The importance of adsorbed cationic surfactant structure in dictating the subsequent interaction of anionic surfactants and polyelectrolytes with pigment surfaces

The adsorption dynamics of the cationic surfactant cetyltrimethylammonium bromide (C16TAB) at the TiO2–water interface was investigated using Fourier transform infrared–attenuated total reflection spectroscopy (FTIR–ATR). Specifically, the response of the adsorbed C16TAB to the anionic surfactant sodium dodecyl sulfate (SDS) is used to discern the structure of the adsorbed C16TAB at the hemimicelle concentration (HMC). In this low concentration regime C16TAB is shown to adsorb as isolated clusters with a ‘defective’ bilayer structure. However, these bilayer structures can be effectively transformed into monolayer structures through the interaction with the non-adsorbing polyelectrolyte sodium polyacrylate (NaPA). It is shown that the structure of the adsorbed C16TAB layer, and not the amount of adsorbed surfactant, dictates the subsequent adsorption of anionic species on negatively charged TiO2 particles.