The physics of athermal nuclei in polymer crystallization

Abstract

The lower temperature limit for sporadic “thermal” nucleation, as estimated in a previous paper (Janeschitz-Kriegl (1997) Colloid Polym Sci), can be verified by a variety of earlier experiments which are compiled in this paper. Below the said limit only “athermal” nuclei are of importance in samples containing no large numbers of hetero-nuclei. The number of athermal nuclei increases tremendously (by many decades) with decreasing temperature. Why these nuclei are dormant and “awake” only at “their” temperature is explained in terms of their growth conditions, which depend on the length of the incorporated (helical) sequences. Also the sluggishness of molecular processes, occurring in the temperature range of metastable conditions, where sporadic nucleation can occur is demonstrated by some of the recalled experiments. Except for very fast industrial processes, where flow plays a dominant role, this sluggishness makes a noticeable influence of the sporadic nucleation on structure formation very improbable.