Abstract: The phase structures of N,Ndimethyl n-dodecyl amine/inorganic acid systems have been investigated by the methods of the pseudo ternary phase diagrams, conductance, polarizing microscope, UV Vis spectra and FTIRspectra. The results can be expressed as follows: (1) With the increase of water phase content, the amine salt aggregated orderly in-different forms such as W/Omicro emulsion, nodus knot catenulate aggregates, layer liquid crystal and O/Wmicro emulsion. (2) In layer liquid crystal, SO₄^2- mainly combined with amine salt cation by two oxygen atoms in bridge. (3) In UV Vis spectrum of layer L.C., there is an absorption about 500 nm and light short circuit" appeared at about 430 nm. These phenomena may be very important for measuring the distance between the layers of the L.C..

Key words: Alkyl amine, Liquid crystal, Aggregation, Pseudo ternary phase diagram