Fabrication of new multilayer heterostructures based on self-assembled layers of poly(amic acid) with various electroactive polymers

Self-assembled films of pyromellitic dianhydride oxydianiline (PMDA-ODA) were fabricated through the alternate adsorption of poly(amic acid) and various polycations including poly(allyl amine) (PAH), polyaniline (PAni), and the tetrahydrothiophene precursor of poly(p-phenylene vinylene) (PPV). In all cases, a linear build-up in thickness with increasing number of bilayers was observed with a high sensitivity of the average bilayer thickness to the ionic strength of the poly(amic acid) solution. By controlling the ionic strength of the PAA solution, the bilayer thickness could be varied from 10 to 100 angstrom, depending on the polycation used. Examination of the self-assembled films of poly(amic acid) and PAni showed that a conductivity of 0.5 S/cm could be achieved prior to conversion of the polyimide, but that the conductivity was drastically reduced when either the ionic strength of the poly(amic acid) solution was increased or when the poly(amic acid) was converted to polyimide. The self-assembly of poly(amic acid) with precursor PPV demonstrated that it was possible to produce a film which can be self-assembled as two ionic precursor polymers and then thermally converted into a film composed of two non-ionic polymers. Advancing sessile water drop contact angle measurements revealed that very hydrophobic surfaces can be generated upon conversion of the PAA/precursor PPV films.