| Reference | [1]. J Chem Phys. 2008 Mar 28;128(12):124505. doi: 10.1063/1.2844797.<br />
Dynamics of glass-forming liquids. XII. Dielectric study of primary and secondary relaxations in ethylcyclohexane.<br />
Mandanici A(1), Huang W, Cutroni M, Richert R.<br />
Author information: (1)Dipartimento di Fisica, Università di Messina, 98100 Messina, Italy.<br />
The dynamics of ethylcyclohexane are investigated by high resolution dielectric spectroscopy aiming to characterize the relevant relaxational features of this simple system in its fluid, supercooled liquid, and glassy states. The dielectric signature of structural relaxation is a primary loss peak with amplitude Deltaepsilon=0.01, and a secondary loss process is found in the glassy state. This beta relaxation is compared with a "slow" process revealed by ultrasonics and with previously found gamma and chi processes in similar materials containing the cyclohexyl group. The results suggest that this secondary process is an intramolecular mode rather than a Johari-Goldstein process, consistent with its persistence in the liquid state at slow relaxation times which exceed those of the alpha process. The dielectric activity of such a slow process requires that the dipole magnitude changes with the intramolecular transition, whereas a change in dipole direction only would be masked by the faster structural relaxation.<br />
DOI: 10.1063/1.2844797 PMID: 18376941<br />
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[2]. J Chem Phys. 2015 Feb 7;142(5):054506. doi: 10.1063/1.4906806.<br />
How much time is needed to form a kinetically stable glass? AC calorimetric study of vapor-deposited glasses of ethylcyclohexane.<br />
Chua YZ(1), Ahrenberg M(1), Tylinski M(2), Ediger MD(2), Schick C(1).<br />
Author information: (1)Institute of Physics, University of Rostock, Wismarsche Str. 43-45, 18051 Rostock, Germany. (2)Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.<br />
Glasses of ethylcyclohexane produced by physical vapor deposition have been characterized by in situ alternating current chip nanocalorimetry. Consistent with previous work on other organic molecules, we observe that glasses of high kinetic stability are formed at substrate temperatures around 0.85 Tg, where Tg is the conventional glass transition temperature. Ethylcyclohexane is the least fragile organic glass-former for which stable glass formation has been established. The isothermal transformation of the vapor-deposited glasses into the supercooled liquid state was also measured. At seven substrate temperatures, the transformation time was measured for glasses prepared with deposition rates across a range of four orders of magnitude. At low substrate temperatures, the transformation time is strongly dependent upon deposition rate, while the dependence weakens as Tg is approached from below. These data provide an estimate for the surface equilibration time required to maximize kinetic stability at each substrate temperature. This surface equilibration time is much smaller than the bulk α-relaxation time and within two orders of magnitude of the β-relaxation time of the ordinary glass. Kinetically stable glasses are formed even for substrate temperatures below the Vogel and the Kauzmann temperatures. Surprisingly, glasses formed in the limit of slow deposition at the lowest substrate temperatures are not as kinetically stable as those formed near 0.85 Tg.<br />
DOI: 10.1063/1.4906806 PMID: 25662653<br />
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[3]. J Phys Chem A. 2012 May 31;116(21):5100-11. doi: 10.1021/jp301043r. Epub 2012 May 16.<br />
Detailed product analysis during low- and intermediate-temperature oxidation of ethylcyclohexane.<br />
Husson B(1), Herbinet O, Glaude PA, Ahmed SS, Battin-Leclerc F.<br />
Author information: (1)Laboratoire Réactions et Génie des Procédés, CNRS, Université de Lorraine, 1 Rue Grandville, BP 20451, 54001 Nancy Cedex, France.<br />
An experimental study of the oxidation of ethylcyclohexane has been performed in a jet-stirred reactor with online gas chromatography, under quasi-atmospheric pressure (800 Torr), at temperatures ranging from 500 to 1100 K (low- and intermediate-temperature zone including the negative temperature coefficient area), at a residence time of 2 s, and for three equivalence ratios (0.25, 1, and 2). Ethylcyclohexane displays important low-temperature reactivity with a well-marked negative temperature coefficient behavior. In addition to 47 products with a mass lower than ethylcyclohexane which have been quantified, many species with a C(8)H(14)O formula (molecular weight of 126) were detected by GC-MS and 7 of them were quantified. These molecules are cyclic ethers, ketones, and aldehydes with the same carbon skeleton as the reactant. Experiments were also carried on under the same conditions for two other C(8) hydrocarbons, n-octane and 1-octene, showing that the reactivity of ethylcyclohexane is close to that of the alkene and lower than that of the alkane. Simulations using a detailed kinetic model of the literature allow a good prediction of the global reactivity and of the main hydrocarbon products for temperatures above 800 K. The main reaction channels leading to the observed reaction products at both low (below 800 K) and intermediate temperature (above 800 K) are discussed.<br />
