. Whereas membrane emulsification fabricated larger (about 30 μm) oil droplets (Figure 1), probe sonication resulted in smaller (sub-μm) droplets and higher stability for a wide range of pH values (acidic to alkaline). The emulsions show high stability against mechanical vibration and offer long-term storage up to one year. Pendant drop tensiometry confirmed that ND particles are adsorbed at the oil/water interface, with a greater decrease in interfacial tension found with increasing ND concentrations in the dispersion. ND coatings become more hydrophilic with increasing pH, according to three-phase contact angle analysis, because of deprotonation of the carboxylic acid groups. Destabilisation of the Pickering emulsion at very high pH was demonstrated in highly alkaline buffers, which is due to the saponification of the vegetable oil and association with cations in solution. This is the first systematic study of carboxylic ND-stabilized Pickering emulsions, and it indicates a very promising prospect for a range of applications.