TIME-DEPENDENT BEHAVIOR OF ELECTRIC BIREFRINGENCE CAUSED BY AN AC FIELD SUPERIMPOSED ON A DC FIELD

Transients of electric birefringence are calculated for the electric field E(t) = E0 cos ωt + Ec where E0 and Ec are the strengths of ac and dc fields, respectively, ω is the angular frequency and t is time. A systematic study of the time-dependent behavior of the electric birefringence is presented in the form of numerous graphs for different values of the reduced frequency ω'=ω/D, D being the rotary diffusion constant, and the parameter x=E0/Ec. Each graph is referred to by a particular value of P. which measures the influence of induced dipolar moments with respect to permanent dipolar moments. For high values of x, the well-known result obtained by Morita and Watanabe in the case of a pure sinusoidal field is found again. The interest of that theoretical study is evidenced by the determination of the molecular parameters P and D from the transient and quasi-steady-state. For that latter regime, an original method of phase angle measurements is proposed. © 1990.