Critical Thinking

CHAPTER in figure 4.0 (b) the plot showed

CHAPTER 4

 

RESULT AND DISCUSSION

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4.1       Characterization
by using Electrochemical Impedance Spectroscopy (EIS)

4.1.1    Impedance analysis

In this analysis, cole – cole plots depicted in
figure 4.0 showed impedance spectra of selected samples. In figure 4.0 (a) the
plot showed incomplete semicircle whereas in figure 4.0 (b) the plot showed a
semicircle with an inclined spike. According to Buraidah, M.
& A. Arof (2011), analysis of the spectra can be divided into two parts as
in low and high frequency regions. At low frequency, inclined spike as shown in
figure 4.0 (b) indicates the effects of blocking electrodes while at high
frequency, semicircle region shown indicates the ionic conductivity at sample
bulk (Buraidah, M. & A. Arof , 2011). Kadir, M., Majid, S., & Arof, A (2010)
stated that ionic conductivity at sample bulk occurred due to the parallel
combination of both bulk resistance and capacitance of the electrolytes. On the
other hand, the inclined spike indicated the polarization of electrode which is
the attributes of diffusion process. In addition, bulk resistance Rb can be
measured from interception of the semicircle and the adjacent line that
corresponding to it. Therefore, the ionic conductivity of electrolyte samples
was measured by using the following formula:

                                  (1)

where
t, is the thickness A is the area of the blocking electrode and Rb is the bulk
resistance polymer electrolyte (Bhargav, 2009).

Based on figure 4.0 (b), the angle of inclined spike is less
than 90o from the real axis. As mentioned by Kadir,
M., Majid, S., & Arof, A (2010) the resulting angle was due to rough
surfaces at the interface of the electrode – electrolyte or inhomogeneity of
salt distribution in sample matrix. Moreover, figure 4.0 also showed the value
of Rb was found to be decreased as the salt content increases. This is due to
the increasing in mobile charge carriers.

 

 

 

 

 

(a)

 

(b)

 

Figure 4.0 Cole
– cole plots of (a) Starch/Chitosan – 2.5wt.% NaI and (b) Starch/Chitosan –
12.5wt.% NaI at room temperature

 

            4.1.2    Conductivity studies

In this study, the conductivity of solid polymer
blend electrolyte obtained was increased with the addition of Sodium salt. The
highest conductivity achieved was at 12.5 wt% of NaI salt which is 2.72 x 10-09 Scm-1. However, further addition of 12.5 wt%
NaI salt decreased the conductivity of the electrolyte. In a previous study, Yusof,
Y., et al. (2014) revealed the highest conductivity achieved was (3.04±0.32)
× 10?4 Scm?1 at 40 wt% of NH4I salt. Similarly, further addition of 40 wt% NH4I
salt decreased the conductivity of the polymer blend – NH4I system. 

Yusof, Y., et
al. (2014) also reported that conductivity of
electrolytes was influenced by the concentration of charge carrier. Therefore,
the addition of salt increases the charge carrier concentration thus increases
the conductivity. In addition, polymer blend as a host also increases the
conductivity of the electrolyte as it provides more complexion sites for ion
migration. Meanwhile, upon addition of salt will effects the conductivity of
the electrolyte due to formation of ions pairs which decreases the free ions
that leads to decrease in conductivity (Khiar & Arof, 2011). The conductivity of solid polymer blend electrolyte with
different composition of NaI salt at room temperature was plotted in Figure 4.1.  

Figure 4.1 Conductivity of
starch chitosan blend solid polymer electrolyte with variation of NaI salt amount.

