Numerical and morphological approach to the mechanism of homogeneous-nucleation-based crystallization in o-terphenyl

To investigate the mechanism of a homogeneous-nucleation-based (HNB) crystallization found in o-terphenyl in its glass transition temperature region, numerical calculations for the crystallization rate were carried out according to a classical nucleation theory, and a quantitative estimation for the size of the crystalline particles was performed based on the results by powder X-ray diffractometry and by fusion calorimetry. The calculation succeeded in producing a crystallization rate close to the experimentally observed rate by taking into consideration both the nucleation enhancement effect due to the decrease in the interfacial energy of the embryo, by making contact with the crystalline surface, and the larger molecular-rearrangement rate for the crystal nucleation due to the beta but not the alpha-process. The crystalline particle formed by the HNB crystallization was found to have a size of similar to 50 nm which is large compared with that expected from homogeneous crystal nucleation. The size of the crystalline particles was reasonably explained by assuming a nucleus-orientation selectivity in the nucleation enhancement effect, and the orientation selectivity is suggested to be a potential origin for the characteristic temperature dependence of the HNB crystallization rate. (C) 1998 Elsevier Science B.V. All rights reserved.