Introduction

Particle monolayers are formed when small colloidal solid particles adsorb at liquid–vapour or liquid–liquid interfaces. Typical examples are latex monolayers at the air–aqueous salt solution and oil–water interfaces. The interaction between particles within the monolayer is dependent on both the properties of the fluids that make up the interface and on the nature of the adsorbed particles. Therefore, a detailed analysis of the interactions in colloidal monolayers is quite complex and distinctions must be made to take into account the different components of the monolayer.

The total interaction between particles in the monolayer determines their stability behaviour. Thus, examples of stable monolayer systems with particles that remain independent for a long time have been reported, in spite of the fact that in a thermodynamic sense, colloidal particles are not stable because of their great surface to volume ratio. Some monolayer systems showed a triangular structure suggesting the existence of long-ranged particle interactions. In other reported systems, however, it was found that particles are unstable and aggregate to form fractal structures or even became organized to form the so-called mesostructures. When fractal structures appear, the particle interaction potential is short ranged and has a minimum at very short distances.