Impurity effects on adhesive energies

Some simple arguments are made about the effect of impurities on adhesive interactions at solid junctions. A universal adhesive force relation is derived for brittle adhesion. The adhesive binding energy, ΔE, is an important parameter in brittle adhesion forces. ΔE has also been shown by others to be important when there is plastic flow. We found that impurity effects on ΔE are determined by the segregation energies to the junction and to the free surfaces. At low temperatures, if it is energetically more favorable for impurities to segregate to the surfaces than to the junction, then the impurities will decrease ΔE. The converse is also true. For example, for self junctions which are in registry, ΔE is decreased if surface segregation is exothermic and increased if it is endothermic. These segregation energy relationships are consistent with the results of a number of experiments on the effects of impurities on adhesion forces and grain boundary embrittlement.