Pressure-viscosity behaviour of ionic liquids, vegetable oils and other lubricants

J. Fernandez1, X. Paredes1, F. Gacino1, M. Comunas1 and A. Pensado1

1University of Santiago de Compostela, Spain

Keywords: pressure
property: viscosity
material: ionic liquids, vegetable oils, synthetic lubricants

In the last years, we have measured in our laboratory dynamic viscosity data at high pressure in a broad range of temperature of poly(propylene glycol) dimethyl ethers, dipentaerythritol esters, pentaerythritol esters, vegetable oils and lately, ionic liquids [1,2]. Our intention, in doing so, is to study their potential uses as lubricants in different applications. As important as it might be knowing the actual viscosity of a lubricant at a specific temperature and pressure, obtaining viscosity data along a range of temperature and pressure grants us access to the determination of other physical properties that affect the lubrication, such as the Viscosity Index (VI), the pressure-viscosity coefficient and the temperature-viscosity coefficient. We can go even further into ascertaining, for example, the behaviour of a lubricant in the Elastohydrodynamic Lubrication regime (EHL), by applying some mathematical expressions that involve the pressure-viscosity coefficient and the dynamic viscosity so that we can calculate the central film thickness values of the lubricant between two surfaces in contact[2]. There is some controversy around the proper way of calculating the pressure-viscosity coefficient mentioned, in order to determine the film thickness. From the extensive database of viscosity values for several families of compounds, in a broad range of temperature and pressure, we can get insights of the influence of the molecular structure on the key properties needed in a fluid to act as a lubricant [2,3]. We present an analysis of the dependence of the molecular structure on viscosity, its derived properties and film thickness, that can help the lubricant engineers to develop products with enhanced performance.

Acknowledgements. This work is being supported by Spanish Ministry of Science and Innovation and the FEDER Program under PSE-420000-2008-4 and CTQ2008-06498-C02-01 projects.

  1. X. Paredes, A.S. Pensado, M.J.P. Comunas, J. Fernandez, J. Chem. Eng. Data 55, 4088 ( 2010)

  2. A.S. Pensado, M.J.P. Comunas, J. Fernandez, Tribol. Lett. 31, 107 (2008)

  3. A.S. Pensado, M.J.P. Comunas, A. A. H. Padua, J. Fernandez, J. Phys. Chem. B. 112, 5563 (2008)

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