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It is part of the MIT group of institutions (established in 1983) which covers 10+ campuses across India and has more than 50,000+ students enrolled across various disciplines at a given point of time. The institute houses 15 schools ranging from Engineering &amp; Technology, Design, Pharmacy, Commerce, Governance among others. It offers undergraduate, postgraduate and PhD programs among different disciplines.&nbsp;

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MIT World Peace University

School of Polymer Engineering

Electromechanical sensors and actuators are important for robotic and aerospace applications. Among various material, poly(vinylidene fluoride) ir its co-polymers are known to exhibit high piezosensitivity. However, due to their higher electrical resistivity the input impedance of subsequent signal processign circuits is required to be very high. A novel technique to decrease the impedance would be blending PVDF with conducting polyaniline (PANI) but without affecting the piezosensitivyt of PVDF. Polyaniline (PANI) was synthesized by well known standard chemical route using dopants HCl and dodecyl benzene sulfonic acid. These PANI powder were blended with PVDF which was first dissolved in DMAc at 50 degrees C to which were added requisite amounts of two types of PANI ranging from 2 to 25 wt percent, stirred for 24 hours to form a homogeneous mixture which was cast in glass petri-dish, followed by complete solvent evaporation at 50 degrees C and then drying under vacuum for 24 hours to give films of PANI-PVDF blends. The piezo-sensitivity of these blends was measured before and after poling in electrical field. The sensitivity factor was dependent on the composition, type of dopant as well as the electric polarization of the blend. The HCl doped PANI blends in PVDF were highly piezo-sensitive than other blend compositions. These various results have been explained on the basis of compatibility, discrete domain formation, nonlinear conduction process for charge transport, orientation of dipoles, and trapping of space charge at inter-domain sites.

Engineering and Technology

World University root node

Proceedings of SPIE - The International Society for Optical Engineering

Effect of dopant ions on piezo-response of polyaniline-poly(vinylidine flouride) blends

The conducting polymers such as polyaniline, polypyrrole and polythiophene were functionalized with copper phthalocyanine using chemical oxidation method. The obtained polymers viz. PANI-CuPc, PPy-CuPc and PT-CuPc were studied as chemical sensors by their response characteristics after exposure to various chemical vapors such as methanol, ammonia and nitrogen dioxide. The results obtained showed that these polymers have moderate sensitivity towards the methanol as well as ammonia vapors whereas they show tremendous sensitivity towards nitrogen dioxide vapors. The sensitivity factor of as high as 50,000 was obtained for PT-CuPc polymers in nitrogen dioxide. In comparison to this, the sensitivity factors of about 100 and 40 were obtained, when these polymers were exposed to ammonia and methanol vapors. The very high selectivity towards the nitrogen dioxide was explained on the basis of charge transfer complex formed between, the phthalocyanine donor and nitrogen dioxide acceptor molecules. On the other hand, ammonia becomes a competing electron donor in CuPc containing conducting polymers. The very low response towards the methanol may be explained on the basis very little charge transfer / interaction between CuPc containing polymers and methanol. Thus, CuPc incorporated conducting polymers have much higher selectivity than their original homopolymer.

School of Mechanical Engineering

Fulltext

Sensors

Conducting Polymers Functionalized with Phthalocyanine as Nitrogen Dioxide Sensors

Rhodamine 6G (R6G), an n-type dye, has been employed at small concentrations (0-15 mM/ monomer) for sensitizing conducting polyaniline (PANI) in solid-state photocells with the configuration Au/PANI/SPE + R6G/ITO. It is observed that a p-n junction is formed at the PANI/dye interface. The photosensitivity factor (S) is observed to be maximum at a dye concentration of 6.3mM/monomer. The variation of the dark (Id) and light (Ii) current with respect to the dye concentration in the linear portion of the current-voltage (I-V) characteristic reveals that light current goes through a maximum whereas dark current remains more or less constant. Thus, it is the variation of the light current (Ii) that is more important and is one of the reasons for maximum photosensitivity at a certain dye concentration. The mechanism of the dye-sensitization process is explained on the basis of the energy band diagram of the materials forming the photocell. The observed photosensitivity is due to the lowering of the potential barrier in the presence of light at the PANI/dye interface.

Journal of Materials Science: Materials in Electronics

Sensitization effect in conducting polyaniline by rhodamine 6G

The effect of dye aggregation at the small concentration (0-4 mM/monomer) of dispersed Prussian Blue (PB) on the photocurrents were studied in solid state cells fabricated using conducting polypyrrole (Ppy) coated electrodes sandwiched with solid polymer electrolytes viz. polyvinyl alcohol (PVA) with phosphoric acid. These exhibit good photoresponse to visible light: photocurrents being 25 times more than that of the dark current values depending on the concentration of the sensitizer and the applied field. The sensitization increases with concentration of the dye at low concentrations but at high concentration formation of dye aggregates (H-type) has a negative impact on the photosensitization process. The current-voltage (I-V) characteristics in such cells reveal that the charge transport is mainly governed by the space charge effects and the sensitization effects are due to the lowering of the potential barrier formed at the Ppy/PVA+PB interface under photoexcitation.

