Dielectric relaxation of n-alkanes at microwave frequencies

Göttmann, O.; Stumper, U.

doi:10.1016/0009-2614(73)80120-4

Cited by 10 publications

(3 citation statements)

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“…On the other hand, dielectric relaxation times τ d are substantially smaller than τ α (Figure ), for example, τ d (20 °C)/τ α (25 °C) = 0.07 for n -dodecane. The τ d values have been taken from microwave and far-infrared spectra of a series of n -alkanes. , Here the τ d values are just defined by the frequency ν d (=(2πτ d ) -1 ) at which the microwave dielectric loss data adopt a relative maximum . A careful analysis shows 23 that, in the 5−500 GHz range, the dielectric spectra of the n -alkanes are subject to a Fröhlich relaxation time distribution (Figure ) involving a minimum and a maximum relaxation time .…”

Section: Discussionmentioning

confidence: 99%

Structural Isomerization and Molecular Motions of Liquidn-Alkanes. Ultrasonic and High-Frequency Shear Viscosity Relaxation

Behrends

Kaatze

2000

J. Phys. Chem. A

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Between 20 and 120 MHz, the complex shear viscosity of n-tetradecane, n-pentadecane, n-hexadecane, and a n-eicosane/n-tetradecane mixture has been measured using a shear impedance spectrometer. The data are compared to ultrasonic absorption spectra of the liquids as measured between 1 MHz and 2 GHz. Relaxational behavior has been found. The extrapolated high-frequency shear viscosity ηs(∞) is distinctly smaller than the static shear viscosity ηs(0). The shear viscosity relaxation time is discussed in light of literature data of the orientational correlation time from depolarized Rayleigh scattering and also of the collision time as resulting from dielectric spectrometry. The assumption appears to be likely that the shear viscosity relaxation is due to rotational isomerizations of the chain molecules. A damped torsional oscillator model has been used to evaluate the spectra. The reasonable number of three carbon atoms per oscillator unit results. The activation energies and enthalpies are derived from measurements at different temperatures.

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Section: Discussionmentioning

confidence: 99%

Structural Isomerization and Molecular Motions of Liquidn-Alkanes. Ultrasonic and High-Frequency Shear Viscosity Relaxation

Behrends

Kaatze

2000

J. Phys. Chem. A

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“…Figure 1.7 gives relaxation frequency range for classical organic functions: alkanes [33,34], alcohols [35][36][37][38][39], alcohol ether [40], acid chlorides [41,42], esters [43,44], aliphatic [45][46][47][48][49][50][51][52][53][54] and aromatic halogens [55,56], aliphatic [57,58], aromatic ketones [59], nitriles [60], and aliphatic [61,62] and aromatic amines [63].…”

Section: Effect Of Imaginary Part: Dielectric Lossesmentioning

confidence: 99%

Microwave‐Material Interactions and Dielectric Properties, Key Ingredients for Mastery of Chemical Microwave Processes

Stuerga¹

2006

Microwaves in Organic Synthesis

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The main focus of the revised edition of this first chapter is essentially the same as the original -to explain in a chemically intelligible fashion the physical origin of microwave-matter interactions and, especially, the theory of dielectric relaxation of polar molecules. This revised version contains approximately 60% new material to scan a large range of reaction media able to be heated by microwave heating. The accounts presented are intended to be illustrative rather than exhaustive. They are planned to serve as introductions to the different aspects of interest in comprehensive microwave heating. In this sense the treatment is selective and to some extent arbitrary. Hence the bibliography contains historical papers and valuable reviews to which the reader anxious to pursue particular aspects should certainly turn.It is the author's conviction, confirmed over many years of teaching experience, that it is much safer -at least for those who rate not trained physicists -to deal intelligently with an oversimplified model than to use sophisticated methods which require experience before becoming productive. Because of comments about the first edition, however, the author has included more technical material to enable better understanding of the concepts and ideas. These paragraphs could be omitted, depending on the level of comprehension of the reader. They are preceded by two different symbols -k for TOOLS and j for CONCEPTS.After consideration of the history and position of microwaves in the electromagnetic spectrum, notions of polarization and dielectric loss will be examined. The orienting effects of electric fields and the physical origin of dielectric loss will be analyzed, as also will transfers between rotational states and vibrational states within condensed phases.Dielectric relaxation and dielectric losses of pure liquids, ionic solutions, solids, polymers and colloids will be discussed. Effect of electrolytes, relaxation of defects within crystals lattices, adsorbed phases, interfacial relaxation, space charge polarization, and the Maxwell-Wagner effect will be analyzed. Next, a brief overview of 1 thermal conversion properties, thermodynamic aspects, and athermal effects will be given.

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“…Dielectric friction is another physical factor that may have an impact on the fast PCET rate . In n ‐alkanes at 20 °C, the dielectric relaxation time, τ D , changes from 2.4 ps in n ‐hexane, to 2.7 ps in n ‐nonane, to 3.2 ps in n ‐decane, and is related to rotation of the ends of the alkyl chains because rotation of whole molecules is an order of magnitude slower . The longitudinal relaxation time, τ L = τ D ( ϵ optical / ϵ static ) is very similar to τ D as in n ‐alkanes ϵ static ≈ ϵ optical .…”

Section: Resultsmentioning

confidence: 99%

Highly Polarized Coumarin Derivatives Revisited: Solvent‐Controlled Competition Between Proton‐Coupled Electron Transfer and Twisted Intramolecular Charge Transfer

Morawski

Kielesiński

Gryko

et al. 2020

Chemistry A European J

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Linking a polarized coumarin unit with an aromatic substituent via an amide bridge results in weak electronic coupling that affects the intramolecular electron‐transfer (ET) process. As a result of this, interesting solvent‐dependent photophysical properties can be observed. In polar solvents, electron transfer in coumarin derivatives of this type induces a mutual twist of the electron‐donating and ‐accepting molecular units (TICT process) that facilitates radiationless decay processes (internal conversion). In the dyad with the strongest intramolecular hydrogen bond, the planar form is stabilized, such that twisting can only occur in highly polar solvents, whereas a fast proton‐coupled electron‐transfer (PCET process) occurs in nonpolar n‐alkanes. The kPCET rate constant decreases linearly with the energy of the fluorescence maximum in different solvents. This observation can be explained in terms of competition between electron‐ and proton‐transfer from a highly polarized (ca. 15 D) and fluorescent locally excited (1LE) state to a much less polarized (ca. 4 D) charge‐transfer (1CT) state, a unique occurrence. Photophysical measurements performed for a family of related coumarin dyads, together with results of quantum‐chemical computations, give insight into the mechanism of the ET process, which is followed by either a TICT or a PCET process. Our results reveal that dielectric solvation of the excited state slows down the PCET process, even in nonpolar solvents.

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Dielectric relaxation of n-alkanes at microwave frequencies

Cited by 10 publications

References 6 publications

Structural Isomerization and Molecular Motions of Liquidn-Alkanes. Ultrasonic and High-Frequency Shear Viscosity Relaxation

Structural Isomerization and Molecular Motions of Liquidn-Alkanes. Ultrasonic and High-Frequency Shear Viscosity Relaxation

Microwave‐Material Interactions and Dielectric Properties, Key Ingredients for Mastery of Chemical Microwave Processes

Highly Polarized Coumarin Derivatives Revisited: Solvent‐Controlled Competition Between Proton‐Coupled Electron Transfer and Twisted Intramolecular Charge Transfer

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