Primary Nucleation in Metastable Solutions of Poly(3-hexylthiophene)

Because of its smallness and low probability of formation,the determination of the size of the critical primary nucleus represents agreat challenge in polymer crystallization. We are still missing a feasibleapproach providing experimental access to primary nucleation. In thiswork, we investigated the dependence of the incubation time on the degreeof supersaturation for a well-defined metastable regime of a prototypicalconjugated polymer, i.e., poly(3-hexylthiophene). On the basis ofKashchiev's nucleation theorem and verified by a simulation model forprimary nucleation based on the kinetics of attaching and detachingcrystalline units, we deduced the number of crystalline units within thecritical nucleus, which, for the investigated parameter range, was found tobe independent of the degree of supersaturation. Thus, we conclude thatclassical nucleation theory, which predicts an increase of the size of criticalnuclei with decreasing degree of supersaturation, may be not valid forweakly supersaturated solutions.