Influence of Interfacial Characteristics on Ostwald Ripening in Hydrocarbon Oil-in-Water Emulsions

Abstract

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.

Extending Emulsion Functionality: Post-Homogenization Modification of Droplet Properties

“…For example, the strength of the electrostatic repulsion between oil droplets tends to increase as their electrical potential increases, whereas the strength of the steric repulsion increases as the thickness of the interfacial layer increases. The rate of Ostwald ripening depends on the interfacial tension and rheology [27]. Interfacial properties may also have an impact on the chemical stability of the oil phase [28], as well as the release of any encapsulated substances [25].…”

Influence of surface viscosity on droplets in shear flow

“…However, first, Harvey et al (2005) suggests that dilational surface viscosity should also be taken into account. Mun & McClements (2006) measured a high dilational modulus of SDS-chitosan interface for example. Second, recent results by Zell et al (2014) cast doubt on previous experimental measurements of shear surface viscosity and then on conclusions drawn from these measurements on emulsion stability.…”

Emulsion Drops with Complex Interfaces: Globular Versus Flexible Proteins

“…[42] Work on interfacial rheology is often motivated by its relevance to the stability and flow behavior of foams and emulsions. Examples include coalescence studies at a planar oil/water interface, [43] where a positive correlation of coalescence stability with the interfacial shear viscosity was established, a discussion of the influence of the dilatational modulus on Ostwald ripening [44] and experiments on the deformation and breakup behavior of emulsion drops covered with a protein emulsifier. [8,45,46] Van Hemelrijck et al [47] performed measurements on compatibilized immiscible polymer blends and attributed a slow relaxation process found in small amplitude oscillatory shear to in-plane interfacial relaxation; they interpreted their results in terms of a modified Palierne emulsion model described by Jacobs et al [48] A theoretical discussion for dilute emulsions was given by Nadim [49] and by Danov.…”