Homogeneous Nucleation and Fractionated Crystallization in Block Copolymers

Abstract

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.

Impact of Nanoscale Confinement on Crystal Orientation of Poly(ethylene oxide)

“…The observed crystallization temperature was close to the temperature for homogeneous nucleation of PEO, between À10 and 0 8C. [19,20,[29][30][31] In contrast, the on-edge crystals of the PEO nanolayers were obtained at a much higher temperature of 20 8C. Furthermore, both the c-and b-axes were parallel to the layer plane.…”

Self-assembly of semicrystalline PE-b-PS diblock copolymers within AAO nanoporous templates

“…Additionally, in this case, the number of clean MDs (PE nanospheres) is six orders of magnitude larger than the number of heterogeneities in bulk PE (see ref. 56). …”

Effect of block asymmetry on the crystallization of double crystalline diblock copolymers

“…3 The crystallization of diblock copolymer with one crystallizable block has been extensively studied in last few decades. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] However, the complexity associated with the crystallization of double crystalline diblock copolymer is poorly understood. In crystallinecrystalline diblock copolymer, the final crystal morphology is driven by the competition between two blocks towards crystallization along with microphase separation.…”