Kerr effect of Xanthan/DTAB aqueous solutions

The Kerr effect of the Xanthan (charged polyelectrolyte; 113 ppm)/DTAB (surfactant) mixture in aqueous solution was studied. The static Kerr constant (B) and mean relaxation times (tau) values as a function of surfactant concentration (C-DTAB) were determined. The observed birefringence (Deltan) is not a linear function of the electric applied field (E-2). For small E values Deltan grows with E-2 and at a certain field value the birefringence tends to saturate. The addition of small quantities of DTAB lowers B values with respect to the Kerr constant of Xanthan (113 ppm) aqueous solution. The relaxation time of the mixtures is linearly dependent on the applied field and it decreases when DTAB concentration increases. The importance of the equivalent point is signalled. It is supposed that the initial rigidity of the polyelectrolite decreases because of the surfactant addition. Conductivity (sigma) values as a function of surfactant concentration are presented.