Two Particles Immersed In a Medium

FIGURE 19.17 Interaction between two parallel cylinder of radius a and length Inb separated by a distance R. 

The equations for the interactions between particles so far derived in this chapter are based on the assumption that the interacting particles are interacting in a vacuum. If the medium between the particles is no longer a vacuum but a second substance (e.g., water), we have to account for the fact that each particle replaces an equal volume of water. It follows from the assumption of the additivity of the van der Waals interaction energies that Hamaker constant A132 for the interaction between two different particles of substances I and 2 immersed in a medium of substance 3 is 

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