Reversing-pulse electric birefringence of multicomponent systems: The formulation and signal simulation for two axially symmetric components in equilibrium and the appearance of unusual signal patterns

Abstract

This paper consists of two parts on reversing-pulse electric birefringence (RPEB) signal patterns. The first is the theoretical formulation of two axially symmetric models coexisting in equilibrium in solution. The present RPEB theory is based on the original Tinoco–Yamaoka theory with classical electric dipole moments, which was recently modified and extended by Yamaoka, Sasai, and Kohno to include various electric and optical parameters and most importantly the ion-fluctuation dipole moment 〈 m 3 2 〉 1 / 2 along the longitudinal direction of axially symmetric molecules. The theory contains the electric polarizability anisotropy Δ α′, which can be either positive or negative in relation to the shape of components. The overall signal can be expressed as the sum of the fractions of two components in proportions to the coefficient F 1 or F 2 (=1 − F 1). The second part is the simulation of theoretical RPEB curves for the two-component system with various sets of electric and hydrodynamic parameters for hypothetical but interesting cases. In consideration of the decay behavior, calculated decay curves were compared with experimentally conceivable signals, classifying them into three categories according to cases: F 1 > 1, 0 < F 1 < 1, and F 1 < 0. Showing humps and/or dips in profiles the simulated RPEB signal in buildup and reverse transients reveals the mechanism of field orientation and electro-optic properties of molecules in solution. The ratio q = 〈 m 3 2 〉 / k t Δ α ′ is the crucial factor that controls the pattern of RPEB signals. If q value of one component is positive and the other is negative, the simulated RPEB curves are characterized by three cases: q > 0, q < −1, and −1 < q < 0. If q > 0 or q < −1, the resultant patterns are often encountered with experimental signals. If −1 < q < 0, many anomalous signal patterns appears.