The Experts below are selected from a list of 237636 Experts worldwide ranked by ideXlab platform
Ting Cai - One of the best experts on this subject based on the ideXlab platform.
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fast Surface Diffusion and crystallization of amorphous griseofulvin
Journal of Physical Chemistry B, 2017Co-Authors: Chengbin Huang, Shigang Ruan, Ting CaiAbstract:Among molecular glasses, griseofulvin (GSF) is one of the fastest crystallizing. To understand this property, we have measured the Surface Diffusion in GSF using the method of Surface grating decay. Surface Diffusion in amorphous GSF is extremely fast, outpacing bulk Diffusion by a factor of 108 at the glass transition temperature Tg (361 K). Among all molecular glasses studied (13 in all), GSF has the second fastest Surface Diffusion (to o-terphenyl) when compared at Tg. The GSF result fits the overall trend for molecular glasses without intermolecular hydrogen bonds, where Surface Diffusion systematically slows down with increasing molecular size. This result is particularly noteworthy because GSF has many hydrogen-bond acceptors but no donors, indicating that, so long as they do not participate in hydrogen bonding, the polar functional groups have a similar effect on Surface Diffusion as the nonpolar hydrocarbon groups. In contrast, the formation of intermolecular hydrogen bonds strongly inhibits surfa...
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fast Surface Diffusion and crystallization of amorphous griseofulvin
The Journal of Physical Chemistry, 2017Co-Authors: Chengbin Huang, Shigang Ruan, Ting CaiAbstract:Among molecular glasses, griseofulvin (GSF) is one of the fastest crystallizing. To understand this property, we have measured the Surface Diffusion in GSF using the method of Surface grating decay. Surface Diffusion in amorphous GSF is extremely fast, outpacing bulk Diffusion by a factor of 10⁸ at the glass transition temperature Tg (361 K). Among all molecular glasses studied (13 in all), GSF has the second fastest Surface Diffusion (to o-terphenyl) when compared at Tg. The GSF result fits the overall trend for molecular glasses without intermolecular hydrogen bonds, where Surface Diffusion systematically slows down with increasing molecular size. This result is particularly noteworthy because GSF has many hydrogen-bond acceptors but no donors, indicating that, so long as they do not participate in hydrogen bonding, the polar functional groups have a similar effect on Surface Diffusion as the nonpolar hydrocarbon groups. In contrast, the formation of intermolecular hydrogen bonds strongly inhibits Surface Diffusion. The Surface crystal growth rate of amorphous GSF is nearly proportional to its Surface Diffusion coefficient, as noted for other systems, supporting the view that Surface crystal growth is controlled by Surface Diffusion. In addition, the fast Surface Diffusion of GSF glasses explains the fast crystal growth along fracture Surfaces and suggests a basis to understand fast crystal growth in the bulk through continuous creation of microcracks.
Dane Morgan - One of the best experts on this subject based on the ideXlab platform.
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factors correlating to enhanced Surface Diffusion in metallic glasses
arXiv: Materials Science, 2021Co-Authors: Ajay Annamareddy, Paul M Voyles, Dane MorganAbstract:The enhancement of Surface Diffusion (DS) over the bulk (DV) in metallic glasses (MGs) is well documented and likely to strongly influence the properties of glasses grown by vapor deposition. Here, we use classical molecular dynamics simulations to identify different factors influencing the enhancement of Surface Diffusion in MGs. MGs have a simple atomic structure and belong to the category of moderately fragile glasses that undergo pronounced slowdown of bulk dynamics with cooling close to the glass transition temperature (Tg). We observe that DS exhibits a much more moderate slowdown compared to DV when approaching Tg, and DS/DV at Tg varies by two orders of magnitude among the MGs investigated. We demonstrate that both the Surface energy and the fraction of missing bonds for Surface atoms show good correlation to DS/DV, implying that the loss of nearest neighbors at the Surface directly translates into higher mobility, unlike the behavior of network- and hydrogen-bonded organic glasses. Fragility, a measure of the slowdown of bulk dynamics close to Tg, also correlates to DS/DV, with more fragile systems having larger Surface enhancement of mobility. The deviations observed in the fragility and DS over DV relationship are shown to be correlated to the extent of segregation or depletion of the mobile element at the Surface. Finally, we explore the relationship between the Diffusion pre-exponential factor (D0) and activation energy (Q) and compare to a ln(D0)-Q correlation previously established for bulk glasses, demonstrating similar correlations from MD as in the experiments and that the Surface and bulk have very similar ln(D0)-Q correlations.
