Ultra-thin composite films from polyimide and electroactive polymer through covalent molecular assembly

Soluble polyimide with hydroxyl pendant groups (HPI) and poly(thiophene-3-acetic acid) (PTAA) were synthesized and used to fabricate a composite film through layer-by-layer (LBL) molecular assembly. The interlayer linkage is established through esters formed between the hydroxyls from HPI and carboxylate groups from PTAA. The LBL assembly was carried out on a quartz slide or silicon wafer surface-modified with 3-aminopropyltrimethoxysilane. Fourier-transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses both confirmed the occurrence of interlayer covalent bonding. Linear increase in UV-vis absorption confirmed LBL growth of the film. After 6-bilayer construction, the composite film showed a reduced surface resistivity compared with that of the bare quartz slide and HPI cast film. Exposure to iodine vapor resulted in a further reduction in surface resistivity of the composite film. The film also showed good thermal stability.