Group Contribution Approaches for Viscosity

Correlations of viscosity with density and refractive index have been evaluated for various homologous series [7] and correlations between viscosity and boiling point and between viscosity and vapor pressure have been reported, for example, for n-alkyl /3-ethoxypropionates [8]. Viscosity correlations with vapor pressure are represented by the Porter equation [9]  

For alkanes, the logarithm of viscosity has been correlated with atomic and with bond contributions to estimate tj at 0 and 20°C [13]. Considering a broader range of structural variety, neither the viscosity nor its logarithm is a constitutionally additive property. Application of the group contribution approach is based on additive parameters that allow viscosity estimations in combination with other experimental data such as density or vapor pressure. The viscosity-constitutional constant, /vc, is such an additive parameter  

Skubla [9] has designed a group contribution scheme which applies for various homologous series. His method relies on eq. 6.2.1 where both coefficients a0 and a have to be derived from group contributions and with respect to Nc. The model applies for n-alkanes, 1-alkenes, n-alkylcyclopentanes and n-alkylcyclohexanes, alkylbenzenes, 1-bromoalkanes, 1-alkanols, di-n-alkyl ethers, carboxylic acids and esters, 1-alkanethiols, 1-aminoalkanes, dialkylamines, alkaneamides, and some 

The method of van Velzen discussed by Grain [1] requires solely molecular structure input. Again, temperature coefficients constitute the additive parameters related with terms for functional groups and various corrections for configurational 

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