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Walter Dannhauser

Bio: Walter Dannhauser is an academic researcher from University at Buffalo. The author has contributed to research in topics: Dielectric & Cole–Cole equation. The author has an hindex of 16, co-authored 26 publications receiving 1125 citations.

Papers
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TL;DR: In this paper, the dielectric constants of the eight lowest aliphatic alcohols have been measured from room temperature to their respective critical temperatures, and the data were analyzed in terms of Kirkwood's correlation factor based on a model of linear, hydrogen-bonded chains with restricted rotation about the hydrogen bond and variable degree of polymerization.
Abstract: The dielectric constants of the eight lowest aliphatic alcohols have been measured from room temperature to their respective critical temperatures. The densities were also measured if they were not previously available. The data were analyzed in terms of Kirkwood's correlation factor based on a model of linear, hydrogen‐bonded chains with restricted rotation about the hydrogen bond and variable degree of polymerization. The equilibrium constants are strongly dependent on the size and shape of the alkyl group. —ΔF°298 (kcal/mole; mole fraction units), —ΔH°298 (kcal/mole), and —ΔS°298 (cal/mole·deg) for hydrogen‐bond formation in the pure liquid are: MeOH, 3.95, 6.50, 8.56; EtOH, 4.10, 8.63, 15.2; n‐PrOH, 3.42, 7.76, 14.6; iso‐PrOH, 2.97, 8.64, 19.1; n‐BuOH, 3.12, 7.70, 15.4; iso‐BuOH, 2.87, 8.73, 19.7; sec‐BuOH, 2.05, 7.97, 19.9; tert‐BuOH, 0.98, 7.28, 21.2.

193 citations

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TL;DR: In this paper, the temperature dependences of static values are examined in terms of finite extent of chainwise molecular coordination by hydrogen bonding, and the rate laws of the dispersions are discussed.
Abstract: Measurements of static dielectric constant were made for all except t‐butyl alcohol from the boiling points to —140°C; dispersion and loss were measured below 0°C in the range 20 cy/sec to 2 Mc/sec. Multiple dispersions were found as in other alcohols. The temperature dependences of static values are examined in terms of finite extent of chainwise molecular coordination by hydrogen bonding, and the rate laws of the dispersions are discussed.

174 citations

Journal ArticleDOI
TL;DR: In this article, a simple molecular model based on hydrogen-bond associative equilibria involving both ring dimers and linear chain n−mers is developed, and equilibrium constants for ring and chain formation are deduced, and it is concluded that entropic factors which can be correlated with the geometry of the molecules are the principal basis for differences between isomers.
Abstract: The equilibrium dielectric constants of eight liquid isomeric octanols have been measured over a wide range of temperature, and the data are analyzed in terms of the Kirkwood correlation factor. A simple molecular model based on hydrogen‐bond associative equilibria involving both ring dimers and linear chain n‐mers is developed. Equilibrium constants for ring and chain formation are deduced, and it is concluded that entropic factors, which can be correlated with the geometry of the molecules, are the principal basis for differences between isomers. At relatively high temperatures those species whose − OH group is most sterically blocked prefer to form rings, while those whose − OH group is relatively accessible tend to form open chains. In all cases, chains become the preferred species at low temperatures. ΔH° for hydrogen‐bond formation in chains is estimated as about − 6.7 kcal/mole; for rings, about − 4.5 kcal/mole. ΔS° varies from − 16 to − 30 eu/mole for chains and from − 13 to − 20 eu/mole for rings.

134 citations

Journal ArticleDOI
TL;DR: In this paper, the dielectric constant and loss of eight isomeric octanols have been measured over a wide range of temperature and frequency, and two distinctly different types of dispersion loci are found: for those alcohols whose sterically hindered that association into linear chains is unfavorable, a very small, very broad dispersion, characterized by relatively short relaxation times, is found.
Abstract: The dielectric constant and loss of eight isomeric octanols has been measured over a wide range of temperature and frequency. Two distinctly different types of dispersion loci are found: For those alcohols whose –OH group is so sterically hindered that association into linear chains is unfavorable, a very small, very broad dispersion, characterized by relatively short relaxation times, is found. For less hindered species, the low‐frequency, relatively slow, dispersion is Debye‐like, and two high‐frequency dispersion regions have been resolved in two compounds. The molar activation energies for all three dispersion regions are closely similar and τ1:τ2:τ3 ∼ 100:10:1. The activation energy for the principal (Debye‐like) dispersion is strongly dependent on the steric hindrance of the –OH group. Activation energies vary from about 8 to 20 kcal so that rupture of a hydrogen bond is an unlikely rate‐determining step.

