Molecular dynamics of the α-relaxation during crystallization of a low-molecular-weight compound: A real-time dielectric spectroscopy study

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Abstract
Low-molecular-weight compounds often crystallizes to systems with 100% crystallinity. There are only a few examples where a small amorphous fraction, characterized by a glass transition, remains after long time crystallization from the melt. The crystallization of such a glass-forming low-molecular-weight compound was investigated in order to monitor the change of the molecular dynamics with increasing crystallinity by dielectric spectroscopy and differential scanning calorimetry (DSC). The measurement of the dielectric α-relaxation was performed in real time during isothermal crystallization above the glass transition. At high crystallinities (above 90%) a shift of the peak position and a broadening of the dielectric spectrum was observed. The calorimetric glass transition temperature shifts in the same region for about 15 K to higher temperatures. No direct information about the morphology of the samples is available at the moment but indirect measurements indicate a layerlike crystalline structure. Then the remaining amorphous fraction can be considered between the crystal layers and the observed changes in the relaxation behavior may be caused by spatial confinement in the order of nanometer.