Novel Fabrication of Conductive Polymers Contained Micro‐Array Gas Sensitive Films Using A Micromanipulation Method

A novel method for fabricating a micro gas sensor film on an indium tin oxide (ITO) electrode patterned using micro‐machining technology was developed. A micromanipulation system equipped with a counter electrode (Au; Ø10 μm) and a microsyringe, which was connected to a microinjection system, was first constructed. With this system, micro gas sensor arrays could be successfully prepared on ITO electrodes. Two kinds of micro gas sensor films were prepared, based on polythiophene (PTh) and poly(3‐n‐dodecylthiophene) (PD). The response behavior of conventional PTh and micro‐PTh films against NH₃ at three different operating temperatures (25, 40 and 60 °C) was investigated by measuring the resistance of the film. With the micro‐PTh film, a reversible response was observed against NH₃ when measured at 40 and 60 °C. In addition, the responsive characteristics of the microsensor films against different testing gases were examined at the three operating temperatures. The resistance of the microsensor films of PTh and PD changed considerably, depending on the type of testing gas, allowing these sensor films to be used for the detection of various gases. Furthermore, the microsensor films had a high stability compared with conventional films prepared from the same polymer.     

DC Electrical Conductivity of the Direct Electrochemically Synthesized Polythiophene Metal Complexes

Electrochemical anodic oxidation of a metal anode in an acetone solution of 2,5-diamino-3,4-dicyanothiophene gave the polythiophene metal complexes of Co, Ni, Cu, Zn, Cd, and Sn. Chemical analyses, as well as FTIR and electronic spectral data, are presented to confirm the formulation of the isolated materials. DC electrical conductivity measurements of the polymer complexes were measured in the range 300–500 K in the annealed and 5% doped forms. The products gave electrical conductivity in the semi-conducting region that increased by heat.     

Synthesis and Characterization of a Thiophene Copolymer for Photovoltaic Application

A soluble thiophene copolymer having polar and non polar side groups was synthesized and its photovoltaics performance was investigated. The synthesized copolymer was characterized using Nuclear Magnetic Resonance (NMR) and optical spectroscopy. Dye sensitized solar cells were fabricated using this copolymer as sensitizer. An open-circuit voltage of 0.50V, a short-circuit current density of 1.195 mA/cm² and an overall power conversion efficiency of 0.3% were measured.     

Sensory Response and Two-Photon-Fluorescence Study of Regioregular Polythiophene Nanoparticles

Nanoparticles of a regioregular and soluble polythiophene were fabricated by mini-emulsion technique. The fabricated nanoparticles were characterized by optical spectroscopy and dynamic light scattering. The fluorescence quenching of these fabricated nanoparticles with 2,4-dinitrotolune (DNT) in aqueous and organic solutions was investigated. Significant fluorescence quenching was observed. The Stern-Volmer constants were determined to be higher than that of the bulk polymer in solution, indicating that the nanoparticles provide better sensitivity in DNT sensing. Strong two-photon-induced fluorescence was measured from these nanoparticles.     

PHOTOELECTRON SPECTROSCOPY STUDY OF AMMONIA-INDUCED CHANGES IN ELECTROSTATICALLY-ASSEMBLED CONJUGATED POLYMER FILMS

ABSTRACT

Exposure of electrostatically assembled polyelectrolyte films comprised of the anionic carboxylic conjugated polymer poly[2-(3-thienyl)-ethanolhydroxycarbonylmethyl-urethane], hereafter referred to as H-PURET, and polycations such as poly(diallyldimethylammonium) chloride, here after referred to as PDADMAC, to aqueous ammonia vapor leads to dra matic changes in the ultraviolet-visible absorption spectrum. In the case of H-PURET/PDADMAC, a shift from 442 to 494 nm is observed upon overnight ammonia exposure. X-ray photoelectron spectroscopy has been used to investigate the mechanism of the changes in optical properties. The C1s, O1s and S2p core levels exhibit negligible ammonia-induced changes. Two N1s peaks are observed in virgin H-PURET/PDADMAC assemblies, and ammonia exposure causes the nitrogen peak corresponding to the H-PURET side chain to become more intense relative to that of the PDADMAC layer. This selective change in the N1s feature suggests that ammonia interacts with the polythiophene side-chain, presumably by deprotonating the fraction of carboxylic acid groups that remain in the H-PURET layer. This deprotonation apparently leads to structural or single chain conformational changes in the conjugated polymer layers that alter the electronic absorption spectrum.     

