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. (c) 2005 Elsevier B.V. All rights reserved.