Polyimide is an excellent material for LB films due to the following advantages:
1. The polyamic acid as a polyimide precursor has hydrophilicity and can readily form a salt with an amine having a long aliphatic chain through a carboxyl group so that the polyamic acid salt has an amphiphilic property. It is also possible to form amphiphilic polyamides using a higher fatty alcohol diester of tetra-acid.
2. The long-chain-containing polyamic acid salt or polyamide resin is heat-treated at 300 ° C to decompose the fat portion or to be treated with a chemical dehydrating agent to form a thermally stable polyimide. Therefore, the long-chain alkyl compounds are no longer present in LB films, making the thickness of films generally lower than that of other LB films with long-chain alkyl compounds. Because there is no difference between hydrophilic and hydrophobic surfaces in the monomolecular layer, the binding between the monomolecular layers is the same and the arrangement is more compact.
3. The polyimide has various structures, and the properties of the LB film can be adjusted as required.
4. Due to the rigidity of the polyimide chain, after the formation of the LB film, it is easy to retain the molecular orientation characteristic generated in the film formation process.