**10. Results and discussion**

Figure 7 shows the prepared PVA solution (a), AniHCl\PVA solution (b). And AniHCl\PVA solution irradiated with 50 kGy -radiation doses (c). It shows that the PVA is a soluble in water appears as clear glycerin like material and after the dissolving of AniHCl

Synthesis of Polyaniline HCl Pallets and Films Nanocomposites by Radiation Polymerization 125

wt% AniHCl formed as films. The optical absorption spectra of the irradiated films were measured by using UV–Visible double beam spectrophotometer with air as a reference. The optical absorption is a useful tool to study electronic transitions in molecules, which can provide information on band structure and band gap energy. The basic principle is that photons from UV-visible light source with energies greater than the band gap energy will be absorbed by the materials under study. The absorption is associated with the electronic transitions from highly occupied molecular orbital (HOMO) -band to lowly unoccupied molecular orbital (LUMO) \*-band of electronic states (Arshak and Korostynska, 2002). The electronic transitions between the valence band (VB) and the conduction band (CV) start at the absorption edge, which corresponds to the minimum energy of band gap *Eg* between

Fig. 8. Shows the UV-visible absorption spectra of PANI nanoparticles dispersed in PVA matrix for AniHCl monomer concentrations of (a) 9, (b) 16.7, (c) 23, and (d) 28.6 wt%.

increase of dose but were not very significant.

The spectra of irradiated films reveal two prominent absorption peaks at 315 and 790 nm assigned to the electronic transitions of chlorine Cl– and C=N bond respectively. The absorbance corresponds to the excitation of outer electrons through -\* electronic transitions at the bands of 315 nm (3.95 eV) and 790 nm (1.57 eV). The absorbance increases with the increase of dose and AniHCl concentration and both peaks become sharper with dose increase, indicating the amount of Cl– and polarons formed (represented by C=N) have increased with dose increase. Both peaks shifted slightly to higher wavelengths with the

the lowest minimum of the CB and the highest maximum of the VB.

it shows the oily color and after an irradiation with 50 kGy the color turned to dark green solution, which is the color of polyaniline PANI. While Fig. 7-d shows the pur pallets of PANI-HCl and the formed films of PVA\ PANI-HCl (e). These obtained materials have been subjected for further characterization.

Upon irradiation, the PVA/AniHCl blend films with doses up to 50 kGy, -rays interacts with the PVA binder liberating electrons by photoelectric effect and Compton scattering and followed by ions of H+ and OH– from the bond scission. However, the contribution of these ions to the final product is not very significant. On the other hand, the interaction of -rays with the AniHCl is dominant due to the fact that HCl is easily dissociated to H+ and Cl– ions by radiation. The protonation of aniline monomer by Cl– produced conducting PANI nanoparticles which can be visualized by the change of color of the un-irradiated PVA/AniHCl blend film from colorless to dark green at 50 kGy, as illustrated by the photograph pictures in Figure 5.14. As mention earlier, the formation of C=N double bonds of imines group produced green colour of PANI and the intensity increases with increasing of dose (*see Raman spectrum*). Before irradiation, all PVA/AniHCl blend films were colourless even exposed in air, suggesting the UV-visible radiation has no influence in the formation of conducting PANI. Only after irradiation with the dose between 20 kGy and 50 kGy, the green colour became intense.

Fig. 7. Shows the prepared PVA solution (a), AniHCl\PVA solution (b), AniHCl\PVA solution irradiated with 50 kGy -radiation dose (c), the PANI-HCl pallets (d) and the formed films of PANI-HCl at different radiation doses.

