Functionalised polyanaline nanofibers

Polyaniline (PAni) is a conducting polymer which switches between distinct states exhibiting dramatically different properties. The colour, conductivity and redox state of PAni all depend on the local chemical environment of the material. Consequently PAni has great potential for sensing applications. The nanostructured form of PAni is particularly interesting as it provides a very large surface-to-volume ratio that can lead to dramatic enhancement of sensor sensitivity and response time. In this work, we focus on derivatising polyaniline nanofibres. Using the technique described, carboxylate terminated side-chains can be covalently bound to solution based fibres

Improving the anti-corrosion properties via surface modification for silicon dioxide by conductive polymer

The modification of silicon dioxide surface via polyaniline (PANI) prepared by in-situ polymerization method. PANI and PANI-SiO 2 were characterized using Fourier transform infrared; X-ray diffraction and digital multimeter was used to measure conductivities for samples. Morphology of the synthesized PANI and PANI-SiO2, were examined using scanning electron microscopy. Samples were then used as pigments through blended with acrylic paint and applied on the surface of carbon steel panels. Corrosion was evaluated for coating of carbon steel panels through; full immersion test, salt spray test and adhesion test up to standards; ASTMG 31, ASTM B117 and ASTM D3359 respectively. Corrosion rate and coating adhesion were calculated after finished exposed periods in acidic Medias. Digital camera also used for monitored corrosion visually on the surface of carbon steel specimens. The results revealed that acrylic paint pigmented by SiO2 modified by polyaniline, more efficiently in corrosion protection for carbon steel than each of PANI and SiO2

Inverse-opal conducting polymer monoliths in microfluidic channels

Inverse opal monolithic flow-through structures of polyaniline (PANI) were achieved in microfluidic channels for lab-on-a-chip (LOC) applications. In order to achieve the uniformly porous monolith, polystyrene (PS) colloidal crystal (CC) templates were fabricated in channel. An inverse opal PANI structure was achieved on-chip, through a two-step process involving the electrochemical growth of PANI and subsequent removal of the template. The effect of electropolymerisation on these structures is discussed. It was found that growth time is critical in achieving an ordered structure with well-defined flow-through pores. This is significant in order to fabricate optimal porous PANI structures that maximise surface area of the monolith and also provide well-defined flow profiles through the micro-channel

Temperature dependent charge transport mechanisms in carbon sphere/polymer composites

Carbon spheres (CS) with diameters in the range $2 - 10 \mu m$ were prepared via hydrolysis of a sucrose solution at $200^o C,$ and later annealed in $N_2$ at $800^o C.$ The spheres were highly conducting but difficult to process into thin films or pressed pellets. In our previous work, composite samples of CS and the insulating polymer polyethylene oxide (PEO) were prepared and their charge transport was analyzed in the temperature range $80 K < T < 300 K.$ Here, we analyze charge transport in CS coated with a thin polyaniline (PANi) film doped with hydrochloric acid (HCl), in the same temperature range. The goal is to study charge transport in the CS using a conducting polymer (PANi) as a binder and compare with that occurring at CS/PEO. A conductivity maxima was observed in the CS/PEO composite but was absent in CS/PANi. Our data analysis shows that variable range hopping of electrons between polymeric chains in PANi-filled gaps between CS takes on a predominant part in transport through CS/PANi composites, whereas in CS/PEO composites, electrons travel through gaps between CS solely by means of direct tunneling. This difference in transport mechanisms results in different temperature dependences of the conductivity.Comment: 7 pages, 6 figure

Crucial role of decoherence for electronic transport in molecular wires: Polyaniline as a case study

In this work we attempt to elucidate the nature of conductivity in polymers by taking the acid-base doped polyaniline (PAni) polymer. We evaluate the PAni conductance by using realistic ab initio parameters and including decoherent processes within the minimal parametrization model of D'Amato-Pastawski. In contrast to general wisdom, which associates the conducting state with coherent propagation in a periodic polaronic lattice, we show that decoherence can account for high conductance in the strongly disordered bipolaronic lattice. Hence, according to our results, there is no need of considering a mix model of "conducting" polaronic lattice islands separated by "insulating" bipolaronic lattice strands as is usually assumed for PAni. We find that without dephasing events, even very short strands of bipolaronic lattices are not able to sustain electronic transport. We also include a discussion of specific mechanisms that should be involved in decoherence rates of PAni and relate them with Marcus-Hush theory of electron transfer.Comment: 11 pages, 10 figures. Submitted to Physical Review

