Hydrophobicity, Hydrophilicity and Silanes

Whether decorative, protective or functional, coatings must contend with water in the environment. A problem distinct from the issue of wet adhesion and hydrolytic stability of coatings is controlling the interaction of water with a coated surface. Very often the descriptors hydrophobic or hydrophilic are applied to coated surfaces. Although the terms hydrophobic and hydrophilic are casually used, they are usually not defined. A growing number of applications ranging from architectural coatings to aortic stents require a precise control and, therefore, precise definition of substrate interaction with water. Silanes are playing an increasing role in controlling the interaction of water with a surface. Silanes are silicon chemicals that possess a hydrolyti-cally sensitive center that can react with inorganic sub-strates such as glass to form stable covalent bonds and organic substitution that alters the physical interactions of treated substrates (Figure 1). Different than most additives, which have a limited performance range, they can achieve surface properties ranging from hydrophobic to hydrophilic