Conditions of nucleation in crystallizable polymers: reconnaissance of positions — a critical evaluation

Abstract

In view of the enormous difficulties in obtaining reliable experimental data for the purpose of structure simulation with the aid of computer programs (presently being so popular), every classifying endeavor must be considered of great importance. One of the goals of such an endeavor is the demarcation of characteristic temperature ranges. With the aid of thermodynamic considerations an estimate of the restricted temperature range of metastable undercooling, in which the classical theory of homogeneous nucleation, as developed for polymer solutions, is valid also for polymer melts (“thermal nucleation”) can be given. This consideration includes a discussion of the course of the relevant interface tensions along the co-existence lines of the P-T diagram. The so-called spinodal crystallization mode (see [1–3]) is found at lower temperatures and seems to be quite common in polymer crystallization. In this connection the so-called athermal nucleation can be identified with a specific process. However, the present author is not in favor of the term “spinodal mode”. This is explained by a comparison with the meaning of spinodal decomposition into two phases in the ordinary gas-liquid phase transition, which always occurs at the lower bound of the metastable undercooling. Remarkably, spinodal decomposition cannot be defined in the same way for the liquid-solid transition. Anyway, the author tries hard to induce unorthodox trains of thought in the hope to revie the discussion of a difficult matter, which has almost gone to sleep, before a satisfying settlement has been reached.