The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Ranko Richert - One of the best experts on this subject based on the ideXlab platform.
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polyamorphism in vapor deposited 2 Methyltetrahydrofuran a broadband dielectric relaxation study
Journal of Chemical Physics, 2021Co-Authors: Jan Philipp Gabriel, Birte Riechers, Anthony Guiseppielie, M D Ediger, Erik Thoms, Ranko RichertAbstract:Depositing a simple organic molecular glass-former 2-Methyltetrahydrofuran (MTHF) onto an interdigitated electrode device via physical vapor deposition gives rise to an unexpected variety of states, as revealed by dielectric spectroscopy. Different preparation parameters, such as deposition temperature, deposition rate, and annealing conditions, lead, on the one hand, to an ultrastable glass and, on the other hand, to a continuum of newfound further states. Deposition below the glass transition temperature of MTHF leads to loss profiles with shape parameters and peak frequencies that differ from those of the known bulk MTHF. These loss spectra also reveal an additional process with Arrhenius-like temperature dependence, which can be more than four decades slower than the main structural relaxation peak. At a given temperature, the time constants of MTHF deposited between 120 K and 127 K span a range of more than three decades and their temperature dependencies change from strong to fragile behavior. This polyamorphism involves at least three distinct states, each persisting for a duration many orders of magnitude above the dielectric relaxation time. These results represent a significant expansion of a previous dielectric study on vapor deposited MTHF [B. Riechers et al., J. Chem. Phys. 150, 214502 (2019)]. Plastic crystal states and the effects of weak hydrogen bonding are discussed as structural features that could explain these unusual states.
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ultrastable and polyamorphic states of vapor deposited 2 Methyltetrahydrofuran
Journal of Chemical Physics, 2019Co-Authors: Birte Riechers, Anthony Guiseppielie, M D Ediger, Ranko RichertAbstract:This work reports results gained from dielectric spectroscopy on the organic molecular glass-former 2-Methyltetrahydrofuran (MTHF), which was deposited onto an interdigitated electrode device by physical vapor deposition. By a suitable selection of preparation parameters (deposition temperature, deposition rate, and annealing conditions), various states of MTHF could be created: ultrastable glass, a liquid state with unusual dielectric properties, or the ordinary liquid state as obtained by supercooling. Observations on kinetic stability as well as on the suppression of dielectric loss in the ultrastable state resemble previous findings for other molecular glass-formers. Remarkably, after annealing just above Tg, all vapor-deposited films of MTHF display a static dielectric constant in the liquid state (es) that is up to a factor of two below that of the ordinary bulk liquid. A structural transition to the ordinary liquid-cooled state of MTHF occurs at temperatures far above its conventional Tg, indicative of polyamorphism: the formation of an unusual structure that is achieved by physical vapor deposition and that differs from the ordinary liquid state obtained by supercooling. The present results also reveal that the dielectric constant of the as deposited glass (e∞) is reduced to practically the value of the squared refractive index, n2.
Nagwa Ghoneim - One of the best experts on this subject based on the ideXlab platform.
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photophysics of nile red in solution steady state spectroscopy
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2000Co-Authors: Nagwa GhoneimAbstract:Abstract Spectroscopic properties of Nile red (NR) in organic solvents, binary solvent mixtures have been studied. Remarkable shifts in the emission band positions have been observed as a function of the polarity of the medium. In solvent mixtures, these shifts can be explained by the process of specific solvation known as dielectric enrichment. The displacement of the fluorescence band was also measured as a function of temperature to obtain the thermochromic shifts (15 cm−1 K−1 in Methyltetrahydrofuran and 13.8 cm−1 K−1 in butanol). Excited state dipole moments were calculated from these shifts.
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photophysics of nile red in solution steady state spectroscopy
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2000Co-Authors: Nagwa GhoneimAbstract:Abstract Spectroscopic properties of Nile red (NR) in organic solvents, binary solvent mixtures have been studied. Remarkable shifts in the emission band positions have been observed as a function of the polarity of the medium. In solvent mixtures, these shifts can be explained by the process of specific solvation known as dielectric enrichment. The displacement of the fluorescence band was also measured as a function of temperature to obtain the thermochromic shifts (15 cm−1 K−1 in Methyltetrahydrofuran and 13.8 cm−1 K−1 in butanol). Excited state dipole moments were calculated from these shifts.
