Phase behavior of gradient copolymer solutions: a Monte Carlo simulation study

Pandav, Gunja; Pryamitsyn, Victor; Gallow, Keith; Loo, Yueh Lin; Genzer, Jan; Ganesan, Venkat

doi:10.1039/c2sm25577d

Cited by 26 publications

(30 citation statements)

References 65 publications

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“…12,13 In these materials, the mesoscale morphology greatly influences their mechanical and transport properties. Recently, there has been interest in making new soft materials by introducing chemical stochasticity into block copolymers, such as tapered diblock copolymers 14 and gradient copolymers, 15−17 due to their ability to relieve packing frustration during self-assembly. Biology also needs to overcome random variability to achieve self-assembly in macromolecular environments in scenarios such as protein folding and chromatin condensation.…”

Section: ■ Introductionmentioning

confidence: 99%

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

Mao¹,

MacPherson²,

He³

et al. 2016

Macromolecules

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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. ■ INTRODUCTIONBlock copolymers have attracted attention in numerous applications because of their ability to self-assemble into nanostructured morphologies. 1−3 Extensive theoretical and experimental studies have predicted and characterized the ordered morphologies of block copolymers with well-defined chemical architecture such as diblock and triblock copolymers. 4−7 In contrast, the phase behavior of multiblock copolymers is less well understood. In particular, theoretical, computational, and experimental studies on random copolymers, whose monomer chemical identities are stochastically arranged along the polymers, are far less prevalent. 8−11 Commercial products such as high impact polystyrene (HIPS), styrene−butadiene rubber (SBR), and Nafion are blends of macromolecules with randomly distributed chemical repeat units. 12,13 In these materials, the mesoscale morphology greatly influences their mechanical and transport properties. Recently, there has been interest in making new soft materials by introducing chemical stochasticity into block copolymers, such as tapered diblock copolymers 14 and gradient copolymers, 15−17 due to their ability to relieve packing frustration during self-assembly. Biology also needs to overcome random variability to achieve self-assembly in macromolecular environments in scenarios such as protein folding and chromatin condensation. 18−20 Despite the abundance of random copolymers in various industrial applications and biological systems, the understanding of their phase behavior and structure− property relationship ...

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Section: ■ Introductionmentioning

confidence: 99%

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

Mao¹,

MacPherson²,

He³

et al. 2016

Macromolecules

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“…This feature is a definite merit in a material design perspective, considering that copolymer melts and blends containing copolymers are affected in their phase behaviors by monomer sequences along copolymer chain contours [10e24]. Among vast choices, recent efforts have been exerted to understand the properties of linear gradient copolymers, in particular, in the molten state [12,14,19], in solutions [21,25], and as interfacial layers [24] and brushes [22,23]. Wang et al studied the phase behavior of the blends of two linear homopolymers and the linear gradient copolymers [13], where the changes in the phase diagrams of the blends upon a fixed chain size ratio between the constituent polymers were considered with varying the composition gradient length.…”

Section: Introductionmentioning

confidence: 99%

Ring gradient copolymers as amphiphiles in their ternary blends with two linear homopolymers

Sun

Cho

2015

Polymer

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“…Meanwhile, for the related gradient copolymer systems that have been studied more frequently in the literature, sequence dispersity is known to affect both the order-disorder transition and microphase domain spacing, among other properties. [33][34][35][36] In the current study, we are motivated to quantify the effects of sequence dispersity for tapered systems. We aim to show both: to what extent the theoretical work employing fixed sequences is representative of statistical sequence systems and, more generally, how sequence dispersity affects the microphase structure.…”

Section: Introductionmentioning

confidence: 99%

“…[33][34][35] Ref. 34 employed Monte Carlo (MC) simulations to study gradient copolymers in solution.…”

Section: Introductionmentioning

confidence: 99%

“…[33][34][35] Ref. 34 employed Monte Carlo (MC) simulations to study gradient copolymers in solution. The polymer sequences could be either "quenched" (sequentially polydisperse), in which each monomer could be A or B with a probability specified by a linear composition profile, or "annealed" (sequentially monodisperse), in which each monomer is partially A and B with a fraction determined by the same linear composition (the pairwise interaction strengths were adjusted according to the fractional monomer type).…”

Section: Introductionmentioning

confidence: 99%

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Effect of sequence dispersity on morphology of tapered diblock copolymers from molecular dynamics simulations

Levine

Seo

Brown

et al. 2016

The Journal of Chemical Physics

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Tapered diblock copolymers are similar to typical AB diblock copolymers but have an added transition region between the two blocks which changes gradually in composition from pure A to pure B. This tapered region can be varied from 0% (true diblock) to 100% (gradient copolymer) of the polymer length, and this allows some control over the microphase separated domain spacing and other material properties. We perform molecular dynamics simulations of linearly tapered block copolymers with tapers of various lengths, initialized from fluids density functional theory predictions. To investigate the effect of sequence dispersity, we compare systems composed of identical polymers, whose taper has a fixed sequence that most closely approximates a linear gradient, with sequentially disperse polymers, whose sequences are created statistically to yield the appropriate ensemble average linear gradient. Especially at high segregation strength, we find clear differences in polymer conformations and microstructures between these systems. Importantly, the statistical polymers are able to find more favorable conformations given their sequence, for instance, a statistical polymer with a larger fraction of A than the median will tend towards the A lamellae. The conformations of the statistically different polymers can thus be less stretched, and these systems have higher overall density. Consequently, the lamellae formed by statistical polymers have smaller domain spacing with sharper interfaces. Published by AIP Publishing. [http://dx

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Phase behavior of gradient copolymer solutions: a Monte Carlo simulation study

Cited by 26 publications

References 65 publications

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

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

Ring gradient copolymers as amphiphiles in their ternary blends with two linear homopolymers

Effect of sequence dispersity on morphology of tapered diblock copolymers from molecular dynamics simulations

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