The Early Stages of the Phase Separation Dynamics in Polydisperse Polymer Blends
Resource
Macromolecules,27(15),4231-4241.
Journal
Macromolecules
Journal Volume
27
Journal Issue
15
Pages
4231-4241
Date Issued
1994-07
Date
1994-07
Author(s)
Cruz, M. Olvera de la
Abstract
The thermodynamics and the dynamics of incompatible polydisperse polymer blends are analyzed. The free energy is constructed following the Flory-Huggins approach, where the degree of incompatibility is characterized by the Flory interaction parameter χ. The Cahn-Hilliard approximation is used to analyze the early stages of spinodal decomposition dynamics of a polymer blend quenched into the unstable region. A blend of polydisperse A polymers with the Schulz-Flory distribution and monodisperse B polymers is analyzed by treating polymer A as a one-, two-, and three-component system with a weight average degree of polymerization and a polydispersity index, which we refer to as two-, three-, and four- component models, respectively. The thermodynamics and the dynamics of incompatible monodisperse A-monodisperse B polymer blends are consistent no matter which model is used. When polymer A is polydisperse, however, [S(k,t)-S(k,0)]/S(k,0),whereS(k,t)is the characteristic structure function, is definitely different in the three different models due to kinetic effects. The differences are dependent on the functional form of the Onsager coefficients. For wavevector-independent Onsager coefficients, the reduced wavevector for which [S(k,t) - S(k,0)]/S(k,0) is a maximum, k*peak, is always equal to 1/√2 in the two-component model, while k*peak increases as χ increases in the three- and four-component models. While for wavevector-dependent Onsager coefficients, k*peak decreases as χ increases in the three different component models. As χ → ∞, the difference in k*peak between two- and three-component models and between three- and four-component models is 0.05 and 0.02, respectively, independent of the weight-average degree of polymerization when the polydispersity index of polymer A is equal to 2.0. When the polydispersity index of polymer A is reduced to 1.5, the difference in k*peak becomes 0.04 and 0.01, respectively. © 1994, American Chemical Society. All rights reserved.
Other Subjects
Approximation theory; Characterization; Decomposition; Dispersions; Dynamics; Polymerization; Quenching; Separation; Structure (composition); Thermodynamics; Degree of incompatibility; Flory interaction parameter; Free energy; Phase separation dynamics; Polydisperse polymer blend; Polydispersity index; Schulz Flory distribution; Wavevector; Polymer blends
Type
journal article