Critical properties of long-chain substances from the hypothesis of functional self-similarity

A method for the construction of the functions fitting the critical properties of homologous series is presented. The method is based on the hypothesis of functional self-similarity and the scaling behaviour of the critical constants of long-chain molecules. Equations for calculating the critical temperatures and pressures of the homologous series with the common formula H(CH2)nR, where R is a radical have been obtained. The parameters of the equations have been determined from experimental data for six homologous series. The presented method allows predicting the critical temperatures or pressures of any member of a homologous series of the given type if the critical temperature/pressure of one substance, which belongs to this series, is known. The proposed method provides better accuracy in comparison with currently used group-contribution methods for most of the homologous series considered.