hydrofobi

Hydrofobi, or hydrophobicity, is a property of substances that repel water or do not readily mix with it. It arises from nonpolar or low-polarity chemical groups that interact poorly with the polar water molecules, leading to phase separation or water beading on surfaces.

Compared with hydrophilic substances that attract and mix with water, hydrophobic materials display high water contact angles; water tends to form beads on hydrophobic surfaces, and very rough or structured surfaces can become superhydrophobic with contact angles exceeding about 150 degrees and low roll-off angles.

The underlying mechanism is often described by the hydrophobic effect: water reorganizes around nonpolar solutes, and aggregation of nonpolar groups reduces the disruption to the water’s hydrogen-bond network, increasing system entropy. Hydrophobic interactions also play a central role in biology, helping to fold proteins and to organize cell membranes that consist of hydrophobic lipid interiors.

Examples of hydrophobic substances include many organic compounds such as alkanes, fats, oils, and waxes. Materials like polyethylene, silicone, fluoropolymers, and untreated wood exhibit hydrophobic surfaces. Natural examples include certain plant and insect surfaces that shed water.

Applications and measurement: hydrophobic materials are used in waterproof clothing, coatings, anti-fouling surfaces, and oil–water separation technologies, as well as in microfluidic devices. Hydrophobicity is commonly quantified by contact-angle measurements, surface-energy estimates, or partition coefficients such as log P, which indicate the preference of a substance for nonpolar versus aqueous phases.

See also: hydrophilic, amphiphilic, surface chemistry, lotus effect.