Nucleation in binary polymer blends: Effects of adding diblock copolymers

Abstract

The effects of adding AB diblock copolymers to A/B binary blends on the structure and thermodynamics of critical nuclei are studied using the self-consistent field theory. At a fixed ratio of the amount of the two homopolymers, depending on the degree of polymerization and composition of the diblocks, their addition to the blends can either increase or decrease the nucleation free energy barrier relative to the pure A/B blends. The qualitative trend can be deduced from the shift in the coexistence boundary and the spinodal. The distribution of diblock copolymers in critical nuclei depends on the composition of the diblocks and the quench depth. Near the coexistence, symmetric diblocks exhibit surfactant behavior, being highly concentrated on the interface of the critical nuclei. Near the spinodal, they act more like co-solvent with a relatively uniform distribution.

Nucleation in A/B/AB blends: Interplay between microphase assembly and macrophase separation

“…In our previous study, we have studied the nucleation in an A / B / AB blend at N Ϸ 3, where macrophase separation occurs without interference of metastable micelles. 34 Here, we study an A / B / AB blend at a much low temperature, N = 20, to examine how micelle formation affects nucleation in A / B / AB blends. We focus our discussion on the case of fixed diblock copolymer concentration while increasing the vol- , the swollen micelle is an intermediate to macrophase separation, and in this case, the first maximum is identified as the first critical nucleus ͑max 1͒, and the local minimum is swollen micelle ͑min͒ and the second maximum is the second critical nucleus ͑max 2͒.…”

“…We consider the excess free energy of creating a single, localized fluctuation structure in the mother phase. 34,41,45,46,49 The mother phase is characterized by the chemical potentials. The basic idea is to focus on an appropriately chosen volume in a large system and ask what the free energy cost is for creating a specified type of fluctuation with its center-of-mass position fixed at the center of the volume ͑i.e., the translational entropy of the single, localized fluctuation structure is not considered͒.…”

“…Effects of diblock copolymer AB on the nucleation of an A / B blend have been studied theoretically 34 and experimentally, 35,36 without explicitly considering the interference of micelle formation. In previous work, 34 we have studied effects of adding diblock copolymers, AB, on the nucleation in the course of macrophase separation in an A / B blend at weak segregation ͑N Ϸ 3͒.…”

“…In previous work, 34 we have studied effects of adding diblock copolymers, AB, on the nucleation in the course of macrophase separation in an A / B blend at weak segregation ͑N Ϸ 3͒. It has been shown that adding diblock copolymer, AB, to the A / B blend can either increase or decrease the nucleation free energy barrier rela-tive to the pure A / B blend.…”

“…SCFT has been successfully extended to study local self-assembled structures such as micelles, emulsion droplets and critical nuclei of macrophase separation. 34,41,[45][46][47][48] Using the SCFT method, we can calculate the density profiles and free energy of localized fluctuation structures ͑e.g., micelles or nuclei/droplets of the new, stable phase during phase transformation͒ at the mean-field level without further approximation. Additionally, we employ a combination of capillary model and diblock copolymer monolayer model.…”