DOI: 10.1021/jp301043r PMID: 22591104<br />
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[4]. J Phys Chem B. 2015 Mar 12;119(10):4076-83. doi: 10.1021/jp5109174. Epub 2015 Feb 26.<br />
Devitrification properties of vapor-deposited ethylcyclohexane glasses and interpretation of the molecular mechanism for formation of vapor-deposited glasses.<br />
Ramos SL(1), Chigira AK, Oguni M.<br />
Author information: (1)Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology , 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8551, Japan.<br />
We constructed an adiabatic calorimeter adapted for the preparation and in situ thermal characterization of vapor-deposited glasses and reported the investigation of the enthalpic states and dynamic properties of ethylcyclohexane (ECH) glasses prepared by vapor deposition in the temperature range of (0.71-0.96)Tg,liq; Tg,liq = (101 ± 1) K is the calorimetric glass transition temperature of the bulk liquid. It was verified that the ECH glasses deposited at temperatures immediately below Tg,liq were characterized by lower enthalpies and higher devitrification temperatures (Tdev), as compared to the glass obtained by supercooling the bulk liquid. The deposition temperature (TD) expected to yield experimentally the entity with the highest Tdev and the lowest enthalpic state was estimated to be 0.93Tg,liq. A model potentially elucidating the fundamental mechanism of formation and devitrification for the glasses prepared via the physical vapor deposition method as a function of TD was proposed. The fundamental point is that the glass is formed by deposition in a molecule-by-molecule fashion and the molecule deposited is frozen in a certain configuration determined by its being itself on the surface. For amorphous entities prepared at a TD much lower than Tg,liq, the surface molecule is frozen mostly as they are deposited. For the entity deposited at TD = 0.93Tg,liq in the case of ECH, the surface molecule is mobile immediately after the deposition to look for its stable configuration only on account of the intermolecular interactions with the molecules beneath and in the same surface layer as itself and freezes in a certain reasonably stable configuration; the molecules below the surface layer have already frozen in and get more stabilization energy through the additional interactions with the surface molecules. As a result, the intermolecular interaction of the molecules accumulated in such a way is stronger than that in the bulk liquid glass. It is argued that this is the fundamental reason why the glass formed immediately below Tg,liq has a lower enthalpy and a higher devitrification temperature than those of the liquid-cooled one.<br />
DOI: 10.1021/jp5109174 PMID: 25692319<br />
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[5]. J Phys Chem B. 2013 Sep 5;117(35):10311-9. doi: 10.1021/jp404256r. Epub 2013 Aug 21.<br />
Molar volumes of ethylcyclohexane and butyronitrile glasses resulting from vapor deposition: dependence on deposition temperature and comparison to alkylbenzenes.<br />
Nakayama H(1), Omori K, Ino-u-e K, Ishii K.<br />
Author information: (1)Department of Chemistry, Gakushuin University, 1-5-1 Mejiro, Toshimaku, Tokyo 171-8588, Japan.<br />
Molar volumes (Vm) of vapor-deposited ethylcyclohexane (ECH) and butyronitrile (BN, sometimes called butanenitrile) glasses were studied as a function of deposition temperature (Td). ECH glasses deposited at Td sufficiently below their glass-transition temperature (Tg) exhibited changes in Vm on heating similarly to alkylbenzenes. At Td close to Tg, ECH formed dense glasses as alkylbenzenes do, although these glasses were only slightly more dense than its supercooled liquid (SCL) states at the same temperatures. For BN, no indication of the formation of dense glasses was observed even at Td close to Tg, and the variations in Vm with the temperature elevation were different from those of alkylbenzenes. Analysis of the initial Vm of the deposited glasses of different compounds demonstrated that its Td-dependence was well correlated with the steepness index (m) of the corresponding SCL. Quantum-chemical calculations concerning dimer formation by the studied compounds showed that the hydrogen bond between a C-H bond in the alkyl group and π-electrons in the phenyl ring stabilizes the alkylbenzene dimers, suggesting the possibility of the dense glass formation and large m of these compounds. The small m value of BN was also discussed on the basis of the calculation results.<br />
DOI: 10.1021/jp404256r PMID: 23919523
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