The objective of the research work presented in this paper is to elucidate the role of surfactants during mechanical emulsification. To find out whether droplet disruption or stabilization, or both, are influenced by emulsifiers, the time for disruption and stabilization were calculated approximately. Recent developments in the institute have shown that elongational flow is the most efficient flow regime to produce emulsions with submicron droplets. Experiments, therefore, were carried out using a high-pressure homogenizer with an orifice valve. To illustrate the emulsification process the process was videotaped using a high-speed camera. Calculations for the experimental conditions investigated show that a large number of subsequent disruption steps can take place in the elongational flow. The surfactant is capable of adsorbing at newly formed droplets between subsequent disruption steps. Thus, the total disruption process can be facilitated by surfactants. Further, comparing adsorption time and residence time in the elongational flow shows that stabilization of newly formed droplets in the elongational flow is possible. The emulsification experiments show that between subsequent disruption steps the surface load is not balanced over the droplet's surface. The results indicate that the adsorption process is governed by adsorption from the subsurface to the surface. The pictures obtained by videotaping support the results of calculations and emulsification experiments: droplet deformation with and without surfactant is not significantly different. If stabilization is poor, droplets recoalesce and the disruption result is reversed. (C) 1999 Elsevier Science S.A. All rights reserved.
