Near surface structure of solvent-free processed polyimide thin film

The surface structure of solvent-free processed poly(pyromellitic dianhydride-oxydianiline) PMDA-ODA is probed using grazing incidence X-ray scattering (GIXS). The films are cured below the (bulk) glass transition temperature of the polyimide. The surface-influenced ordering in the top 10 nm of the film is comparable to that of films which were cast and cured from polymeric precursor solutions in a polar solvent that complexed prior to the conversion to polyimide (PI). This shows that the surface effects are the dominant force to influence the near surface ordering. The crystal orientation closer to the surface has more fiber texture with the b-axis perpendicular to the surface and the a- and c-axes randomly oriented in the film plane. Line shape analysis as a function of X-ray penetration depth and changes in the unit cell dimensions suggests that the distortion is at the ether linkage of the ODA unit. The decrease in crystal distortion and amorphous halo peaks relative to crystalline peaks, as penetration depth decreases, shows that both the quality and quantity of the order improves closer to the air/PI interface.