Field strength dependence of the electric birefringence of potassium polystyrenesulfonate solutions

Abstract

AbstractThe electric birefringence of potassium polystyrenesulfonate (KPSS) in water and dioxane–water mixtures is proportional to the square of the field strength for limiting low fields. Saturation of the birefringence is observed at higher field strength. This effect is the more pronounced, the lower the polyelectrolyte concentration. The specific Kerr constant decreases with increasing polyelectrolyte concentration and with increasing dioxane content. On the other hand, the electric birefringence of KPSS in glycerol–water and ethylene glycol–water mixtures is related to the field strength E by the equation, Δn/c = KEn, where c is the polyelectrolyte concentration, and K and n are constants. The exponent n changes from 1.05 to 1.70 in the range of the concentration studied (1.71 × 10−4−1.01 × 10−3 g./cm.3) in 50.9% glycerol–water. The deviation from the Kerr law is the more marked, the larger the fraction of glycerol. Alternatively the two‐term equation, Δn/c = AE + BE2, reproduces the data fairly well. The coefficient A decreases with increasing polyelectrolyte concentration in 50.9% glycerol–water, whereas B initially increases, reaches a maximum, and then decreases. The appearance of the first‐power term can not be explained by any existing theories of electric birefringence.