3.1. Electrochemical synthesis of PPy nanowires
3.1.2. Effects of parameters on electrochemical polymerization of polypyrrole
After the first PPy nanowires synthesized, we continued to study some parameters which have strong influence on morphology and electrical properties of PPy products.
0.000.02 0.040.06 0.080.10 0.120.14 0.160.18 0.200.22 0.240.26 0.280.30 0.320.34 0.36
0 30 60 90 120 150 180 210 240 270 300 330 360 390
Current density [mA/cm2 ]
Time [s]
Saturated current density (mA/cm2)
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i. Effect of concentration of pyrrole
Different volumes of pyrrole monomer were added to 50 mL electrolyte containing LiClO4 0.1M, PBS (pH=7) as shown in the table 3.1, respectively.
Pyrrole(mL) 0.1 0.3 0.5 0.7 0.9 1 1.2
Jsat.10-3 (mA/cm2) 1 1.8 17 6.9 3 9 6 Table 3.1. Current density (mA/cm2) vs added volume of pyrrole monomer (mL).
In this work, we tried to apply different quantity of pyrrole in 50 mL electrolyte solution containing LiClO4 0.1M, PBS (pH=7). The current density, recorded by using different concentration of Pyrrole monomer from the current density vs time curve, proves that 0.5 mL of pyrrole monomer will give stronger density value or smaller resistance of the membrane, shown in Fig 3.1.
Figure 3.4. The saturated current density of the electrochemical curve vs.pyrrole monomer concentration.
The scanning electronic microscope images (SEMs) shown in figure 3.5 are also in good agreement with that found in current density curve.
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Figure 3.5. SEM images of PPy structures synthesized at different added volume of pyrrole. (a) 0.1 mL; (b) 0.3 mL; (c) 0.5 mL; (d) 0.7 mL; (e) 1 mL; (f) 1.2 mL.
e f
c d
a b
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At low concentration of pyrrole monomer (0.1-0.3 mL), PPy formed straggling on surface’s electrode, figure 3.6 (a),(b). It can be seen that at 0.5 mL, PPy nanowires grow over electrode with evenly diameter and length of a few m, figure 3.6(c).
When the concentration of monomer increases far from 0.5 mL point, PPy chain grows too fast, hard to control, leading to the formation of crowd, clusters and cauliflowers form, figure 3.6 (d),(e),(f).
ii. Effect of concentration of gelatin
A volume of 50 mL electrolyte contains LiClO4 0.1M, PBS (pH=7), 0.5 mL pyrrole with different percentage weight of gelatin was prepared in table 3.2, respectively.
Gelatin %wt 0 0.02 0.04 0.08 0.12 0.16 0.2
jsat 0.002 0.003 0.012 0.020 0.015 0.018 0.018 Table 3.2. Current density (mA/cm2) vs different concentration of gelatin (%wt).
Figure 3.6. The current density recorded vs. different concentration of gelatin.
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Figure 3.7. SEM images of PPy structures potentiostatically synthesized at different gelatin concentration. (a) 0%; (b)0.02%;(c) 0.04%; (d) 0.08%; (e) 0.12%;(f) 0.16%.
(a) (b)
(c) (d)
(e) (f)
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Fig 3.6 presents the current density, recorded by using different gelatin concentration (in 50 mL electrolyte, LiClO4 0.1M, PBS, pH = 7 and 0.5 mL pyrrole).
The Fig 3.6 shows that, the maximum value of current density is observed at 0.08% wt of gelatin, indicating the best conductivity of obtained PPy membrane
It can be seen clearly that when electrochemical synthesis taken place in the absent of gelatin, only cauliflower form was obtained. It might be explained that the polypyrrole chains were grown randomly in orientation and size, leading to form clusters as shown in figure 3.7(a).
At low concentration (<0.08%wt), gelatin was not close enough to form the mold for polymer to grow, figure 3.7 (b), (c).
At specific concentration (0.08%), the gelatin molecules bonded together to create the soft molds. As a result, the PPy nanowires, as seen in Fig 3.7 (d), were around 50 nm of diameter, and very consistent on the surface of the electrode.
When the gelatin quantity becomes more concentrated (greater than 0.08%), a cross-link among the gelatin peptide molecules occurs to form helix, islands on which polypyrrole synthesized, leading to the formation of crowds of PPy, figure 3.7 (e),(f).
iii. Effect of Reaction time
To investigate the impact of reaction time, all parameters were kept unchanged while the potentiostat voltage was swept on the electrode from 200 seconds to 1600 seconds..
Reaction time (s) 200 400 800 1000 1200 1600
jsat (mA/cm2) 0.001 0.02 0.012 0.014 0.014 0.018
Table 3.3. Current density (mA/cm2) vs Reaction time (second).
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A volume of 50 mL electrolyte containing LiClO4 0.1M, PBS (pH=7), 0.5 mL pyrrole in which the polymerization was occurred in different times as shown in table 3.3
Figure 3.8. The current density recorded vs. different sweeping (reaction time).
Figure 3.8 presents the current density recorded versus different reaction time.
The figure showed that, the maximum obtained value of current density was observed when the reaction time was 400 seconds. Same conclusion was achieved as the scanning electronic microscope was performed with corresponding samples, Fig 3.9.
When the reaction is too short, the monomers don’t have enough time to attach together at applied voltage to form the nanowires. However, when the polymerization is too long, the nanowires can bond together to form the clusters, then membrane with cauliflower structure.
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Figure 3.9. SEM images of PPy structures potentiostatically synthesized at different reaction time. (a) 200s; (b) 400s; (c) 800s; (d)1000s; (e) 1200s; (f) 1600s.
(a) (b)
(d) (c)
(e) (f)
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In summary, the proper condition used to prepare PPy nanowires is 0.5 mL pyrrole, 0.08% wt gelatin and 400 s of reaction time. A number of experiments were carried out under the same condition to test the reproducibility.
Figure 3.10. Morphologies of PPy nanowires prepared at optimized condition.
Fig 3.10 shows that all the PPy products synthesized at the proper condition were in nanowire-like form. The surface of PPy nanowires is fine and smooth, exhibiting relatively high quality. The nanowires have an average diameter of about 50-70 nm, indicating that the technique for PPy fabrication is reproducibility and can be used for DNA application.
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