(627c) Local Processes in Spontaneous Emulsification

Abstract. Micro and/or Nano emulsions are often formed when an organic liquid gently comes in contact with water in the presence of a surfactant, even with a positive interfacial tension. Many years of research made it clear that the driving force for spontaneous emulsification arises from the differences of the bulk chemical potentials of various components, which trigger various coupled transport processes that lead to Sternling-Scriven or Landau-Darrieus instabilities near the interfacial regions. While extraordinary theoretical developments attempted to describe the emulsification processes within the formalisms of equilibrium and non-equilibrium thermodynamics, the local processes underlying the spontaneous emulsification, however, still remain elusive. In this research, we attempt to shed light on some of the local processes that involve the transfer of surfactant as well as molecular water from one phase to another (i.e. water to oil), and the subsequent evolution of certain unstable morphologies. The experimental methods used to interrogate these local processes were based on UV spectroscopy, Acoustic attenuation method, Continuous Flow Hydrodynamic Fractionation, Langmuir Blodgett film balance and vapor phase like osmosis. The comparison of the experimental results with MD simulations illustrated the roles of inverted emulsions that are formed in the organic phase, which subsequently fuse with the oil-water interface thus forming oil in water emulsions in the aqueous phase. These processes lead to either strong or weak fluctuation of components just below the interface with characteristic noise that resembles those found in earthquakes. These athermal noises announce fast (athermal) diffusion of the emulsion droplets from the interface towards the bulk of water. Various additives that thwart the diffusion of various species also led to the inhibition of spontaneous emulsification, which were also codified in the concentration fluctuation noises below the interface.