Rotational
relaxation times of coumarin 151 dye in Triton X-100 micelle gradually
increase with added NaCl, and is interpreted as the increased
microviscosity due to strong hydration of Na+ ions in the
Palisade layer, causing the entrapped water molecules to form clusters
around the ions. Contrary to this, with added LiCl, rotational
relaxation times initially decrease and then show a sudden increase
beyond about 1 M salt. This is attributed to the complexation of Li+
ions with surfactant oxoethylene groups at lower LiCl concentrations.
At higher LiCl concentrations, the above complexation apparently gets
saturated, and the excess Li+ ions in the Palisade layer
cause a sudden increase in the microviscosity via the strong hydration
of these ions, as it happens with Na+ ions at all the salt concentrations.