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mechanisms of bulk and Surface Diffusion in metallic glasses determined from molecular dynamics simulations
Acta Materialia, 2021Co-Authors: Ajay Annamareddy, Paul M Voyles, J H Perepezko, Dane MorganAbstract:Abstract The bulk and Surface dynamics of Cu50Zr50 metallic glass were studied using classical molecular dynamics (MD) simulations. As the alloy undergoes cooling, it passes through liquid, supercooled, and glassy states. While bulk dynamics showed a marked slowing down prior to glass formation, with increasing activation energy, the slowdown in Surface dynamics was relatively subtle. The Surface exhibited a lower glass transition temperature than the bulk, and the dynamics preceding the transition were accurately described by a temperature-independent activation energy. Surface dynamics were much faster than bulk at a given temperature in the supercooled state, but Surface and bulk dynamics were found to be very similar when compared at their respective glass transition temperatures. The manifestation of dynamical heterogeneity, as characterized by the non-Gaussian parameter and breakdown of the Stokes-Einstein equation, was also similar between bulk and Surface for temperatures scaled by their respective glass transition temperatures. Individual atom motion was dominated by a cage and jump mechanism in the glassy state for both the bulk and Surface. We utilize this cage and jump mechanisms to separate the activation energy for Diffusion into two parts: (i) cage-breaking barrier (Q1), associated with the rearrangement of neighboring atoms to free up space and (ii) the subsequent jump barrier (Q2). It was observed that Q1 dominates Q2 for both bulk and Surface Diffusion, and the difference in activation energies for bulk and Surface Diffusion mainly arose from the differences in cage-breaking barrier Q1.
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factors correlating to enhanced Surface Diffusion in metallic glasses
Journal of Chemical Physics, 2021Co-Authors: Ajay Annamareddy, Paul M Voyles, Dane MorganAbstract:The enhancement of Surface Diffusion (DS) over the bulk (DV) in metallic glasses (MGs) is well documented and likely to strongly influence the properties of glasses grown by vapor deposition. Here, we use classical molecular dynamics (MD) simulations to identify different factors influencing the enhancement of Surface Diffusion in MGs. MGs have a simple atomic structure and belong to the category of moderately fragile glasses that undergo pronounced slowdown of bulk dynamics with cooling close to the glass transition temperature (Tg). We observe that DS exhibits a much more moderate slowdown compared to DV when approaching Tg, and DS/DV at Tg varies by two orders of magnitude among the MGs investigated. We demonstrate that both the Surface energy and the fraction of missing bonds for Surface atoms show good correlation to DS/DV, implying that the loss of nearest neighbors at the Surface directly translates into higher mobility, unlike the behavior of network-bonded and hydrogen-bonded organic glasses. Fragility, a measure of the slowdown of bulk dynamics close to Tg, also correlates to DS/DV, with more fragile systems having larger Surface enhancement of mobility. The deviations observed in the fragility–DS/DV relationship are shown to be correlated to the extent of segregation or depletion of the mobile element at the Surface. Finally, we explore the relationship between the Diffusion pre-exponential factor (D0) and the activation energy (Q) and compare it to a ln(D0)–Q correlation previously established for bulk glasses, demonstrating similar correlations from MD as in the experiments and that the Surface and bulk have very similar ln(D0)–Q correlations.
Chengbin Huang - One of the best experts on this subject based on the ideXlab platform.
