M. V. N. Ambika Prasad

Synthesis, characterization and low frequency a.c. conduction of polyaniline/fly ash composites

In situ polymerization of aniline was carried out in the presence of fly ash (FA) to synthesize polyaniline/ fly ash (PANI/FA) composites. The PANI/FA composites have been synthesized with various compositions (15, 20, 30 and 40 wt%) of FA in PANI. The composites, thus synthesized have been characterized by infrared spectroscopy and X-ray diffraction. The morphology of these samples was studied by scanning electron microscopy. Further the a.c. conductivity of these composites have been investigated in the frequency range 102–106 Hz. The presence of polarons and bipolarons are made responsible for frequency dependence of a.c. conductivity in these composites. The Cole-Cole plots indicate clear shift in the distribution of relaxation times as the wt% of FA in PANI changes. These composites show almost symmetric semicircles of Cole-Cole plots indicating the Debye-type relaxation in their polarization response.

Synthesis, characterization and conductivity studies of polypyrrole-fly ash composites

In situ polymerization of pyrrole was carried out in the presence of fly ash (FA) to synthesize polypyrrole-fly ash composites (PPy/FA) by chemical oxidation method. The PPy/FA composites have been synthesized with various compositions (10, 20, 30, 40 and 50 wt%) of fly ash in pyrrole. The surface morphology of these composites was studied with scanning electron micrograph (SEM). The polypyrrole-fly ash composites were also characterized by employing X-ray diffractometry (XRD) and infrared spectroscopy (IR). The a.c. conductivity behaviour has been investigated in the frequency range 102–106 Hz. The d.c. conductivity was studied in the temperature range from 40–200°C. The dimensions of fly ash in the matrix have a greater influence on the observed conductivity values. The results obtained for these composites are of greater scientific and technological interest.

Humidity sensing behaviour of polyaniline/magnesium chromate (MgCrO 4 ) composite

Abstract‘In situ’ polymerization of polyaniline (PANI) was carried out in the presence of magnesium chromate (MgCrO4) to synthesize PANI/ceramic (MgCrO4) composite. These prepared composites were characterized by XRD, FTIR and SEM, which confirm the presence of MgCrO4 in polyaniline matrix. The temperature dependent conductivity measurement shows the thermally activated exponential behaviour of PANI / MgCrO4 composites. The decrease in electrical resistance was observed when the polymer composites were exposed to the broad range of relative humidity (ranging between 20 and 95% RH). This decrease is due to increase in surface electrical conductivity resulting from moisture absorption and due to capillary condensation of water causing change in conductivity within the sensing materials. PANI / MgCrO4 composites are found to be sensitive to low humidity ranging from 20 to 50 % RH.

Dielectric Spectroscopy of Polyaniline/Stanic Oxide (PANI/SnO2) Composites

Conducting polyaniline/Stanic oxide (PANI/SnO 2 ) composites have been synthesized by insitu deposition technique by placing fine graded SnO 2 in polymerization mixture of aniline. The PANI/SnO 2 composites have been synthesized with various compositions viz., 10, 20, 30, 40 and 50 wt % of SnO 2 in PANI. The ac conductivity was studied in the frequency range 10 2 –10 6 Hz. It is observed from the ac conductivity studies that the ac conductivity is found to be constant up to 10 5 Hz and thereafter it increases steeply which is a characteristic feature of disordered materials. The dielectric behaviour was also investigated in the frequency range 10 2 –10 6 Hz. It is observed that initially the values of dielectric constant decreases up to 30 wt % and later it increases. It is seen that the tan δ values decreases upto 30 wt % and then increases thereafter. At higher frequencies these composites exhibit almost zero dielectric loss. The dimensions of SnO 2 particles in the matrix have a greater influence on the conductivity values and the observed dielectric values.

Effect of 8 MeV electron irradiation on the optical properties of doped polymer electrolyte films

The effect of electron beam (EB) irradiation on the optical properties of cadmium chloride (CdCl2)-doped polyethylene oxide (PEO) is studied. The films are characterized using Fourier transform infrared spectroscopy (FTIR) in KBr medium. The morphology study of the films is conducted using a scanning electron microscope. The optical absorption study is carried out with the help of ultraviolet‐visible absorption spectroscopy. The doped films are exposed to a beam of 8 MeV electron at 25, 50, 75, 100 kGy doses. The FTIR results of the films after EB irradiation shows the appearance of new peaks, and shifts in the position of peak prove the formation of hydrogen bonding. The optical absorption edges shift towards higher frequency upon EB irradiation, which indicates a lowering of the energy gap. This can be evidenced by the formation of carbonaceous clusters, which are estimated using the modified Tauc’s equation. The optical parameters, namely absorption coefficient, optical direct and indirect band gaps (Eg), band edges and optical activation energy (Ea), are determined for different EB doses. These results reveal that the optical properties of the irradiated doped films are attributable to changes in the linear electronic polarizability of the material rather than its band gap or electronic structure. The obtained tunability in the optical properties of the EB-irradiated doped polymer electrolytes makes it of considerable interest in a number of optical applications.

