There is usually a good correlation between bonding and wetting, but not always. Two different cases where this correlation can break down are: 1) where the surface is wettable but the structure beneath (the "bulk property" of the material) the surface is too weak to have good bond strength and 2) where the surface is not wettable by water but there is still excellent bonding. Two examples of the first are the bonding of PTFE (Teflon®) and the bonding of a waxy or oily surface.
Polytetrafluoroethylene (PTFE) can be plasma treated to give good wetting by water or adhesives; however, when the surface is bonded the measured bond-strength is about half to three-quarters of that obtained by using a commercially acquired sodium etchant. It has been demonstrated by many that the surface structure of PTFE is very weak because there is almost no cross-linking within the material composition. The top layer of the polymer will shear off with the adhesive, even if the surface is treated with plasma to give good and uniform wetting.