Influence of some factors affecting the stationary value of the electric birefringence of aqueous solutions of poly(styrene sulphonates) in the presence of 0.01 mol dm–3 NaCl

Abstract

The stationary values of the electric birefringence obtained by applying rectangular pulses to aqueous Na-poly(styrene sulphonates)–0.01 mol dm^–3 NaCl solutions have been studied for five different samples of polyelectrolytes ranging from M_w= 1.8 × 10⁵ to 12 × 10⁵ g mol^–1. The corresponding Kerr constants determined at low electric field strengths were not linearly dependent on the polyelectrolyte concentration in the concentration region explored, which covered both the the dilute and semi dilute regimes. The specific Kerr constant at infinite dilution increased with molar mass to the power 0.7. In the semi-dilute regime a scaling law was found of the form (K/K^*)∼(C/C^*)^0.8, where K^* is the Kerr constant in the dilute concentration regime extrapolated to the critical concentration C^*. This concentration and molar mass dependence cannot yet be fully understood in terms of proposed theories. The study of the field strength dependence of the electric birefringence indicates that smaller parts of the chain contribute to the orientation mechanism responsible for the induced macroscopic anisotropy. It is likely that progressive deformation of the more or less flexible chains by high electric fields also plays a role.