Search

In this paper, applying the density scaling idea to an associated liquid 4-methyl-2-pentanol used as an example, we identify different pressure-volume-temperature ranges within which molecular dynamics is dominated by either complex H-bonded networks most probably leading to supramolecular structures or non-specific intermolecular interactions like van der Waals forces. In this way, we show that the density scaling law for molecular dynamics near the glass transition provides a sensitive tool to detect thermodynamic regions characterized by intermolecular interactions of different type and complexity for a given material in the wide pressure-volume-temperature domain even if its typical form with constant scaling exponent is not obeyed. Moreover, we quantify the observed decoupling between dielectric and mechanical relaxations of the material in the density scaling regime. The suggested methods of analyses and their interpretations open new prospects for formulating models based on proper effective intermolecular potentials describing physicochemical phenomena near the glass transition. [ABSTRACT FROM AUTHOR]

Abstract: This study reports on an ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as a promising engine lubricant candidate . This IL has a relatively low viscosity of 4.7cSt (similar to 0W-10 racing engine oil), a low viscosity–pressure (V–P) coefficient of 6.5GPa−1 at 100°C, a high viscosity index of 159, and a high onset decomposition temperature of 472°C. The ionic liquid delivers substantially lower friction in mixed lubrication (ML) and provides better scuffing protection in boundary lubrication (BL) than those of hydrocarbon lubricants with similar viscosities. The low ML friction is possibly attributed to its low V–P coefficient and a hypothetical multi-layer boundary film at the interface. In BL, the tribochemical reactions between the IL and the contact surfaces to form a protective tribo-film are believed to be responsible for the IL's superior anti-scuffing behavior. Microstructural examination and chemical composition analysis were conducted on the wear scars from both the top surface and the cross section to study the wear mode and characterize the tribo-film and near-surface structure. [Copyright &y& Elsevier]

Abstract: We outline the procedures used to establish benchmark physical property data for the Third Industrial Fluid Properties Simulation Challenge. For both challenge problems, this involved measurement of new data, including bubble-point pressures of ethanol/HFC-227ea mixtures at 343.13 K, and the viscosity of 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, and 1,2,4-butanetriol at 373K and 0.1 and 250MPa. When possible, measurements were compared with published literature data. Recommended values are provided with corresponding uncertainty estimates. [Copyright &y& Elsevier]

In the classical approach to elastohydrodynamic lubrication (EHL) a single parameter, the pressure-viscosity coefficient, quantifies the isothermal pressure dependence of the viscosity for use in prediction of film thickness. Many definitions are in current use. Progress toward a successful definition of this property has been hampered by the refusal of those working in classical EHL to acknowledge the existence of accurate measurements of the piezoviscous effect that have existed for nearly a century. The Hamrock and Dowson pressure-viscosity coefficient at high temperature requires knowledge of the piezoviscous response at pressures which exceed the inlet pressure and may exceed the Hertz pressure. The definition of pressure-viscosity coefficient and the assumed equation of state must limit the use of the classical formulas, including Hamrock and Dowson, to liquids with high Newtonian limit and to low temperature. Given that this problem has existed for at least fifty years without resolution, it is reasonable to conclude that there is no definition of pressure-viscosity coefficient that will quantify the piezoviscous response for an analytical calculation of EHL film thickness at temperatures above ambient., (© 2022. The Author(s).)