Thermal behavior of several organic glasses

The thermal behavior of the glass forming organic compounds 2-cyclo-octylamino-5-nitropyridine (COANP), N-4-nitrophenyl-L-prolinol (NPP), 2-N-prolinol-5-nitropyridine (PNP), which are good candidates for applications in nonlinear optics, have been investigated by differential scanning calorimetry. The glass transition temperature, the crystallization temperature and melt temperature has been identified on each of these glasses. Glass transition and crystallization temperatures were found to depend on the heating rate. Knowing this fact, the activation energy of the crystallization process and frequency factor was determined by the Kissinger and Avrami non-isothermal methods. The values of the kinetic parameters obtained from the two models are in excellent agreement. The glass forming ability was discussed based on the crystallization kinetic parameters. The dependence of the glass transition temperature on heating rate was discussed using the empirical relationship of Lasocka. Multistep crystallization from the glass-like disordered state for NPP have been found during the heating of the sample on continuous cycling. Their structural differences were studied using X-ray diffraction technique. The normal and anomalous crystallization occurred to NPP was discussed.