Relaxation of the magnetic field-induced birefringence in ferrosmectics

Ferrosmectics are magnetic liquid crystals which consist of a lyotropic lam ellar phase in which colloidal particles of maghemite are incorporated. The rotational dynamics of the colloidal particles is studied by measuring the linear birefringence relaxation of an oriented ferrosmectic sample submitt ed to a pulse of magnetic field. Two characteristic time scales are found f or the relaxation rate. The shorter ( similar to 5 mu s) is the characteris tic Brou'nian relaxation time of the particles in the isotropic colloidal s uspension (ferrofluid), The slow evolution ( similar to 15 ms), due to the presence of the lyotropic matrix, can be interpreted as due to the adsorpti on of some particles on the surfactant layers, (C) 1999 Published by Elsevi er Science B.V. All rights reserved.