Fabrication and structural analysis of aromatic polyimide ultra-thin films with different fluorine contents

The structural characterizations of aromatic polyimide (PI) ultra-thin films with different fluorine contents were studied. Three types of polyamic acid (PAA) were produced from polymerization of biphenyl dianhydride (BPDA)/4,4′-oxydianiline (ODA), BPDA/2,2′-bis(trifluromethyl)benzidine (TFDB), and 4,4′-(hexafluoro isopropylidene)-diphthalic anhydride (6FDA)/TFDB in N,N-dimethylacetamide (DMAc). Polyamic acid alkyl salts (PAAS) using O,O′,O″-trihexadecanoyl-triethanolamine were transferred onto a Si-wafer substrate to prepare Langmuir–Blodgett (LB) films. The behaviors of PAAS monolayers at the air/water interface were confirmed with π–A isotherms and Brewster Angle Microscopy (BAM) images. The behaviors of PAAS monolayers at the air/water interface depend on the fluorine contents. As there is more fluorine in the main chain of PAAS, the area per molecule of each monolayer was increased. The structure of PAAS LB films with 10, 20, 30, and 40 layers on a substrate were investigated by UV–vis spectroscopy, X-ray diffraction (XRD), X-ray reflectivity, and IR spectroscopy. The obtained PAAS LB films were imidized with a thermal treatment at 300 °C. The imidization of PI ultra-thin film was identified by IR spectrum. Atomic force microscopy (AFM) images showed that the particle size of PI ultra-thin films on a Si-wafer were about 7–25 nm.