Analysis of DC and AC properties of a humidity sensor based on polyaniline–chromium oxide composites

Polyaniline–Chromia (PANI–Cr₂O₃) composites were synthesized by in situ polymerization. The prepared composites were characterized by scanning electron microscopy, X-ray diffraction and Fourier transforms infrared spectroscopy. The structural studies confirm the polymerization of aniline over Cr₂O₃ particles which results into strong interaction between PANI and Cr₂O₃ particles. Direct current conductivity of composites increases with increase in temperature. Among all composites, 30 wt% shows high conductivity. The humidity sensing mechanism of the PANI–Cr₂O₃ composites is studied and change in its resistance with respect to percentage relative humidity ranging from 20 to 95 % is recorded. The humidity sensing studies shows that the change in the resistance is due to the uncurling of polymer chains by the absorption of water vapor which leads to increase in conduction paths. The results indicate better humidity sensing response by the addition of Cr₂O₃ particles to PANI, among all the composites, 30 wt% composite shows higher sensitivity.     

Studies of the curing kinetics and thermal stability of epoxy resins using a mixture of amines and anhydrides

This article describes the curing and thermal behavior of diglycidyl ether of bisphenol A with phthalic anhydride (PA)/pyromellitic anhydride/diaminodiphenyl sulfone (DDS) or a mixture of anhydrides and amines in varying ratios as curing agents. The kinetics of the curing behavior was investigated with a multiple‐rate method. The activation energy of the curing reaction as determined in accordance with Ozawa's method was found dependent on the structure of the anhydride and on the ratio of amines to anhydrides. The activation energy was highest with sample DP3 (0.25 : 0.75) and DM3 (0.25 : 0.75). We evaluated the thermal stability of epoxy resin, cured isothermally, by recording thermogravimetric traces in a nitrogen atmosphere. The char yield was highest for resins cured with a mixture of DDS and PA (0.5 : 0.5) and a mixture of DDS and pyromellitic dianhydride (0.25 : 0.75). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3919–3925, 2006     

Designing genetic regulatory networks using fuzzy Petri nets approach

In this paper, we have successfully presented a fuzzy Petri net (FPN) model to design the genetic regulatory network. Based on the FPN model, an efficient algorithm is proposed to automatically reason about imprecise and fuzzy information. By using the reasoning algorithm for the FPN, we present an alternative approach that is more promising than the fuzzy logic. The proposed FPN approach offers more flexible reasoning capability because it is able to obtain results with fuzzy intervals rather than point values. In this paper, a novel model with a new concept of hidden fuzzy transition (HFT) to design the genetic regulatory network is developed. We have built the FPN model and classified the input data in terms of time point and obtained the output data, so the system can be viewed as the two-input and one output system. This method eliminates possible false predictions from the classical fuzzy model thereby allowing a wider search space for inferring regulatory relationship. The experimental results show the proposed approach is feasible and acceptable to design the genetic regulatory network and investigate the dynamical behaviors of gene network.     

Structural details, electrical properties, and electromagnetic interference shielding response of processable copolymers of aniline

Processable copolymers of aniline with 2-alkylanilines were prepared by in situ chemical oxidative polymerization route. Formation of copolymers was confirmed by X-ray diffractometer (XRD), UV–Vis, and solubility measurements. XRD revealed that copolymerization leads to increase in inter-chain spacing and reduction of doping levels. UV–vis results showed that incorporation of substituted anilines in copolymeric backbone leads to decrease in conjugation, the extent of which is directly related to size of alkyl substituent. The electrical conductivities of these copolymers were slightly less than pure polyaniline, but noticeable improvement in the solution processability was observed. In addition, these copolymers also provided shielding against electromagnetic interference (EMI) with ~99 % attenuation of incident energy. Among various copolymers, 95:5 copolymer of aniline with 2-isopropyl aniline (CP95Ip) gave best performance in terms of electrical conductivity (12.8 S/cm), solubility (4.9 g/L in N-methyl pyrrolidone), and EMI shielding effectiveness (?23.2 dB) values.     

Pollen morphology and its taxonomic potential in some selected taxa of Caesalpiniaceae observed under light microscopy and scanning electron microscopy

