Ahmet Peksoz

Dynamic Nuclear Polarization in Some Aliphatic and Aromatic Solutions as Studied by Fluorine‐Electron Double Resonance

Dynamic nuclear polarization experiments were performed to study the solutions of the stable free radical α,γ‐Bisdiphenylene‐β‐phenyl allyl complex with benzene (1∶1) in some highly fluorinated aliphatic and aromatic solvents. In solutions examined in this study, the Overhauser effect, which normally arises due to both dipolar and scalar interactions between the unpaired electrons of the free radical molecules and fluorine nuclei of solvent molecules occurs mainly. 1‐Iodotridecafluorohexane, 2,2,3,4,4,4‐Hexafluoro‐1‐butanol, N‐methyl‐bis‐trifluoroacetamide, hexafluoroacetylacetone, octafluorotoluene, and hexafluorobenzene were used as the solvents. The experiments were performed at a low field double resonance NMR spectrometer, which operates at 1.53 mT. The NMR enhancements depend on competition between intermolecular magnetic interactions. The measurements were performed at four different temperatures to test the dipolar and the scalar part of the coupling between the fluorine nucleus (19F) and the unpaired electron. It was found that the dipolar interactions are more effective for the aliphatic solvents, while the scalar interactions are more effective for the aromatics. The nuclear‐electron coupling parameter varies between 0.018 and 0.157 in all aliphatic solvents and between −0.063 and −0.035 in aromatic solvents.

Giant Magneto–Impedance Effect in Thin Zinc Oxide Coated on Co-Based (2705 X) Amorphous Ribbons

ZnO film coated Co-based (2705 X) amorphous ribbons are prepared by the successive ionic layer adsorption and reaction technique. The influence of coating on giant magneto-impedance (GMI) has been investigated over a frequency range from 0.1 to 3.5 MHz and under a static magnetic field between -8 and +8 kA/m. The highest GMI ratio of 15.63% was obtained in the coated Co-based amorphous ribbons which is 80% higher than the sample without coating. The results indicate that the surface coating process plays an important role in the GMI effect.

A Low Field Fluorine-Electron Double Resonance Study for GALV and BDPA in Some Aliphatic and Aromatic Solvents

Abstract Dynamic nuclear polarization experiments were performed to study the solutions of the stable free radicals Galvinoxyl and α,γ -Bisdiphenylene-β -phenyl allyl complex with benzene (1 : 1) in some highly fluorinated aliphatic and aromatic solvents. The measurements were performed at four different temperatures to test the dipolar and the scalar part of the coupling between the fluorine nucleus (19F) and the unpaired electron. It was found that in the samples with Galvinoxyl the dipolar interactions are more effective for the aromatic solvents, while the scalar interactions are more effective for the aliphatics. An alteration from negative to positive region for the nuclear-electron coupling parameter informing on scalar or dipole-dipole interaction was observed only for 2,2,3,4,4,4-Hexafluoro- 1-butanol solvent with increasing temperature. The nuclear-electron coupling parameter varies between −0.003 and 0.228 in all aliphatic solvents and between 0.180 and 0.318 in aromatic solvents. Overhauser enhancement was not observed in the samples prepared with Hexadecafluoroheptane, Heptafluorobutyric acid, and Nonafluoropentanoic acid for both free radicals in all temperatures. These solvents may have scavenging effects on the radicals due to their behaviour.

Electrochemical synthesis of polyaniline/inorganic salt binary nanofiber thin films for electrochromic applications

Polyaniline conductive polymer thin films without or with LiClO4 inorganic salt were coated by electrochemical deposition method on ITO surface. Electrochromic stability test, electrochemical behavior, coloring performance, optical properties and surface formations of the produced films were studied in detail. The deposited films were found to have a good stability. Electrochemical analysis showed that the conductivity of LiClO4 doped PANI film was higher than that of the PANI. Oxidation and reduction peaks, and potentials differed significantly depending on the content of the electrolytes. SEM studies demonstrated that the surface of each film consisted of completely nanofibers. Addition of LiClO4 to the deposition electrolyte decreased substantially the diameter of these nanofibers. PANI film with LiClO4 exhibited four colors, while pure PANI film had three different colors. The EDX results obtained from the surface of LiClO4 doped PANI material indicated that PANI and LiClO4 could be successfully linked to form PANI/LiClO4 binary thin film.