Figure 8 shows the UV-visible absorption spectra of an irradiated AniHCl\PVA composite at different radiation doses at 0, 10, 20, 30, 40, and 50 kGy and for a concentration of 28.6

it shows the oily color and after an irradiation with 50 kGy the color turned to dark green solution, which is the color of polyaniline PANI. While Fig. 7-d shows the pur pallets of PANI-HCl and the formed films of PVA\ PANI-HCl (e). These obtained materials have

Upon irradiation, the PVA/AniHCl blend films with doses up to 50 kGy, -rays interacts with the PVA binder liberating electrons by photoelectric effect and Compton scattering and followed by ions of H+ and OH– from the bond scission. However, the contribution of these ions to the final product is not very significant. On the other hand, the interaction of -rays with the AniHCl is dominant due to the fact that HCl is easily dissociated to H+ and Cl– ions by radiation. The protonation of aniline monomer by Cl– produced conducting PANI nanoparticles which can be visualized by the change of color of the un-irradiated PVA/AniHCl blend film from colorless to dark green at 50 kGy, as illustrated by the photograph pictures in Figure 5.14. As mention earlier, the formation of C=N double bonds of imines group produced green colour of PANI and the intensity increases with increasing of dose (*see Raman spectrum*). Before irradiation, all PVA/AniHCl blend films were colourless even exposed in air, suggesting the UV-visible radiation has no influence in the formation of conducting PANI. Only after irradiation with the dose between 20 kGy and 50

Fig. 7. Shows the prepared PVA solution (a), AniHCl\PVA solution (b), AniHCl\PVA solution irradiated with 50 kGy -radiation dose (c), the PANI-HCl pallets (d) and the

50.0 kGy 40.0 kGy 30.0 kGy 20.0 kGy 10.0 kGy 00.0 kGy

e

Figure 8 shows the UV-visible absorption spectra of an irradiated AniHCl\PVA composite at different radiation doses at 0, 10, 20, 30, 40, and 50 kGy and for a concentration of 28.6

formed films of PANI-HCl at different radiation doses.

a b c d

been subjected for further characterization.

kGy, the green colour became intense.

wt% AniHCl formed as films. The optical absorption spectra of the irradiated films were measured by using UV–Visible double beam spectrophotometer with air as a reference. The optical absorption is a useful tool to study electronic transitions in molecules, which can provide information on band structure and band gap energy. The basic principle is that photons from UV-visible light source with energies greater than the band gap energy will be absorbed by the materials under study. The absorption is associated with the electronic transitions from highly occupied molecular orbital (HOMO) -band to lowly unoccupied molecular orbital (LUMO) \*-band of electronic states (Arshak and Korostynska, 2002). The electronic transitions between the valence band (VB) and the conduction band (CV) start at the absorption edge, which corresponds to the minimum energy of band gap *Eg* between the lowest minimum of the CB and the highest maximum of the VB.

Fig. 8. Shows the UV-visible absorption spectra of PANI nanoparticles dispersed in PVA matrix for AniHCl monomer concentrations of (a) 9, (b) 16.7, (c) 23, and (d) 28.6 wt%.

The spectra of irradiated films reveal two prominent absorption peaks at 315 and 790 nm assigned to the electronic transitions of chlorine Cl– and C=N bond respectively. The absorbance corresponds to the excitation of outer electrons through -\* electronic transitions at the bands of 315 nm (3.95 eV) and 790 nm (1.57 eV). The absorbance increases with the increase of dose and AniHCl concentration and both peaks become sharper with dose increase, indicating the amount of Cl– and polarons formed (represented by C=N) have increased with dose increase. Both peaks shifted slightly to higher wavelengths with the increase of dose but were not very significant.

Synthesis of Polyaniline HCl Pallets and Films Nanocomposites by Radiation Polymerization 127

<sup>4</sup> 1= 09.0 % AniHCl

Fig. 9. Shows the exponentially increment of absorbance at 790 nm due to the formation of

0 5 10 15 20 25 30 35 40 45 50

Dose (kGy)

Fig. 10. Shows the ln (loge) absorbance (ln *y*) vs. dose at different AniHCl concentrations and

0 5 10 15 20 25 30 35 40 45 50

Dose (kGy)

y = 0.0651x - 3.4927 y = 0.0563x - 2.6351 y = 0.0519x - 1.9997 y = 0.0477x - 1.5964

