An amphipathic (a.k.a. amphiphilic) molecule contains both hydrophobic and hydrophilic groups. The hydrophobic group can be a long carbon chain, with the form: CH₃(CH₂)_n, with 4 < n < 16. The hydrophilic group falls into one of the following categories:

1. Ionic Molecules
   • Anionic (with respect to the charge on the group maintaining hydrophobia). Examples are:
     • fatty acids: RCO₂^-Na⁺;
     • sulfates: RSO₄^-Na⁺;
     • sulfonates: RSO₃^-Na⁺.
   • Cationic. These are generically bactericidal and hence non-biodegradable.
2. Amphoteric Molecules. Examples are phospholipids, one of the main constituents of biological membranes: they insulate the cells from the surrounding medium.
3. Non-Ionic Molecules. A small polymer is grafted onto a hydrophobic segment.
4. Block Copolymers
5. Floation additives

See also

• Free surface energy
• Sodium dodecyl sulfate
• Surfactant