Hydrophobic Interactions

When you add some drops of oil to water, the drops combine to form a larger drop. This comes about because water molecules are attracted to each other and are cohesive because they are polar molecules. Oil molecules are non polar and thus have no charged regions on them. This means that they are neither repelled or attracted to each other. The attractiveness of the water molecules for each other then has the effect of squeezing the oil drops together to form a larger drop.
Since it looks like the oil molecules are avoiding the water, this type of interaction is called a hydrophobic interaction. Previous Page
Hydropholbic interactions along with hydrophilic interactions help to determine the three dimensional shape of biologically important molecules and structures such as proteins and cell membranes.