Morphological and Optical Properties of Polypyrrole Nanoparticles Synthesized by Variation of Monomer to Oxidant Ratio (original) (raw)
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Chemical Changes and Photoluminescence Properties of UV Modified Polypyrrole
International journal of electrochemical science
Effects of ultraviolet light (325 nm) irradiation on polypyrrole (PPy) properties were studied by time-resolved, standard photoluminescence (PL), optical absorption, and X-ray photoelectron (XPS) spectroscopies. PPy samples were prepared in thin films on gold, quartz, and H-terminated monocrystalline diamond (MCD) substrates by electrochemical and chemical oxidation. After the UV irradiation, all PPy samples converged to the same PL spectrum independent of initial preparation methods or substrates. We observed formation of a new, highly intensive PL band at 540 nm accompanied with few per cent increase in transmittance and structural and chemical changes of the PPy chains. The changes occurred only when the light intensity was from 0.1 to 10 W/cm(2). The effect was reduced in vacuum. Thermal annealing had no influence. We explain the effect by chemical and structural modifications of PPy that lead to a permanent increase in quantum yield of intrachain exciton recombination.
Chemical Physics Letters, 1998
Ž . Ž Absorption, photoluminescence PL and PL excitation PLE spectra of a solution and a thin film of poly pentylphenyl-. Ž . Ž . Ž . silylene 1 are measured and compared to those of poly methylphenylsilylene 2 . The sharper and stronger 3.6 eV absorption and the mirror image of the absorption and PL spectra of 1 suggest that 1 is spatially homogeneous. The broad PL which appears in 2 is scarcely observable in the 1 film around 2.7 eV, in the range from room temperature to 20 K. A Ž comparison of the PLE spectra shows that the origins of the broad PL of 1 and 2 are different. To obtain poly alkylarylsily-. lene derivatives with high molecular weights which show no visible PL, the alkyl pendants should be pentyl or longer. q
Photoinduced Structural Changes in Poly(4-Vinyl Pyridine): A Luminescence Study
2000
In the present work we show a way of controlling photoluminescence (PL) properties through photoinduced quasi-crystal formation in a system based on poly(4-vinyl pyridine) (P4VPy). Under UV irradiation at 380 nm, concentrated solutions of P4VPy in pyridine turn into gel. This phase transition results in changes in the optical properties of this polymer. The position of the PL maximum can be changed continuously from 440 to 480 nm during irradiation. After several minutes of UV irradiation a new red-shifted PL at 492 nm appears upon excitation by light of a wavelength corresponding to that of the initial PL maximum, which is also red-shifted during irradiation. Solutions of P4VPy in pyrimidine show similar behavior, but those in pyridazine do not exhibit such behavior. We have found that the reason for the observed changes in the electronic properties is a photoinduced directional ordering of polymer molecules in a special quasi-crystal formation. The process originates from a structural change in the side chain of P4VPy, namely, protonation of the polymeric pyridine after solvation. During irradiation, the polymeric pyridinium ion interacts with neutral polymeric pyridine molecules. Interchain interaction through hydrogen bonds lead to an electronic property change. We observed that the process of photoinduced sol-gel transformation is reversible. Mechanical perturbation or heating can convert the gel back to a fluid solution. The red-shifted PL is not observed, and the initial PL is blue-shifted to 450 nm and stays there.
Synthetic Metals, 1992
Polypyrrole (PPy) is one of the most extensively investigated of the electronically conductive polymers. Nevertheless, there is still much we do not understand about this interesting and useful material. One of the most persistent mysteries involves simple chemical composition. Doped PPy should have the empirical formula C4H3NXz, where X-is the dopant counterion and z is the fractional doping level; z is typically on the order of 0.3. However, elemental analyses of PPy typically show empirical formulae like C4H3NXz O r, where y ranges from 0.3 to 0.7 unaccounted for oxygen atoms per pyrrole ring. This paper presents IR spectral data which suggest that the oxygen in PPy is present as covalently bound hydroxide. Analogous IR investigations of poly(N-methylpyrrole) films show that this polymer is also hydroxylated. The hydroxy substitution present in these polymers undoubtedly results from nucleophilic attack by water on the nascent polycationic chains.
