Electric Birefringence of Aqueous Solutions of a Rigid Polyelectrolyte. Polarization Mechanisms and Anomalous Birefringence Signals

We present an electric birefringence study of aqueous solutions of an intrinsically rigid polyelectrolyte, xanthan, and of mixed solutions with an oppositely charged surfactant, DTAB. The stationary electric birefringence as well as built-up and decay processes give information on the polarization mechanisms of the polyelectrolyte and on the role played by counterions. By adding a cationic surfactant (DTAB), that replaces the small Nal" counterions of the polymer, we could obtain further insights into the role of condensed counterions in these mechanisms. In some cases, anomalous birefringence signals appear, revealing a new polarization mechanism likely due to field induced interactions within polymer surfactant aggregates.