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Surface Diffusion in glasses of rod like molecules posaconazole and itraconazole effect of interfacial molecular alignment and bulk penetration
Soft Matter, 2020Co-Authors: Wei Zhang, Chengbin Huang, Camille Bishop, M D EdigerAbstract:The method of Surface grating decay has been used to measure Surface Diffusion in the glasses of two rod-like molecules posaconazole (POS) and itraconazole (ITZ). Although structurally similar antifungal medicines, ITZ forms liquid-crystalline phases while POS does not. Surface Diffusion in these systems is significantly slower than in the glasses of quasi-spherical molecules of similar volume when compared at the glass transition temperature Tg. Between the two systems, ITZ has slower Surface Diffusion. These results are explained on the basis of the near-vertical orientation of the rod-like molecules at the Surface and their deep penetration into the bulk where mobility is low. For molecular glasses without extensive hydrogen bonds, we find that the Surface Diffusion coefficient at Tg decreases smoothly with the penetration depth of Surface molecules and the trend has the double-exponential form for the Surface mobility gradient observed in simulations. This supports the view that these molecular glasses have a similar mobility vs. depth profile and their different Surface Diffusion rates arise simply from the different depths at which molecules are anchored. Our results also provide support for a previously observed correlation between the rate of Surface Diffusion and the fragility of the bulk liquid.
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fast Surface Diffusion and crystallization of amorphous griseofulvin
Journal of Physical Chemistry B, 2017Co-Authors: Chengbin Huang, Shigang Ruan, Ting CaiAbstract:Among molecular glasses, griseofulvin (GSF) is one of the fastest crystallizing. To understand this property, we have measured the Surface Diffusion in GSF using the method of Surface grating decay. Surface Diffusion in amorphous GSF is extremely fast, outpacing bulk Diffusion by a factor of 108 at the glass transition temperature Tg (361 K). Among all molecular glasses studied (13 in all), GSF has the second fastest Surface Diffusion (to o-terphenyl) when compared at Tg. The GSF result fits the overall trend for molecular glasses without intermolecular hydrogen bonds, where Surface Diffusion systematically slows down with increasing molecular size. This result is particularly noteworthy because GSF has many hydrogen-bond acceptors but no donors, indicating that, so long as they do not participate in hydrogen bonding, the polar functional groups have a similar effect on Surface Diffusion as the nonpolar hydrocarbon groups. In contrast, the formation of intermolecular hydrogen bonds strongly inhibits surfa...
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fast Surface Diffusion and crystallization of amorphous griseofulvin
The Journal of Physical Chemistry, 2017Co-Authors: Chengbin Huang, Shigang Ruan, Ting CaiAbstract:Among molecular glasses, griseofulvin (GSF) is one of the fastest crystallizing. To understand this property, we have measured the Surface Diffusion in GSF using the method of Surface grating decay. Surface Diffusion in amorphous GSF is extremely fast, outpacing bulk Diffusion by a factor of 10⁸ at the glass transition temperature Tg (361 K). Among all molecular glasses studied (13 in all), GSF has the second fastest Surface Diffusion (to o-terphenyl) when compared at Tg. The GSF result fits the overall trend for molecular glasses without intermolecular hydrogen bonds, where Surface Diffusion systematically slows down with increasing molecular size. This result is particularly noteworthy because GSF has many hydrogen-bond acceptors but no donors, indicating that, so long as they do not participate in hydrogen bonding, the polar functional groups have a similar effect on Surface Diffusion as the nonpolar hydrocarbon groups. In contrast, the formation of intermolecular hydrogen bonds strongly inhibits Surface Diffusion. The Surface crystal growth rate of amorphous GSF is nearly proportional to its Surface Diffusion coefficient, as noted for other systems, supporting the view that Surface crystal growth is controlled by Surface Diffusion. In addition, the fast Surface Diffusion of GSF glasses explains the fast crystal growth along fracture Surfaces and suggests a basis to understand fast crystal growth in the bulk through continuous creation of microcracks.
Philip D Rack - One of the best experts on this subject based on the ideXlab platform.
