A substance is hydrophobic if it has the property of hydrophobicity. This means that it cannot be dissolved in or mixed with water. Oil is the most common example of hydrophobic substances.
The word “hydrophobia” comes from the Greek and means phobia of water. There is a disease with that name, which is also called rabies. In chemistry, a substance that has the property of hydrophobicity is called hydrophobic, that is, it repels water, or does not mix or dissolve in it . They are also known as hydrophobic substances.
The hydrophobic molecules that these substances contain are usually nonpolar molecules. Nonpolar molecules are not electrically charged , so they lack attraction. Water, on the other hand, is an electrically polar substance, which has a positive and a negative pole. Not being able to interact with water, nonpolar molecules group together, and the amount of water around them increases. On the other hand, in apolar solvents such as organic solvents , hydrophobic substances dissolve easily.
There are also superhydrophobic materials, which are practically impossible to get wet. The surfaces of these elements are highly resistant to moisture and are considered self-cleaning.
Hydrophobicity and lotus effect
Hydrophobicity is the most characteristic property of hydrophobic substances: the quality that prevents them from being soluble in water . It occurs when a molecule cannot interact with water. Upon coming into contact with it, the nonpolar molecule breaks the hydrogen bonds of the water molecules, forming a network-shaped structure. This gives it more organization than free water molecules and allows them to stick together. A very simple example to observe this phenomenon is to place a few drops of oil in a cup. The oil drops will seek to clump together even if we don’t move the container.
Currently, hydrophobicity is of great scientific interest, especially in the field of nanotechnology, due to the innumerable applications that superhydrophobic elements can have in everyday life and technology.
Since 1963, for example, the “ lotus effect ”, a self-cleaning property of superhydrophobic materials, has been studied. The name derives from the lotus plant, which naturally exhibits this property. To know the hydrophobicity of a surface, its contact angle with the water is measured. The greater the contact angle, the greater the hydrophobicity.
Difference Between Hydrophobic and Lipophilic
The terms hydrophobic and lipophilic are sometimes used interchangeably, as if they meant the same thing. However, they are different concepts. As mentioned before, hydrophobic substances repel or do not mix with water. On the other hand, lipophilic substances are those that have a certain affinity with fats. In any case, most hydrophobic substances, except fluorocarbons and silicones, are at the same time lipophilic. That is, they can also easily bind to fats .
Examples of hydrophobic substances
There are various hydrophobic substances or materials in their natural state, and also artificial. Some of the most common examples are:
- Hydrophobic substances : here we can include oils, petroleum, fats and alkanes, as well as other organic compounds.
- Superhydrophobic materials: coatings, kitchen elements with Teflon, fabrics and paints. They are also used to collect dew or for agricultural irrigation. They are generally made with layers of silicones or fluorocarbons. In nature, these materials are found in some insects. Also, in plants such as lotus, nasturtiums, alchemilla, nopal and cane.
- Tuñon, I. Statistical Molecular Chemistry . 2008. Spain. Synthesis.
- Vollhardt, P. and Schore. organic chemistry . 2006 (5th edition). Spain. Omega
- Fernández Cañete, A. (2003). Study of hydrophobicity and self-cleaning in materials with surface nanotreatments. (Final Degree Project, Autonomous University of Barcelona). Barcelona. Autonomous University of Barcelona.