1

2

3

the gradient is used to determine the dose sensitivity *D*0**.** 

1= 9.00 wt % AniHCl 2= 16.7 wt % AniHCl 3= 23.0 wt % AniHCl 4= 28.6 wt % AniHCl


0

0.5

1

1.5

Absorbance at 790 nm

2

2= 16.7 % AniHCl 3= 23.0 % AniHCl 4= 28.6 % AniHCl

2.5

ln absorbance

PANI

The absorbance at 790 nm is due to the creation of C=N double bond of imines group representing the polarons in conducting PANI that gives the green colour. This result is in agreement with previous study carried out by Rao, *et al*. (2000), in which the absorption band for the chemically prepared conducting PANI salt peaking in the range of 420 – 830 nm depending on the degree of oxidation. Earlier Malmonge and Mattoso (1997) found that the absorption band of chemically synthesized PANI was 630 nm and when exposed to Xrays, the peak became sharper and shifted to 850 nm leading to an increase of the conductivity. Recent study by Cho *et al*. (2004) showed that the absorption bands were peaking at 740 – 800 nm for PANI chemically prepared by hydrochloric acid doping and dispersed in PVA matrix.

The unirradiated PVA/AniHCl film showed a broad peak at 315 nm because of the presence of Cl– in AniHCl monomer and no other peak is visible in UV region. The peak increases in intensity at higher concentration of AniHCl monomer. As the dose increases the absorbance at 315 nm increases due to increased formation of chlorine Cl– ions from the dissociation of HCl. Solid phase of HCl was present as the residual of radiation doping of imines group which can be seen from SEM micrographs in Figure 5.4. De Albuqerque, *et al*. (2004) measured UV-Visible spectra of emeraldine salt solution and found two absorption peaks at 320 nm and 634 nm. The presence of the absorption peak at 315 nm has been reported by Azian (2006) for irradiated PVA/AniHCl composites below 20 kGy and was confirmed by the UV-Visible spectroscopy measurements on HCl solution.

#### **11. Quantitative analysis formation of PANI composites**

Figure 9 shows the absorbance at 790 nm band for conducting PANI composites that increases exponentially with dose and can be fitted to the theoretical relationship of the form:

$$y = y\_0 \exp(D \,/ \, D\_0) \tag{3}$$

where *y* is the absorbance at dose *D*, <sup>0</sup> *y* is the absorbance at zero doses and *D*0 is the dose sensitivity parameter.

The exponential increase of absorbance of PANI nanoparticles turns out to be of similar trend with the exponential increase of C=N formation determined from the Raman scattering measurement. This indicates the same phenomenon measured by two different methods produces almost similar result. Thus, the quantitative analysis of polarons could be extracted by either the Raman scattering or the optical absorbance method. The values of *D*0 from the absorbance of PANI composites at different AniHCl concentrations were determined from the inverse of the gradient ln *y* vs. dose, as shown in Figure 9 and plotted for different AniHCl concentrations. The result shows a decrease in the *D*0 value with the increase of AniHCl concentration. Thus, the PVA/PANI composites became more radiosensitive at higher AniHCl concentration as shown in Figure 10. The linear relationship between *D*0 and AniHCl concentration *C* is *D*0 = -0.29*C* + 23.7.

The absorbance at 790 nm is due to the creation of C=N double bond of imines group representing the polarons in conducting PANI that gives the green colour. This result is in agreement with previous study carried out by Rao, *et al*. (2000), in which the absorption band for the chemically prepared conducting PANI salt peaking in the range of 420 – 830 nm depending on the degree of oxidation. Earlier Malmonge and Mattoso (1997) found that the absorption band of chemically synthesized PANI was 630 nm and when exposed to Xrays, the peak became sharper and shifted to 850 nm leading to an increase of the conductivity. Recent study by Cho *et al*. (2004) showed that the absorption bands were peaking at 740 – 800 nm for PANI chemically prepared by hydrochloric acid doping and

