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Cholesterol appended bispyridinium isophthalamide dichloride (1) has been designed and synthesize... more Cholesterol appended bispyridinium isophthalamide dichloride (1) has been designed and synthesized. While compound 1 forms a gel in CHCl3, the cholesterol appended bispyridinium isophthalamide dihexafluorophosphate (1a) analogue that results from 1 on anion exchange does not form a gel in any solvent combination. The chloroform gel of 1 is pH responsive and shows thermally activated ionic conductivity. It serves as a medium for the specific detection of Ag+ ions over a series of examined cations. Compound 1a, on the other hand, acts as a selective Cl− ion detector by forming a gel in chloroform in the presence of tetrabutylammonium chloride.

In this Brief Report, we have investigated the conductivity spectra at different temperatures for... more In this Brief Report, we have investigated the conductivity spectra at different temperatures for the model glasses (AgI)
x−
(AgPO
3)
(1−x),
0⩽x⩽0.6 and estimated mobile
Ag
+ ions contributing to the transport process. We have
shown that a fraction of the total Ag
+ ions contribute to the transport process. We have further observed that the
fraction of Ag
+ ions contributing to the transport process is independent of temperature as well as the AgI content. The
mobility of Ag
+ ions increases, leading to an enhancement of the conductivity due to AgI doping. These results are
highly important in order to reveal the role of AgI for ion transport in fast ion conducting glasses.

The effect of ZnO nanoparticles on the structure and ionic relaxation of LiI salt doped poly(ethy... more The effect of ZnO nanoparticles on the structure and ionic relaxation of LiI salt doped poly(ethylene oxide) (PEO) polymer electrolytes has been investigated. X-ray diffraction, high resolution transmission electron microscopy and field emission scanning electron microscopy show that ZnO nanoparticles dispersed in the PEO-LiI polymer electrolyte reduce the crystallinity of PEO and increase relative smoothness of the surface morphology of the nanocomposite electrolyte. The electrical conductivity of the nanocomposites is found to increase due to incorporation of ZnO nanoparticles. We have shown that the structural modification due to insertion of ZnO nanoparticles results in the enhancement of the mobility i.e., the hopping rate of mobile Li+ ions and hence the ionic conductivity of PEO-LiI-ZnO nanocomposite electrolyte.

The present article demonstrates an intensive study upon the temperature dependent current densit... more The present article demonstrates an intensive study upon the temperature dependent current density (J)-voltage (V) characteristics of moderately doped polypyrrole nanostructure and its silver nanoparticles incorporated nanocomposites. Analysis of the measured J–V characteristics of different synthesized nano-structured samples within a wide temperature range revealed that the electrical conduction behavior followed a trapped charge-limited conduction and a transition of charge transport mechanism from deep exponential trap limited conduction to shallow traps limited conduction had been occurred due to the incorporation of silver nanoparticles within the polypyrrole matrix. A direct evaluation of carrier mobility as a function of electric field and temperature from the measured J–V characteristics illustrates that the incorporation of silver nanoparticles within the polypyrrole matrix enhances the carrier mobility at a large extent by reducing the concentration of traps within the polypyrrole matrix. The calculated mobility is consistent with the Poole-Frenkel form for the electrical field up to a certain temperature range. The nonlinear low temperature dependency of mobility of all the nanostructured samples was explained by Mott variable range hopping conduction mechanisms. Quantitative information regarding the charge transport parameters obtained from the above study would help to extend optimization strategies for the fabrication of new organic semiconducting nano-structured devices.

The relaxation dynamics and charge-transport mechanisms of different benzene tetracarboxylic acid... more The relaxation dynamics and charge-transport mechanisms of different benzene tetracarboxylic acid (BTCA)-doped polyaniline (PANI) nanostructures had been probed by the electric ac response of the samples from 42 Hz up to 5 MHz within the temperature range 133–303 K. The experimental results reveal that the overall frequency-dependent transport properties of these nanostructures significantly depend on the difference in morphologies obtained from the BTCA doping at different concentrations. The above study also illustrates the common origin of the charge-transport mechanism, and the relaxation of these PANI nanostructures and the hopping models is most suitable to describe the electrical response in the measured temperature and frequency range. The observed morphology-dependent variation of the ac and dc conductivity has been correlated with the simultaneous and consistent deviation of the degree of localization of the polaron lattice sites and the hopping lengths, evaluated from the qualitative analysis of the experimental data.

