Lithium cations are known to form complexes with the oxygen atoms of poly(oxyethylene) chains. The effect of Li+ on the surface properties of three block-copolymers containing poly(oxyethylene) (PEO) have been studied. Two types of copolymers have been studied, a water soluble one of the pluronic family, PEO-b-PPO-b-PEO, PPO being poly(propyleneoxyde), and two water insoluble ones: PEO-b-PS and PEO-b-PS-b-PEO, PS being polystyrene. In the case of the pluronic the adsorption kinetics, the equilibrium surface tension isotherm and the aqueous/air surface rheology have been measured, while for the two insoluble copolymers only the surface pressure and the surface rheology have been studied. In all the cases two different Li+ concentrations have been used. As in the absence of lithium ions, the adsorption kinetics of pluronic solutions shows two processes, and becomes faster as increases. The kinetics is not diffusion controlled. For a given pluronic concentration the equilibrium surface pressure increases with [Li+], and the isotherms show two surface phase transitions, though less marked than for [Li+] = 0. A similar behavior was found for the equilibrium isotherms of PEO-b-PS and PEO-b-PS-b-PEO. The surface elasticity of these two copolymers was found to increase with [Li+] over the whole surface concentration and frequency ranges studied. A smaller effect was found in the case of the pluronic solutions. The results of the pluronic solutions were modeled using a recent theory that takes into account that the molecules can be adsorbed at the surface in two different states. The theory gives a good fit for the adsorption kinetics and a reasonably good prediction of the equilibrium isotherms for low and intermediate concentrations of pluronic. However, the theory is not able to reproduce the isotherm for [Li+] = 0. Only a semi-quantitative prediction of the surface elasticity is obtained for [pluronic] <= 1 x 10(-3) mM. (C) 2013 Elsevier Inc. All rights reserved.