We report a theoretical study on the liquid-liquid interfacial behavior of the species involved in the extraction of Cs+ by a calix[4]arene-crown6 ionophore (L): the free Cs+ Pic(-) and Cs+ Cl- salts, the LCs+ and LCs+ Pic(-) complexes, and uncomplexed L. Based on molecular dynamics simulations, we calculated the free energies changes for migration from the interface into the aqueous and the organic phases, respectively. For free L and for the LCs+ complex, with or without Pie-counterion, an energy minimum is found close to the interface, on the chloroform side, showing that these species behave as surfactants. This contrasts with the uncomplexed Cs+, which diffuses spontaneously from the interface to water and displays no energy minimum. A remarkable counterion effect is found with Pic(-) which displays a high affinity for the interface, while Cl- prefers the bulk aqueous phase. The questions of ion extraction by ionophores, counterions, concentration and synergistic effects in assisted cation transfer through the liquid-liquid interface between immiscible liquids are discussed from the interfacial point of view.