Abstract
The law of corresponding states has been demonstrated for a number of pure substances and binary mixtures and provides evidence that the transport properties viscosity and diffusion can be determined from a molecular shape function, often taken to be a LennardβJones 12β6 potential, that requires two scaling parameters: a well depth Ξ΅~ij~ and a collision diameter Ο~ij~, both of which depend on the interacting species i and j. We obtain estimates for Ξ΅~ij~ and Ο~ij~ of interacting species by finding the values that provide the best fit to viscosity data for binary mixtures and compare these to calculated parameters using several βcombining rulesβ that have been suggested for determining parameter values for binary collisions from parameter values that describe collisions of like molecules. Different combining rules give different values for Ο~ij~ and Ξ΅~ij~, and for some mixtures the differences between these values and the bestβfit parameter values are rather large. There is a curve in (Ξ΅~ij~, Ο~ij~) space such that parameter values on the curve generate a calculated viscosity in good agreement with measurements for a pure gas or a binary mixture. The various combining rules produce couples of parameters Ξ΅~ij~, Ο~ij~ that lie close to the curve and, therefore, generate predicted mixture viscosities in satisfactory agreement with experiment. Although the combining rules were found to underpredict the viscosity in most of the cases, Kong's rule was found to work better than the others, but none of the combining rules consistently yields parameter values near the bestβfit values, suggesting that improved rules could be developed. Β© 2010 Wiley Periodicals, Inc.*This article is a U.S. Government work and, as such, is in the public domain of the United States of America.
Int J Chem Kinet 42: 713β723, 2010