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The electric birefringence anomaly in colloidal and micellar systems

1989; Volume: 93; Issue: 2 Linguagem: Inglês

10.1002/bbpc.19890930216

0005-9021

Miguel Ángel, H. Hoffmann, U. Krämer, H. Thurn,

Material Dynamics and Properties

Abstract Rod‐like micelles of perfluorosurfactants in aqueous solution were examined by using the transient and dynamic electric birefringence method. Tetraethylammoniumperfluoroctanesulfonat shows in the overlap region of the rods between 5 mM and 15 mM up to three different relaxation times τ 1 , τ 2 and τ 3 between a few μs and several ms. A forth very long relaxation time τ 4 (seconds) appears at higher concentrations. The relaxation processes with the time constants τ 1 , τ 3 and τ 4 have a negative birefringence, while τ 2 has a positive sign. In the anomaly region the total birefringence can change sign as a function of the total surfactant concentration and of the field strength. The anomalous behaviour of the time and frequence dependence of the electric birefringence is explained on the basis of intermicellar interaction. It is assumed, that the external electric field induces an additional anisotropic Lorentz‐field, which changes dramatically the local Lorentz‐field around the micelles. As a result both the correlation of the center of masses and the correlation of the rodlike micelles changes. This gives rise to the processes τ 1 , τ 2 and τ 3 . The largest relaxation time τ 4 seems to be due to a deformation and relaxation of a temporary network, which is built by the rodlike micelles.