Thermal analysis of paraffins by calorimetry

Paraffins of sufficient chain length can serve as model compounds for flexible macromolecules. They crystallize almost completely and do not suffer from chain folding as long as their chain length is less than about 10 nm. The melting and crystallization of a paraffin, C50H102 (n-pentacontane), was analyzed as such a model compound with both, standard differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC) using saw-tooth modulation and quasi-isothermal modulation with very small amplitude (0.05 K). The supercooling due to nucleation was shown to be strongly cooling-rate dependent. There was practically no supercooling needed for crystallization from the melt with cooling rates up to 10 K/min, and values of up to 10 K were found for cooling rates of 30 K/min. Melting was completed within 1 K with quasi-isothermal modulation, but 66% of total melting occurred over a much narrower temperature range of 0.1 K or less. A 'reversing' melting in the paraffin was detected by TMDSC and the previously proposed integral analysis is found to be a useful tool for quantitative analysis of the thermal transition. Published by Elsevier Science B.V.