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The hydrophobic effect depends on the temperature, which leads to "cold denaturation" of proteins. [19] The hydrophobic effect can be calculated by comparing the free energy of solvation with bulk water. In this way, the hydrophobic effect not only can be localized but also decomposed into enthalpic and entropic contributions. [3]
Water on hydrophobic surfaces will exhibit a high contact angle. Examples of hydrophobic molecules include the alkanes, oils, fats, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of oil spills, and chemical separation processes to remove non-polar substances from polar compounds. [2]
In some cases, both hydrophilic and hydrophobic properties occur in a single molecule. An example of these amphiphilic molecules is the lipids that comprise the cell membrane . Another example is soap , which has a hydrophilic head and a hydrophobic tail, allowing it to dissolve in both water and oil.
[3] [1] [7] [8] [9] The Expasy Protscale website lists a total of 22 hydrophobicity scales. [10] There are clear differences between the four scales shown in the table. [11] Both the second and fourth scales place cysteine as the most hydrophobic residue, unlike the other two scales. This difference is due to the different methods used to ...
Substances that are hydrophobic ('water-fearing') do not dissolve well in water, whereas those that are hydrophilic ('water-friendly') do. An example of a hydrophilic substance is sodium chloride. In an aqueous solution the hydrogen ions (H +) and hydroxide ions (OH −) are in Arrhenius balance ([H +] [OH −] = K w = 1 x 10 −14 at 298 K).
Micelles are spheres with a hydrophobic core formed by the non-polar tail of wetting solution molecules and are surrounded by a hydrophilic layer arising from the molecules’ polar heads. [4] Extra wetting solution molecules will be forced to form micelles instead of adhering to the surface, hence the surface tension remains constant.
It is dependent on various conditions which affect each the volume of the hydrophobic chain, the cross sectional area of the hydrophilic head group, and the length of the hydrophobic chain. Things that can affect these include, but are not limited to, the properties of the solvent, the solvent temperature, and the ionic strength of the solvent.
Batch processing a hydrophobic material is a costly and time-consuming technique, and the coatings produced are usually hazy, precluding applications on lenses and windows, and fragile materials. The second class of self-cleaning surfaces are hydrophilic surfaces which do not rely solely on the flow of water to wash away dirt.