Effect of pH on Formation of Polyaniline Monolayer

  • Siti Amira Othman
  • Shahidan Radiman
  • Irman A.Rahman
  • Khoo Kok Siong
  • Md Soot Hj Ahmad
Keywords: PANI-EB, Monolayer, Langmuir Blodgett, pH, Pressure


Recently Langmuir Blodgett (LB) monolayer has been considered by various researchers, as a potential technique for the production of ultra thin films with control molecular orientations. LB films based on conducting polymer are attractive candidates for a variety of applications such as biosensors, ion sensors, integrated optics and molecular electronics devices. Decrease in the pH of the sub-phase increases the level of doping (protonation) of polyaniline emeraldine base (PANI-EB). This research intends to study the effect of pH on formation of PANI-EB monolayer to determine the stability of PANI-EB monolayer that formed in acidic subphase that can be seen through pressure (π) – trough area (cm2) by using Langmuir Blodgett (LB) trough. Methods to prepare monolayer are powder method, liquid homogeneous method, sub-phase preparation method and monolayer formation method. For PANI's effect in different pHs (1, 3, 5, 7), U.V.- visible spectrum can be seen above 300nm which showed there were π-π* transfer in the benzenoid chain of polyaniline which indicated that polyaniline has been protonated when an acidic sub-phase was employed for spreading the monolayer, in contrast to the LB monolayer spread on neutral sub-phase. From the π – cm2 graph study, stability of monolayer formation could be achieved in injection of 750μl with surface pressure 12 mN / m and barrier speed 10cm2 / min. Liquid phase could be seen at trough area 170-72 cm2, where polyaniline molecules are still in the random state. Whereas, solid phase (70-60 cm2) were found to have linear relationship between π and cm2. Eventually the collapse pressure, πc is reached because of the force exerted upon it became too strong. FTIR spectra proved there was a distinct decrease in intensity with an increase in pH. As a conclusion, pH value plays a vital role in formation of uniform, thin and good control of PANI- EB monolayer.