A hydrophobe is a substance that repels water molecules, they are non-polar and interact well with other non-polar solvents. On the other hand, a hydrophile is a substance which has affinity to water such that it can interact or be dissolved by water.
AmphiphileAn amphiphile is a substance or technically, a chemical compound that is hydrophilic (water-loving) as well as lipophilic (fat-loving). A very good example of this is the very common dishwashing liquid soap.
Both hydrophiles and hydrophobes play a very important role in sustaining life on Earth. How? Think, what if the ground did not absorb water? It would just glide over the Earth's surface due to gravity. Similarly, what if there weren't bodies that could hold water and not absorb them? There would be no water left to survive. Imagine what would happen if a bucket absorbed water instead of holding it, or if your towel repelled water instead of absorbing it. Sounds funny, doesn't it? But this is why these two properties are of great use in day-to-day life.
Let's take a deeper a look at both and compare them for better understanding.
What happens when you pour water on either of the two? When water is poured over a hydrophilic surface it will instantly form droplets and would barely touch the surface. On the contrary, water would be either absorbed or would be spread over a large area of the surface. The hydrophobicity or hydrophilicity of a surface is measured by the 'contact angle'. If this term is alien to you, it simply means the angle formed between a water droplet's edge and the surface beneath it.
In case of hydrophobic substances, the contact angle is ideally 90 degrees or more. However, if the droplet spreads, and the angle drops below 90 degrees, it is considered to be a hydrophilic substance. The intensity to absorb or repel water can vary with different substances possessing different molecular arrangement.
Current research on the topic shows more interest towards superhydrophobic or superhydrophilic substances. The former is considered to have a contact angle of more than 160 degrees, whereas the latter makes a contact angle summing up to less than 20 degrees. Many chemical engineers believe that it is this extremity that is actually useful in engineering. For instance, the water-cooled surface condensers in power plants are superhydrophobic which enable droplets to instantly slide off, allowing new ones to replace them. On the other hand, surfaces that need to be prevented from overheating are often superhydrophilic to ensure maximum contact between the water and the surface. A water-cooled engine is a good example of the latter.
There are almost countless examples of each. As said previously, a bucket made up of plastic is hydrophobic, similarly oils, greasy substances, wax, fats, leaves of plants, etc are listed under hydrophobic surfaces. The leaf of the lotus plant has superhydrophobic properties; it is a water-dwelling plant and possesses a naturally occurring, wax-like superhydrophobic surface which protects the plant from getting waterlogged.
Examples for hydrophilic substances include, detergents, alcohols, salts, cotton, and the like. Superhydrophilicity has been applied in several ways; for instance, it is used to defog or self clean glass, or easily clean oil spots.