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simulating the effects of Surface Diffusion on electron beam induced deposition via a three dimensional monte carlo simulation
Nanotechnology, 2008Co-Authors: Daryl A Smith, Jason D Fowlkes, Philip D RackAbstract:The effects that adsorbed precursor Surface Diffusion has on electron beam induced deposition are explored via a three-dimensional Monte Carlo simulation. Initially the growth rate and resolution are compared for a common set of deposition conditions with a variable Surface Diffusion coefficient ranging from 0 to 1 × 10(-8) cm(2) s(-1). The growth rate and resolution are shown to both be enhanced as the growth changes from a mass transport limited regime to a reaction rate limited regime. The complex interplay between the vertical growth rate, the lateral growth rate, the interaction volume and the adsorbed and diffused precursor species are discussed. A second scenario is also simulated in which only gas diffused from a constant source at the perimeter of the simulation boundary is assumed (no gas phase adsorption). At low Diffusion coefficients, the diffusing gas is consumed by secondary and backscattered electrons and experimentally observed ring-like structures are generated. At higher Diffusion coefficients, the Diffusion length is sufficient for the precursor atoms to diffuse to the center (and up the pillar sidewalls) to generate nanowires.
Sheik S Rahman - One of the best experts on this subject based on the ideXlab platform.
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pore scale lattice boltzmann simulation of micro gaseous flow considering Surface Diffusion effect
International Journal of Coal Geology, 2017Co-Authors: Junjian Wang, Qinjun Kang, Li Chen, Sheik S RahmanAbstract:Abstract Recent studies have shown that adsorbed gas and its Surface Diffusion have profound influence on micro-gaseous flow through organic pores in shale gas reservoirs. In this paper, a multiple-relaxation-time (MRT) LB model is adopted to estimate the apparent permeability of organic shale and a new boundary condition, which combines Langmuir adsorption theory with Maxwellian diffusive reflection boundary condition, is proposed to capture gas slip and Surface Diffusion of adsorbed gas. The simulation results match well with previous studies carried out using Molecular Dynamics (MD) and show that Maxwell slip boundary condition fails to characterize gas transport in the near wall region under the influence of the adsorbed gas. The total molar flux can be either enhanced or reduced depending on variations in adsorbed gas coverage and Surface Diffusion velocity. The effects of pore width, pressure as well as Langmuir properties on apparent permeability of methane transport in organic pores are further studied. It is found that the Surface transport plays a significant role in determining the apparent permeability, and the variation of apparent permeability with pore size and pressure is affected by the adsorption and Surface Diffusion.
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apparent permeability prediction of organic shale with generalized lattice boltzmann model considering Surface Diffusion effect
Fuel, 2016Co-Authors: Junjian Wang, Qinjun Kang, Li Chen, Sheik S RahmanAbstract:Abstract Gas flow in shale is associated with both organic matter (OM) and inorganic matter (IOM) which contain nano-pores ranging in size from a few to hundreds of nano-meters. In addition to the non-continuum effect which leads to an apparent permeability of gas higher than the intrinsic permeability, the Surface Diffusion of adsorbed gas in organic pores also can influence the apparent permeability through its own transport mechanism. In this study, a generalized lattice Boltzmann model (GLBM) is employed for gas flow through the reconstructed shale matrix consisting of OM and IOM. The Expectation–Maximization (EM) algorithm is used to assign the pore size distribution to each component, and the dusty gas model (DGM) and generalized Maxwell–Stefan model (GMS) are adopted to calculate the apparent permeability accounting for multiple transport mechanisms including viscous flow, Knudsen Diffusion and Surface Diffusion. Effects of pore radius and pressure on permeability of both IOM and OM as well as effects of Langmuir parameters on OM are investigated. The effect of total organic content and distribution on the apparent permeability of the reconstructed shale matrix at different Surface diffusivity is also studied. It is found that the influence of pore size and pressure on the apparent permeability of organic matter is affected by the Surface Diffusion of adsorbed gas. Moreover, Surface Diffusion plays a significant role in determining apparent permeability and the velocity distribution of shale matrix.
