Similarities of the Collective Interfacial Dynamics of Grain Boundaries and Nanoparticles to Glass‐Forming Liquids

Zhang, Hao; Douglas, Jack F.

doi:10.1002/9781118540350.ch19

Cited by 5 publications

(4 citation statements)

References 156 publications

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“…It is not immediately clear whether or not the scaling in eq applies in the T regime below the onset temperature T A for non-Arrhenius relaxation, a regime that is evidently the most practically interesting for polymeric and other GF liquids. We can anticipate that anharmonic interaction effects become more prevalent in the T regime below T A and that these interactions presumably give rise to collective particle motion underlying the non-Arrhenius relaxation. ,,,,− In Section , we show that the growth of collective motion identified in our simulated polymer melts follows an increase in the anharmonic interaction strength, as quantified by the derivative of the bulk modulus with respect to P .…”

Section: Resultsmentioning

confidence: 71%

“…We further examine the remarkable thermodynamic scaling through a consideration of the extent of collective motion in GF liquids, as quantified by the average length L of stringlike cooperative motion observed generally in simulations of GF liquids, − ,,,− ,− which has been found to play a key role in determining the activation energy for relaxation and which is closely related to the configurational entropy in the GET . In particular, many past works have shown that L / L A , where L A is a residual collective motion occurring at T A and is something not envisioned in the original AG model, corresponds to the AG counterpart, s c * / s c .…”

Section: Resultsmentioning

confidence: 97%

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Equation of State and Entropy Theory Approach to Thermodynamic Scaling in Polymeric Glass-Forming Liquids

Douglas

2021

Macromolecules

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Numerous experimental and computational studies have established that most liquids seem to exhibit a remarkable, yet poorly understood, property termed "thermodynamic scaling", in which the structural relaxation time τ α , and many other dynamic properties, can be expressed in terms of a "universal" reduced variable, TV γ , where T is the temperature, V is the material volume, and γ is a scaling exponent describing how T and V are linked to each other when either quantity is varied. Here, we show that this scaling relation can be derived by combining the Murnaghan equation of state (EOS) with the generalized entropy theory (GET) of glass formation. In our theory, thermodynamic scaling arises in the non-Arrhenius relaxation regime as a scaling property of the fluid configurational entropy density s c , normalized by its value s c * at the onset temperature T A of glass formation, s c /s c *, so that a constant value of TV γ corresponds to a reduced isoentropic fluid condition. Molecular dynamics simulations on a coarse-grained polymer melt are utilized to confirm that the predicted thermodynamic scaling of τ α by the GET holds both above and below T A and to test whether the extent L of stringlike collective motion, normalized its value L A at T A , also obeys thermodynamic scaling, as required for consistency with thermodynamic scaling. While the predicted thermodynamic scaling of both τ α and L/L A is confirmed by simulation, we find that the isothermal compressibility κ T and the long-wavelength limit S(0) of the static structure factor do not exhibit thermodynamic scaling, an observation that would appear to eliminate some proposed models of glass formation emphasizing fluid "structure" over configurational entropy. It is found, however, that by defining a low-temperature hyperuniform reference state, we may define compressibility relative to this condition, δκ T , a transformed dimensionless variable that exhibits thermodynamic scaling and which can be directly related to s c /s c *. Further, the Murnaghan EOS allows us to interpret γ as a measure of intrinsic anharmonicity of intermolecular interactions that may be directly determined from the pressure derivative of the material bulk modulus. Finally, we show that many phenomenological relationships related to the glass formation and melting of materials can be understood based on the Murnaghan EOS and thermodynamic scaling.

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Section: Resultsmentioning

confidence: 71%

Section: Resultsmentioning

confidence: 97%

Equation of State and Entropy Theory Approach to Thermodynamic Scaling in Polymeric Glass-Forming Liquids

Douglas

2021

Macromolecules

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“…We can anticipate that anharmonic interaction effects become more prevalent in the T regime below T A and that these interactions presumably give rise to collective particle motion underlying the non-Arrhenius relaxation. 49,50,93,120,[125][126][127][128][129][130][131][132][133][134][135][136][137][138][139][140][141] In Section 3.7, we show that the growth of collective motion identified in our simulated polymer melts follows an increase in the anharmonic interaction strength, as quantified by the derivative of the bulk modulus with respect to P .…”

Section: Thermodynamic Scaling In the Non-arrhenius Relaxation Regimementioning

confidence: 73%

“…We further examine the remarkable thermodynamic scaling through a consideration of the extent of collective motion in GF liquids, as quantified by the average length L of stringlike cooperative motion observed generally in simulations of GF liquids, [49][50][51]93,120,[125][126][127][128][129][130][131][132][133][134][135][136][137][137][138][139][140][141] which has been found to play a key role in determining the activation energy for relaxation and which is closely related to the configurational entropy in the GET. 32 In particular, many past works have shown that L/L A , where L A is a residual collective motion occurring at T A and is something not envisioned in the original AG model, 72 corresponds to the AG counterpart, s * c /s c .…”