Frequency-Dependent Conductivity and Dielectric Permittivity of Polyaniline/TiO2 Composites

Conducting polyaniline/Titanium di-oxide (PANI/TiO2) composites have been synthesized by insitu deposition technique by placing fine graded TiO2 in polymerization mixture of aniline. The PANI/TiO2 composites have been synthesized with various compositions viz., 10,20,30,40 and 50 wt % of TiO2 in PANI. The ac conductivity was studied in the frequency range 102–106 Hz. It is observed from the ac conductivity studies that the ac conductivity is found to be constant up to 105 Hz and there after it increases steeply which is a characteristic feature of disordered materials. The dielectric behaviour was also investigated in the frequency range 102–106 Hz. It is observed from the dielectric studies that the value of dielectric constant decreases up to 20 wt % and later it increases rapidly up to 50 wt %. Similarly it is also seen that the tan δ values decreases rapidly up to 20 wt % and then increases up to 40 wt %, thereafter slowly increases up to 50 wt %. At higher frequencies these composites exhibit almost zero dielectric loss. The dimensions of TiO2 particles in the matrix have a greater influence on the conductivity values and the observed dielectric values.

Dielectric Spectroscopy of Pani-CaTiO3 Composites

The stability, processability and electrical and optical properties of polyaniline (PANI) have led to its being investigated for use in a wide variety of applications. Much of the initial work centered on the wide range of conductivity that can be achieved, covering some 20 orders of magnitude. Although (PANI) can indeed form highly conductive materials upon doping, the long-term stability of these materials may be a problem. It is probable that it will be the semi conductive and photoconductive properties of this polymer that will prove more useful in nature. In the present work, synthesis of polyaniline (PANI) is carried out by chemical oxidation method by using various percentages (10, 20, 30, 40 and 50 wt%) of CaTiO 3 in PANI by in situ polymerization. The composites are characterized by using various techniques such as XRD, IR and SEM spectroscopy. From these studies it is observed that CaTiO 3 is homogeneously distributed in PANI. The dielectric constant and dielectric tangent loss are studied by sandwiching the pellets of these composites between the silver electrodes. It is observed from these studies of the dielectric constant that, it decreases exponentially with frequency. From the studies of dielectric tangent loss, it is observed that PANI-CaTiO3 decreases as a function of frequency. Both PANI and its composites exhibit the small value of dielectric loss at higher frequency. The AC conductivity is studied in the frequency range from 10 2 –10 7 Hz. From these studies it is found that, AC conductivity remain constant at low frequency and increase rapidly at higher frequency, which is characteristic behaviour of disordered materials.

Synthesis, Characterization and Electrical Properties of Polyaniline/BaTiO3 Composites

Conducting polyaniline/BaTiO 3 (PANI/BT) composites have been synthesized by ‘in situ’ deposition technique by placing fine graded BaTiO 3 in polymerization mixture of aniline. The composites are characterized using various techniques such as SEM, XRD and IR spectroscopy. The electrical properties such dc conductivity and ac conductivity are studied by sandwitching the pellets of these composites between the silver electrodes. It is observed that in both the cases the values of conductivities increases up to 30 weight % of BaTiO 3 in polyaniline and decreases thereafter. Initial increment in conductivity is due to extended chain length of polyaniline where polarons possess sufficient energy to hop between favorable sites. Beyond 30 weight % of BaTiO 3 in polyaniline, the blocking of charge carriers takes place reducing the conductivity values. The polyaniline/ BaTiO 3 composites are poled by applying constant voltage for a fixed time to study their electrical hysteresis characteristics. It is observed that the area under the curve depends on the content of BaTiO 3 in polyaniline.

Impedance Spectroscopic Studies on Nanometric Polyaniline/CdO Composites

The frequency dependent conductivity and dielectric behavior of PANI/CdO polymer nanocomposites based on polyaniline/CdO with SDBSA have been studied. The formation of nanocomposites and changes in the structural and microstructural properties of the materials were investigated by X-ray diffraction (XRD), FTIR and SEM techniques. The variation of ac conductivity with frequency obeys Jonscher power law except a small deviation in the low frequency region due to electrode polarization effect. The dc conductivity increases with increase in CdO concentration. Studies of dielectric properties at lower frequencies show that the relaxation contribution is superimposed by electrode polarization effect. The appearance of peak for each concentration in the loss tangent suggests the presence of relaxing dipoles in the polymer nanocomposite. On addition of CdO, the peak shifts towards higher frequency side indicating the speed up the relaxation time. Analysis of frequency dependence of dielectric and modulus formalism suggests that the electronic and polymer segmental motions are strongly coupled.

EFFECT OF CONFIGURATION ON THE BINDING OF AN ELECTRON TO A FIXED LINEAR ELECTRIC QUADRUPOLE

Abstract A quantum mechanical investigation has been made of the binding of an electron to a finite linear electric quadrupole in two configurations, one of which has two positive charges, each of charge + q , symmetrically placed about a negative charge -2 q , and the other has the signs of the charges reversed. When the expectation value of the Hamiltonian is minimized in a variational calculation using Gaussian wave functions and then set to equal zero, the solution of the resulting equation gives the value of the minimum quadrupole moment required to assure the existence of a bound state. It has been found that the ratio of minimum quadrupole moments required to bind an electron for the first and second configurations is 7.9.