The structure of self-assembled surfactant films at the solid/liquid interface is investigated using Fourier transform infrared spectroscopy/attenuated total internal reflection spectroscopy (FT-IR/ATR) techniques, to understand the structural transitions taking place at the interface. The structural transitions, as determined from the ATR technique, are correlated to the change in interfacial properties, such as contact angle and zeta potential, and the presence/absence of steric repulsive barriers in the presence of surfactants at the interface. A transition to randomly oriented self-assembled spherical aggregates appears to take place at concentrations below the bulk critical micelle concentration, directly from hemi-micelles, without the formation of bilayers. The onset of steric repulsive forces in the presence of surfactants was found to occur within the same concentration range, where the transition of the interface structure to predominantly spherical aggregates occurs.