Section: Thermodynamic Scaling Based On Molecular Dynamics Simulationmentioning

confidence: 99%

Equation of State and Entropy Theory Approach to Thermodynamic Scaling in Polymeric Glass-Forming Liquids

Douglas,

2021

Preprint

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Numerous experimental and computational studies have established that most liquids seem to exhibit a remarkable, yet poorly understood, property termed 'thermodynamic scaling' in which the structural relaxation time τ α , and many other dynamic properties, can be expressed in terms of a 'universal' reduced variable, T V γ , where T is the temperature, V is the material volume, and γ is a scaling exponent describing how T and V are linked to each other when either quantity is varied. Here, we show that this scaling relation can be derived by combining the Murnaghan equation of state (EOS) with the generalized entropy theory (GET) of glass formation. In our theory, thermodynamic scaling arises in the non-Arrhenius relaxation regime as a scaling property of the fluid configurational entropy density s c , normalized by its value s * c at the onset temperature T A of glass formation, s c /s * c , so that a constant value of T V γ corresponds to a reduced isoentropic fluid condition. Molecular dynamics simulations on a coarse-grained polymer melt are utilized to confirm that the predicted thermodynamic scaling of τ α by the GET holds both above and below T A and to test whether the extent L of stringlike collective motion, normalized its value L A at T A , also obeys thermodynamic scaling, as required for consistency with thermodynamic scaling. While the predicted thermodynamic scaling of both τ α and L/L A is confirmed by simulation, we find that the isothermal compressibility κ T and the long wavelength limit S(0) of the static structure factor do not exhibit thermodynamic scaling, an observation that would appear to eliminate some proposed models of glass formation emphasizing fluid 'structure' over configurational entropy. It is found, however, that by defining a low temperature hyperuniform reference state, we may define a compressibility relative to this condition, δκ T , a transformed dimensionless variable that exhibits thermodynamic scaling and which can be directly related to s c /s * c . Further, the Murnaghan EOS allows us to interpret γ as a measure of intrinsic anharmonicity of intermolecular interactions that may be directly determined from the pressure derivative of the material bulk modulus. Finally, we show that many phenomenological relationships related to the glass formation and melting of materials can be understood based on the Murnaghan EOS

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Role of string-like collective atomic motion on diffusion and structural relaxation in glass forming Cu-Zr alloys

Zhang

Zhong

Douglas

et al. 2015

The Journal of Chemical Physics

103

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We investigate Cu-Zr liquid alloys using molecular dynamics simulation and well-accepted embedded atom method potentials over a wide range of chemical composition and temperature as model metallic glass-forming (GF) liquids. As with other types of GF materials, the dynamics of these complex liquids are characterized by "dynamic heterogeneity" in the form of transient polymeric clusters of highly mobile atoms that are composed in turn of atomic clusters exhibiting string-like cooperative motion. In accordance with the string model of relaxation, an extension of the Adam-Gibbs (AG) model, changes in the activation free energy ΔGa with temperature of both the Cu and Zr diffusion coefficients D, and the alpha structural relaxation time τα can be described to a good approximation by changes in the average string length, L. In particular, we confirm that the strings are a concrete realization of the abstract "cooperatively rearranging regions" of AG. We also find coexisting clusters of relatively "immobile" atoms that exhibit predominantly icosahedral local packing rather than the low symmetry packing of "mobile" atoms. These two distinct types of dynamic heterogeneity are then associated with different fluid structural states. Glass-forming liquids are thus analogous to polycrystalline materials where the icosahedrally packed regions correspond to crystal grains, and the strings reside in the relatively disordered grain boundary-like regions exterior to these locally well-ordered regions. A dynamic equilibrium between localized ("immobile") and wandering ("mobile") particles exists in the liquid so that the dynamic heterogeneity can be considered to be type of self-assembly process. We also characterize changes in the local atomic free volume in the course of string-like atomic motion to better understand the initiation and propagation of these fluid excitations.

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Similarities of the Collective Interfacial Dynamics of Grain Boundaries and Nanoparticles to Glass‐Forming Liquids

Cited by 5 publications

References 156 publications

Equation of State and Entropy Theory Approach to Thermodynamic Scaling in Polymeric Glass-Forming Liquids

Equation of State and Entropy Theory Approach to Thermodynamic Scaling in Polymeric Glass-Forming Liquids

Equation of State and Entropy Theory Approach to Thermodynamic Scaling in Polymeric Glass-Forming Liquids

Role of string-like collective atomic motion on diffusion and structural relaxation in glass forming Cu-Zr alloys

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