**3.4.2.5 Surface morphology study**

40 Electropolymerization

The second stage: includes the loss of the dopant species , SO3 and one OH-radical and H2O of sulfuric acid in the temperature range between 100 oC and 250 oC , the weight loss for this step was found to be(14.68%) which is in good agreement with the calculated value

The third stage: in the temperature range between 250 oC and 400 oC, includes the benzenoid ring and 5 molecules of OH-.The weight loss for this step was found to be (24.8

The fourth step: the remaining part of the polymer decomposition,was found to be 56.17 in

%) which is in good agreement with the calculated value(24. 6%).

the range 400-600 oC and the calculated value is equal to 56.1. c.f. Table 6

Fig. 13. TGA of POCP and POHP.

Table 6. TGA analysis of POCP and POHP

(14.7%)

In most conditions, a homogeneous, smooth and well-adhering brown POCP or black POHP films were electrodeposited on platinum electrode surfaces. The X-ray diffraction pattern shows that the prepared polymers are amorphous as shown in Figure 14 (a and b).

The surface morphology of the polymers obtained at the optimum conditions was examined by scanning electron microscopy. The SEM micrographs show a smooth lamellar surface feature of POCP and a smooth feature with uniform thickness for POHP (c.f., Fig 14 (c and d)).

Fig. 14. XRD and SEM of POCP and POHP adhere Pt surfaces.

Electropolymerization of Some Ortho-Substituted Phenol Derivatives on Pt-Electrode from

rate of hydrogen ion across this modified electrode.

more acidic solutions but it is a good sensor in moderate pH range.

Aqueous Acidic Solution; Kinetics, Mechanism, Electrochemical Studies and Characterization of… 43

From Figure 15 and Table 7, it is clear that the calculated potentiometric slope decreased as the polymer film thickness increased. Where the thin film of POCP electrode shows potentiometric slope equal to 40.7mV/pH and the thickest POCP shows decrease in potentiometric slope equal to 26.60 mV/pH, this decrease may be attributed to the diffusion

But when we use more limited pH range (4-9) as shown in Fig. 16 we noticed that the potentiometric response improved where the potentiometric slope was found to be 56.19 mV/pH for the thin POCP and decreased to 28.11 mV/pH for the thickest POCP film, from this result we noticed that this electrode might not an effective pH sensor for more basic or

Fig. 15. POCP response at different pH values (2-12), the prepared film after different no of

cycles.
