Aqueous colloidal suspensions play an important role in our daily lives. They appear naturally as for example milk or blood, and also find many industrial applications such as for paint, pharmaceutical products and in the oil industry. For understanding the physical properties and also the design of such colloidal systems, the knowledge about the relevant forces is necessary, which can be incorporated in a predictive theoretical model. In aqueous suspensions, repulsive electrostatic forces play a major role through double layer forces even when the particles themselves carry no charge [1]. An important omnipresent force for any colloidal systems are the van der Waals forces [1], which are typically attractive but can be repulsive [2–4] for certain combination of materials. These two forces are essential for understanding the stability of colloids.

Colloidal suspensions are composed of nano-to micro-sized particles. The van der Waals force between such macroscopic bodies arises through the interaction of their constituting atoms. For distances smaller than 10 nm between the objects the fluctuating electromagnetic interaction can be treated as instantaneous, but for larger separations retardation effects need to be considered [5]. An early approach describing the van der Waals force relies on the pairwise summation of the interacting dipoles [6]. Since many-body effects are neglected, the method of pair wise summation cannot be correct and can thus serve only as an approximation, which becomes only valid for rather extreme conditions such as for dilute gases [7] or in the weak interaction limit [8].