SOURCE:

Faculty: Physical Sciences
Department: Physics And Industrial Physics

CONTRIBUTORS:

Nkamuo, C. J.
Nwokoye, A.O.C.
Ekpunobi, A. J.

ABSTRACT:

Poly (o–phenylenediamine) (PoPD) was synthesized in hydrochloric acid (HCl) using
potassium dichromate as an oxidant by chemical oxidation method and was also
deposited as thin films on FTO substrates with varying pH values of the reaction
medium by electropolymerization technique using three electrodes. Dihydrogen sodium
phosphate and disodium hydrogen phosphate were used for the phosphate buffer. The
pH 1.0, 1.5, 2.0 and 9.0 was varied by adding phosphoric acid or sodium hydroxide
solutions. 1.2V d.c supply voltage was used with the deposition time of five minutes.
The prepared polymer samples were characterized by UV-VIS spectroscopy, Raman
spectroscopy, SEM, XRD, BET surface area, profilometry and four point probe. The
spectral results indicated that the synthesized PoPD film has a head to tail type
arrangement with the benzenoid and quinoid structures in the phenazine – like
backbone and the absorption bands are Bathochromic shift. The results also show that
the deposited films have low reflectance and the pH values of the reaction medium
affect reflective power of the film produced in such medium. The film deposited at
strong acidic condition of pH of 1.0 has the least reflective power. Also the optical
density ) of the PoPD was determined as 0.64 which revealed (ΔOD that the polymer is
electrochromic. More unevenly dispersed particles of the Poly (o - phenylenediamine)
polymer were observed from the SEM images. The result of the XRD revealed that the
samples are amorphous in nature with several minor peaks centered between 2θ =15°
and 2θ =17 °C . The thermogravimetric analysis (TGA) results showed that a weight
loss occurred. The point of the greatest rate of change on the weight loss curve (point
of inflection) is found to be 275 0C and is the peak temperature of the degradation of
the PoPD. The results obtained from the Raman spectra confirmed that the PoPD
powdered and polymer thin film samples contain phenazine ring ladder – structure
made of quinoids and benzenoids imine units. The values of the electrical conductivity
show that the PoPD samples fabricated are conducting polymers. The electrical
conductivity of the PoPD films decreases towards lower acid medium but increases as
the pH moves towards weak alkaline medium. The results also revealed that the PoPD
powdered polymer is made up of mesopores. Based on the results obtained from Uv-Vis
spectroscopy, the optical density of the film electropolymerized at pH value of 1.5
makes the PoPD a suitable material for use in electrochromic devices (display devices,
monitors, smart glasses / windows).