Biomedical Engineering Reference
In-Depth Information
The DC conductivity is given by the conductivity values at 0 Hz. The conductivity
for dry starch at 80°C was found to be ~10 -12 S/cm. Figure 9 shows the variation in
conductivity at 0.05 Hz for starch in 51 and 75% humidity. It is observed that the con-
ductivity increases with increasing temperatures and it reaches a maximum at ~80°C.
The profiles look similar for starch containing 51 and 75% humidity. At low tempera-
tures ~ -80°C, the conductivities are nearly the same. The conductivity reaches maxi-
mum value at ~80°C for starch in 75% humidity. The decrease in the conductivity at
temperatures >80°C is due to evaporation of water at higher temperatures.
Figure 9
CoNClusioN
The dielectric characteristics of starch are highly modified in the presence of water.
In the absence of water the dielectric spectra shows a local relaxation at low tem-
peratures regions. Inclusion of water shows the presence of yet another relaxation at
higher temperatures. The relaxation observed at higher temperatures is indicative of
Maxwell-Wagner-Relaxation that arises from the charge carriers accumulated at the
interphase between amorphous and crystalline regions. This indicates that the addition
of water gives rise to both crystalline and amorphous regions in the starch films. The
relaxation frequencies increase with the increase in the water content in the samples
indicating that the presence of water increases the flexibility of the polymer chains.
The conductivities also increase as the water content increases. The decrease in the
 
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