Synthesis and Characterization of Multi‐Walled Carbon Nanotube/Polythiophene Composites

Multi‐walled carbon nanotube (MWCNT)/polythiophene (PTh) composites have been prepared by in situ chemical oxidative polymerization. PTh is synthesized onto the sidewalls of the MWCNTs, which play a role as hard templates for PTh to produce one‐dimensional nanostructures. The morphology and structures of the MWCNT/PTh composites are characterized by High‐resolution transmission electron microscopy, x‐ray diffraction, and Fourier transform infrared spectrometry. Their electrical property and thermal stability are determined using vector network analyzer and thermal gravimetric analyzer. Moreover, the mechanism of MWCNT/PTh nanowire formation is described. The studies show that the composites are nanowires with core‐shell structure, in which the outer shells and inner cores are formed by PTh and MWCNTs, respectively. The addition of MWCNTs does not change the backbone structure of PTh and affect the amorphous condition of PTh very slightly, however, it improves the electrical conductivity and thermal stability of PTh.     

Fabrication of nano-structured polythiophene nanoparticles in aqueous dispersion

The synthetic route of unsubstituted polythiophene (PT) nanoparticles was investigated in aqueous dispersion via Fe³⁺-catalyzed oxidative polymerization. With this new synthetic method, high conversion of thiophene monomers was obtained with only a trace of FeCl₃. The dispersion state showed that the PT nanoparticles were well dispersed in many polar solvents, compared to non-polar solvents, such as acetone, chloroform, hexane, and ethyl acetate. To compare the photoluminescence properties between PT nanoparticle dispersion and PT bulk polymers, the PL intensities were measured in the same measuring conditions. Further, core–shell poly(styrene/thiophene) (poly(St/Th)) latex particles were successfully prepared by Fe³⁺-catalyzed oxidative polymerization during emulsifier-free emulsion polymerization. The different polymerization rates of each monomer resulted in core–shell structure of the poly(St/Th) latex particles. The PL data of the only crumpled shells gave evidence that the shell component of core–shell poly(St/Th) latex particles is indeed PT, which was corroborated by SEM data. PL intensity of the core–shell poly(St/Th) nanoparticle dispersion was much higher than that of the PT nanoparticle dispersion, due to its thin shell layer morphology, which was explained by the self-absorption effect.     

Synthesis and characterization of poly(3-thiophene acetic acid)/Fe3O4 nanocomposite

Poly(3-thiophene acetic acid)/Fe₃O₄ nanocomposite is synthesized by the precipitation of Fe₃O₄ in the presence of poly(3-thiophene acetic acid) (P3TAA). Structural, surface, morphological, thermal properties and conductivity characterization/evaluation of the nanocomposite were performed by XRD, FT-IR, TEM, TGA, and conductivity measurements, respectively. The capping of P3TAA around Fe₃O₄ nanoparticles was confirmed by FT-IR spectroscopy, the interaction being via bridging oxygens of the carboxylate and the nanoparticle surface through bidentate binding. The crystallite and particle size were obtained as 9 ± 2 nm and 11 ± 1 nm from XRD line profile fitting and TEM image analysis, respectively, which reveal nearly single crystalline nature of Fe₃O₄ nanoparticles. Magnetization measurements reveal that P3TAA coated magnetite particles do not saturate at higher fields. There is no coercivity and remanence revealing superparamagnetic character. Magnetic particle size calculated from the theoretical fitting as 9.1 nm which coincides the values determined from TEM micrographs and XRD line profile fitting. The comparison to the TEM particle size reveals slightly modified magnetically dead nanoparticle surface.     

Synthesis and characterization of poly(3-thiophenyl acetic acid) (P3TAA)-BaFe12O19 nanocomposite

We have presented a method for the fabrication of poly(3-thiophenyl acetic acid) (P3TAA)-BaFe₁₂O₁₉ nanocomposites by the in situ polymerization of P3TAA in the presence of synthesized BaFe₁₂O₁₉ nanoparticles. The nanoparticles and the nanocomposite were analyzed by XRD, FTIR, TGA, TEM, VSM and conductivity techniques for structural and physicochemical characteristics. Crystallographic analysis revealed the phase as hexaferrite and X-ray line profile fitting yielded a crystallite size of 32 nm. The particles, observed by TEM, exhibit irregular shapes and sizes between 100 and 500 nm, revealing polycrystalline character when compared with the crystallite size from XRD. FTIR and TGA analysis results show that P3TAA is conjugated to the particle surface via a carboxylate group and that the composite has a polymer content of ∼10%. Magnetic hysteresis curves do not saturate at high fields, which is a characteristic feature of fine particle systems with grain sizes smaller than 1 μm. Conductivity measurements showed a semiconductor character of the nanocomposite.