Liquid-solid-solid thermal behaviour of n-C44H90 + n-C50H102 and n-C25H52 + n-C28H58 paraffinic binary mixtures

The equilibrium phase behaviour and thermal characteristics of n-C25H52 + n-C28H58 and n-C44H90 + n-C50H102 binary systems have been studied using a differential scanning calorimeter (DSC). As in the case of pure polymorphic n-alkanes, both the melting and crystallization thermograms for n-C25H52 + n-C28H58 mixtures exhibit two major peaks, α and β, corresponding to the liquid-solid and solid-solid transitions. Hence, isomorphous solid solutions were formed for these mixtures. Interestingly, the peak-to-peak temperature difference (ΔTpeaks = Tα − Tβ) for binary mixtures does not vary linearly with the mixture composition. More importantly, ΔTpeaks does not depend on the cooling rate. For n-C44H90 + n-C50H102 mixtures, on the other hand, the likelihood to form either isomorphous or eutectic systems was dependent on the thermal history of the prepared mixture. Once formed, however, eutectic and/or isomorphous systems were found to be stable over long periods of time.