The effect of stereoisomerism on dynamic viscosity: A study of cis-decalin and trans-decalinversus pressure and temperature

Abstract

Decahydronaphthalene (decalin) exists in two stereoisomeric molecular configurations, a cis and a trans configuration. The cis and trans isomers have different physical properties. In this work, a study of the stereoisomeric effect on the dynamic viscosity (and density) versus pressure and temperature has been carried out up to 100 MPa in the temperature range 293.15 K to 353.15 K. The viscosity of cis-decalin is higher than the one of trans-decalin in the considered temperature and pressure ranges due to the twisted structure of cis-decalin compared to the relative more symmetric and rigid structure of trans-decalin. Further, the density of cis-decalin is around 3% higher than for trans-decalin. The measured data have been used in order to perform an analysis of the stereoisomeric effects using recently developed viscosity approaches with a physical and theoretical background. For the hard-sphere scheme it has been found that the roughness factor is related to the specific structure of the stereoisomeric molecules, whereas the same hard-core volume is obtained for cis-decalin and trans-decalin. In the case of the free-volume model, the term arising from the energy barrier, which the molecules have to cross in order to diffuse, is approximately the same for cis-decalin and trans-decalin, but the characteristic molecular length and the molecular overlap of the free volume are different, and strongly related to the structural configuration of the stereoisomeric decalin molecules.