Materials Chemistry and Physics

Effect of dye aggregation on the photosensitization effect of conducting polypyrrole sensitized with Prussian Blue

Conducting polyaniline/barium titanate (PANI/BaTiO3) composites exhibiting piezoresistivity properties have been synthesized by the in situ deposition technique by placing a fine grade powder of BaTiO3 in the polymerization reaction mixture. The polyaniline was formed preferentially on the ceramic panicles giving a much higher yield for PANI than in absence of the BaTiO3 These composites exhibited piezoresistivity with the piezosensitivity being maximum at a certain composition. The current-voltage characteristics clearly revealed a nonlinear space charge controlled charge transport process. A large hysteresis in these characteristics was also observed which was dependent on the BaTiO3 content in a composite. The various results have been explained on the basis of the charge transport mechanism in the heterogeneous conducting material having insulating domains dispersed in it. © 2001 Materials Research Society.

Journal of Materials Research

Piezoresistivity of conducting polyaniline/BaTiO3 composites

Our experimental observations shows that certain dyes when incorporated in solid polymer electrolytes (SPE) can serve as an excellent candidates for optical humidity sensing. Crystal Violet (CV) and Methylene Blue (MB) are incorporated in PVA/H3PO4, which is known to be a SPE and a good proton conductor. Films of PVA/H3PO4 containing dyes are studied for use in optical humidity sensing and the interesting results are discussed in this paper. A mechanism is proposed for the changes observed in the optical properties of such films by the variation of humidity. © 2001 Elsevier Science B.V. All rights reserved.

Sensors and Actuators, B: Chemical

Charge transfer complex-forming dyes incorporated in solid polymer electrolyte for optical humidity sensing

The structure development and mechanical properties of polypropylene (PP) composite containing polyethylene terephthalate (PET) fibres were studied both in the presence and absence of a compatibilizer such as maleic anhydride (MA). The structural and morphological studies were carried out by WAXD, optical microscopy and SEM techniques. In the absence of MA, the PET fibres in PP showed transcrystalline morphology and thus proved to be a strong nucleating agent for PP spherulites. On the other hand, in the presence of MA, no transcrystalline growth of PP was observed on the surface of PET fibres. The fibre to matrix bonding was better in presence of MA than without it, as was revealed by SEM of fractured surfaces. The mechanical properties viz. impact strength and tensile modulus showed enhancement for these composites as compared to pure PP. However, pronounced increase in the properties was seen for PET fibres filled PP composite without MA. The above findings could be understood in terms of high aspect ratio for PET fibres, transcrystalline morphology, good fibre-matrix adhesion and nucleating ability of PET fibres in PP matrix. © 2001 Elsevier Science Ltd.

Polymer

Structure development and properties of PET fibre filled PP composites

The structure development and crystallization behaviour of polypropylene (PP) containing nanoparticles of calcium phosphate prepared by a new route based on matrix mediated control of growth and morphology was investigated by X-ray diffraction (XRD), optical microscopy and DSC techniques. The results obtained were compared with that of PP containing conventionally prepared calcium phosphate (CaPO). Both nanoparticle filled PP as well as CaPO filled PP crystallized in monoclinic α crystalline phase. However, considerable changes were observed in the relative intensities of the XRD peaks, especially the peak II (040 reflection), in the case of PP filled with nanosize calcium phosphate. The isothermal crystallization curves showed dramatic increase of crystallization rate and decrease in t1/2 value for PP/nanoparticulate composites resulting in a rapid decrease in the ultimate spherulite size as compared to PP/CaPO samples. The nucleating efficiency was found to be dependent on the particle size as inverse exponential power law. These results were further confirmed by DSC analysis. The optical transparency of the PP/nanoparticle composites was found to be much higher than that containing conventional CaPO for the same concentrations and this could be associated with the reduction in the PP crystallite size. © 2001 Elsevier Science Ltd.

Structure development and crystallization behaviour of PP/nanoparticulate composite

Nanosize particles of calcium phosphate were prepared by a new technique based on matrix mediated control of growth and morphology using polymer blends. The particle size could be reduced down to the order of 10 nm at a certain composition of the blend. These particles were stabilized and could be handled easily due to the polymer matrix surrounding them. Their crystal structure and size was confirmed by X-ray diffraction and electron microscopy. © 2000 Elsevier Science Ltd. All rights reserved.

Control of nanoparticle size of fillers by polymer blend technique

An isothermal crystallization behavior is observed for poly(propylene) (PP) on the surface of poly(ethylene terephthalate) (PET) fibers. The extensive nucleation on the fiber surface is followed by the development of a transcrystalline phase, while normal PP spherulites appear much later than the transcrystalline phase in regions far from the interface. The crystallization kinetics is followed by spot-intensity measurements at selected areas on the picture frame near the fibers, showing that the kinetics in the transcrystalline zone is quite different from that in the PP bulk. Furthermore, a preferential orientation of the b-axis and/or bc-planes of PP crystallites along the c-axis of PET fibers is found, suggesting that the crystal structure of the fiber material could also influence the development of this phase. © Wiley-VCH Verlag GmbH, 2001.