From the melt via mesomorphic and granular crystalline layers to lamellar crystallites: A major route followed in polymer crystallization?

Based on broad and detailed evidence from a large variety of experiments on several polymer systems carried out by other authors and ourselves, a nove l concept for understanding the crystallization of polymers from the melt i s developed. The experiments generally indicate that the formation and grow th of the lamellar crystallites is a multi-step process passing over interm ediate states. We suggest a specific route which is compatible with the obs ervations. It is proposed that the initial step is always the creation of a mesomorphic layer which spontaneously thickens, up to a critical value, wh ere it solidifies through a cooperative structural transition. The transiti on produces a granular crystalline layer, which transforms in the last step into homogeneous lamellar crystallites. The model leads to predictions abo ut the temperature dependencies of the crystal thickness and the growth rat e which are at variance with conventional views but in agreement with findi ngs in recent experiments.