  Lanthanum phosphate (LaPO4) nanorods dispersed in the non-aqueous solvent of
ethylene glycol form a system exhibiting large intrinsic birefringence, high
colloidal stability and the ability to self-organize into liquid crystalline
phases. In order to probe the electro-optical response of these rod dispersions
we study here the electric-field-induced birefringence, also called Kerr
effect, for a concentrated isotropic liquid state with an in-plane a.c.
sinusoidal electric field, in conditions of directly applied (electrodes in
contact with the sample) or externally applied (electrodes outside the sample
cell) fields. Performing an analysis of the electric polarizability of our
rod-like particles in the framework of Maxwell-Wagner-OKonski theory, we
account quantitatively for the coupling between the induced steady-state
birefringence and the electric field as a function of the voltage frequency for
both sample geometries. The switching time of this non-aqueous transparent
system has been measured, and combined with its high Kerr coefficients and its
features of optically isotropic offstate and athermal phase behavior, this
represents a promising proof-of-concept for the integration of anisotropic
nanoparticle suspensions into a new generation of electro-optical devices.
