**4.3.2 Fourier Transform Infrared Spectroscopy (FTIR)**

The main fundamental of FTIR is to determine structural information about a molecule. The main principle of FTIR is related to the interferometry which is an optic study. It separates infrared beam of light which serves as light source radiation into two ray beams. Once the beam of infrared is passed through the sample, the molecules would absorb the infrared radiation and then excite to a higher energy state. Thus, the energies associated with these vibrations are quantized; within a molecule, only specific vibrational energy levels are allowed. The amount of energy absorbed at each wavelength was recorded. The frequencies which have been absorbed by the sample are determined by detector and the signal is amplified. Hence, IR spectrum was obtained. FTIR spectroscopy is not only applied in the crystalline region of complexation, whereas the complexation in amorphous phase can also be determined.

FTIR analysis was performed by using Perkin–Elmer FTIR spectroscopy RX 1 in the wave region between 4000 and 400 cm-1. The resolution of the spectra was 4 cm-1 and recorded in the transmittance mode.

Characterization of High Molecular Weight Poly(vinyl chloride) –

amount of lithium cations.

illustrated as below:




**log [**

*σ***( Scm-1 )]**





Lithium Tetraborate Electrolyte Plasticized by Propylene Carbonate 177

electric field is applied. The ionic conductivity is eventually enhanced with these higher amorphous and more flexible polymer chains. The increase in ionic conductivity is also owing to the high dielectric constant of PC. High dielectric constant could allow the greater dissolution of Li2B4O7 and offers a result in increasing the number of charge carriers, promoting the ionic hopping mechanism. The ionic conductivity is reduced to 4.20×10-8 Scm-1 with increasing the PC mass loadings further. This is suggestive of the decrease in effective number of charge carriers for ionic transportation as a result of the domain of short–range ion–plasticizer interactions within the polymer matrix (Stephan et al., 2002). Hence, the ionic conductivity is lower than of other plasticized–polymer electrolytes because of the reduced

Fig. 5. The variation of logarithm of ionic conductivity of plasticized–based polymer electrolytes as a function of weight percentage of PC at ambient temperature.

Upon addition of 20 wt% of PC, the ionic conductivity is rising up further to the maximum level of 4.12×10-6 Scm-1 at room temperature. Again, the contribution from plasticizer is the main attributor for this enhancement of ionic conductivity. The incorporation of plasticizer increases the ionic conductivity through two ways. High plasticizer concentration would open up the narrow rivulets of plasticizer–rich region and lead to greater ionic migration. Moreover, it provides a large free volume of a relatively superior conducting region by reducing the crystalline degree of the polymer electrolytes (Rhoo et al., 1997; Stephan et al., 2000b). General expression of ionic conductivity of a homogenous polymer electrolyte is

0 5 10 15 20 25 30 35 40 45

**Percentage of PC (wt %)**

���� �������� � where �� is the number of charge carriers type of *i*, �� is the charge of ions type of type of *i*, and �� is the mobility of ions type of *i.* Based on the equation above, the quantity and mobility of charge carriers are the main factors that could affect the ionic conductivity of