81 citations

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TL;DR: In this article, a qualitative model of dielectric relaxation based on ideas of Litovitz and Anderson and Ullman is proposed to explain the results of the debye equation.
Abstract: Dielectric constant and loss have been measured in the frequency range 0.1 − 5 × 106 Hz over a wide range of temperature and pressures to 4 kbar for the following compounds: 2‐octanol, 7‐methyl‐, 6‐methyl‐, 5‐methyl‐, and 2‐methyl‐3‐heptanol. For each compound, most of the dispersion is well described by the Debye equation. At high frequencies additional regions of dispersion appear which could be resolved in three of the compounds. Activation parameters are derived for all of the compounds and are functions of pressure, temperature, and the nature of the alcohol's alkyl group. A qualitative model of dielectric relaxation based on ideas of Litovitz and Anderson and Ullman is proposed to explain the results.

70 citations


Cited by
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TL;DR: In this article, a broad correlation of non-debye behavior with non-Arrhenius relaxations was found for different types of glass formers, distinguished by their respective molecular complexity.
Abstract: Deviations from thermally activated and from exponential response are typical features of the vitrification phenomenon and previously have been studied using viscoelastic, dielectric, calorimetric, optical, and other techniques. Linear response data from literature on about 70 covalent glass formers, ionic melts, supercooled liquids, amorphous polymers, and glassy crystals are surveyed. Except for orientational glasses and monohydric aliphatic alcohols a distinct but broad correlation of non‐Debye behavior with non‐Arrhenius relaxations is found. Within the broad trend several groups of materials, distinguished by their respective molecular complexity, can be identified and are shown to exhibit narrow correlations. At a given degree of deviation from Arrhenius behavior externally imposed stresses are relaxed with a departure from exponential behavior which is stronger the more the molecular or atomic subunits of the glassforming material are interconnected with each other.

2,146 citations

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TL;DR: The dielectric loss factor and permittivity of 8-16 mol% solutions of chlorobenzene, o−dichlorobenzenes, and 1-chloronaphthalene in cis-decalin were measured by DTA as mentioned in this paper.
Abstract: The dielectric loss factor and dielectric permittivity of 8–16 mol% solutions of chlorobenzene, o‐dichlorobenzene, and 1‐chloronaphthalene in cis‐decalin; 50–60 mol% mixtures of pyridine with chlorobenzene, bromobenzene, 1‐chloronaphthalene, and toluene; 50–60 mol% mixtures of tetrahydrofuran with bromobenzene and 1‐chloronaphthalene; the pure liquids cis‐decalin, o‐terphenyl, iso‐propylbenzene, propylene carbonate; and two fused salt systems, 45 mol% Ca(NO3)2–KNO3 mixture and Ca(NO3)2·4H2O have been measured from 50 Hz to 1 × 105 Hz from − 196° in the vitreous state to about 30° above their respective glass transition temperatures. The Tg's of the organic glasses have been measured by DTA. With the exception of propylene carbonate, all glasses show the presence of one secondary relaxation between − 196° and their respective Tg's either as a peak or shoulder in a tanδ–temperature plot at a single frequency, or in the dielectric loss spectrum. Arrhenius plots of the frequency of maximum loss against temper...

1,519 citations

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TL;DR: A detailed review of the current literature reveals the lack of predictive understanding of the microscopic mechanisms that govern the structure-property relationships in deep eutectic solvents, and highlights recent research efforts to elucidate the next steps needed to develop a fundamental framework needed for a deeper understanding.
Abstract: Deep eutectic solvents (DESs) are an emerging class of mixtures characterized by significant depressions in melting points compared to those of the neat constituent components. These materials are promising for applications as inexpensive "designer" solvents exhibiting a host of tunable physicochemical properties. A detailed review of the current literature reveals the lack of predictive understanding of the microscopic mechanisms that govern the structure-property relationships in this class of solvents. Complex hydrogen bonding is postulated as the root cause of their melting point depressions and physicochemical properties; to understand these hydrogen bonded networks, it is imperative to study these systems as dynamic entities using both simulations and experiments. This review emphasizes recent research efforts in order to elucidate the next steps needed to develop a fundamental framework needed for a deeper understanding of DESs. It covers recent developments in DES research, frames outstanding scientific questions, and identifies promising research thrusts aligned with the advancement of the field toward predictive models and fundamental understanding of these solvents.

