Structural origin of fractional Stokes-Einstein relation in glass-forming liquids

Pan, Shaopeng; Wu, Zhen; Wang, W. H.; Li, M. Z.; Xu, Limei

doi:10.1038/srep39938

Cited by 30 publications

(22 citation statements)

References 51 publications

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“…This is reinforced further, by other studies showing that fractional SER in metallic glasses is coupled with the formation of large clusters of trapped atoms that percolate through the liquid. 84,85 Our results thus shed new light onto the structural properties of supercooled water, by means of a framework that steps away from the current paradigm of local order parameters to embrace the full complexity of the water network including the evolution of the empty space as well as topological properties of the HB network.…”

Section: Discussionmentioning

confidence: 84%

Insights into the Emerging Networks of Voids in Simulated Supercooled Water

et al. 2020

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The structural evolution of supercooled liquid water as we approach the glass transition temperature continues to be an active area of research. Here, we use molecular dynamics simulations of TIP4P/Ice to study the changes in the connected regions of empty space within the liquid which we interrogate using the Voronoi-voids network.We observe two important features: supercooling enhances the fraction of non-spherical voids and different sizes of voids tend to cluster forming a percolating network. By examining order parameters such as the local structure index (LSI), tetrahedrality and topological defects, we show that water molecules near large void clusters tend to be slightly more tetrahedral than those near small voids, with a lower population of underand over-coordinated defects. We show further that the distribution of closed rings of water molecules around small and large void clusters maintain a balance between 6 1 and 7 membered rings. Our results highlight the changes of the dual voids and water network as a structural hallmark of supercooling which provides insights into the molecular origins of cooperative effects that underlie density fluctuations occurring on the sub-nanometer and nanometer length scale. The percolation of the voids and the hydrogen bond network around the voids, may serve as useful order parameters to investigate density fluctuations in supercooled water.

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Section: Discussionmentioning

confidence: 84%

Insights into the Emerging Networks of Voids in Simulated Supercooled Water

et al. 2020

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“…* yylu@ciac.ac.cn † ljan@ciac.ac.cn ‡ zgw@caltech.edu Another anomalous behavior in the glass-forming liquids is the breakdown of the Stokes-Einstein (SE) relation, which relates the self-diffusion coefficient D to the viscosity or equivalently to the relaxation time τ α [9][10][11][12]. While for normal liquids the product Dτ α is temperature-independent, numerous studies [13][14][15][16][17][18][19] in recent decades have shown that this relation is violated in glass-forming liquids at low temperatures. Conceptually, Hodgdon and Stillinger [20,21] associated this violation with dynamic heterogeneity; however, there is considerable debate as to the mechanistic explanation.…”

Section: Introductionmentioning

confidence: 99%

Two-step relaxation and the breakdown of the Stokes-Einstein relation in glass-forming liquids

Mei

et al. 2019

Phys. Rev. E

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It is well known that glass-forming liquids exhibit a number of anomalous dynamical phenomena, most notably a two-step relaxation in the self-intermediate scattering function and the breakdown of the Stokes-Einstein (SE) relation, as they are cooled toward the glass transition temperature. While these phenomena are generally ascribed to dynamic heterogeneity, specifically to the presence of slow-and fast-moving particles, a quantitative elucidation of the two-step relaxation and the violation of the SE relation in terms of these concepts has not been successful. In this work, we propose a classification of particles according to the rank order of their displacements (from an arbitrarily defined origin of time), and we divide the particles into long-distance (LD), medium-distance, and short-distance (SD) traveling particle groups. Using molecular-dynamics simulation data of the Kob-Andersen model, we show quantitatively that the LD group is responsible for the fast relaxation in the two-step relaxation process in the intermediate scattering function, while the SD group gives rise to the slow (α) relaxation. Furthermore, our analysis reveals that τ α is controlled by the SD group, while the ensemble-averaged diffusion coefficient D is controlled by both the LD and SD groups. The combination of these two features provides a natural explanation for the breakdown in the SE relation at low temperature. In addition, we find that the α-relaxation time, τ α , of the overall system is related to the relaxation time of the LD particles, τ LD , as τ α = τ 0 exp(τ LD /k B T).

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“…Evoy et al [296] find a best fit to their and literature data for C = 1.66 and t = 0.93. The SER is known to break down for glassy polymer systems in the limit of T g or high viscosity (e.g., [298,299]). When applied to atmospheric conditions in the planetary boundary layer and above, it is found that the diffusive mixing time based on the regular SER overestimates the result based on the fractional SER by a factor of three and higher in regions where mixing time is an hour or more.…”

Section: Organic Aerosol Diffusivity Modelsmentioning

confidence: 99%

Current State of Atmospheric Aerosol Thermodynamics and Mass Transfer Modeling: A Review

Semeniuk

Dastoor

2020

Atmosphere

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A useful aerosol model must be able to adequately resolve the chemical complexity and phase state of the wide particle size range arising from the many different secondary aerosol growth processes to assess their environmental and health impacts. Over the past two decades, significant advances in understanding of gas-aerosol partitioning have occurred, particularly with respect to the role of organic compounds, yet aerosol representations have changed little in air quality and climate models since the late 1990s and early 2000s. The gas-aerosol partitioning models which are still commonly used in air quality models are separate inorganics-only thermodynamics and secondary organic aerosol (SOA) formation based on absorptive partitioning theory with an assumption of well-mixed liquid-like particles that continuously maintain equilibrium with the gas phase. These widely used approaches in air quality models for secondary aerosol composition and growth based on separated inorganic and organic processes are inadequate. This review summarizes some of the important developments during the past two decades in understanding of gas aerosol mass transfer processes. Substantial increases in computer performance in the last decade justify increasing the process detail in aerosol models. Organics play a central role during post-nucleation growth into the accumulation mode and change the hygroscopic properties of sulfate aerosol. At present, combined inorganic-organic aerosol thermodynamics models are too computationally expensive to be used online in 3-D simulations without high levels of aggregation of organics into a small number of functional surrogates. However, there has been progress in simplified modeling of liquid-liquid phase separation (LLPS) and distinct chemical regimes within organic-rich and inorganic-rich phases. Additional limitations of commonly used thermodynamics models are related to lack of surface tension data for various aerosol compositions in the small size limit, and lack of a comprehensive representation of surface interaction terms such as disjoining pressure in the Gibbs free energy which become significant in the small size limit and which affect both chemical composition and particle growth. As a result, there are significant errors in modeling of hygroscopic growth and phase transitions for particles in the nucleation and Aitken modes. There is also increasing evidence of reduced bulk diffusivity in viscous organic particles and, therefore, traditional secondary organic aerosol models, which are typically based on the assumption of instantaneous equilibrium gas-particle partitioning and neglect the kinetic effects, are no longer tenable.

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Structural origin of fractional Stokes-Einstein relation in glass-forming liquids

Cited by 30 publications

References 51 publications

Insights into the Emerging Networks of Voids in Simulated Supercooled Water

Insights into the Emerging Networks of Voids in Simulated Supercooled Water

Two-step relaxation and the breakdown of the Stokes-Einstein relation in glass-forming liquids

Current State of Atmospheric Aerosol Thermodynamics and Mass Transfer Modeling: A Review

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