Curing monitoring of phenolic resol resins via atomic force microscope and contact angle

An atomic force microscope was used to investigate Si₃N₄ tip interactions with various curing conditions in three different molar ratios. Also the surface free energy and acid-base character of resol resin were investigated using contact angle analysis. The adhesion force between tip and surface can be calculated from the deflection distance of cantilever and the cantilever spring constant. The acid-base property of surface was characterized by calculating the work of acid-base interaction according to Fowkes' and Good's theory. And then, the adhesion force was compared to surface free energy. The result was that the hydrophobic effect also plays a significant role in adhesion force. At the same curing temperature the adhesion force for the more hydrophobic F/P = 2.5 resol resin was comparatively lower than hydrophilic F/P = 1.3 and 1.9 resin.