Ammonium perfluorononanoate (APFN) is an anionic surfactant that in water forms liquid crystalline phases (Lyotropic liquid crystal).

The nematic phase is of the type I, and the aggregates have a positive and diamagnetic anisotropy.

The change of phase at the lamellar-nematic temperature has been ascribed to order-disorder transitions.

It has recently been shown that the lamellar phase of the APFN/2H2O system form multilamellar vesicles under shear rate.

[2] In 2020, a California bill was passed banning APFN as an intentionally added ingredient from cosmetics.