911 citations

Journal ArticleDOI
TL;DR: In this paper, the important general dynamic and thermodynamic properties of structural glass-forming substances and classify them into 12 different categories, including those relating to the high frequency fast relaxation, the Johari-Goldstein β-relaxation, and the slow structural α-Relaxation.
Abstract: We review the important general dynamic and thermodynamic properties of structural glass-forming substances and classify them into 12 different categories. Our understanding of glass-forming substances is incomplete until all these properties have been explained. The dynamic properties considered include those relating to the high frequency fast relaxation, the Johari–Goldstein β-relaxation, and the slow structural α-relaxation. Practically all the important relaxation and diffusion processes in the time region extending from 10−13 to 106 s have been discussed. We show from experimental data that the properties in different categories bear some relations to each other. Some issues that impede progress of our understanding of the behavior of glass-forming substances are accentuated by formulating them as questions. Answers to these questions by future experimental and theoretical investigations will improve our understanding. Specific suggestions for future research efforts that can provide some answers to these questions are also made. Within the same property in each category, by examining a large number of glass-formers, a pattern of variation is found which correlates with the departure of the structural relaxation of the glass-former from exponential decay or the quantity, (1−β), where β is the fractional exponent in the Kohlrausch expression, exp[−(t/τ)β]. These patterns, as well as their correlations with (1−β), suggest that the salient dynamic properties (or phenomenology) of glass-forming substances are all governed by the non-exponential nature of the structural relaxation, i.e., the quantity (1−β). Therefore, a theory or model capable of relating the structural relaxation time τ to (1−β) has the potential of explaining many of the salient dynamic properties of glass-forming substances.

392 citations

Journal ArticleDOI
TL;DR: A brief review of the progress made in the study of relaxations of molecular liquids near and below the glass transition temperature in the context of present theories of glass structure, as well as some new results on the relaxation of rigid molecular liquids and plastic crystalline solids.
Abstract: It has been known for many years that substances in the glassy state retain some degree of molecular mobility that is detectable by a dielectric or a mechanical relaxation, or by an N M R experiment. These relaxations have been termed secondary or p relaxations and they occur on a time scale many times shorter than that of the main relaxation responsible for the glass transition itself.' The presence of such relaxations has generally been associated with the motion of a side group attached to a polymer chain, o r with a certain type of movement of the chain itself, and has been explained in terms of hindered internal molecular modes of motion that remain active even when the molecule as a whole is frozen in place in a glassy matrix.' Several years ago we studied a number of glasses made from molecular liquids2 lacking either a side chain or any other internal degree of freedom capable of giving rise to a relaxation traditionally invoked for polymers and network glasses. The study revealed a remarkable similarity in the dielectric relaxations of these glasses to those of polymers, and a surprisingly uniform pattern of behavior. The main conclusion drawn from the study was that the molecular mobility seen as p relaxations is intrinsic to the nature of the glassy state. It became apparent then that a theory for the structure of grossly disordered solids must necessarily consider such relaxations as arising from a motion over the potential energy barriers similar in origin to those involved in the glass transition itself. There is, however, another approach to the study of grossly disordered solids, such as glasses. One may start from a perfect crystal, relatively well understood both theoretically and experimentally because the translational symmetry allows enormous simplification of the algebra, and approach the glassy state gradually. An orientationally disordered or plastic crystal is intermediate between a perfect crystal and a glass in that, although there is a long-range order of molecular positions, there is no long-range order in the molecular orientations. This paper presents a brief review of the progress made in the study of relaxations of molecular liquids near and below the glass transition temperature in the context of present theories of glass structure, as well as some new results on the relaxation of rigid molecular liquids and plastic crystalline solids, and the implication these results have for the concepts of the glass transition phenomenon.

381 citations