Stabilization and destabilization of emulsions
Emulsions are dispersions in which one or more liquids are dispersed as droplets in another liquid (the continuous phase). The liquids involved are immiscible. Some examples of emulsions in our day-to-day life are milk, margarine, mayonnaise, espresso coffee, various lotions and creams, among others. Furthermore, emulsions are found at different stages in the petroleum industry, such as in the production, transportation and processing of crude oil.
From a thermodynamic point of view, emulsions are unstable systems. This fact stems from the second law of thermodynamics, which implies the spontaneous reduction of the interfacial area of systems composed of two or more liquids. Therefore, emulsions are only formed with the supply of some form of energy to the system, and, in the absence of a mechanism that stabilizes the interfaces between the droplets and the continuous phase, phase separation will occur spontaneously.
GReo investigates the stabilization and destabilization mechanisms of emulsions and the influence of droplet deformation on stability through the following studies: (i) Coalescence, flocculation and sedimentation of droplets; (ii) Interfacial tension and interface rheology; (iii) Microscopic visualization of droplets in shear; (iv) Numerical simulations of droplet deformation; (v) Effect of deformation on the stability of emulsions and (vi) Analysis of demulsifiers in preventing the formation or inversion of emulsions.
Several tools are employed by GReo to study emulsions. Highlights include (i) rotational rheometers with Double Wall Ring geometry (DHR-3 and ARES-G2 from TA Instruments) and tensiometers (K100C from Kruss GMBH, TE 1C from Lauda and Traker H from Teclis Instruments) to measure interfacial properties; (ii) Langmuir vessel to determine the Langmuir isotherms and the dilatational modulus; (iii) Langmuir vessel coupled to a rheometer, to study the effect of surface pressure on shear interfacial rheology; (iv) determination of the droplet size distribution with optical microscope Eclipse LV100 from Nikon or Scanning Electron Microscope (SEM) with cryogenic system; (v) phase separation visualization experiments with a photographic camera; (vi) use of an optical microscope with counter-rotating motor coupled to the TA Instruments DHR-3 rheometer to visualize the flow and relate the state of the microstructure with the rheology and (vii) Turbiscan stability analyzer to evaluate the stability of dispersions ( emulsions, foams and suspensions) concentrates.
Infrastructure: rotational rheometer; Langmuir vat tensiometers; Polarized optical microscope with shear module and temperature control; Scanning Electron Microscope (SEM) with cryogenic system for analysis of fluid samples; Turbiscan stability analyzer; visualization experiments.