Pollen micromorphology is not only used to check the functional and structural evolution in plants but also to solve the taxonomic problem related to the classification of plants. Therefore, keeping in view the significance of pollen traits, selected taxa of the subfamily Caesalpiniaceae was collected from different geographical regions of Pakistan. The species were then analyzed under both light microscopy and scanning electron microscopy techniques to investigate the importance of micromorphological characters of pollen in the identification and classification of species. Great variation was recorded in equatorial shape, surface ornamentation, tectum, polar diameter, equatorial diameter, and exine thickness. However, little variation was observed in pollen type, polar shape, and fertility of pollen. The equatorial shape of five types was observed: prolate, prolate-spheroidal, spheroidal-subprolate, subspheroidal-prolate, and subspheroidal. Four types of surface ornamentation, psilate, granulate, clavate, and perforate, were recorded. Tectum of five types, intactate, reticulate regulate, medium reticulate, tactate, and striate, was observed. Sexine was thicker than nexine in all studied species. The largest polar diameter was observed in Caesalpinia pulcherrima 64.1 μm while the smallest in Parkinsonia aculeata 26.1 μm. The largest equatorial diameter was found in C. pulcherrima of 70.25 μm whereas the smallest in P. aculeata 27.57 μm. All the pollens analyzed were tricolporate. All studied species have a fertility ratio of more than 90%. A taxonomic key was developed to show the variation in pollen features and delimit species for the correct identification. In conclusion, the pollen traits were found useful to define species boundaries at various taxonomic ranks and will strengthen the taxonomy of this subfamily. Besides, this study also explored the palynological traits and their implication in the taxonomy of the subfamily Caesalpiniaceae.     

Synthesis of copper-ferrous (CuFe) nanowires via electrochemical method and its investigations as a fluid sensor

The special behaviour of nanowires with respect to electrical conductivity makes them suitable for sensing application. In this paper, we present a copper-ferrous (CuFe) nanowires based sensor for detection of chemicals. CuFe nanowires were synthesized by template-assisted electrochemical method. By optimizing the deposition parameters, continuous nanowires on a copper substrate were synthesized. The morphological and structural studies of the synthesized CuFe nanowires were carried out using scanning electron microscope (SEM) and X-ray diffraction (XRD). Substrates containing CuFe nanowires were moulded to form a capacitor. Different chemicals were used as dielectric in the capacitor which showed that the capacitance was a nonlinear function of the dielectric constant of fluid unlike the linear relation shown by conventional capacitors. This unique property of the nanowires based capacitors may be utilized for developing fluid sensors with improved sensitivity.     

Electrical and mechanical properties of PMMA/reduced graphene oxide nanocomposites prepared via in situ polymerization

We report the effect of filler incorporation techniques on the electrical and mechanical properties of reduced graphene oxide (RGO)-filled poly(methyl methacrylate) (PMMA) nanocomposites. Composites were prepared by three different techniques, viz. in situ polymerisation of MMA monomer in presence of RGO, bulk polymerization of MMA in presence of PMMA beads/RGO and by in situ polymerization of MMA in presence of RGO followed by sheet casting. In particular, the effect of incorporation of varying amounts (i.e. ranging from 0.1 to 2 % w/w) of RGO on the electrical, thermal, morphological and mechanical properties of PMMA was investigated. The electrical conductivity was found to be critically dependent on the amount of RGO as well as on the method of its incorporation. The electrical conductivity of 2 wt% RGO-loaded PMMA composite was increased by factor of 10⁷, when composites were prepared by in situ polymerization of MMA in the presence of RGO and PMMA beads, whereas, 10⁸ times increase in conductivity was observed at the same RGO content when composites were prepared by casting method. FTIR and Raman spectra suggested the presence of chemical interactions between RGO and PMMA matrix, whereas XRD patterns, SEM and HRTEM studies show that among three methods, the sheet-casting method gives better exfoliation and dispersion of RGO sheets within PMMA matrix. The superior thermal, mechanical and electrical properties of composites prepared by sheet-casting method provided a facile and logical route towards ultimate target of utilizing maximum fraction of intrinsic properties of graphene sheets.     

Elastic and Thermal Properties of Double Doped Orthovanadate: Eu1−x (La0.254Y0.746) x VO3

We present the effect of A-site double doping (La_0.254Y_0.746) on elastic and thermal properties of EuVO₃ in a wide doping range (0≤x≤1), using a modified rigid ion model (MRIM). Various lattice distortions and their relation to bulk modulus has been investigated systematically. The effect of the lattice distortions on thermodynamic properties of Eu_1?x (La_0.25Y_0.74) _x VO₃ has been explored by an atomistic approach. The computed results emphasize that the Debye temperature decreases while the specific heat increases with increase in doping concentration (x). The computed temperature dependent (1 K≤T≤300 K) specific heat trends are in accordance with the corresponding experimental data at various compositions. Future scope of MRIM has also been discussed.     

Synthesis,charge transport studies,and microwave shielding behavior of nanocomposites of polyaniline with Ti-doped γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

This article reports the synthesis, charge transport studies, and microwave shielding properties of polyaniline–Ti-doped γ-Fe₂O₃ nanocomposite. The composite has been prepared by the in situ chemical oxidative polymerization using dodecylbenzenzesulfonic acid as a dopant. These resulting polymer composites have been found thermally stability up to 260 °C with magnetization value of ~10 emu/g. The temperature dependence of electrical conductivity reveals the applicability of Mott’s 3D-VRH model. The composites has shown the shielding effectiveness of 35.64–45.20 dB (>99.99% attenuation) in 12.4–18 GHz (Ku-Band) frequency range. The enhancement of SE has been due to combination of dielectric and magnetic losses leading to decrease in skin depth increase in total (σ_T) conductivity and better matching of input impedance.