ABSTRACT
Emulsions are immiscible suspensions of one liquid in another liquid, such as oil in water (O/W) with the use of either emulsier or surfactants, to create a repulsive force between droplets, and therefore, it prevents instability toward emulsion. This process is called emulsication. They are thermodynamically unstable system that will revert back to complete-phase separation to reduce its interfacial tension, making the Gibbs energy positive. This interfacial tension can be reduced signicantly by adding amphiphilic surface-active agents, or surfactants, which are soluble in at least one of the liquid phases. A polar or nonpolar liquid that disperses into a system is referred to as the hydrophilic-lipophilic balance (HLB) (Myers, 1999), and a numerical HLB scheme exists for classifying surfactants in terms of their relative solubility in aqueous or oil phases such as O/W or water in oil (W/O). Also, these emulsiers adsorb to newly formed droplets surface, forming a barrier that prevents it from aggregation. Gravitational separation can be prevented by weighting agents; they are dense hydrophobic components added to low-density oils. Ripening inhibitors or retarders are water-insoluble components added to polar oils to prevent Ostwald ripening, for example, corn oil that is added to orange oil to prevent droplet growth (McClements et al., 2012). For hydrogel/gel preparation, texture modiers are substances used to increase the viscosity or gel aqueous solutions, thereby retarding or preventing droplet movement for cosmetic purposes. Selecting the most appropriate emulsier or stabilizer for a particular application is one of the most important factors determining the long-term stability and physicochemical properties of emulsion system (McClements, 2005). The quantity and quality of each substance associated with the composition, the dispersing method used, the temperature, and the order of addition are some of the many factors that must be considered when preparing an emulsion (Meyers, 1999). There are some unstable mechanisms that emulsion undergoes if stability is not proper, and these mechanisms can destabilize the emulsion that causes the droplet size distribution to change from monomodal to bimodal (Sole et al., 2012). These include phase separation, coalescence, sedimentation, occulation, and Ostwald ripening. Phase separation occurs when density difference is more between the two phases. Coalescence and aggregation are similar terms but it differs slightly due to changing in the droplet size.