George C Benson - One of the best experts on this subject based on the ideXlab platform.
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excess enthalpies of the ternary mixtures tetrahydrofuran diisopropyl ether or 2 Methyltetrahydrofuran n heptane at 298 15 k
Fluid Phase Equilibria, 2004Co-Authors: Zhaohui Wang, Daisuke Kodama, George C BensonAbstract:Excess molar enthalpies, measured at 298.15 K in a flow microcalorimeter, are reported for the ternary mixtures (tetrahydrofuran + diisopropyl ether + n-heptane) and (tetrahydrofuran + 2-Methyltetrahydrofuran + n-heptane). Smooth representations of the results are described and used to construct constant excess molar enthalpy contours on Roozeboom diagrams. The latter are compared with diagrams obtained when the model of Liebermann and Fried is used to estimate the excess enthalpies of the ternary mixtures from the physical properties of the components and their binary mixtures.
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excess molar enthalpies of the ternary mixtures diisopropyl ether or 2 Methyltetrahydrofuran cyclohexane n heptane at 298 15 k
Thermochimica Acta, 2003Co-Authors: Zhaohui Wang, George C BensonAbstract:Microcalorimetric measurements of excess molar enthalpies, at 298.15 K, are reported for the two ternary systems formed by mixing either diisopropyl ether or 2-Methyltetrahydrofuran with binary mixtures of cyclohexane and n-heptane. Smooth representations of the results are presented and used to construct constant excess molar enthalpy contours on Roozeboom diagrams. It is shown that useful estimates of the ternary enthalpies can be obtained from the Liebermann and Fried model, using only the physical properties of the components and their binary mixtures.
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excess enthalpies of 2 Methyltetrahydrofuran n alkane binary mixtures at 298 15 k
Journal of Chemical & Engineering Data, 2001Co-Authors: Zhaohui Wang, George C BensonAbstract:Excess molar enthalpies, measured at 298.15 K in a microcalorimeter, are reported for the binary systems formed by mixing 2-Methyltetrahydrofuran with hexane, heptane, octane, decane, or dodecane. Smooth representations of the results are described.
Zhaohui Wang - One of the best experts on this subject based on the ideXlab platform.
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excess enthalpies of the ternary mixtures tetrahydrofuran diisopropyl ether or 2 Methyltetrahydrofuran n heptane at 298 15 k
Fluid Phase Equilibria, 2004Co-Authors: Zhaohui Wang, Daisuke Kodama, George C BensonAbstract:Excess molar enthalpies, measured at 298.15 K in a flow microcalorimeter, are reported for the ternary mixtures (tetrahydrofuran + diisopropyl ether + n-heptane) and (tetrahydrofuran + 2-Methyltetrahydrofuran + n-heptane). Smooth representations of the results are described and used to construct constant excess molar enthalpy contours on Roozeboom diagrams. The latter are compared with diagrams obtained when the model of Liebermann and Fried is used to estimate the excess enthalpies of the ternary mixtures from the physical properties of the components and their binary mixtures.
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excess molar enthalpies of the ternary mixtures diisopropyl ether or 2 Methyltetrahydrofuran cyclohexane n heptane at 298 15 k
Thermochimica Acta, 2003Co-Authors: Zhaohui Wang, George C BensonAbstract:Microcalorimetric measurements of excess molar enthalpies, at 298.15 K, are reported for the two ternary systems formed by mixing either diisopropyl ether or 2-Methyltetrahydrofuran with binary mixtures of cyclohexane and n-heptane. Smooth representations of the results are presented and used to construct constant excess molar enthalpy contours on Roozeboom diagrams. It is shown that useful estimates of the ternary enthalpies can be obtained from the Liebermann and Fried model, using only the physical properties of the components and their binary mixtures.
