Interfacial energy polymer blend phase separation

The addition of block copolymers to a binary polymer mixture can aid compatibilization of the components of the blend by reduction of the interfacial energy between the two phase separated domains. Copolymers can depress the build-up of the interfacial energy between the phases and/or make a favourable contribution to the entropy changes on mixing at the homogeneous/hetero-geneous phase separation temperature with the result that phase separation is delayed. 

In a fundamental sense, the miscibility, adhesion, interfacial energies, and morphology developed are all thermodynamically interrelated in a complex way to the interaction forces between the polymers. Miscibility of a polymer blend containing two polymers depends on the mutual solubility of the polymeric components. The blend is termed compatible when the solubility parameter of the two components are close to each other and show a single-phase transition temperature. However, most polymer pairs tend to be immiscible due to differences in their viscoelastic properties, surface-tensions, and intermolecular interactions. According to the terminology, the polymer pairs are incompatible and show separate glass transitions. For many purposes, miscibility in polymer blends is neither required nor de-... 

Many polymer blends or block polymer melts separate microscopically into complex meso-scale structures. It is a challenge to predict the multiscale structure of polymer systems including phase diagram, morphology evolution of micro-phase separation, density and composition profiles, and molecular conformations in the interfacial region between different phases. The formation mechanism of micro-phase structures for polymer blends or block copolymers essentially roots in a delicate balance between entropic and enthalpic contributions to the Helmholtz energy. Therefore, it is the key to establish a molecular thermodynamic model of the Helmholtz energy considered for those complex meso-scale structures. In this paper, we introduced a theoretical method based on a lattice model developed in this laboratory to study the multi-scale structure of polymer systems. First, a molecular thermodynamic model for uniform polymer system is presented. This model can... 

In general, a block copolymer added to immiscible polymer blend significantly suppresses the growth rate of phase-separated domains due to the reduction of interfacial tension resulting from a preferential localization of block copolymer at the interface. However, the retardation effect by the block copolymer is found to be dependent upon the structure of the block copolymer added, such as the interaction energy, the chain length, and the composition of block copolymer. 

In the light of the phase diagram derived earlier for a eonductive polymer blend (Figure 11.124), the energy dissipation meehanism by redispersion ean be understood. It is the energy input driven way baek, of the system from the equilibrium interfacial energy curve at the flocculation point to the fully dispersed, but still phase-separated boundary. 

If one uses a coarse-grained approach, one has to identify the relevant properties that the description on the coarser scale has to capture. In the following, we specifically consider wetting phenomena in a binary AB polymer blend that exhibits liquid-liquid phase separation between an A-rich and a B-rich phase. The thermodynamics of the surface enrichment layers is dictated by the free energies of the solid in contact with the two coexisting phases. Yaw Ybw> their interfacial tension,... 

The interphase is a separate phase with its own characteristics and two interfacial tension coefficients, Vj -f V2 = Vjj, with Vj2 being the experimental quantity. The lattice theories predict that in binary blends (1) there is a reciprocity between Vi2 and the interphase thickness, VjjA/ = constant (2) the surface energy is proportional to (3) polymer chain ends concentrate at the interface and (4) any low molecular weight component migrates to the interface. In consequence, the inter-phase is characterized by low entanglement density and viscosity, often evidenced by the interlayer slip [3]. 

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