PHENOMENA OF DOUBLE EMULSIONS COALESCENCE
An emulsion is a system composed of two immiscible liquid phases where one phase is dispersed as droplets within the other phase. There are two types of emulsions: oil emulsions in water (O / W), and water in oil emulsions (W / O). At present the study of emulsions is of both scientific and technological importance because of the potential applications of the same. Emulsions are systems widely found in industries such as food, pharmaceutical, cosmetics, agrochemicals, paints, oil, etc.. In the food industry products such as creams, mayonnaise, dressings, ice and butter are emulsions. In the pharmaceutical industry and medical emulsion systems have been used since its inception in the administration of drugs and oils. Besides the above, a number of related systems, that although can not be classified as emulsions, physical and structural characteristics similar to emulsions. Such is the case of foams, lipid bilayers of the plasma membrane, liposomes, etc.. (FIGURE 1)
In particular, the study of double emulsion W / O / W (water droplets in oil globules dispersed in water) is of great relevance for its application in the encapsulation of chemically sensitive or volatile ingredients (FIGURE 2). This type of emulsions allows prolonged release of the contents. In the best scenario is desirable not only meet but to control that process.
Figure 2
The main mechanism that determines the kinetics of release of the material in the emulsion W / O / W is the phenomenon of coalescence, and thus its study is of interest. There are several experimental studies devoted to studying the phenomenon of double coalescence in emulsions, however, so far not studied the effect of gravity on the temporal evolution of the same. It was only through computer simulation that the effect of gravity has been introduced into the analysis. In this regard we aim to contribute to complete the analysis. For the foregoing is necessary to make double emulsion globules of different sizes, materials used for this ultra pure water, a hydrophilic surfactant, SDS, a lipophilic surfactant, Span 80 and dodecane. To produce the first double emulsion produces a reverse emulsion (W / O) using an aqueous solution at 1 M NaCl, dodecane and Span 80. Subsequently the emulsion is dispersed in an aqueous solution of SDS to 1 CMC, which produces a direct emulsion (O / W). Finally the emulsion is dispersed in an aqueous solution of SDS at 30 CMC, and thus yielding a double emulsion. The double emulsion is placed in a glass cell of about 1.5 x 1.5 cm base and 200 microns high and is observed by the technique of digital video microscopy, which involves placing the cell in an optical microscope and mounted on it a digital camera, which by the right software system records images every so often. Subsequently, these images are analyzed to determine the cell size over time and from these data yields the time evolution of the system and therefore recognizing each stage of the coalescence phenomenon. (Figure 3 and 4)
 |
 |
FIGURE 4
The time course of blood to different concentrations of surfactant is shown in the following figure. In (A) shows the curve for the system to a concentration of 2% (by weight) lipophilic surfactant, it can be divided into 4 regions. In the first, the external coalescence phenomenon seems to predominate, while in the second region the phenomenon of internal coalescence is more important as the globule size does not change significantly but inside the droplets begin to coalesce together forming large droplets size. In the third region is witnessing a significant change in the diameter of the bead due to the expulsion of the internal drop. Finally, the fourth region the phenomenon of external coalescence results in a slow but steady removal of water into the continuum.
In (B), (C) and (D) shows the time course for lipophilic surfactant concentrations of 1, 0.5 and 0.1% (by weight), respectively. These systems share the same phenomenology: the curve evolution can be divided into 2 parts, the first external coalescence phenomenon is more relevant, while in the second internal and external coalescence are present significantly, resulting in the formation of large drops within the globule and in turn a gradual decrease in diameter. The time scale is the factor that is more variation modified with lipophilic surfactant. Currently work on the development of a primitive model that allows us to predict and explain the observed behavior. The future goal is to refine the model in a way that allows us to more accurately predict the behavior of double emulsions of the water in oil in water and provide us with information to extend the study to similar systems.