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 (Dapp, obtained by QELS methods) as the added salt concentration is lowered below 10 mM. Spectra were obtained for high‐molecular‐weight poly(lysine) (800,000) in 0.5 mM KCl, using a driving frequency of 90 Hz. It was observed that the linewidth, hence apparent diffusion coefficient (DSF), increased with electric field strength (E) over the range 6 < E < 30 V/cm. As might be anticipated, the asymptotic limit, DSF(E = 0), was almost numerically equivalent to Dapp at this KCl concentration. As E approached the upper limit value of 31 V/cm, the value of DSF approached the high salt (500 mM KCl) value of Dapp. These observations are discussed in terms of small‐ion dispersion effects.