Thermodynamic scaling of the viscosity of van der Waals, H-bonded, and ionic liquids

Roland, C. M.; Bair, Scott; Casalini, R.

doi:10.1063/1.2346679

Cited by 257 publications

(296 citation statements)

References 79 publications

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“…The master curve also shows some curvature or inflection, and similar features are observed for other systems in both experiments and simulations. 9,10,13 To examine the change in the dynamics, we have studied the trajectories of the ions. They show complexity reflecting the geometrical correlation among successive motions.…”

Section: Resultsmentioning

confidence: 99%

“…[1][2][3][4] Although supercooled liquids and glasses including ionic systems show complicated heterogeneous dynamics, [5][6][7] an existence of a simple scaling behavior of the dynamic properties, x ) T (TV γ ) (where T is temperature and V is the specific volume), has been reported for many systems, [8][9][10][11] where x can be the relaxation time τ or viscosity η, while γ is a material constant.…”

Section: Introductionmentioning

confidence: 99%

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Molecular Dynamics Study of Thermodynamic Scaling of the Glass-Transition Dynamics in Ionic Liquids over Wide Temperature and Pressure Ranges

2010

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Experimentally, superpositioning of dynamic properties such as viscosity, relaxation times, or diffusion coefficients under different conditions of temperature T, pressure P, and volume V by the scaling variable TV γ (where γ is a material constant) has been reported as a general feature of many kinds of glass-forming materials. In the present work, molecular dynamics (MD) simulations have been performed to study the scaling of dynamics near the glass-transition regime of ionic liquids. Scaling in the simulated 1-ethyl-3-methylimidazolium nitrate (EMIM-NO 3 ) system has been tested over wide ranges of temperatures and pressures. TV γ scaling of the dynamics is well described by master curves with γ ) 4.0 ( 0.2 and 3.8 ( 0.2 for cation and anion, respectively. Structures and Coulombic terms of the corresponding states are found to be quite similar. The temperature and pressure dependence of the pair correlation function show similar trends and therefore can be superpositioned onto the master curve. Although the behaviors with γ ) 4 might be expected from the relation, γ ) n/3, for the dynamics with the soft-core-type potential U ) ε(σ/r) n , with n ) 12, pair potentials used in the MD simulation have a more complex form, and not all the repulsive terms can play their roles in the heterogeneous structures determined by ion-ion interactions. Scaling is related to the common part of effective potentials related to the pair correlation functions, including the many-body effect in real space.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Study of Thermodynamic Scaling of the Glass-Transition Dynamics in Ionic Liquids over Wide Temperature and Pressure Ranges

2010

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“…Roland et al 56 have shown that like other glassforming materials, IL viscosities scale with molecular volume as ϰ 1 / ͑TV ␥ ͒ where the scaling exponent ␥ spans the range from 2.25 to 2.9.…”

Section: Viscosity and Transport In Ilsmentioning

confidence: 99%

Spotlight on ionic liquids

Castner

Wishart

2010

The Journal of Chemical Physics

381

328

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Ionic liquids are an emerging class of materials with a diverse and extraordinary set of properties. Understanding the origins of these properties and how they can be controlled by design to serve valuable practical applications presents a wide array of challenges and opportunities to the chemical physics and physical chemistry community. We highlight here some of the significant progress already made and future research directions in this exciting area.

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“…[3][4][5][6]The exponent γ of the thermodynamic scaling also provides a measure of the relative importance of the density and temperature in controlling glassy dynamics. Hence, not surprisingly, a large body of experiments [7][8][9][10][11][12][13] and simulations [14][15][16][17][18][19][20] have probed the nature of thermodynamic scaling of glass-forming liquids since the first observation by Tölle et al for orthoterphenyl. [21] The existence of thermodynamic scaling is well established for as diverse materials as van der Waals liquids, polymers, ionic liquids, weakly hydrogen-bonded systems, etc.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic scaling of dynamics in polymer melts: Predictions from the generalized entropy theory

Freed

2013

The Journal of Chemical Physics

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Many glass-forming fluids exhibit a remarkable thermodynamic scaling in which dynamic properties, such as the viscosity, the relaxation time, and the diffusion constant, can be described under different thermodynamic conditions in terms of a unique scaling function of the ratio ρ γ /T , where ρ is the density, T is the temperature, and γ is a material dependent constant. Interest in the scaling is also heightened because the exponent γ enters prominently into considerations of the relative contributions to the dynamics from pressure effects (e.g., activation barriers) vs. volume effects (e.g., free volume). Although this scaling is clearly of great practical use, a molecular understanding of the scaling remains elusive. Providing this molecular understanding would greatly enhance the utility of the empirically observed scaling in assisting the rational design of materials by describing how controllable molecular factors, such as monomer structures, interactions, flexibility, etc., influence the scaling exponent γ and, hence, the dynamics. Given the successes of the generalized entropy theory in elucidating the influence of molecular details on the universal properties of glass-forming polymers, this theory is extended here to investigate the thermodynamic scaling in polymer melts. The predictions of theory are in accord with the appearance of thermodynamic scaling for pressures not in excess of ∼ 50 MPa. (The failure at higher pressures arises due to inherent limitations of a lattice model.) In line with arguments relating the magnitude of γ to the steepness of the repulsive part of the intermolecular potential, the abrupt, square-well nature of the lattice model interactions lead, as expected, to much larger values of the scaling exponent. Nevertheless, the theory is employed to study how individual molecular parameters affect the scaling exponent in order to extract a molecular understanding of the information content contained in the exponent. The chain rigidity, cohesive energy, chain length, and the side group length are all found to significantly affect the magnitude of the scaling exponent, and the computed trends agree well with available experiments. The variations of γ with these molecular parameters are explained by establishing a correlation between the computed molecular dependence of the scaling exponent and the fragility. Thus, the efficiency of packing the polymers is established as the universal physical mechanism determining both the fragility and the scaling exponent γ.

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Thermodynamic scaling of the viscosity of van der Waals, H-bonded, and ionic liquids

Cited by 257 publications

References 79 publications

Molecular Dynamics Study of Thermodynamic Scaling of the Glass-Transition Dynamics in Ionic Liquids over Wide Temperature and Pressure Ranges

Molecular Dynamics Study of Thermodynamic Scaling of the Glass-Transition Dynamics in Ionic Liquids over Wide Temperature and Pressure Ranges

Spotlight on ionic liquids

Thermodynamic scaling of dynamics in polymer melts: Predictions from the generalized entropy theory

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