Dielectric study of dynamics of organic glasses

The dynamics of organic compounds 2-cyclo-octylamino-5-nitropyridine (COANP ), (S)-2-N-alpha-(methylbenzylamino)-5-nitropyridine (MBANP), 2-(N-prolinol )-5-nitropyridine (PNP), and N-(4-nitrophenyl)-(L)-prolinol (NPP) were stud ied by dielectric relaxation spectroscopy in the frequency range of 10 Hz-2 MHz and differential scanning calorimetry (DSC). The dielectric and DSC st udies showed that COANP, MBANP and PNP underwent glass transition. However, NPP crystallized so rapidly upon cooling that the glass state could not be observed. It was found that the crystalline process of COANP did not slow the structure relaxation of COANP glass. The relaxation times fitted well t o the empirical Vogel-Fulcher equation tau = tau(infinity) exp[E-a/k(b)(T - T-VF)]. The activation energies E-a and the Vogel-Fulcher temperature T-VF were 54.5 meV and 239 K for COANP, 86.2 meV and 249 K for MBANP and 84.9 m eV and 245 K for PNP, respectively. The crystalline temperatures of COANP a nd MBANP were given as 300 K and 330 K, respectively. An anomalous behaviou r of the dielectric permittivity of PNP glass was observed.