Micellar Solutions of Octyl-18-crown-6

The solution properties of the novel surfactant octyl-18-crown-6 (C-8 Phi(6)) have been investigated with phase diagram, light-scattering, and surface tension measurements. This tenside is made up of an octyl hydrophobic chain attached to a 18-crown-6 ether and cyclic polar head-group that is highly selective for complexing Ki ions. The results show that C-8 Phi(6) produces micellar structures in water and in KCl aqueous solutions, with a radius of about 30 Angstrom. Addition of potassium ions in a molar ratio of 0.4 (KCl/C-8 Phi(6)) increases the hydrophilicity of the surfactant, as shown by the increment of the phase separation temperature, and produces a slight shift in the critical micellar concentration value, as it results from surface tension measurements. The intermicellar interaction parameter alpha, obtained from QELS experiments, has been discussed. Pure C-8 Phi(6) micelles experience attractive intermicellar interactions overimposed to the hard-sphere interactions, while the K+ complexation of the surfactant polar head-groups leads to a decrease of the average attractive component of the interaction. These results show that intermicellar interactions are selectively controlled and modulated by simply adding a proper salt that can be complexed by the polar head-groups of the surfactant.