Surface Interactions in Nonvacuum Media

The equations for surface interactions given above were derived for the situation in which the interacting units were separated by a vacuum. Obviously, for practical purposes, that usually represents a rather unrealistic situation. Real life dictates that in all but a few situations, interacting units be separated by some medium that itself contains atoms or molecules that will impose their own effects on the system as a whole. How will the relevant equations be modified by the presence of the intervening medium  

Qualitatively, the preceding discussion of surface interactions tells us that free surfaces are inherently unstable and will usually experience a net attraction for similar surfaces in the vicinity. The practical repercussion is that if only the van der Waals forces were involved, systems involving the formation and maintenance of expanded interfaces would all be unstable and spontaneously revert to the condition of minimum interfadal area, thereby making impossible the preparation of paints, inks, cosmetics, many pharmaceuticals, many food products, emulsions of all kinds, foams, bilayer membranes, etc. It would be a decidedly different world we lived in. In fact, life as we know it (or can conceive of it) would not exist Obviously, something is or can be involved at interfaces that alters the simple situation described above and makes things work. In the following chapters we will introduce other actors that allow nature (and humankind, when we re lucky) to manipulate surfaces and interfaces to suit our purposes. 

Dipole, Induced Dipole, and Hydrogen Bonding (Acid-Base) Interactions 

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