What is the difference between hydrophobic and hydrophilic?
Hydrophobic and hydrophilic are the characteristics of a surface or a chemical and relate to the ability to attract or repel water. A hydrophobic substance or chemical is one which does not "like" water and hence does not dissolve in it. This is the reason a hydrophobic chemical will either float on top of the water's surface or sink down to the bottom, depending on its density. Oil is hydrophobic and has a density less than that of water. This is the reason that when dispersed in water, oil forms a layer on top of it. A hydrophilic substance, on the other hand, likes water and immediately dissolves in it. Alcohols are good examples of hydrophilic substances and readily dissolve in water.
Note that a surface can also be characterized as hydrophobic (such as teflon) or hydrophilic, and such surfaces can be prepared by specific chemical procedures.
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