Rings and Loops from Wormlike Micelles in Viscoelastic Solutions from Perfluoro-Surfactants

In a previous publication on the perfluoro-surfactant tetraethylammonium perfluorooctanesulfonate (C₈F₁₇SO₃N(C₂H₅)₄) it was shown that the system forms visocelastic solutions. Electric birefringence measurements on solutions of the systems revealed four different relaxation times (1) (see figure 2). The fastest relaxation time t₁ around one msec was assumed to come from the rotation of small wormlike micelles with a length of about 20 – 30 nm. The t₃ process was assumed to be due to a hindered rotation of somewhat longer rods.

Now, many years later, we have studied the systems with the Cryo-TEM method. The results were very surprising. Rings and loops of wormlike micelles were observed at 10mM instead of the expected small rodlike micelles (see fig. 1). Obviously the system tries to avoid endcaps and forms closed rings. The t₃ process seems to come from the relaxation of the persistence length of long wormlike micelles.