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Articles written in Bulletin of Materials Science

• AC conductivity and broadband dielectric spectroscopy of a poly(vinyl chloride)/poly(ethyl methacrylate) polymer blend

Alternating-current (ac) conductivity and dielectric relaxation behaviour of a poly(vinyl chloride)/poly(ethyl methacrylate) polymer blend have been investigated intensively in a frequency range from 1 × 10⁻¹ to 2 × 10⁷ Hz through a temperature range from 300 to 393 K. The variation of σac of pure and polyblend samples showed a plateau region at high temperature and low frequency and this plateau region is decreased with decreasing temperature. Values of the exponent $n$ are less than unity indicative of the correlated barrier hopping for conduction. The values of the exponent $n$ are used to calculate the binding energy (Wm) of the charge carriers. The investigation of the frequency dependence of ε' for pure and polyblend samples showed a dielectric dispersion. The high values of dielectric constant at a low frequency and high temperature are attributed to the effects of space charge due to the electrode polarization. The complex electric modulus (M*) of pure and polyblend samples has been investigated. It is found that the real part of the complex electric modulus, M' is increased non-linearly as the frequency increased and reached the steady state at higher frequencies for all samples. On the other hand, the imaginary part of the complex electric modulus, M'' is characterized by a relaxation peak. The different modes of relaxation, such as interfacial polarization and dipolar relaxation, are detected in low and high frequency regions in the variation plot of M'' against frequency. The activation energy values of both interfacial polarization and α-relaxation are calculated.

• AC conductivity and dielectric relaxation of chitosan/poly(vinyl alcohol) biopolymer polyblend

Polyblend samples of chitosan/poly(vinyl alcohol) (PVA) have been prepared using a casting technique. Scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis measurementsrevealed that chitosan and PVA are compatible with each other. Alternate current (AC) conductivity and dielectric relaxation features of pure and polyblend samples are analysed in the frequency range of 0.1 Hz to 100 kHz covering abroad temperature range from room temperature to 423 K. Variation of AC conductivity, $\rho_{\rm AC}$, of pure and chitosan/PVA polyblend samples is found to be characterized by a plateau region at low frequency and high temperature, and this plateau region increases with increase in temperature. Based on the behaviour of the exponent $s$ $vs$. temperature, AC conductivitydependence on frequency is found to be correlated with overlapping-large polaron tunnelling (OLPT) model. The polyblend samples showed an improvement in their dielectric properties compared to the pure materials. The dielectric constant, $\epsilon '$, of polyblend samples was increased by increasing the content of PVA. The dielectric dispersion was observed in the variation of $\epsilon '$ against frequency for all samples. The high values of $\epsilon '$ for all samples at high temperature and low frequency are attributed to space charge polarization. Also, loss tangent-frequency behaviour of pure chitosan, PVA andall polyblend samples showed two distinguished relaxation peaks with different values of activation energies. The first relaxation peak is termed as interfacial polarization or Maxwell–Wagner–Sillars polarization due to heterogeneity of thepolyblend samples, whereas, the second relaxation peak is termed as $\delta$-relaxation and $\alpha$-relaxation, for pure chitosan and PVA, respectively.

• Characterization and molecular dynamic studies of chitosan–iron complexes

Chitosan–iron (Cs–Fe) complexes are prepared electrochemically in an aqueous acidic medium in onecompartment cell at different times. XRD pattern of Cs–Fe complex samples has been investigated in the range from 5° to 50° and revealed that chitosan is characterized by certain crystalline peaks at 8.73°, 11.92° and 18.96°. In addition, the crystallinity of Cs–Fe complex samples is increased with increasing the content of Fe$^{3+}$. Ultraviolet–visible (UV–Vis) and Fourier transform-infrared (FTIR) spectroscopies have been used to investigate the optical properties of Cs–Fe complex samples. UV analysis showed that pure chitosan is characterized by absorption band at 214 nm resulted from the amide linkages and at 311 nm, as a shoulder which is attributed to intraligand $n$ ${\rightarrow}$${\pi} and {\pi} {\rightarrow}$${\pi}^*$ transitions of the chromophoric C=O group. On the other hand, two new bands are observed in Cs–Fe complex samples at nearly 350 and 389 nm with increasing Fe$^{3+}$ content. The optical parameters of all the samples, such as optical band gap energy ($E_g$), Urbachenergy ($E_U$), dispersion energy ($E_d$) and oscillator energy ($E_o$) have been estimated. It is found that these parameters are significantly affected due to the Fe$^{3+}$ content. FTIR spectra revealed that many of the characteristic bands of pure chitosan have been affected either in its position or its intensity due to the presence of Fe$^{3+}$, confirming that the formation of complex between chitosan and Fe$^{3+}$ is occurred. Dielectric relaxation spectroscopy technique has been used to investigate the dielectric properties of pure chitosan and Cs–Fe complex samples in a wide range frequency and a temperature range extended from RT to 433 K. The investigation showed that the existence of Fe$^{3+}$ resulted in a modification in the dielectric constant (${\varepsilon}'$) and dielectric loss (${\varepsilon}"$) behaviour. Dielectric loss tangent (tan ${\delta}$) showed that pure chitosan is characterized by two different types of relaxations, whereas Cs–Fe complex samples are characterized by only one relaxation process.

• # Bulletin of Materials Science

Volume 45, 2022
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020