High Sensitivity DNA Detection Using Gold Nanoparticle Functionalised Polyaniline Nanofibres

Polyaniline (PANI) nanofibres (PANI-NF) have been modified with chemically grown gold nanoparticles to give a nanocomposite material (PANI-NF–AuNP) and deposited on gold electrodes. Single stranded capture DNA was then bound to the gold nanoparticles and the underlying gold electrode and allowed to hybridise with a complementary target strand that is uniquely associated with the pathogen, Staphylococcus aureus (S. aureus), that causes mastitis. Significantly, cyclic voltammetry demonstrates that deposition of the gold nanoparticles increases the area available for DNA immobilisation by a factor of approximately 4. EPR reveals that the addition of the Au nanoparticles efficiently decreases the interactions between adjacent PANI chains and/or motional broadening. Finally, a second horseradish peroxidase (HRP) labelled DNA strand hybridises with the target allowing the concentration of the target DNA to be detected by monitoring the reduction of a hydroquinone mediator in solution. The sensors have a wide dynamic range, excellent ability to discriminate DNA mismatches and a high sensitivity. Semi-log plots of the pathogen DNA concentration vs. faradaic current were linear from 150 × 10−12 to 1 × 10−6 mol L−1 and pM concentrations could be detected without the need for molecular, e.g., PCR or NASBA, amplification

Probing Spin-Charge Relation by Magnetoconductance in One-Dimensional Polymer Nanofibers

Polymer nanofibers are one-dimensional organic hydrocarbon systems containing conducting polymers where the non-linear local excitations such as solitons, polarons and bipolarons formed by the electron-phonon interaction were predicted. Magnetoconductance (MC) can simultaneously probe both the spin and charge of these mobile species and identify the effects of electron-electron interactions on these nonlinear excitations. Here we report our observations of a qualitatively different MC in polyacetylene (PA) and in polyaniline (PANI) and polythiophene (PT) nanofibers. In PA the MC is essentially zero, but it is present in PANI and PT. The universal scaling behavior and the zero (finite) MC in PA (PANI and PT) nanofibers provide evidence of Coulomb interactions between spinless charged solitons (interacting polarons which carry both spin and charge)

Potassium Iodide-Functionalized Polyaniline Nanothin Film Chemiresistor for Ultrasensitive Ozone Gas Sensing.

Polyaniline (PANI) nanostructures have been widely studied for their sensitivity to atmospheric pollutants at ambient conditions. We recently showed an effective way to electropolymerize a PANI nanothin film on prefabricated microelectrodes, and demonstrated its remarkable sensing performance to be comparable to that of a one-dimensional nanostructure, such as PANI nanowires. In this work, we report further progress in the application of the PANI nanothin film chemiresistive sensor for the detection of ozone (O₃) by modifying the film with potassium iodide (KI). The KI-PANI sensor exhibited an excellent sensitivity to O₃ (8⁻180 ppb O₃ concentration rage) with a limit of detection of 230 ppt O₃, and exquisite selectivity against active chemicals such as nitrogen dioxide (NO₂) and sulfur dioxide (SO₂). The sensing mechanism of the sensor relied on iodometric chemistry of KI and O₃, producing triiodide ( I 3 - ) that partially doped and increased electrical conductivity of the PANI film. The sensitivity and selectivity of the KI-functionalized PANI film demonstrates the potential use for KI-PANI-based O₃ sensing devices in environmental monitoring and occupational safety

Binary pulsars as dark-matter probes

During the motion of a binary pulsar around the Galactic center, the pulsar and its companion experience a wind of dark-matter particles that can affect the orbital motion through dynamical friction. We show that this effect produces a characteristic seasonal modulation of the orbit and causes a secular change of the orbital period whose magnitude can be well within the astonishing precision of various binary-pulsar observations. Our analysis is valid for binary systems with orbital period longer than a day. By comparing this effect with pulsar-timing measurements, it is possible to derive model-independent upper bounds on the dark-matter density at different distances $D$ from the Galactic center. For example, the precision timing of J1713+0747 imposes $\rho_{\rm DM}\lesssim 10^5\,{\rm GeV/cm}^3$ at $D\approx7\,{\rm kpc}$. The detection of a binary pulsar at $D\lesssim 10\,{\rm pc}$ could provide stringent constraints on dark-matter halo profiles and on growth models of the central black hole. The Square Kilometer Array can improve current bounds by 2 orders of magnitude, potentially constraining the local density of dark matter to unprecedented levels.Comment: 8+3 pages, 7 figures. To appear in Phys. Rev. D; v2: matches published versio