Influence of interfacial characteristics on Ostwald ripening in hydrocarbon oil-in-water emulsions

The influence of the nature of the interfacial membrane on the kinetics of droplet growth in hydrocarbon oil-in-water emulsions was investigated. Droplet growth rates were determined by measuring changes in the droplet size distribution of 1 wt % n-tetradecane or n-octadecane oil-in-water emulsions using laser diffraction. The interfacial properties of the droplets were manipulated by coating them with either an SDS layer or with an SDS-chitosan layer using an electrostatic deposition method. The emulsion containing SDS-coated octadecane droplets did not exhibit droplet growth during storage for 400 h, which showed that it was stable to Ostwald ripening because of this oils extremely low water-solubility. The emulsion containing SDS-coated n-tetradecane droplets showed a considerable increase in mean droplet size with time, which was attributed to Ostwald ripening associated with this oils appreciable water-solubility. On the other hand, an emulsion containing SDS-chitosan coated n-tetradecane droplets was stable to droplet growth, which was attributed to the ability of the interfacial membrane to resist deformation because of its elastic modulus and thickness. This study shows that the stability of emulsion droplets to Ostwald ripening can be improved by using an electrostatic deposition method to form thick elastic membranes around the droplets.