The confinement of crystallizable blocks within AB or ABC microphase-separated block
copolymers in the nanoscopic scale can be tailored by adequate choice of composition, molecular weight,
and chemical structure. In this work we have examined the crystallization behavior of a series of AB and
ABC block copolymers incorporating one or two of the following crystallizable blocks: polyethylene, poly(ε-caprolactone), and poly(ethylene oxide). The density of confined microdomain structures (MD) within
block copolymers of specific compositions, in cases where the MD are dispersed as spheres, cylinders, or
any other isolated morphology, is much higher than the number of heterogeneities available in each
crystallizable block. Therefore, fractionated crystallization takes place with one or several crystallization
steps at decreasing temperatures. In specific cases, the clear observation of exclusive crystallization from
homogeneous nuclei was obtained. The results show that, regardless of the specific morphological features
of the MD, it is their vast number as compared to the number of heterogeneities present in the system
that determines the fractionated character of the crystallization or in extreme cases homogeneous
nucleation. The self-nucleation behavior was also found to depend on the composition of the copolymers.
When the crystallizable block is confined into spheres or cylinders and exhibits homogeneous nucleation,
the self-nucleation domain disappears. This is a direct consequence of the extremely high density of
microdomain structures that need to be self-seeded (on the order of 1015−1016/cm3). Therefore, to increase
the density of self-nuclei, the self-nucleation temperature has to be decreased to values so low that
extensive partial melting is achieved, and some of the unmelted crystal fragments can be annealed, in
some cases even before self-nucleation takes place.
Self-nucleation (SN) is a special nucleation process triggered by selfseeds or self-nuclei that are generated in a given polymeric material by specific thermal protocols or by inducing chain orientation in the molten or partially molten state. SN increases the nucleation density of polymers by several orders of magnitude, producing significant modifications to their morphology and overall crystallization kinetics. In fact, SN can be used as a tool for investigating the overall isothermal crystallization kinetics of slow-crystallizing materials by accelerating the primary nucleation stage in a previous SN step. Additionally, SN can facilitate the formation of one particular crystalline phase in polymorphic materials. The SN behavior of a given polymer is influenced by its molecular weight, molecular topology, and chemical structure, among other intrinsic and extrinsic characteristics. This review paper focuses on the applications of DSC-based SN techniques to study the nucleation, crystallization, and morphology of different types of polymers, blends, copolymers, and nanocomposites.
The existence of a "memory" of the previous crystalline state, which survives melting and enhances re-crystallization kinetics by a self-nucleation process, is wellknown in polymer crystallization studies. Despite being extensively investigated, since the early days of polymer crystallization studies, a complete understanding of melt memory effects is still lacking. In particular, the exact constitution of self-nuclei is still under debate. In this perspective, we provide a comprehensive and critical overview of melt memory effects in polymer crystallization. After the phenomenology of the process and some key concepts are introduced, the main experimental results of the last decades are summarized. Analogies and discrepancies of the melt memory characteristics of different polymeric systems are highlighted. Based on this background, the most significant interpretations and theories of melt memory effects are described; underlining that different interpretations may apply to various specific cases. Recent insights on self-nucleation, gained thanks to a multi-technique approach (combining calorimetry, rheology, infrared and dielectric spectroscopy), are presented. The role of intra/inter-chain segmental contacts in the strength of melt memory effects, and the differences between homopolymers and copolymers behavior, are discussed. Finally, we identify areas where further research in the field is needed to shed light on the longstanding questions regarding the origin of melt memory effects in semi-crystalline polymers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.