The present study depicts a one-pot strategy to fabricate silver-polyaniline hybrid nanocomposite... more The present study depicts a one-pot strategy to fabricate silver-polyaniline hybrid nanocomposites with superior and tunable electrical properties, supported by structural characterizations and detail analysis of their temperature dependent current density (J)–voltage (V) characteristics. TEM micrographs clearly reveal that the nanocomposites synthesized by this one-pot strategy contain higher dispersion of sliver nanoparticle within the polyaniline matrix with respect to that obtained from the embedment of externally pre-synthesized silver nanoparticles. The results obtained from the analysis of J–V characteristics indicate the prevalence of trapped charge-limited conduction mechanism in doped polyaniline and its nanocomposites. For the nanocomposites obtained from one-pot strategy, a transition of charge transport mechanism from deep exponential trap limited to shallow traps limited conduction has been occurred due to higher dispersion of silver nanoparticles within the polyaniline matrix. Such distinct variation of charge conduction is absent in the nanocomposites obtained from the embedment of externally pre-synthesized silver nanoparticles. A direct evaluation of carrier mobility as a function of electric field and temperature illustrates that the incorporation of only ∼13 to 18 wt% of silver nanoparticles within the polyaniline matrix enhances the carrier mobility in a large extent by reducing the concentration of traps within the polymer matrix. The calculated mobility is consistent with the Poole–Frenkel form for the electrical field up to a certain temperature range. The nonlinear low temperature dependency of mobility of all the nanostructured samples has been explained by Mott variable range hopping conduction mechanisms. Qualitative estimation of various disorder parameters such as optimal hopping distance, localization lengths etc., would help us to outspread the strategies for the fabrication of new organic semiconducting nano-structured devices.

The electrical conductivity relaxation in moderately doped polypyrrole and its nanocomposites rei... more The electrical conductivity relaxation in moderately doped polypyrrole and its nanocomposites reinforced with different proportion of silver nanoparticles was investigated in both frequency and time domain. An analytical distribution function of relaxation times is constructed from the results obtained in the frequency domain formalism and is used to evaluate the Kohlrausch-Williams-Watts (KWW) type decay function in the time domain. The thermal evolution of different relaxation parameters was analyzed. The temperature-dependent dc electrical conductivity, estimated from the average conductivity relaxation time is observed to depend strongly on the nanoparticle loading and follows Mott three-dimensional variable range hopping (VRH) conduction mechanism. The extent of charge carrier localization calculated from the VRH mechanism is well correlated to the evidences obtained from the structural characterizations of different nanostructured samples.

The present work aims at studying electrical relaxations in silver–polyaniline nanocomposites usi... more The present work aims at studying electrical relaxations in silver–polyaniline nanocomposites using dielectric spectroscopy. The nanocomposites of dodecylbenzenesulfonic acid-doped polyaniline (PANI) with different concentrations of silver nanoparticles (~6–12 nm) are synthesized by simple wet-chemical route. The temperature dependence of dc conductivity in all the samples follows three-dimensional variable range-hopping conduction mechanism. The loss factor, after having subtracted the dc contribution, shows a relaxation peak which simultaneously attributes to the frequency dispersion in conductivity spectra. The observed dielectric relaxation is well fitted by the Havriliak–Negami function, and the fitting parameters are determined. The temperature dependence of characteristic relaxation frequency and dc conductivity is in line with each other and bear a resemblance to the origin of dc transport and dielectric relaxation in these systems. The temperature behavior of the relaxation strength confirms that an exclusive hopping conduction of polarons in the disordered PANI matrix can be considered as the origin of the observed electrical properties of the systems. Further, the self-similar behavior of the real part of normalized ac conductivity, within the measured temperature range, also confirms the above inferences. The variation of frequency exponent with temperature suggests that ac conduction is due to the correlated barrier hopping of polarons which strongly affected by the dispersion of silver nanoparticles within the PANI matrix.

