Investigations of the Electro-Optical Birefringence of Polydisperse Bentonite Suspensions

Colloidal suspensions of bentonite were observed to undergo a negative electro-optical birefringence at low-voltage fields even in dilute suspensions, a phenomenon not reported earlier. Experimental results do not support a previous theory that the sign of birefringence is reversed because of various particle sizes. Although interaction between particles was found to augment this low-voltage anomalous behavior, we believe that in dilute solutions this behavior is caused by some inherent property of the bentonite micelle. This contention is supported by variation in the relaxation times in negative and positive birefringence regions, thus suggesting orientation on two different axes in the two respective regions.