Thin polyimide films prepared by ionic self-assembly

Layer-by-layer electrostatic deposition of polyelectrolytes was used to modify a gold substrate with polydiallyl dimethylammonium chloride and an Ultem-type poly(amic acid) salt. Following deposition, heat treatment converted the poly(amic acid) salt into a polyimide. A decrease in the thin film thickness and a substantial increase in the interfacial contact angle accompanied thermal treatment. Results froth cyclic voltammetry measurements also show that the imidized surface had a decreased dielectric constant relative to an unmodified or a poly(amic acid)-modified interface. Each of these results is consistent with formation of the polyimide. Infrared spectra of the thin films formed by the electrostatic deposition were virtually identical with spectra obtained when the polyimide was formed by the normal spin casting procedure. These results suggest that the electrostatic method for depositing precursors of polyimides followed by heat treatment produces thin films that have structural and physical properties consistent with those of spin cast polyimide thin films.