"Impact of Conformational and Chemical Correlations on Microphase Segregation in Random Copolymers"

Shifan Mao: Quinn J. MacPherson, Steve S. He, Elyse Coletta, and Andrew J. Spakowitz; Macromolecules, 06/01/16.

Additional Authors: Quinn J. MacPherson, Steve S. He, Elyse Coletta, and Andrew J. Spakowitz

Abstract:

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Random copolymers play an important role in a range of soft materials applications and biological phenomena. An individual monomer is typically a single chemical unit whose length is comparable to or less than a Kuhn length, resulting in a monomer segment that is structurally rigid at length scales of a segregated domain. Previous work on random copolymer phase segregation addresses the impact of correlations between the chemical identities along the chains for flexible polymers. In these works, a single monomer unit is effectively a large polymer block that behaves as a random walk without conformational correlation associated with semiflexibility. In our work, we develop a model of semiflexible random copolymers using the wormlike chain model to capture conformational correlation of the polymer chains. To address the thermodynamics of microphase segregation and the structure of the segregated domains, we develop a random phase approximation up to quartic order in density fluctuations that leverages our exact results for the statistical behavior of the wormlike chain model. In this work, we focus on the quadratic-order expansion of the free energy, which provides the mean-field spinodal of the homogeneous phase. We explore the impact of conformational and chemical correlations on the formation of inhomogeneous microphases at the spinodal point. We show that the onset of phase segregation and the correlation length of domains are extremely sensitive to chain rigidity.