Formation of nanorods and nanoparticles of polyaniline using Langmuir Blodgett technique: Performance study for ammonia sensor

Langmuir Blodgett (LB) technique is explored to produce dopant induced nanostructures, especially nanorod and nanoparticles of conducting polyaniline (PANI) emeraldine salt. PANI emeraldine base is doped using camphor sulfonic acid (CSA), p-toluene sulfonic acid (PTSA) and perfluoro-octanoic acid (PFOA). The doped emeraldine salt is deposited using LB on a silicon substrate and is characterized using a transmission electron microscope (TEM), a differential scanning calorimeter, an optical microscope, and IR spectra. TEM analysis reveals the formation of dispersed nanorods of less than 100 nm diameter of PANI-CSA. Dispersed nanoparticles of less than 80 nm diameter are formed for PANI doped with PTSA, while connected nanoparticles are found in the case of PANI-PFOA. Among the three different systems the rod-like nanostructure of PANI-CSA exhibits the highest conductivity. Study of dynamic response (conductivity variation) of these PANI nanostructures when exposed to ammonia vapor predicts that the dispersed rod-like PANI-CSA exhibits the fastest response characteristics (shortest response time and time constant), while the connected nanoparticles of PANI-PFOA show the most sluggish response. The significance is in the design of ammonia sensor of improved characteristics.