Interfacial shear rheology of mixed polyelectrolyte-surfactant layers.
We have studied the shear rheology of mixed surface layers containing polyelectrolytes and surfactants of opposite charges. The layers containing rigid polyelectrolytes are solidlike and can even exhibit brittle behavior. More flexible polyelectrolytes lead to more viscoelastic layers and very flexible ones to purely viscous layers. A relaxation time on the order of tens of seconds was found with the less flexible polymers. In the DNA case, it was possible to show that this relaxation time decreases with the inverse shear rate, as in three-dimensional soft solids. These short times suggest that the polymer chains might not be entangled between the surface layers containing neutral polymers.