liquid crystal display (LCD) devices. However, static charge may accumulate on the surface of the PI film or the PI/component interface due to rubbing. This is often hazardous to the electronic components or LCD devices, as it could lead to shorts or failure of thin fifilm transistors. Therefore, it is desirable that the PI insulating or bilayers is shown in the inset. The reasonably linear correlations alignment layers exhibit reduced surface resistivities within the reveal that the LbL assembly process is uniform and each deposition range of 10⁶~10¹⁰ Ω/² (ohms per square) so that the static charge of PTAA chloride or HPI contributes almost equally to the growth can be dissipated.

Since covalent bonds have high bond energies (320-1000 KJ/ mol) giving rise to better mechanical and thermal properties, we investigated the feasibility of forming covalently cross-linked composite films comprising polyimide and a conducting polymer in order to develop materials with reduced surface resistivities. This was accomplished by making direct use of preformed hydroxylfunctionalized PI (HPI) and poly (thiophene-3-acetic acid) (PTAA). The films are fabricated by casting the blended solutions of the two polymers and also via layer-by-layer (LbL) covalent assembly. In both techniques, the chains are linked through ester bonds between the hydroxyls in the polyimide and the carboxyl groups in polythiophene, ensuring mechanical, chemical and thermal robustness. The composite films fabricated using these two techniques display electrical conductivities suitable for antistatic applications.

Cleaned quartz slides and silicon wafers were immersed in solution of 3-aminopropyltrimethoxysilane in toluene to derivatise the substrate with amine groups. Substrates obtained thus were then soaked alternately in polythiophene acetic acid chloride and polyimide solutions and subsequently rinsed and dried. The assembled structure is shown schematically in Figure 1.

The layer-wise growth of the composite film is demonstrated by UV-visible absorption spectra as shown in Figure 2. Increase of absorption intensities at 448 nm and 258 nm with the number of bilayers is shown in the inset. The resonably linear correlations reveal that the LbL assembly process is uniform and each deposition of PTAA chloride or HPI contributes almost equally to the growth of the film.

Figure 3 shows the profiles of surface resistivity for both the cast and LbL assembled composite films. Upon alternately doping (by exposure to iodine vapour) and de-doping (by thermal treatment) the film, the resistivity decreases and increases, respectively.

When cured at temperatures above 150°C, both types of films suffered conductivity decays that could not be fully restored, but the decay of the LbL film was not as sharp as that of the cast film. Thus, the cast PI composite film was found to be advantageous in its larger surface conductivity but with less stability; LbL assembled PI composite film was better in the stability of its conductivity despite a smaller value. This difference may be due to the more compact architecture of the LbL film compared with the random molecular structure within the cast film.