Surface observation of Langmuir—Blodgett films of polyamic acid alkylamine salts and polyimide by atomic force microscopy and friction force microscopy

The surface morphology of polyamic acid alkylamine salts and polyimide Langmuir—Blodgett (LB) films was observed by atomic force microscopy (AFM) and friction force microscopy (FFM). Three kinds of amines possessing different numbers of alkyl chains were used for the preparation of the polyamic acid salt LB films. In the case of the polyamic acid salt LB films prepared using one-chain alkylamines, the AFM and FFM images afforded an island-like structure which was attributed to the self-aggregation of alkyl chains. The surface structure was not modified at the different deposition surface pressures from 10 to 30 mN/m. Although the polyamic acid salt LB films prepared using two-chain alkylamines afforded uniform surface structure at 10 mN/m, the higher compression up to 30 mN/m changed the LB film into island-like structure. A rather smooth surface was observed for the polyamic acid salt LB films prepared by using three-chain alkylamines. Many domains and boundary regions formed at a low deposition surface pressure tended to be aggregated closely with increasing deposition surface pressure. After conversion of the polyamic acid one-chain alkylamine salt LB films into the polyimide LB films, the surface images showed some defects which corresponded to the bare substrate. The polyimide LB films prepared from the polyamic acid two- or three-chain alkylamine salts afforded uniform surface structure.