The unirradiated PVA/AniHCl film showed a broad peak at 315 nm because of the presence of Cl– in AniHCl monomer and no other peak is visible in UV region. The peak increases in intensity at higher concentration of AniHCl monomer. As the dose increases the absorbance at 315 nm increases due to increased formation of chlorine Cl– ions from the dissociation of HCl. Solid phase of HCl was present as the residual of radiation doping of imines group which can be seen from SEM micrographs in Figure 5.4. De Albuqerque, *et al*. (2004) measured UV-Visible spectra of emeraldine salt solution and found two absorption peaks at 320 nm and 634 nm. The presence of the absorption peak at 315 nm has been reported by Azian (2006) for irradiated PVA/AniHCl composites below 20 kGy and was confirmed by the UV-Visible spectroscopy measurements on HCl

Figure 9 shows the absorbance at 790 nm band for conducting PANI composites that increases exponentially with dose and can be fitted to the theoretical relationship of the

where *y* is the absorbance at dose *D*, <sup>0</sup> *y* is the absorbance at zero doses and *D*0 is the dose

The exponential increase of absorbance of PANI nanoparticles turns out to be of similar trend with the exponential increase of C=N formation determined from the Raman scattering measurement. This indicates the same phenomenon measured by two different methods produces almost similar result. Thus, the quantitative analysis of polarons could be extracted by either the Raman scattering or the optical absorbance method. The values of *D*0 from the absorbance of PANI composites at different AniHCl concentrations were determined from the inverse of the gradient ln *y* vs. dose, as shown in Figure 9 and plotted for different AniHCl concentrations. The result shows a decrease in the *D*0 value with the increase of AniHCl concentration. Thus, the PVA/PANI composites became more radiosensitive at higher AniHCl concentration as shown in Figure 10. The linear relationship between *D*0 and AniHCl concentration *C* is *D*0 = -0.29*C*

exp 0 0 *y y DD* (/ ) (3)

**11. Quantitative analysis formation of PANI composites** 

dispersed in PVA matrix.

solution.

form:

+ 23.7.

sensitivity parameter.

Fig. 9. Shows the exponentially increment of absorbance at 790 nm due to the formation of PANI

Fig. 10. Shows the ln (loge) absorbance (ln *y*) vs. dose at different AniHCl concentrations and the gradient is used to determine the dose sensitivity *D*0**.** 

Synthesis of Polyaniline HCl Pallets and Films Nanocomposites by Radiation Polymerization 129

Fig. 12. Shows the absorbance at 315 nm for the consumption of Cl– in composite

0 5 10 15 20 25 30 35 40 45 50

1= 9.00 wt % AniHCl 2= 16.7 wt % AniHCl 3= 23.0 wt % AniHCl 4= 28.6 wt % AniHCl

Dose (kGy)

versus dose for consumption of Cl– at different AniHCl

0 10 20 30 40 50 Dose (kGy)

1= 9.00 wt % AniHCl 2= 16.7 wt % AniHCl 3= 23.0 wt % AniHCl 4= 28.6 wt % AniHCl

PVA/PANI nanoparticles vs. radiation dose.

Fig. 13. Shows the ln

0 <sup>1</sup> *<sup>y</sup> A* 

concentrations to deduce the dose sensitivity *D*0.





ln (1-y/Ao)




0

0

0.5

1

1.5

Absorbance at 315 nm

2

2.5

3

Fig. 11. Shows the deduction of Dose sensitivity *D*0 of PANI nanoparticles versus AniHC concentration

#### **12. Quantitative analysis of HCl formation**

Figure 12 shows the absorbance at 315 nm band due to the formation of HCl versus radiation dose. The absorbance increases exponentially following the radiation dose increment and leading to saturation at doses higher than 50 kGy, indicating chlorine ions Clwere being consumed for the formation of conducting PANI composites. The relation between the absorbance of Cl- and dose could be fitted to the relation of the form:

$$\mathbf{y} = A\_0 \{ 1 - \exp(-D/D\_0) \} \tag{4}$$

where *y* is the absorbance at the applied dose *D* for each concentration, *A*0 is the difference between the absorbance at 50 kGy and 0 Gy for each concentration. The values of *D*0 for the formation of crystalline HCl at different AniHCl concentrations can be determined from the inverse of the gradient ln 0 <sup>1</sup> *<sup>y</sup> A* versus dose, as shown in Figure 13. The values of *D*0 at different AniHCl concentrations are shown in Figure 14 which can be written in the form

*D*0 = 15.75 C + 14.456.

