Influence of the distribution general shape of n-alkane molar concentrations on the structural state of multi-alkane mixtures

Abstract X-ray diffraction analyses were carried out on four commercial multi-alkane samples and their fifty-fifty weight mixtures which present molar concentration distributions of the “normal logarithmic” type: all these systems form a single solid phase which is isostructural to the β′ ordered intermediate solid solution of n-alkane binary molecular alloys: they are the n-alkanes with carbon atom numbers, n, close to the mean composition in carbon atoms of the mixtures which are in the majority and which impose a single molecule layer thickness. Structural and differential thermal analyses highlighted in the course of cooling from liquid state the successive appearance of three solid solutions in a synthetic mixture whose the molar concentration distribution (from C18 to C36) has a shape of the “decreasing exponential” type as observed in petroleum cuts: the smaller chains, which here are in the majority, do not succeed in making the longer chains bend, too numerous, to form a single solid solution.