Dr. Arno Laesecke came to the Thermophysics Division of NIST in 1988 with fellowships from the German Science Foundation (Deutsche Forschungsgemeinschaft) and the Joy L. Barton Charitable Trust. In 1991, he joined the corporate research of Daimler-Benz AG (now Daimler AG) at Ulm (Germany) where he participated in the early development of a fuel-cell-powered electric car. He returned to NIST in 1992 and became a staff member after his naturalization in 1993. His research interests include the study of transport properties from both an experimental and theoretical standpoint. He conceived and codeveloped the steady-state mode for hot-wire instruments for more accurate thermal conductivity measurements of gases, and improved the polarization technique for measurements of polar liquids. His focus has been on viscosity, though, where he has made major contributions for alternative refrigerants, alternative fuels, and standard reference measurements. He complements the experimental transport property research with molecular dynamics simulations, and also studies metastable phases and their stability limits. An avid scholar of the history of science, Dr. Laesecke has a deep appreciation of the grand achievements of 19th and early 20th century thermodynamicists, and enjoys placing his and other modern works in the context of earlier contributions.
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Standard Reference Viscometry
Although the viscosity of helium is now known with substantially higher accuracy [W. Cencek et al. J. Chem. Phys., 136(2012), 224303], most viscometry is still referenced to the absolute measurement of the viscosity of water at 20 °C and atmospheric pressure by Swindells, Coe, and Godfrey at the National Bureau of Standards (NBS) published in 1952. Viscosity is one of the widest ranging properties spanning 20 orders of magnitude from the least viscous gas to the most viscous liquids and solids. Accurate viscometry is vital for industrial societies because their economic metabolism depends on the flow of gases and liquids in all sectors and from hydrogen to gasoline to crude oil. Thus, accurate viscometry needs to be backed by numerous standard reference materials that cover the property variation range and the pressure and temperature conditions at which flow occurs. Currently, certified viscosity reference standards are only available at atmospheric pressure. To characterize materials over an extended range, an absolute viscometer with a torsionally vibrating crystal sensor is being developed for temperatures up to 600 K, pressures up to 68 MPa, and dynamic viscosities up to 1 Pa·s. The targeted uncertainty is 1 % or less.
Viscosity of Nonpolar+Polar Binary Liquid Mixtures
The transition from petroleum-derived fuels to biofuels poses considerable challenges for property science because it involves blends of nonpolar hydrocarbons with polar compounds such as alcohols, esters, and possibly heterocyclic compounds. Viscosity is a property of prime interest with regard to fuels. Thus, the transition to biofuels generates particular thrust to improve the understanding of mixture viscosities.
Nonpolar+polar binary liquid systems exhibit often minima in their viscosity-composition dependences. A systematic study of this phenomenon combining targeted measurements, data compilation, and ab initio calculations of molecular sizes, shapes, and charge distributions makes it possible to predict the occurrence of viscosity-composition minima reliably. They arise when the polar mixture component is smaller than the nonpolar but has a higher viscosity than the latter. Predicted viscosity minima for the mixture n-tetradecane + 2-propanol were confirmed by measurements.
Visualization of Molecular Size, Shape, and Charge Distribution:
While measurements remain the primary pathway to knowledge, not everything needs to be measured anymore because of advances in computational molecular science. Experimenters should take advantage of these possibilities to perform measurements on systems that are computationally intractable and to better understand the results of their endeavors.
Computational determination of molecular structures in ab initio calculations has the advantage of showing the molecular geometry and, more importantly, the charge distribution across molecular structures. This additional information makes polarity for the ﬁrst time visible and thus facilitates the understanding of the role of electrostatic forces in intermolecular interactions ranging from weak attractions to hydrogen bonds, associations and ionic bonds. An example is shown in the following graphic which juxtaposes polar ethanol molecules to nonpolar iso-octane. This mixture is a model system for blends of gasoline with bioethanol.
History of Science
"The historical approach to understanding of scientific fact is what differentiates the scholar in science from the mere experimenter." Edwin. G. Boring (1886-1968), Harvard Psychologist
For the NIST Centennial in 2001, Dr. Laesecke wrote the first complete English translation of the inaugural speech that Heike Kamerlingh Onnes gave in 1882 on the occasion of his appointment as Professor at the University of Leiden (The Netherlands). The PDF of the paper entitled "Through Measurement to Knowledge" is available here. Other historical studies of Dr. Laesecke include the emerging discovery of gas-liquid-solid triple points of pure substances before Gibbs' phase rule, the sometimes explosive progress in the understanding of metastable phases of matter, the implications of the Third Law of Thermodynamics (1906) for temperature, and the rediscovery of the Ashurst-Hoover scaling for dynamic properties 30 years after its initial proposal in 1975.
Laesecke, A.(2014). Sealed Gravitational Capillary Viscometers for Volatile Liquids. Chapter 4.5 in M. J. Assael, A. R. H. Goodwin, V. Vesovic, & W. A. Wakeham (Eds.): Experimental Thermodynamics Volume IX – Advances in Transport Properties of Fluids Cambridge, UK: Royal Society of Chemistry, ISBN 978-1-84973-677-0.
Laesecke, A. and J. L. Burger. Viscosity Measurements of DNA Solutions with and without Condensing Agents. Biorheol., 51(2014), 15-28.
Huber, M. L., Perkins, R. A., Laesecke, A., Friend, D. G., Sengers, J. V., Assael, M. J., Metaxa, I. M., Vogel, E., Mares, R., and Miyagawa, K., New International Formulation for the Viscosity of H2O, J. Phys. Chem. Ref. Data, 38(2), 101-125, 2009.