Fig. 11. Shows the deduction of Dose sensitivity *D*0 of PANI nanoparticles versus AniHC

0 5 10 15 20 25

Concentration % of AniHCl

Figure 12 shows the absorbance at 315 nm band due to the formation of HCl versus radiation dose. The absorbance increases exponentially following the radiation dose increment and leading to saturation at doses higher than 50 kGy, indicating chlorine ions Clwere being consumed for the formation of conducting PANI composites. The relation

where *y* is the absorbance at the applied dose *D* for each concentration, *A*0 is the difference between the absorbance at 50 kGy and 0 Gy for each concentration. The values of *D*0 for the formation of crystalline HCl at different AniHCl concentrations can be determined from the

different AniHCl concentrations are shown in Figure 14 which can be written in the form

����(� � ����(�����)) (4)

versus dose, as shown in Figure 13. The values of *D*0 at

between the absorbance of Cl- and dose could be fitted to the relation of the form:

0 <sup>1</sup> *<sup>y</sup> A* 

concentration

0

5

10

Sensitivity

D0

15

20

25

inverse of the gradient ln

*D*0 = 15.75 C + 14.456.

**12. Quantitative analysis of HCl formation** 

Fig. 12. Shows the absorbance at 315 nm for the consumption of Cl– in composite PVA/PANI nanoparticles vs. radiation dose.

Fig. 13. Shows the ln 0 <sup>1</sup> *<sup>y</sup> A* versus dose for consumption of Cl– at different AniHCl concentrations to deduce the dose sensitivity *D*0.

Synthesis of Polyaniline HCl Pallets and Films Nanocomposites by Radiation Polymerization 131

28.6% AniHCl

Fig. 15. Shows Variation of direct allowed energy gap for AniHCl monomer concentrations of 28.6 wt% at different doses (example for plot of (*α*(*v*)*hν*)2 vs. *hν*. By extrapolation a straight

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6

1 2

1= 28.6 wt % AniHCl 2= 23.0 wt % AniHCl 3= 16.7 wt % AniHCl 4= 09.0 wt % AniHCl 3

4

5

h*v* (eV)

Fig. 16. Shows the band gap energy *E*g vsersus dose for PANI composites at different

10 15 20 25 30 35 40 45 50

Dose (kGy)

line of *α*(*v*)*hν*)2 versus *hν* curves for (*α*(*v*)*hν*)2 = 0)

0.0E+00

1.0E+09

2.0E+09

1= 10 kGy 2= 20 kGy 3= 30 kGy 4= 40 kGy 5= 50 kGy

((*v*) h*v*)2

3.0E+09

monomer concentrations

0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

Eg (eV)

Fig. 14. Shows the dose sensitivity *D*0 of composite of PVA/PANI nanoparticles versus monomer concentration for consumption of Cl–

#### **13. Band gap of PANI nanoparticles**

At high absorption level, > 104 cm-1, the absorption coefficient α(*ν*)*hν* is related to the band gap *Eg* according to the Mott and Davis (1979) using the following relation:

