Seven alkylammonium perfluorocarboxylates (CnH2n+1NH3+CmN2m+1COO-; n + m = 15, n = 2, 4, 6, 8, 10, 12, 14) were synthesized, and their physicochemical properties were investigated. Melting points (mp) and heats of fusion of the solids were determined by differential scanning calorimetry, and the crystal structures were examined by X-ray diffraction analysis. The critical micelle concentration and aqueous solubility for C14H29NH3+CF3COO- and C12H25NH3+C3F7COO- were obtained from the electric conductivity method, while reproducible data were not obtainable for the other five amphiphiles. The size of the molecular aggregates was observed by a phase contrast microscope, and very large aggregates of micrometers in size were found to be formed. These results indicate that the properties of solids and solutions depend not only on hydrocarbon but also on fluorocarbon chains. The time dependence of the electric conductance was traced immediately after dilution of concentrated C4H9NH3+C11F23COO- solution, and the dissociation rate of the aggregates to monomers was obtained over the temperature range from 20 to 45 degrees C. The activation energy of the dissociation process was found to be 76 kJ mol(-1).