Comparison of polypyrrole, poly(3,4-dimethylpyrrole) and poly(3-methoxy-4-methylpyrrole)
Synthetic Metals, 1995
As-grown polypyrrole (Ply), poly(3,4-dimethylpyrrole) (DMPPy) and poly(3-methoxy-4-methylpyrrole) (MMPly) films doped with p-toluenesulfonate were characterized. The FT-IR spectra of thick films originate by selective scattering and should be interpreted as due to a molecular solid and not to functional group frequencies. Electronic absorption spectra agree with the polaron-bipolaron absorption model, although for MMPly strong differences between the energy gap of neutral and doped polymers should be taken into account to fulfil the model. DMPly shows an electrical conductivity dependence of the type ~r=A exp(B/Tl/4), in a higher range of temperatures than Ply and MMPPy.
Polypyrrole nanoparticles and dye absorption properties
Synthetic Metals, 2005
Polypyrrole (PPy) nanoparticles were prepared by using microemulsion polymerization processes at 3 • C. Particle characterization was performed by using FTIR, elementary analysis, UV-vis spectra and scanning electron microscope (SEM). The size of the nanoparticles varied from about 50 to 100 to 100 to 200 nm with the change in concentration of surfactant from 0.8 to 0.44 M. Polypyrrole nanoparticles were dedoped by a 10% NaOH solution, followed by a redoping process using a nuclear fast red kernechtrot dye, which has a sulfonate group. Dedoping changed the optical absorption properties of the nanoparticles.
Spectroscopic investigation of oxidation of p-toluene sulfonic acid doped polypyrrole
Synthetic Metals, 2001
Oxidative degradation of electrochemically synthesized p-toluene sulfonic acid doped polypyrrole, PTS-PPY was studied by the application of evolved gas analysis using IR spectroscopy and direct insertion probe pyrolysis mass spectrometry techniques. It has been observed that PPY ®lms prepared in aqueous media contained high concentration of oxygenated species even if the synthesis potential was kept low. The extent of overoxidation associated to ketone formation increased by increasing the applied potential and thermal ageing. The decrease in conductivity is attributed to the replacement of dopant, as a result of nucleophlic attack on the polycationic chain, by hydroxide and/or O 2 . Pyrolysis analyses also indicated that chemically prepared samples were oxygenated in air more readily and yielded mainly C=O groups. Presence of hydroxide groups for these samples may be associated with the adsorption of H 2 O in air or H 2 O present during synthesis as an impurity. The direct insertion probe pyrolysis mass spectrometry technique was shown to be a very powerful technique for not only determining the thermal decomposition products but a investigating the interaction of dopant and oxygenated species with the polymer matrix. #
Synthesis, characterization, morphological and electrical studies of polypyrrole nanostructures
Nucleation and Atmospheric Aerosols, 2019
Conducting polypyrrole was synthesized by three independent methods such as inverse micro emulsion polymerization (MIP), nano polymerization (Nano PPy) and bulk polymerization (Bulk PPy) and the samples were characterized by FESEM, XRD, FTIR and UV-visible Spectroscopy. DC conductivity studies of the samples were investigated by Keithley two probe method and it was found that polypyrrole by MIP method shows highest dc conductivity value as 5.3672x10-7 Smˉ1 while Nano PPy and Bulk PPy as 1.8911x10-7 and 0.8564x10-7 Smˉ1 respectively. In UV-visible spectroscopy, polypyrrole showed absorption peak at 380nm corresponding to π to π* excitation transition which confirms conjugated polypyrrole structure in all samples with absorbance 0.2809, 0.0861 and 0.6142 for MIP PPy, Nano PPy and bulk PPy respectively. FTIR spectra show maximum absorbance for Bulk PPy. Peak at 1457 cm-1 , 1557 cm-1 (C=C stretching of pyrrole rings), (N-H bending vibrations), 1376 cm-1 and 1300 cm-1 (stretching peaks of C=N and C-N bonds) confirms polypyrrole formation 1. FESEM images of polypyrrole shows spherical morphology for MIP PPy and Bulk PPy while nano PPy possess globular morphology with agglomeration of particles; with particle size in nano range. The peaks obtained for all polypyrrole samples were broad in X-ray diffraction studies confirming its amorphous nature. It also indicates poor crystallinity and short range arrangement of PPy chains.
Poly(pyrrole) (PPY) XPS Reference Core Level and Energy Loss Spectra
Surface Science Spectra, 2005
XPS measurements of poly͑pyrrole͒ recorded with a SSX-100 spectrometer in standardized experimental conditions are presented: survey scan, high resolution core level spectra as well as the energy loss regions of carbon, nitrogen and oxygen peaks are analyzed. This is part of a contract work aiming to record spectra in the very same conditions of some 40 different polymers.