Dielectric properties of aromatic polyimide films treated by nanosecond pulsed electrical discharges generated in distilled water were evaluated with respect to permittivity and its dependency on discharge time. The relative permittivity of the polyimide films decreased after treatment by water plasma. The largest decrease was observed after a short discharge time, from a value of 3.6 for the untreated sample to 1.92 for the 10 min plasma treated samples. XRD analysis has shown a slight increase of the degree of intermolecular ordering and stronger π-π interactions during plasma treatment over shorter periods of time. However, the distance between the chains was also increasing, giving rise to an increased free volume. This effect may be responsible for the decrease of the relative permittivity of the polymer film.
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