Potential parameters of methyl and methylene obtained from second virial coefficients of n-alkanes

Abstract

The second virial coefficients of a number of n-alkanes (from butane to hexadecane) have been evaluated by using the Rotational Isomeric State model. Methyl and methylene groups have been modelled as Lennard-Jones (12 – 6) interaction sites centered on the position of the carbon atoms. Equal size has been assigned to the methyl and methylene groups but differences in the well-depth of the potential were considered. We have chosen the values of the potential well-depths of methyl and methylene group to fit the second virial coefficient of several n-alkanes in a range of about 300 K. The agreement with experimental results is good. Then, it is shown that a simple site-site potential model is able to reproduce the second virial coefficient of several n-alkanes in a wide range of temperatures.