Hydrophilicity (from ancient Greek ὕδωρ hýdor "water" and φίλος phílos "loving") means water-loving , which means that a substance interacts strongly with water (or other polar substances). The opposite of hydrophilicity is hydrophobicity . According to the IUPAC definition, hydrophilicity is the solvation tendency of a molecule in water. If a surface is very attractive to water, it is also called superhydrophilicity .
Hydrophilic substances are usually water-soluble, but there are also hydrophilic substances that are not water-soluble, e.g. B. some hydrogels or colestipol hydrochloride. For this reason, hydrophilic is not to be equated with water-soluble . Hydrophilic substances are usually either salts (ionic compounds) or polar substances that dissolve well in water, which is also polar.
Hydrophilicity only relates to the interaction with water and not to solubility or the ability to attract and bind water. A substance that can do this is called hygroscopic . Hydrophilic substances are often lipophobic at the same time , so they do not dissolve very well in fats or oils . Substances that are hydrophilic and lipophilic are called amphiphilic ; these include, for example, surfactants . Amphiphilia is a special property of a molecule that carries hydrophobic and hydrophilic groups .
Surfaces can also be hydrophilic. These are always covered by a mostly invisible film of water. Most metals are hydrophilic, as are glass surfaces. Hydrophilic surfaces have contact angles close to 0 ° with respect to water .
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