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excess enthalpies of the ternary mixtures diisopropyl ether or 2 Methyltetrahydrofuran hexane hexadecane at 298 15 k
Journal of Chemical & Engineering Data, 2002Co-Authors: Zhaohui Wang, And George C BensonAbstract:Excess molar enthalpies, measured at 298.15 K in a flow microcalorimeter, are reported for diisopropyl ether + hexane + hexadecane and for 2-Methyltetrahydrofuran + hexane + hexadecane. Smooth representations of the results are described and used to construct constant excess molar enthalpy contours on Roozeboom diagrams. The latter are compared with diagrams obtained when the model of Liebermann and Fried is used to estimate the excess molar enthalpies of the ternary mixtures from the physical properties of the components and the excess molar enthalpies of their binary mixtures.
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excess enthalpies of 2 Methyltetrahydrofuran n alkane binary mixtures at 298 15 k
Journal of Chemical & Engineering Data, 2001Co-Authors: Zhaohui Wang, George C BensonAbstract:Excess molar enthalpies, measured at 298.15 K in a microcalorimeter, are reported for the binary systems formed by mixing 2-Methyltetrahydrofuran with hexane, heptane, octane, decane, or dodecane. Smooth representations of the results are described.
Birte Riechers - One of the best experts on this subject based on the ideXlab platform.
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polyamorphism in vapor deposited 2 Methyltetrahydrofuran a broadband dielectric relaxation study
Journal of Chemical Physics, 2021Co-Authors: Jan Philipp Gabriel, Birte Riechers, Anthony Guiseppielie, M D Ediger, Erik Thoms, Ranko RichertAbstract:Depositing a simple organic molecular glass-former 2-Methyltetrahydrofuran (MTHF) onto an interdigitated electrode device via physical vapor deposition gives rise to an unexpected variety of states, as revealed by dielectric spectroscopy. Different preparation parameters, such as deposition temperature, deposition rate, and annealing conditions, lead, on the one hand, to an ultrastable glass and, on the other hand, to a continuum of newfound further states. Deposition below the glass transition temperature of MTHF leads to loss profiles with shape parameters and peak frequencies that differ from those of the known bulk MTHF. These loss spectra also reveal an additional process with Arrhenius-like temperature dependence, which can be more than four decades slower than the main structural relaxation peak. At a given temperature, the time constants of MTHF deposited between 120 K and 127 K span a range of more than three decades and their temperature dependencies change from strong to fragile behavior. This polyamorphism involves at least three distinct states, each persisting for a duration many orders of magnitude above the dielectric relaxation time. These results represent a significant expansion of a previous dielectric study on vapor deposited MTHF [B. Riechers et al., J. Chem. Phys. 150, 214502 (2019)]. Plastic crystal states and the effects of weak hydrogen bonding are discussed as structural features that could explain these unusual states.
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ultrastable and polyamorphic states of vapor deposited 2 Methyltetrahydrofuran
Journal of Chemical Physics, 2019Co-Authors: Birte Riechers, Anthony Guiseppielie, M D Ediger, Ranko RichertAbstract:This work reports results gained from dielectric spectroscopy on the organic molecular glass-former 2-Methyltetrahydrofuran (MTHF), which was deposited onto an interdigitated electrode device by physical vapor deposition. By a suitable selection of preparation parameters (deposition temperature, deposition rate, and annealing conditions), various states of MTHF could be created: ultrastable glass, a liquid state with unusual dielectric properties, or the ordinary liquid state as obtained by supercooling. Observations on kinetic stability as well as on the suppression of dielectric loss in the ultrastable state resemble previous findings for other molecular glass-formers. Remarkably, after annealing just above Tg, all vapor-deposited films of MTHF display a static dielectric constant in the liquid state (es) that is up to a factor of two below that of the ordinary bulk liquid. A structural transition to the ordinary liquid-cooled state of MTHF occurs at temperatures far above its conventional Tg, indicative of polyamorphism: the formation of an unusual structure that is achieved by physical vapor deposition and that differs from the ordinary liquid state obtained by supercooling. The present results also reveal that the dielectric constant of the as deposited glass (e∞) is reduced to practically the value of the squared refractive index, n2.