Langmuir-Blodgett films of polyaniline: Fabrication and transport studies

Abstract

Langmuir-Blodgett films of polyaniline have been fabricated and characterized electrically and optically. We found that the doping level of the films, determined from optical-absorption spectra, can be controlled by adding HCl or camphorsulfonic acid. The addition of neutral KCl salt to the subphase enhances the doping. A systematic effect of the acid on the isotherm was found, and related to the size of the corresponding counter ion. The conductivity of the doped films was studied as a function of film thickness, temperature (77 KϽT Ͻ300 K), and electric field (0ϽFр10 5 V/cm). The low-field conductivity obeyed the behavior ln(T)ϰ Ϫ(T 0 /T) 1/2 over the whole temperature range measured, and ln(F)ϰF 1/(1ϩ) with Ϸ0.9 at higher fields. The results suggest three-dimensional variable-range hopping in a parabolic quasigap, possibly a Coulomb gap.

Polyaniline Langmuir–Blodgett films: formation and properties

“…The thickness of the four-layer film was found to be 12.5 AE 0.5 nm, giving a mean thickness of 31 A ˚per layer. This is in excellent agreement with the XPS results, and is within the range of previous data that reported monolayer film thicknesses between 1.6 nm to 6 nm, depending on the dopant and solvent used to dissolve the PAN, 15,17,18,26 although the methods used previously were somewhat indirect.…”

“…Those used most often include photochemical synthesis, vacuum evaporation, plasma polymerisation and Langmuir-Blodgett (LB) deposition. 4,5,[8][9][10][11][12][13][14][15][16][17][18] The latter has proven particularly attractive due to its simplicity, low cost and the fact that the layer is deposited under well-defined conditions.…”

“…The surface potential of these layers was also measured. 37,38 Stubb and coworkers 15,29 measured the conductivity of doped PAN LB films as a function of film thickness, temperature and electric field. Contractor et al 28,39 deposited PAN LB layers after dissolving the emeraldine base in N-methylpyrrolidone, and investigated the effect of the subphase pH, temperature and counter ion on the isotherm.…”

Layers of Polyaniline Nanotubes Deposited by Langmuir–Blodgett Method

“…Independently of the dopant, Langmuir isotherms of PANI revealed parallel or tilted orientation of the polymer with respect to the water surface. The area values reported for PANI and poly alkoxyanilines doped with small inorganic anions 31,32,46 are of the order of 20 Å 2 for the acidic subphase. The increase of the pH value causes an increase of the mean molecular area up to 60 Å 2 .…”

High-frequency response of polymeric light-emitting diodes

“…The details of the PHT and PANI LB film deposition can be found elsewhere. 5,6 To fabricate ac LEDs, we first deposited seven layers of PANI LB films on an indium tin oxide ͑ITO͒ coated glass substrate ͑sheet resistance less than 10 ⍀/ᮀ͒ followed by 12 or 26 layers of PHT LB films. Another eight layers of PANI LB films were further deposited and as the top electrode aluminum ͑Al͒ was evaporated at a pressure below 10 Ϫ5 Torr.…”