A substance is called lipophilic (from the Greek "fat loving", from λίπος lípos "fat" and φίλος philos "loving", "friend") if it can be easily dissolved in fats and oils or if it dissolves well in fats and oils can. Examples of lipophilic substances are petroleum and biogenic oils and fats. According to the IUPAC definition, lipophilicity is the affinity of a substance or molecule to a lipophilic environment.
Lipophilic substances are often at the same time hydrophobic (water-insoluble), i. H. Water repellent. However, lipophilicity is not to be equated with hydrophobicity . Some substances are hydrophobic and lipophobic at the same time , e.g. B. fluorocarbons , silicones and some ionic liquids such. B. BMIIm , which are usually neither water nor fat soluble. Substances that are lipophilic and hydrophilic are referred to as amphiphilic , e.g. B. some alcohols . The opposite of lipophilicity is lipophobia . The octanol-water partition coefficient is a measure of lipophilicity. The HLB value is a measure of the hydrophilic and lipophilic properties of a molecule. Surfactants have lipophilic and hydrophilic molecular areas.
In reality, hydrophobic substances do not repel water. It is rather the case that water-insoluble substances, such as fats, are in a very “orderly state”. In principle, the small water molecules can interact with the large fat molecules, but in order to be able to dissolve fats, the mobile water molecules would have to align themselves very well with the fat molecules. This alignment is very unlikely with a liquid and therefore it is not realized by the molecules. The insolubility of water in fat and vice versa is thus an effect that can be attributed to entropy . Closed systems aim to maximize their entropy. A high entropy corresponds to a high degree of disorder (see also thermodynamics and statistical mechanics ).
Many flavors and vitamins are lipophilic, which is why fat is also known as a flavor carrier, which in the form of butter or a "dash of cream " often enhances the taste of a dish. In addition, oils and fats can improve the absorption and utilization of vitamins. A good example of this are the carotenes as an important precursor of the vitamin A metabolism.
Also diamond is lipophilic and also hydrophobic. This property is used in diamond mines to separate worthless dead rock from diamond. The diamond-containing gravel is mixed with water and then rinsed over surfaces coated with Vaseline. The water film on the wet dead rock prevents the dead rock from sticking to the petroleum jelly. The diamonds, on the other hand, are barely wetted by the water and adhere to the petroleum jelly, from where they are regularly removed. Based on the same principle, diamond jewelry tends more than other gemstones to become contaminated with skin oil after a short period of wear, which can be easily removed with a soap solution.