Amphiphile

An amphiphile is a molecule with both water-attracting and water-repelling regions. This combination lets it interact with water and nonpolar substances.

Hydrophobic effect: The tendency of nonpolar substances to aggregate in water, reducing disruption of water’s hydrogen-bond network. It drives amphiphilic tails to cluster away from water.
Hydrophilic: Having an affinity for water, often through charge or the ability to form hydrogen bonds. An amphiphile’s hydrophilic region interacts favorably with water.
Phospholipid: A lipid with a phosphate-containing polar head and hydrophobic fatty-acid tails. Phospholipids are amphiphiles that assemble into cell membranes.
Surfactant: A substance that lowers surface or interfacial tension, often by accumulating at an interface. Most familiar surfactants are amphiphiles, though the terms describe different properties.
Micelle: A roughly spherical aggregate in which amphiphiles arrange their hydrophilic regions outward and hydrophobic regions inward. It is a common structure formed by amphiphiles in water.
Hydrophobicity: The tendency of a substance to avoid contact with water, commonly associated with nonpolar surfaces. An amphiphile’s hydrophobic region avoids water and favors nonpolar surroundings.
Cell membrane: A selectively permeable boundary surrounding a cell, built mainly from a lipid bilayer and proteins. Its bilayer depends on amphiphiles arranging hydrophilic surfaces around a hydrophobic core.
Hydrotrope: A compound that increases the aqueous solubility of hydrophobic substances, usually without forming conventional micelles. Hydrotropes can aid solubilization without the typical amphiphilic architecture.
Bilayer: A two-layer sheet of amphiphilic molecules with hydrophobic regions between hydrophilic surfaces. Amphiphiles form bilayers when their geometry favors sheets over micelles.
Polar molecule: A molecule with an uneven distribution of electrical charge, producing a permanent dipole. Polar groups often make amphiphile head regions water-compatible.

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