Transient electric birefringence studies of xanthan solutions

Transient electric birefringence studies have been performed on heat denatured xanthan in 4 m urea. The induced birefringence was positive, the Kerr law was obeyed at low field amplitudes and the birefringence saturated at high fields. The orientation mechanism appears to be mainly induced dipolar in character and the magnitude of the induced dipole moment can be explained on the basis of counterion polarization. The molecules behave as independent rods of mean length 0.65 μm with no evidence for ‘hindered rotation’ in moderately concentrated solutions. The molecular rigidity is attributed to extension of the polyanion due to charge charge repulsions or steric hindrance due to the side chains.