QELS‐SEF study on poly(lysine) in the extraordinary phase: Effect of electric field strength on the apparent diffusion coefficient

The technique of quasielastic light scattering (QELS) in the presence of a sinusoidal electric field (QELS‐SEF) was used to examine the diffusion of poly(lysine) in the extraordinary phase , which is defined by the anomalously small value in the apparent diffusion coefficient ( D app , obtained by QELS methods) as the added salt concentration is lowered below 10 m M . Spectra were obtained for high‐molecular‐weight poly(lysine) (800,000) in 0.5 m M KCl, using a driving frequency of 90 Hz. It was observed that the linewidth, hence apparent diffusion coefficient ( D SF ), increased with electric field strength ( E ) over the range 6 < E < 30 V/cm. As might be anticipated, the asymptotic limit, D SF ( E = 0), was almost numerically equivalent to D app at this KCl concentration. As E approached the upper limit value of 31 V/cm, the value of D SF approached the high salt (500 m M KCl) value of D app . These observations are discussed in terms of small‐ion dispersion effects.