Hydrophobicity

Hydrophobicity is the tendency of a surface or substance to resist contact or interaction with water. It arises from different causes in molecular solutions and at solid surfaces.

Hydrophobic effect: The tendency of nonpolar molecules or groups to associate in water, driven largely by changes in water’s organization and entropy. It explains why nonpolar molecules cluster rather than remain dispersed in water.
Polarity: An uneven distribution of electric charge within a bond or molecule. Molecular polarity helps explain why water interacts readily with some substances but not others.
Cell membrane: A selectively permeable lipid bilayer surrounding cells and many cellular compartments. Its hydrophobic interior limits the passage of water-soluble substances.
Hydrophilicity: The tendency of a substance or surface to interact favorably with water. It is the opposite tendency, although real surfaces can show mixed water affinities.
Contact angle: The angle at which a liquid interface meets a solid surface, used to characterize wetting. A large water contact angle is a common measure of surface hydrophobicity.
Water: A polar chemical compound with formula H₂O, whose molecules form an extensive hydrogen-bond network. Water’s polarity and hydrogen bonding shape both hydrophobic effects and surface wetting.
Protein folding: The process by which a protein adopts its functional three-dimensional structure. Hydrophobic residues tend to become buried away from water in many soluble proteins.
Amphiphile: A molecule containing both water-attracting and water-avoiding regions. Amphiphiles combine hydrophilic and hydrophobic behavior within one molecule.
Surface free energy: The excess free energy associated with a material’s surface compared with its bulk. Low-energy surfaces often interact weakly with water and resist wetting.
Intermolecular force: An interaction between separate molecules, including dispersion forces, electrostatic interactions, and hydrogen bonding. Competing intermolecular forces determine whether water favors contact with another substance.

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