Ammonium perfluorononanoate (APFN) is an anionic surfactant that in water forms liquid crystalline phases (Lyotropic liquid crystal). It is the ammonium salt of perfluorononanoic acid.
The phase diagram of APFN/HO system is delineated by the presence of a lamellar phase and a nematic phase with awide isotropic solution. The nematic phase is of the type I, and the aggregates have a positive and diamagnetic anisotropy. In the presence of a magnetic field, the aggregates align parallel to the field direction. The change of phase at the lamellar-nematic temperature has been ascribed to order-disorder transitions.