Molecular Relaxation in a Fluctuating Environment

Anderson, James E.; Ullman, Robert

doi:10.1063/1.1712250

Cited by 135 publications

(55 citation statements)

References 15 publications

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“…The main reason is that the structural fluctuations are faster than the reorientation time of the -OH group and of the making and breaking of the hydrogen bonds. Since the environments of the reference dipole are homogeneous and these are changing faster than the reorientation time of the molecule then the relaxation time as per Anderson and Ulmann model 44 is of the Debye type. For the case of 5-methyl-2-hexanol under investigation, the -OH group as already stated is at position 2 of the carbon chain and the hydrogen-bonded chain is not that straight due to the presence of the methyl group at position 5 (or position 2 from the second end of the chain), the time taken by the -OH group to change the direction involves the spinning motion about the hydrogen-bonded chain axis which is bent compared to that for 2-ethyl-1-hexanol.…”

Section: Resultsmentioning

confidence: 99%

Effect of high hydrostatic pressure on the dielectric relaxation in a non-crystallizable monohydroxy alcohol in its supercooled liquid and glassy states

Pawlus

Paluch

Nagaraj

et al. 2011

The Journal of Chemical Physics

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The complex relative permittivity of a non-crystallizable secondary alcohol, 5-methyl-2-hexanol, is measured over a wide range of temperatures and pressures up to 1750 MPa (17.5 kbar). The data at atmospheric pressure (P = 0.101 MPa) are analyzed in terms of three processes, and the results are in complete agreement with that of O. E. Kalinovskaya and J. K. Vij [J. Chem. Phys. 112, 3262 (2000)]. Process I is of the Debye type and process II is of the Davidson-Cole type, whereas process III is identified as the Johari-Goldstein relaxation process. For pressures of ∼500 MPa and higher, processes I and II are seen to merge into each other to form a single dominant process which unambiguously cannot be resolved into more than one process. The dielectric relaxation strength of process I decreases slightly initially with pressure and when the two processes have merged at elevated pressures, the total relaxation strength increases with increase in pressure. Process III is better resolvable at higher pressures especially above T g in the supercooled liquid state for the reason that the separation in the time scales between the dominant and the JG relaxation process increases at elevated pressures. Surprisingly we find a change in the slope in the plot of log τ JG vs. 1/T for P = 1750 MPa. The results for the relaxation time of alcohols are compared with the Kirkwood correlation factor, g, and it is found that higher is the g, lower is the relaxation time for process I, and it is more of the Debye type. On a reduction in g brought about by an increase in pressure at lower temperatures, the dominant process becomes non-Debye though extensive hydrogen bonding is still present. The dielectric strength of the merged processes increases with increase in pressure. The values of the steepness index, m = |d log τ /d(T g /T)| T = Tg for processes I and II are different for P = 0.1 MPa. However the value of m, for the composite process, which is a merger of processes I and II, for P = 1750 MPa is almost the same for process II at P = 0.1 MPa. From the results of the activation volume, activation enthalpy, and a comparison of the relaxation times with the g factor, we conclude that both processes I and II are significantly affected by hydrogen bonding and both contribute to the structural relaxation.

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Section: Resultsmentioning

confidence: 99%

Effect of high hydrostatic pressure on the dielectric relaxation in a non-crystallizable monohydroxy alcohol in its supercooled liquid and glassy states

Pawlus

Paluch

Nagaraj

et al. 2011

The Journal of Chemical Physics

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“…If the two processes coexist, a ColeDavidson term a ¼ 0:5 is obtained. Glarum's theories have been extended by Anderson and Ulman [79]. They assumed that the orientation process is function of an environmental property called the free volume.…”

Section: Fundamentals Of Microwave-matter Interactions 29mentioning

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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“…[43][44][45] A somewhat unrelated mechanism that can account generally for both a single relaxation time and a distribution of relaxation times was proposed by Anderson and Ullman. 46 These arise from two conditions of the relative rates of fluctuations of the dipole with respect to the potential energy contour of its surroundings. In this fluctuating environment model, the dipolar reorientation occurs faster than the ͑molecular͒ environment of the dipole relaxes, i.e., the dielectric relaxation time is less than the structural relaxation time.…”

Section: B the Nature Of The Dielectric Relaxation Processesmentioning

confidence: 99%

Effects of induced steric hindrance on the dielectric behavior and H bonding in the supercooled liquid and vitreous alcohol

Johari

Kalinovskaya

Vij

2001

The Journal of Chemical Physics

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The extent of H bonding in alcohols may be reduced by sterically hindering its OH group. This technique is used here for investigating the reasons for the prominent Debye-type dielectric relaxation observed in monohydroxy alcohols ͓Kudlik et al., Europhys. Lett. 40, 549 ͑1997͒; Hansen et al., J. Chem. Phys. 107, 1086 ͑1997͒; Kalinovskaya and Vij, ibid. 112, 3262 ͑2000͔͒, and broadband dielectric spectroscopy of supercooled liquid and glassy states of 1-phenyl-1-propanol is performed over the 165-238 K range. In its molecule, the steric hindrance from the phenyl group and the existence of optical isomers reduce the extent of intermolecular H bonding. The equilibrium permittivity data show that H-bonded chains do not form in the supercooled liquid, and the total polarization decays by three discrete relaxation processes, of which only the slower two could be resolved. The first is described by the Cole-Davidson-type distribution of relaxation times and a Vogel-Fulcher-Tammann-type temperature dependence of its average rate, which are characteristics of the ␣-relaxation process as in molecular liquids. The second is described by a Havriliak-Negami-type equation, and an Arrhenius temperature dependence, which are the characteristics of the Johari-Goldstein process of localized molecular motions. The relaxation rate's non-Arrhenius temperature dependence has been examined qualitatively in terms of the Dyre theory, which considers that the apparent Arrhenius energy itself is temperature dependent, as in the classical interpretations, and quantitatively in terms of the cooperatively rearranging region's size, without implying that there is an underlying thermodynamic transition in its equilibrium liquid. The relaxation rate also fits the power law with the critical exponent of 13.4, instead of 2-4, required by the mode-coupling theory, thereby indicating the ambiguity of the power-law equations.

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Molecular Relaxation in a Fluctuating Environment

Cited by 135 publications

References 15 publications

Effect of high hydrostatic pressure on the dielectric relaxation in a non-crystallizable monohydroxy alcohol in its supercooled liquid and glassy states

Effect of high hydrostatic pressure on the dielectric relaxation in a non-crystallizable monohydroxy alcohol in its supercooled liquid and glassy states

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

Effects of induced steric hindrance on the dielectric behavior and H bonding in the supercooled liquid and vitreous alcohol

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