ABSTRACT
An excellent example of this situation can be seen in the phenomenon that exhibits a very high (sessile droplet) contact angle on a highly hydrated hydrogel, e.g., of gelatin, of a polymer that is known to be highly hydrophilic, as shown in Chapter 23. The very high sessile droplet contact angle of water on a gelatin hydrogel does not mean that gelatin molecules are hydrophobic. A highly hydrated gel cannot be formed with hydrophobic polymers to start with. A very high contact angle water on a gelatin hydrogel is due to the fact that most hydrophilic moieties are located or facing toward the bulk phase of a gel that contains abundant water, and the top surface is populated with the hydrophobic portion of gelatin molecules facing air.
