Fluorinated aromatic polyimide films were treated by pulse electrical discharges formed in water or isopropanol. The relative permittivity, measured in large domains of frequencies and temperatures by broadband dielectric spectroscopy, slightly decreased after plasma discharge in both types of liquids. The dipolar relaxation calculated by Arrhenius equation showed that the liquid plasma treatment decreases the rotational potential energy barrier for non-cooperative motions of dipoles, as a consequence of an increased free volume of plasma exposed films. Higher values of hardness, Young's modulus, and an improved elongation were also measured for the plasma treated samples, indicating molecular rearrangements that occur after plasma treatment.