Molecular arrangements of self-assembled surfactant films: characterization from atomic force microscopy data.

Abstract

The adsorbed surfactant film molecular arrangement with thickness of approximately 5 nm is determined by measurements of the film dielectric permittivity. Before the advent of atomic force microscopy the dielectric permittivity was a macroscopic parameter, appropriate only for describing uniform environments since its profile was difficult to measure for local intermolecular interactions and its spatial distribution was frequently settled without experimental justification. Here, we show that atomic force microscopy made it possible to measure the dielectric permittivity profile in a scale below 5 nm for adsorbed layers of self-assembled surfactant films in water. The measured values of the film's dielectric permittivity and the film's thickness determine the compactness of the adsorbed film and consequently the presence of water molecules in the film and the conformal structure of the adsorbed molecules.