Effect of homologous impurity on the solid-solid phase transition of normal-alkane (hexatriacontane) crystal studied by time-resolved X-ray measurements

The effect of impurities on the solid-solid phase transition of solution-gr own normal alkane (hexatriacontane) crystals was investigated using differe ntial scanning calorimetry (DSC)I time-resolved small-angle X-ray scatterin g (SAXS) and polarizing microscopy. Normal-dotriacontane was used in this w ort; as a homologous impurity. Six kinds of crystals were grown using two d ifferent solution concentrations (S-C) and three kinds of impurity fraction s (I-F). DSC results show that the temperature of the solid-solid phase tra nsition decreases with I-F and S-C. Time-resolved SAXS measurements exhibit a dynamic change of the solid-solid phase transition where the onset tempe rature of the transition is also lowered by I-F and S-C. A Streak-like patt ern which was apparent in the low-angle scattering clarifies that flat-shap ed defects parallel to the lamellar surface increase with I-F and S-C. The transition frontier observed by Polarizing microscopy indicates that molecu les of more than 10(4) lamellae: cooperatively accompany the solid-solid ph ase transition. The onset temperature as measured by SAXS is more than 1 de grees C higher than that measured by DSC. The deviation is explained by the time lag for growing the bulk (secondary) nucleation from local (primary) nucleation sites of the solid-solid phase transition.