Diamagnetic susceptibility of solid and liquid paraffins

Abstract

Experimental values for the diamagnetic susceptibility of a series of mono-disperse n-paraffins ranging between 6 and 50 carbon atoms in the solid (melt and solution crystallized) and in the liquid state are reported. From the dependence of the molecular susceptibility, ScHM, on the molecular weight, information about the intermolecular interactions between adjacent chain molecules and on the arrangement of the methyl end-groups is obtained. The ScHM values of melt- and solution-crystallized paraffins are, within experimental error, indistinguishable from each other. For C₁₂H₂₆ and C₄₄H₉₀ the specific susceptibility ScHM /M rises at the melting point within a few °C and reaches a plateau which characterizes the liquid state II. For the paraffin C₂₄H₅₀ an intermediate plateau between the melting point and the final true liquid state is observed and is called liquid state I. After cooling below the melting point TM, the ScHM value of the equilibrium state can be obtained after a short time only from liquid state I, while from liquid state II days and weeks are needed for this. By combining this information with the observed ScHM values, it is concluded that in liquid state I a higher or smectic-like order exists similar to mesophases, well-known in liquid crystals, while in the real liquid state II this order is lost.