Structures of water-insoluble complexes of polyethyleneimine (PEI) and fluorinated acids, varying in chain length from 4 to 16, were examined via contact angle measurements, X-ray diffraction, and infrared spectroscopy. The wettability of complex surfaces was shown to decrease with increasing chain length. The surface energy of the complexes can be adjusted in the range from about 19 to 9 mN/m. Complexes of PEI with perfluorobutanoic acid and perfluoropentanoic acid are amorphous. Complexes with perfluoroheptanoic acid, perfluorodecanoic acid, and perfluorododecoanoic acid are mesomorphous, while the complex with perfluorohexadecanoic acid is partially crystalline.