A low field proton–electron double resonance study for paramagnetic solutions

Dynamic nuclear polarization has been observed in solutions of a series of aromatic hydrocarbons with Galvinoxyl and α,γ-Bisdiphenylene-β-phenyl allyl complex with benzene (1 : 1) free radicals in a low magnetic field of 1.44 mT. The measurements were performed at three different temperatures to test the dipolar and the scalar part of the coupling between the hydrogen nucleus (1H) and the unpaired electron. At all temperatures and concentrations, negative Overhauser enhancements were measured, indicating that the proton–electron interaction is predominantly dipolar. The observed enhancements vary from −36 to −325 for the samples with BDPA, whereas it varies from −47 to −282 for the samples with GALV. Overhauser enhancement was not observed in the samples prepared with Ethylbenzene, Tetralin and Quinoline for only GALV free radical at all concentrations and temperatures. These solvents may have scavenging effects on the GALV radical due to their behaviour. The high and low frequency relaxation components were calculated for all samples and the relation between them is compared with theory. It was observed that dissolved molecular oxygen in the o-Xylene solvent medium with BDPA and GALV causes the 1H NMR signal enhancement to decrease dramatically. These findings will be discussed in detail.

Dynamic Nuclear Polarization in Highly Fluorinated Solutions

The Overhauser effect type dynamic nuclear polarization experiments were performed to study solutions of the stable free radical α,γ-Bisdiphenylene-β-phenyl allyl complex with benzene (1:1) in some highly fluorinated aliphatic and aromatic solvents. In solutions examined in this study, it occurs mainly the Overhauser effect, which normally arises due to both dipolar and scalar interactions between the unpaired electrons of the free radical molecules and fluorine nuclei of solvent molecules. 1-Iodotridecafluorohexane, N-Methyl-bis-trifluoroacetamide, Octafluorotoluene and Hexafluorobenzene were used as the solvents. The experiments were performed at a low field double resonance NMR spectrometer, which operates at 1.53 mT. The NMR enhancements depend on competition between intermolecular magnetic interactions. It was studied to investigate variation of EPR spectra with four different temperatures. It was found as temperature increases, peak points of EPR spectra decreases.

Analytical Information on the Asphaltenes from a Few Standard Characterization Techniques

Abstract The asphaltene has been obtained from asphalt cement with penetration grade 60, which is extracted from crude Libya petroleum. The elemental composition and some structural properties of the asphaltene samples are determined by various methods, such as SEM, infrared spectroscopy, and X-ray analysis. Some experiments are performed on 1H dynamic nuclear polarization (DNP) in a number of asphaltene suspensions in organic solvents. The frequency dependence of the DNP enhancement under conditions of weak EPR saturation in a low magnetic field is obtained and interpreted as the EPR line shape of some free radicals present in the samples.

Dynamic Nuclear Polarization in Suspensions Consisting of Pure and Mixed Chlorobenzene and Pyridine and Asphaltene Extracted from Asphalt Cement with Penetration Grad 60

The Overhauser effect type dynamic nuclear polarization experiments were performed to study suspensions of asphaltene in pure and mixed chlorobenzene and pyridine at a low magnetic field of 1.44 mT and in four different temperatures (− 10, 7, 23, and 38°C). The asphaltene was extracted from asphalt cement with penetration grad 60. Intermolecular spin-spin interactions occur between nuclear spins of hydrogen in the suspending fluid medium and the unpaired electron spins in the asphaltene micelles. The electron paramagnetic resonance spectrum of the asphaltene was obtained and the saturation experiments were applied to the samples prepared in vacuum. For all suspending fluid media used in this work, the dipole-dipole interaction is predominant due to the negative signal enhancements. In all temperatures, the dipolar part is the smallest (− 9.17) for pure pyridine solvent medium at − 10°C and the highest (− 38.2) for pure chlorobenzene solvent medium at 38°C and between these two limits for mixed solvent media at all temperatures.

Intermolecular Magnetic Spin–Spin Interactions in Solution State at 1.53 mT

Overhauser dynamic nuclear polarization (DNP) technique can provide a dramatic increase in the signal obtained from nuclear magnetic resonance experiments owing to the magnetic spin–spin interactions between 1H nuclei of the solvent and electrons delocalized on the asphaltene in crude petroleum or asphalt. Studies on 1H Overhauser DNP enhancements at 1.53 mT are reported for benzene solvent medium with three different radical sources: Iran crude petroleum, MC30 liquid asphalt, and MC800 liquid asphalt for a range of radical concentrations. The results show that protons of benzene are good detectors for dipolar coupling. GRAPHICAL ABSTRACT

DNP sensitivity of 19F‐NMR signals in hexafluorobenzene depending on polarizing agent type

Low field dynamic nuclear polarization or low field magnetic double resonance technique enables enhanced nuclear magnetic resonance signals to be detected without increasing the strength of the polarizing field. The study reports that the dynamic nuclear polarization of 19F nuclei in hexafluorobenzene solutions doped with nitroxide, BDPA, MC800 asphaltene and MC30 asphaltene free radicals at 15 G. The 19F nuclei in all solutions gave positive DNP enhancements changing between 3.42 and 189.54, corresponding to predominantly scalar interactions with the unpaired electrons in the radicals. DNP sensitivity of 19F nuclei in hexafluorobenzene was observed to be changed significantly depending on the radical type. Nitroxide was found to have the best DNP performance among the polarizing agents. Copyright