ABSTRACT
In this chapter we discuss the affinity of water to surfaces, with special emphasis on the two extreme cases of high and low affinity. Such sympathy or antipathy was described in the previous chapter, but limited to the formation of water monolayers. Here, we consider the case of bulk water in contact with such surfaces. Hydrophilic surfaces become wetted (covered) by water and hydrophobic surfaces exhibit quite the opposite behavior, a phenomenon known as dewetting. Mother Nature provides us with several examples of hydrophobic surfaces, such as the well-known case of lotus leaves, and there is an enormous interest in controlling the water-repellent character of surfaces, with applications in different domains, which can be achieved through an engineered manipulation of such surfaces with artificial coatings. In addition to the intrinsic chemical affinity the structuration of surfaces leads to increased hydrophobicity, which leads to the term superhydrophobicity with almost perfect repellence. This is one of the many relevant activities in nanotechnology. We also explore the curious case of objects (nanoparticles, materials, surfaces, etc.) exhibiting both high and low affinity to water, deserving the adjective amphiphilic.
