Effect of the addition of polyelectrolytes on monolayers of carboxybetaines

We have studied the effect of the addition of sodium poly(styrene sulfonate) polymers on the properties of monolayers formed by the adsorption of two carboxybetaines with different number of separation methylenes between their charged groups. Fluorescence and surface tension measurements indicate that above the critical aggregation concentration a surfactant-polymer complex of electrostatic origin is formed in bulk. The complexes have a negative charge that is repelled by the negative charge of the surfactant adsorbed at the interface; consequently, the monolayer seems to be exclusively formed by surfactant carboxybetaines. The high-frequency surface viscoelasticity of the monolayers was studied by surface dynamic light-scattering measurements. The behavior of the dilational elasticity and viscosity is explained by relaxation involving molecular reorientation within the adsorbed layer.