$$\alpha(\nu)l\nu = \mathcal{B}(l\nu - E\_{\mathcal{R}})^m \tag{5}$$

where, *hν* is the energy of the incidence photon, *h* is the Planck constant, *E*g is the optical band gap energy, *B* is a constant known as the disorder parameter which is dependent on composition and independent to photon energy. Parameter *m* is the power coefficient with the value that is determined by the type of possible electronic transitions, i.e.1/2, 3/2, 2 or 1/3 for direct allowed, direct forbidden, indirect allowed and indirect forbidden respectively. The band gap denotes the energy between the valence bands (VB) and the conduction band (CB). The direct allowed band gap at different doses were evaluated from the plot of (*α*(*v*)*hν*)2 vs. *hν*. By extrapolation a straight line of *α*(*v*)*hν*)2 versus *hν* curves for (*α*(*v*)*hν*)2 = 0, the band gap can be determined as shown in Figure 15**.** The results showed that band gap *E*g value decreases with the increase of the radiation dose shown in Figure 16. The decrease in the band gap energy with increasing dose is attributed to more conducting PANI nanoparticles formed and as more polarons in the irradiated composite reduce the band gap between VB and CB for the – \* electronic transition. We found that when the doses were increased from 10 to 50 kGy the band gap decreases from 1.36 to 1.18 eV for 9 wt %, from 1.28 to 1.09 eV for 16.7 wt %, from 1.21 to 1.04 eV for 23 wt % and from 1.12 to 1.00 eV for 28.6 wt %.

Fig. 14. Shows the dose sensitivity *D*0 of composite of PVA/PANI nanoparticles versus

gap *Eg* according to the Mott and Davis (1979) using the following relation:

 

At high absorption level, > 104 cm-1, the absorption coefficient α(*ν*)*hν* is related to the band

0 0.04 0.08 0.12 0.16 0.2 0.24 0.28 Concentration of AniHCl %

() ( )*<sup>m</sup> <sup>g</sup>*

where, *hν* is the energy of the incidence photon, *h* is the Planck constant, *E*g is the optical band gap energy, *B* is a constant known as the disorder parameter which is dependent on composition and independent to photon energy. Parameter *m* is the power coefficient with the value that is determined by the type of possible electronic transitions, i.e.1/2, 3/2, 2 or 1/3 for direct allowed, direct forbidden, indirect allowed and indirect forbidden respectively. The band gap denotes the energy between the valence bands (VB) and the conduction band (CB). The direct allowed band gap at different doses were evaluated from the plot of (*α*(*v*)*hν*)2 vs. *hν*. By extrapolation a straight line of *α*(*v*)*hν*)2 versus *hν* curves for (*α*(*v*)*hν*)2 = 0, the band gap can be determined as shown in Figure 15**.** The results showed that band gap *E*g value decreases with the increase of the radiation dose shown in Figure 16. The decrease in the band gap energy with increasing dose is attributed to more conducting PANI nanoparticles formed and as more polarons in the irradiated composite reduce the band gap between VB and CB for the – \* electronic transition. We found that when the doses were increased from 10 to 50 kGy the band gap decreases from 1.36 to 1.18 eV for 9 wt %, from 1.28 to 1.09 eV for 16.7 wt %, from 1.21 to 1.04 eV for 23 wt % and from 1.12 to 1.00

 

*h Bh E* (5)

monomer concentration for consumption of Cl–

y = -15.73 *C* + 14.456

**13. Band gap of PANI nanoparticles** 

8

9

10

11

Dose sensitivity Do

12

13

14

15

eV for 28.6 wt %.

Fig. 15. Shows Variation of direct allowed energy gap for AniHCl monomer concentrations of 28.6 wt% at different doses (example for plot of (*α*(*v*)*hν*)2 vs. *hν*. By extrapolation a straight line of *α*(*v*)*hν*)2 versus *hν* curves for (*α*(*v*)*hν*)2 = 0)

Fig. 16. Shows the band gap energy *E*g vsersus dose for PANI composites at different monomer concentrations

Synthesis of Polyaniline HCl Pallets and Films Nanocomposites by Radiation Polymerization 133

Fig. 17. Conductivity of the PVA/AniHCl composites versus frequency at different

1

2

3

4

5

1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 f (Hz)

6

1= 0.00% 2= 09.0% 3= 16.7%

7

Fig. 18. The dc conductivity of PVA/AniHCl composites vs. AniHCl monomer

0 10 20 30 40 AniHCl concentration (wt%)

concentrations of AniHCl.

1.0E-08

1.0E-07

1.0E-06

(S/m)

1.0E-05

1.0E-04

1.0E-03

concentration.

1.0E-08

1.0E-07

1.0E-06

1.0E-05

(S/m)

1.0E-04

1.0E-03
