Induced Crystallization of Polyelectrolyte-Surfactant Complexes at the Gas-Water Interface

Synchrotron x-ray and surface-tension studies of a strong polyelectrolyte (PE) in the semidilute regime ($\sim 0.1M$ monomer charges) with varying surfactant concentrations show that minute surfactant concentrations induce the formation of a PE-surfactant complex at the gas-solution interface. X-ray reflectivity and grazing angle x-ray diffraction show the complex PE-surfactant resides at the interface and the alkyl chains of the surfactant form a two-dimensional liquidlike monolayer. With the addition of salt (NaCl), columnar crystals with distorted-hexagonal symmetry are formed.