Primary nucleation in metastable solutions of poly(3-hexylthiophene)

Due to its smallness and low probability of formation, the determination of the size of the critical primary nucleus represents a great challenge in polymer crystallization. We are still missing a feasible approach providing experimental access to primary nucleation. In this work, we investigated the dependence of the incubation time on the degree of supersaturation for a well-defined metastable regime of a prototypical conjugated polymer, i.e., poly(3-hexylthiophene). Based on Kashchiev’s nucleation theorem and verified by a simulation model for primary nucleation based on the kinetics of attaching and detaching crystalline units, we deduced the number of crystalline units within the critical nucleus, which, for the investigated parameter range, was found to be independent of the degree of supersaturation. Thus, we conclude that classical nucleation theory, which predicts an increase of the size of critical nuclei with decreasing degree of supersaturation, may be not valid for weakly supersaturated solutions.