Phase equilibria in copolymer/homopolymer ternary blends: Molecular weight effects

Abstract

Directed assembly of asymmetric ternary block copolymer-homopolymer blends using symmetric block copolymer into checkerboard trimming chemical patternThe phase behavior of ternary blends of an A-B random copolymer with two homopolymers (A and B) is investigated within the Flory-Huggins lattice theory. We restrict consideration to the formation of (isotropic) liquid phases. For compositionally symmetric systems in which the two homopolymers have equal molecular weights, two different topologies are found for the phase diagrams according to the length of the copolymer relative to the homopolymers. Namely, upon lowering the temperature, a three-liquid-phase region emerges either continuously via a tricritical point if the copolymer is long enough, or discontinuously otherwise. This change in phase behavior, an entropy of mixing effect, occurs when the copolymer length is a fraction 2/5 of the homopolymer molecular weight. The properties of the (symmetric) tricritical points are discussed, as well as the phase behavior of systems in which the copolymer is not symmetrical in composition and/or the two homopolymers differ in size. This Flory-Huggins approach should be valid for blends containing random copolymers, but also, at high enough temperatures, for blends that contain block copolymers, the temperature range of validity being broader for smaller block copolymers. The critical behavior of systems containing block copolymers is described by the simple Flory-Huggins theory over a range delineated by isotropic Lifshitz points. These Lifshitz points are located within the random phase approximation.

The structure and phase transitions in polymer blends, diblock copolymers and liquid crystalline polymers: The Landau‐Ginzburg approach

“…The two most useful scattering intensities, are obtained by taking the inverse of the vertex function matrix Eq(6.1), and are given below: 12) in agreement with Broseta and Fredrickson 34) and 13) in agreement with Leibler 92) .…”

Ternary Polymer Blends as Model Surfactant Systems

“…For R A ) R B ) R, the transition from microphase to macrophase separation is predicted to occur at a total homopolymer volume fraction of 1/(1 + 2R 2 ). 16 This indicates that, as N h increases relative to N AB , more diblock is required to solubilize the homopolymers into a single-phase microstructure.…”

Nucleation in binary polymer blends: Effects of adding diblock copolymers

“…The roles of AB diblock copolymers on the equilibrium, bulk properties in A/B blends are relatively well understood: The diblocks can either act as surfactants to lower the interfacial tension by adsorbing at the A/B interface, or serve as co-solvent and distribute uniformly throughout the blends to improve their compatibility, or phase separate into a new copolymer-rich phase. [6][7][8][9][10] However, there has been no theoretical work that elucidates the roles of the diblocks in the nucleation event that leads to phase separation. Therefore, our study will nicely complement previous theoretical work on the equilibrium, bulk properties, and will provide the theoretical basis for controlling the nucleation behavior in A/B blends by the addition of the AB diblock copolymers.…”

“…First, multicomponent homopolymer and block copolymer blends are systems of wide industrial applications and theoretical interest. [2][3][4][5][6] The A/B/AB ternary system serves as the simplest model system for understanding the complex phase behaviors in such blends. The roles of AB diblock copolymers on the equilibrium, bulk properties in A/B blends are relatively well understood: The diblocks can either act as surfactants to lower the interfacial tension by adsorbing at the A/B interface, or serve as co-solvent and distribute uniformly throughout the blends to improve their compatibility, or phase separate into a new copolymer-rich phase.…”