INVESTIGATION OF EQUILIBRIUM CRYSTALLIZATION PROCESSES OF NORMAL-ALKANE MULTICOMPONENT SYSTEMS

The thermodynamic equilibrium between multicomponent melt and several solid solutions is computed for n-alkane mixtures consisting of many different homologues. The algorithm is based on the knowledge of the equations of state for the multicomponent melt and the solid solutions. Using pair interaction energies for the solid phases, which include the relative chain length differences of a pair of molecules, the sets of transcendental equations for the heterogeneous equilibrium can be solved by numerical methods. The results obtained from these calculations are compared with structure properties of the n-alkane solid solutions, which are evaluated from differential scanning calorimetry and X-ray measurements. It follows that the crystallization behaviour of the mixtures can be described by using just one pair interaction parameter, K = 3500 cal mol-1, in a temperature range between liquidus and solidus. Further theoretical predictions for the miscibility of homologues in the solid state are obtained, which are of great interest for the crystallization processes in oligomer systems such as fractions of linear polyethylene with extended chain crystals.