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

X-ray diffraction analyses were carried out on four commercial multi-alkane samples and their fifty-fifty weight mixtures which present molar concentr ation distributions of the "normal logarithmic" type: all these systems for m a single solid phase which is isostructural to the beta ' ordered interme diate solid solution of n-alkane binary molecular alloys: they are the n-al kanes 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 m olecule layer thickness. Structural and differential thermal analyses highl ighted in the course of cooling from liquid state the successive appearance of three solid solutions in a synthetic mixture whose the molar concentrat ion distribution (from C-18 to C-36) has a shape of the "decreasing exponen tial" type as observed in petroleum cuts: the smaller chains, which here ar e in the majority, do not succeed in making the longer chains bend, too num erous, to form a single solid solution.