 

 

 

 

 

 

 

 

 

 

4.1.3    Dielectric analysis

Dielectric studies describe the conductivity
behavior of the solid polymer electrolyte (Khiar & Arof, 2011). The trend of ionic conductivity
in polymer electrolyte was calculated by using the formula of dielectric
constant ?r and dielectric loss ?i as shown as follows:

                        (2)

             (3)

Dielectric constant ?r, represents the
measurement of stored charge in the material while dielectric loss ?i
represents the energy loss due to ion movements when rapid reversal of electric
field polarized (Navaratnam et al., 2015). Zi and Zr are the imaginary and
real part of impedance respectively. Co is the vacuum capacitance whereas ? is
the angular frequency. Figure 4.2 (a) and (b) illustrated the plot of ?r
and ?i versus frequency with variation of salts. The result showed
that at low frequency, both ?r and ?i increases while
decreases at high frequency. This can be explained by the electrode
polarization and space charge effect at low frequency that causes the high
values of both ?r and ?i, con?rming the non-Debye
behavior of the system (Yusof, Shukur, Illias, & Kadir,
2014). Conversely, at high frequency the
duration of electric field reversal occurs rapidly causing the diffusion of ion
is not feasible. Thus, accumulation of charges at the interface of electrode
and electrolyte is decreased (Kumar, Tiwari, & Srivastava, 2012).   

 

(a)

(b)

Figure 4.2 Frequency
dependence of (a) ?r and (b) ?i at room temperature.

 

 

 

 

4.1.4    Dielectric loss tangent

Figure 4.3 depicts the variation of dielectric loss
tangent in all samples of electrolyte system. Based on the results the tangent
peak was shifted at higher frequency with the addition of salt composition (E.Bementa, 2016). This implies to the behaviors of
mobile ions that moves rapidly as the number of carrier ions increases due to
the high conductivity of the system. Therefore, the transport properties were
improved and caused the relaxation time to become shorter (Khiar & Arof, 2011). 
Figure 4.4 was referred as the variation of relaxation time and
conductivity for all samples of electrolyte system. The result showed the value
of relaxation time become shorter as it reach 12.5 wt% of NaI. As studied by Bhargav, Mohan, Sharma, and Rao (2009),
the relaxation time decreased as the salt content increased. This can be
explained by Shukur, Ithnin, and Kadir (2014)
which stated the behavior of relaxation time was due to the effect of ionic
charge carriers that changed in the direction of applied field. 

Figure
4.3 Variation of dielectric loss tangent at
various frequencies for all electrolyte samples.

Figure 4.4 Variation of
relaxation time and conductivity for all electrolyte systems.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4.2       Characterization
by using Fourier Transform Infrared Analysis

 

IR spectroscopy was used to study the interactions
between starch – chitosan and starch/chitosan – NaI. The spectrum of starch and chitosan blend showed interaction at
3288.58 cm-1 where an O – H hydroxyl band was appeared. Yusof,
Y., et al. (2014) reported the same finding where hydroxyl bands of starch and
chitosan originally from 3280 cm-1 and 3354 cm-1 respectively were shifted to
3288 cm-1 when both are blended at (80:20) wt % of starch and chitosan. At
2924.25 cm-1, it can be seen there was a peak appear indicating there is a C –
H stretch of starch and chitosan. As a justification, Mathew, Brahmakumar, and Abraham (2006)
stated that C – H stretch of starch and chitosan were found at 2926 cm-1 and
2925 cm-1 respectively. Furthermore, interaction of starch and chitosan can be
further explained by the peaks appeared at 1557.88 cm-1 and 1644.81 cm-1.This
can be referred to previous study where the C = O (amide I) and NH (amide II)
of chitosan appeared at 1648 cm-1 and 1561 cm-1 respectively, are quite near in
 number (El-Hefian, Nasef, & Yahaya, 2012). Based on information gained, the
interaction was confirmed when the position of C = O (amide I) and NH (amide
II) of chitosan were shifted from 1648 cm-1 and 1561 cm-1 to 1644.81 cm-1 and
1557.88 cm-1 respectively. As suggested by (Xu,
Kim, Hanna, & Nag, 2005) interaction was
occurred between the hydroxyl and amino groups of starch and chitosan
respectively.

