Light Sheet Visualization of the Shear-Induced Flow Pattern of Cationic Surfactant Solutions in a Searle Geometry

摘要

The flow patterns in a Searle gap of two dilute cationic surfactant solutions, tetradecyl trimethyl ammonium salicylate (TTASal) and hexadecyl trimethyl ammonium salicylate (HTASal), are investigated by means of a light sheet visualization. Although the surfactant solutions differ only slightly in the chain length of the surfactant molecule and in concentration, the observed structures in flow are significantly different. In the case of the TTASal solution the observed structures are dark and only a short temporal evolution takes place, with a final state of inwardly and outwardly developing string-like structures similar for all shear rates above a critical value and with a limited amount of structures for high shear rates. The structures in the HTASal solution are in contrast mainly hight and the temporal evolution is quite long, becomes faster with shear rate and shows different states in accordance to the shear rates. For higher shear rates typically first finger-like, afterwards bubble-like structures and finally a kind of homogenization can be observed.