J. Kleinen and J. Venzmer
A frequently used approach to obtain the desired flow behavior of surfactant formulations is to utilize the surfactant aggregates themselves. This can be done by converting spherical micelles to worm-like micelles by addition of a hydrophobic thickener; additionally, the surfactant aggregates can be bridged by using hydrophilic, associative thickeners. Challenging in this respect are formulations which are sulfate-free and/or contain short-chain surfactants. In order to understand the rheological behavior and how to build viscosity in such formulations, one needs to go beyond the limits of mechanical rheology, i.e. by using microrheology. An additional challenge – at first sight unrelated to the rheology – is the foaming performance. It will be shown that the foamability can be well predicted by a rheological characterization of dilutions, specifically the determination of the normal force at high shear rates. This method can also explain why formulations containing biopolymers are challenging when it comes to foaming performance.
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