Interfacial drop dynamics in a simple shear field

Dynamic interfacial phenomena were investigated by subjecting liquid drops to a simple shear field, which was generated by a Couette cylinder apparatus. Various studies of drop dynamics were carried out, including deformation tests, the position of the critical streamline (external to the drop), and the period of circulation around internal streamlines. Significant dynamic interfacial behavior was observed in a liquid-liquid system that contained no added surfactant. Drops behaved much like rigid bodies in the internal circulation and the critical streamline experiments. Very large effects were caused by either the inter- facial dilational viscosity (k) or by interfacial tension gradients, which have similar effects as k. The interfacial shear viscosity (c) was also observed, but to a lesser degree. Values for these effects were about 3-33 surface poise for the K-type effects, and 0.18 surface poise for the e effect. Trace impurities that acted as surfactants may have been responsible for these results. Dynamic interfacial behavior, though smaller in magnitude, was also observed in a surfactant, low interfacial tension system, which was intended to somewhat resemble the liquids encountered in micellar chemical flooding. High concentrations of the surfactant were used to reduce the possibility of developing interfacial tension gradients. Effects caused by either the interfacial dilational viscosity or interfacial tension gradients were apparently negligible, whereas the interfacial shear viscosity appeared to be in the range of 0.03 to 0.21 surface poise. The potential of very small surfactant concentrations to cause significant dynamic interfacial behavior was demonstrated. Trace impurities that act as surfactants, for example, could induce these effects by creating large interfacial tension gradients. Conversely, high concentrations of surfactant would decrease the chances of such effects occurring.