 

 

 

On the other hand, the interaction between polymer
blend and salts are showed by the shifting of O – H groups of starch and
chitosan, C = O (amide I) and NH (amide II) of chitosan to a lower wavenumbers. In other words, the increasing of salt
in polymer blend affect the intensity peaks of following groups. In addition of
2.5wt % and 12.5 wt % NaI, the O – H group was downshifted to 3271.50 cm-1 and
3286 cm-1 respectively.

Similarly Yusof, Y., et al. (2014) also reported
that addition of NH4I salt lowers the O – H group of the polymer blend. Regarding  C = O (amide I) and NH (amide II) of
chitosan, addition of 2.5wt % NaI lowers the wavenumber to 1640.07 cm-1 and
1551.55 cm-1 whereas addition of 12.5 wt % NaI lowers the wavenumber to 1644.09
cm-1 and 1556.04 cm-1 respectively. This
interaction indicates the formation of polymer host and salt complex. Figure 4.5
shows the interactions of starch/chitosan polymer and NaI salt at various
compositions.

 

 

 

                                         

(a)                                                         (b)

Figure 4.5 (a) IR spetra for (i) starch – chitosan film (ii) 2.5wt% NaI (iii) 5.0wt%
NaI (iv) 7.5wt% NaI (v) 10.0wt% NaI (vi) 12.5wt% NaI (vii) 15.0wt% NaI in the
range of 2890 – 3390 cm-1 , (b) IR spetra for (i) starch – chitosan film (ii)
2.5wt% NaI (iii) 5.0wt% NaI (iv) 7.5wt% NaI (v) 10.0wt% NaI (vi) 12.5wt% NaI
(vii) 15.0wt% NaI in the range of 1520 – 1770 cm-1

 

 

 

 

 

 

 

4.3       Characterization by using Field Emission
Scanning Electron Microscope (FESEM)

FESEM image shows the surface morphology of polymer electrolyte
samples. Figure 4.6 (a) shows the rough surface of starch – chitosan blend
without addition of salt. This indicates the crystalline phase is present in
the system. This phenomena also reported by Noor, Ahmad, Talib, and Rahman (2010)
in their study where the surface roughness is due to the crystalline phase.
Addition of salt in the polymer blend improved the surface of polymer
electrolyte as it become smoother and reduces the crystallinity by dissociating
and randomly distributed in the electrolyte (Noor et al., 2010).

In this study, FESEM micrograph shows smoother
surface of polymer electrolyte as the amount of salts increased. As a comparison,
starch – chitosan film surface is rough due to less in homogeneity than the
surface system that contain 2.5wt % NaI. This trend was improved continuously
as the amount of salt increases. In addition, Yusof, Illias, and Kadir (2014)
suggested that smooth and homogenous surface of electrolyte film indicates that
polymer blend is miscible with the salt. In this study, electrolyte system
containing 12.5wt % NaI salt in figure 4.6 (f) showed the smoothest surface as
it reflects on its highest conductivity value. According to Shukur, Ithnin, Illias, and Kadir (2013),
the increased in conductivity was due to the increase in the amorphous phase in
the electrolyte system. Moreover, due to addition of salt the structures of the
system become porous. The porosity is the main influences of the ionic
conductivity of an electrolyte as it provide transportation of charges through
pores. Therefore, the higher the amount of salts causes the increment in pore
connectivity as well as increase in ionic conductivity (Yusof, Shukur, et al., 2014).

However, when the salt added is more than 12.5wt %
the morphology showed solid particles were structured out from the surface as
shown as in figure 4.6 (g). This is because the salt has recrystallized due to
decrease in ability of polymer host to accommodate the salt (Yusof, Shukur, et al., 2014). As a result, the charge carriers
were reduced and lead to decrease in ionic conductivity.   

 

(a)

(b)

(c)

(d)

(e)

(f)

(g)

Figure 4.6 FESEM images of (a) starch – chitosan
blend containing (b) 2.5wt% NaI (c) 5.0wt% NaI
(d) 7.5wt% NaI (e) 10.0wt% NaI (f) 12.5wt% NaI (g) 15.0wt% NaI

 

 

 

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