MOLECULAR-DYNAMICS OF THE ALPHA-RELAXATION DURING CRYSTALLIZATION OF A LOW-MOLECULAR-WEIGHT COMPOUND - A REAL-TIME DIELECTRIC-SPECTROSCOPY STUDY

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-fo rming low-molecular-weight compound was investigated in order to monit or the change of the molecular dynamics with increasing crystallinity by dielectric spectroscopy and differential scanning calorimetry (DSC) . The measurement of the dielectric alpha-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 calorimetri c glass transition temperature shifts in the same region for about 15 K to higher temperatures. No direct information about the morphology o f the samples is available at the moment but indirect measurements ind icate 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 confineme nt in the order of nanometer. (C) 1998 American Institute of Physics. [S0021-9606(98)50321-2].