Indian Journal of Physics, 2011

Poly (vinyl chloride)(PVC) is a cheapest plastic. Importance of PVC based ionomer has been gradua... more Poly (vinyl chloride)(PVC) is a cheapest plastic. Importance of PVC based ionomer has been gradually being popularizing due to compatibility of PVC with a number of salts to replace polyethylene oxide based ionomer. Under present investigation few of chloride group of PVC chain have been replaced by basic thiouronium group and these thiouronium groups are further oxidized to sulfonate group. Introduction of thiouronium group in PVC is confirmed through FTIR and further its oxidation to sulfonate group is also confirmed by FTIR. Conductivity in different stoichiometric ratio of PVCTU and PVCSO3H was studied and found that PVCTU: PVCSO3H in 1:1 ratio has conductivity near to pure PVC (10−9 Ohm-1 cm−1) and increases with proportion of PVCSO3Na in the mixture (10−6 Ohm−1 cm−1) for pure PVC, PVCTU has less conductivity not much significant.

Alternating current conduction in disordered solids is discussed, from a general point of view. A... more Alternating current conduction in disordered solids is discussed, from a general point of view. As regards experiment, it is argued that the observed power-law behavior of the frequency-dependent conductivity, o-(w), is probably not fundamental, that the Ngai relation between dc and ac conductivity activation energies follows from independent experimental facts, that the shape of the modulus peak has no fundamental significance, and that there are interesting mechanical analogies to the observed ac electrical behavior. As regards hopping models for ac conduction, it is shown that three commonly used arguments against the existence of a distribution of activation energies are all incorrect. Also, it is shown that o-Qo) =~ o-(0) only if there are correlations in the directions of different charge carrier jumps; in particular this result implies o-Qo) = o-(0) for all frequencies in the continuous time random walk (CTRW) model. In the final section a number of open problems are listed, and suggestions are made for future work. 0022-3093/91/$03.50

Given a fitting model, such as the Kohlrausch-Williams-Watts ͑KWW͒/stretched-exponential response... more Given a fitting model, such as the Kohlrausch-Williams-Watts ͑KWW͒/stretched-exponential response, three plausible approaches to fitting small-signal frequency or time-response data are described and compared. Fitting can be carried out with either of two conductive-system formalisms or with a dielectric-system one. Methods are discussed and illustrated for deciding which of the three approaches is most pertinent for a given data set. Limiting low-and high-frequency log-log slopes for each of the four immittance levels are presented for several common models; cutoff effects are considered; and an anomaly in the approach to a single-relaxation-time Debye response for one of the conductive-system approaches is identified and explained. It is found that the temporal response function for the most appropriate conductive-system dispersion ͑CSD͒ approach, designated the CSD1, one long used in approximate form for frequency-response data analysis, does not lead to stretched-exponential transient behavior when a KWW response model is considered. Frequency-domain fitting methods and approaches are illustrated and discriminated using 321 and 380 K Na 2 O-3SiO 2 data sets. The CSD1 approach using a KWW model is found to be most appropriate for fitting these data exceedingly closely with a complex nonlinear least-squares procedure available in the free computer program LEVM. Detailed examination and simulation of the approximate, long-used CSD1 modulus fitting formalism shows the unfortunate results of its failure to include separately the effects of the always present high-frequency-limiting dielectric constant, ⑀ Dϱ . The stretched-exponential exponent, ␤, associated with this fitting approach has always been misidentified in the past, and even after its reinterpretation, the result is likely to be sufficiently approximate that most physical conclusions derived from such fitting will need reevaluation.

Indian Journal of Physics, 2011