What is the difference between hydrophilic and hydrophobic?
Contributed by: Hutch W.
Date of publication: September 30, 2011

Hydrophilic and Hydrophobic
Hydrophilic and hydrophobic – lots of people probably don't know what those words mean. Think of hydrophobic as water hating and hydrophilic as water loving. For example, think about what happens when you mix water and oil. The oil does not mix with the water because the water molecules are actually pushing away the oil. But what happens when you mix water and sugar? They like each other. So, the sugar dissolves into the water. Oil is hydrophobic, and sugar is hydrophilic.


Soap Molecules
Let’s look at a soap molecule, for example. A soap molecule has two ends, the head and the tail. The head of a soap molecule is hydrophilic, and the tail is hydrophobic. When added with water, the hydrophilic part of the soap molecule gets to touch and be in water, while the hydrophobic part of the molecule gets to stick up and out of the water.
jhw_soap_molecule.jpg
Figure 1: This is a picture of what a soap molecule does when it is in water. The head of the molecule is in the water, and the tail is sticking up and out of the water.



Uses for Hydrophilic and Hydrophobic Substances
Hydrophilic and hydrophobic substances are useful for many industries; for example, contact eye lenses. They need to be made without any hydrophobic material so that they will stay on the eye. Because the eye is wet, hydrophilic substances are used to make contact lenses. The contact lens is made of a material that works with the water-based secretions in the eye. Also, products like dry bags are made with hydrophobic material. The water slides off the bag and cannot get inside.
jhw_contact_lenses.jpg


Figure 2: This contact lens is made of a hydrophilic material.


Glossary
hydrophilic (adj.) (Greek = ‘water loving’)
Describing a molecule that exerts a strong intermolecular force towards water molecules, usually as the result of ionic or highly polar bonding.

hydrophobic (adj.) (Greek = ‘water hating’)
Describing a molecule that does not exert a strong intermolecular force on water molecules.

molecule
The smallest part of a chemical compound that can exist without it losing its chemical identity.






Citations
Percy Harrison and Gillian Waites. The Cassel Dictionary of Science. London: Cassel, 1997. Print.

Carl H. Snyder. The Extraordinary Chemistry of Ordinary Things. New York: John Wiley and Sons, Inc. 1998. Print.

Tash Hughes. "Hydrophilic Substances." Word Constructions. Tash Hughes, 2007. Web. Sept. 19, 2011.

"Biochemistry." Compton's by Britannica. Encyclopedia Britannica Online School Edition.

Encyclopedia Britannica, Inc. 2011. Sept. 23, 2011. Web.