Interfacial tension as the determinant of the emulsion droplet size

Isabel Gessner, 2011

The stability of emulsions is highly dependent on their droplet size distribution. Control of this parameter during the emulsification process is hence of great interest for a wide range of applications. In this work, different sample preparation methods were tested to find the best way of producing ultrafine stable droplets. A general approach was to utilize the ultralow interfacial tension, and the corresponding bicontinuous structure at the inversion point of the basic thermodynamically stable microemulsion, which is a crucial factor for the formation of small and kinetically stable emulsion droplets. The influence of the temperature on the droplet size was probed by use of time- and temperature-dependent dynamic light scattering experiments. All measurements were performed using H2O/NaCl ? n-octane ? C12E5 as a model system for general systems of the type H2O/NaCl – n-alkane – pure non-ionic surfactant (CiEj). Homogenization of the emulsions was accomplished using a high speed blender (Ultra-Turrax®). Small emulsion droplets with a radius of 85 nm were obtained by homogenization at the ?-point (T ? 33 °C, g ? 6 wt.% C12E5, ? = 0.50 and ? = 0.001) and subsequent dilution with tempered double distilled water/C12E5. When homogenization was conducted at temperatures below 33 °C, meaning in the 2-region, the droplet size distribution was temperature-dependent, and small stable droplet radii below 100 nm were not observed. Thus, the method of preparation determines the size for all emulsions.