(2iw) Intricacies of Spontaneous Emulsification

Micro and/or nano emulsions are often formed when an organic liquid comes in contact with water in the presence of a surfactant, with low, but, evidently with positive interfacial tension. Many years of research suggested various mechanism under this phenomenon; hydrodynamic disturbances caused by the interfacial mass transfer being one of those. Nevertheless, the detailed steps underlying the proposed mechanisms still remain unclear. In this research, we interrogated the formation of such emulsions with diesel/water and several other model systems with the surfactant (a mixture of dodecanoic acid and an anionic surfactant) was present in the aqueous phase. Several methods were used, in which UV spectroscopy has been one of the indispensable techniques, which has been used in three ways. First the UV beam was made to pass through the aqueous phase slightly below the interface, which interrogated the fluctuation of the concentration of the organic solvent present in water in the form of emulsion droplets. Next, the beam was passed about 4 mm below the interface, which allowed measurements of the diffusion of droplets from the interface to down in the bulk aqueous phase. In several cases, the measured diffusivities are orders of magnitude higher than the Stokes-Einstein diffusivity; furthermore, they showed a strong correlation with the interfacial concentration fluctuation as obtained from the first method thereby signifying that the droplet diffusion is controlled by athermal fluctuations. In the third method, the UV beam was made to pass through the organic phase above the interface, from which the transfer of surfactant from the aqueous to the oil phase was probed. Apart from studying the evolution of surfactant concentration in the oil phase, this method allowed measurements of chemical shifts of the functional groups of the surfactants, which is consistent with the formation of inverted (water in organic phase) emulsions in the oil phase. The diffusion of water in the organic phase was estimated using a method in which a drop of concentrated sugar solution was held about 1 mm above the interface. The volume of the droplet increased with time as the water underwent a vapor phase osmosis from the aqueous to the solvent phase. These and the UV spectroscopic studies provided the complementary evidence that the water vapor diffused in oil seems to form inverted emulsion in the organic phase, which forms oil in water emulsion via fusion with the interface. In certain situations when no emulsion was evident in the aqueous phase, both the transfer of water and the surfactants from the aqueous to the organic phase was thwarted.

Research Interests:

I am a broadly trained chemical engineer with core expertise in Fluid dynamics, emulsion science, interfacial phenomena, colloidal science, soft polymers (hydrogels and elastomers), molecular dynamics, electrochemistry, and membrane technology. I work on both experiments and modeling to understand the process of emulsion formation in oil-water systems by thermodynamic and kinetic pathways, and process development in the water purification studies, polymeric sensors and membrane synthesis.

Teaching Interests:

My primary interests in teaching include the following subjects: Fluid mechanics, Heat transfer, Separation sciences, Polymer technology, Surface and colloidal science.