Grafted polymer chains suppress nanoparticle diffusion in athermal polymer melts

Lin, Chiu‐Chu; Griffin, Philip J.; Chao, Huikuan; Hore, Michael J. A.; Ohno, Kohji; Clarke, Nigel; Riggleman, Robert A.; Winey, Karen I.; Composto, Russell J.

doi:10.1063/1.4982216

Cited by 38 publications

(58 citation statements)

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“…The model and method derivations follow closely those of our previous works for both the SCFT ,, and DMFT ,, methods. We place an explicit particle grafted with A- and B-type discrete Gaussian polymer chains in an explicit solvent, S, as shown in Figure a.…”

Section: Methodsmentioning

confidence: 65%

“…Furthermore, the previous studies used a mean-field approximation, even for the systems in solution, where it is understood that fluctuations are prominent and that the mean-field approximation is inaccurate. 28 Here, we investigate the effects of fluctuations and of nonuniform grafting site distributions on the brush structure of a single particle using a combination of SCFT and a fluctuating dynamic mean-field theory [29][30][31]. The DMFT method used in this study is similar to the MC-SCMF model used to study planar mixed brushes with the small caveat that we use Langevin dynamics rather than Monte Carlo moves to update the particle positions; this is largely irrelevant in the analysis of equilibrium phenomena.…”

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confidence: 99%

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Fluctuation Effects on the Brush Structure of Mixed Brush Nanoparticles in Solution

Koski

Frischknecht

2018

ACS Nano

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A potentially attractive way to control nanoparticle assembly is to graft one or more polymers on the nanoparticle, to control the nanoparticle-nanoparticle interactions. When two immiscible polymers are grafted on the nanoparticle, they can microphase separate to form domains at the nanoparticle surface. Here, we computationally investigate the phase behavior of such binary mixed brush nanoparticles in solution, across a large and experimentally relevant parameter space. Specifically, we calculate the mean-field phase diagram, assuming uniform grafting of the two polymers, as a function of the nanoparticle size relative to the length of the grafted chains, the grafting density, the enthalpic repulsion between the grafted chains, and the solvent quality. We find a variety of phases including a Janus phase and phases with varying numbers of striped domains. Using a nonuniform, random distribution of grafting sites on the nanoparticle instead of the uniform distribution leads to the development of defects in the mixed brush structures. Introducing fluctuations as well leads to increasingly defective structures for the striped phases. However, we find that the simple Janus phase is preserved in all calculations, even with the introduction of nonuniform grafting and fluctuations. We conclude that the formation of the Janus phase is more realistic experimentally than is the formation of defect-free multivalent mixed brush nanoparticles.

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Section: Methodsmentioning

confidence: 65%

mentioning

confidence: 99%

Fluctuation Effects on the Brush Structure of Mixed Brush Nanoparticles in Solution

Koski

Frischknecht

2018

ACS Nano

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“…Most often, GNPs are dispersed in a matrix of polymer chains or oligomers having the same chemistry as the grafted chains. Several theoretical, experimental, and computational approaches have been used in the last 30 years to investigate the structural properties and dynamics of these systems. − …”

Section: Introductionmentioning

confidence: 99%

Universal Polymeric-to-Colloidal Transition in Melts of Hairy Nanoparticles

et al. 2021

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Two different classes of hairy self-suspended nanoparticles in the melt state, polymer-grafted nanoparticles (GNPs) and star polymers, are shown to display universal dynamic behavior across a broad range of parameter space. Linear viscoelastic measurements on well-characterized silica-poly(methyl acrylate) GNPs with a fixed core radius (R core) and grafting density (or number of arms f) but varying arm degree of polymerization (N arm) show two distinctly different regimes of response. The colloidal Regime I with a small N arm (large core volume fraction) is characterized by predominant low-frequency solidlike colloidal plateau and ultraslow relaxation, while the polymeric Regime II with a large N arm (small core volume fractions) has a response dominated by the starlike relaxation of partially interpenetrated arms. The transition between the two regimes is marked by a crossover where both polymeric and colloidal modes are discerned albeit without a distinct colloidal plateau. Similarly, polybutadiene multiarm stars also exhibit the colloidal response of Regime I at very large f and small N arm. The star arm retraction model and a simple scaling model of nanoparticle escape from the cage of neighbors by overcoming a hopping potential barrier due to their elastic deformation quantitatively describe the linear response of the polymeric and colloidal regimes, respectively, in all these cases. The dynamic behavior of hairy nanoparticles of different chemistry and molecular characteristics, investigated here and reported in the literature, can be mapped onto a universal dynamic diagram of f/[R core 3/ν0)1/4] as a function of (N armν0 f)/(R core 3), where ν0 is the monomeric volume. In this diagram, the two regimes are separated by a line where the hopping potential ΔU hop is equal to the thermal energy, k B T. ΔU hop can be expressed as a function of the overcrowding parameter x (i.e., the ratio of f to the maximum number of unperturbed chains with N arm that can fill the volume occupied by the polymeric corona); hence, this crossing is shown to occur when x = 1. For x > 1, we have colloidal Regime I with an overcrowded volume, stretched arms, and ΔU hop > k B T, while polymeric Regime II is linked to x < 1. This single-material parameter x can provide the needed design principle to tailor the dynamics of this class of soft materials across a wide range of applications from membranes for gas separation to energy storage.

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“…As suggested by Zhao et al, the two critical variables in the context of this study are the NP diffusion rate and the rate of polymer crystallization, that is, nucleation and growth rates. There are several groups working on the former topic, − namely, the diffusion of NPs and polymers in a nanocomposite, and we specifically highlight the experimental works of Composto and Winey et al , and the recent theoretical work of Ge et al It was experimentally shown that, while the formation of a physically adsorbed polymer layer slowed down NP diffusion, NPs chemically grafted with a dense polymer brush were slowed even more significantly. Importantly, in the latter case, the results were independent of grafting density (over a relatively large range) in the dense brush range.…”

Section: Introductionmentioning

confidence: 99%

Polymer Spherulitic Growth Kinetics Mediated by Nanoparticle Assemblies

et al. 2021

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We systematically examine the role of the self-assembly state of polymer-grafted silica nanoparticles (GNPs) on the spherulitic growth kinetics of a poly(ethylene oxide) (PEO) matrix. The nanoparticles (NPs) are functionalized with either unimodal or bimodal polymer brushes to systematically control their self-assembly within the semicrystalline polymer matrix. In the former case, we employ a poly(methyl methacrylate) (PMMA) brush (miscible with PEO), while the latter has a short dense polystyrene (PS carpet) brush, which is immiscible with the PEO matrix, and a long, sparse PMMA brush. The unimodal GNPs always yield well-dispersed NPs possibly because both the silica NP surface and the PMMA interact favorably with the PEO. The addition of the short PS carpet makes the interaction between the surface and the matrix PEO unfavorable. However, since the NPs also have grafted PMMA chains, they act akin to surfactants and provide access to a range of self-assembled structures. In all cases, the addition of NPs decreases the PEO spherulitic growth rates. Surprisingly, we find that the spatial dispersion of NPs does not change the secondary nucleation activation energy barrier of the PEO crystallization, such that the temperature dependence of spherulite growth kinetics is relatively unaffected by the NPs. Instead, the main effect of the NPs on spherulitic growth kinetics arises from variations of the melt's viscosity. Two apparently "universal" trends are foundbare NPs and large assemblies of GNPs appear to approximately follow the same dependence for the role of additives on polymer viscosity. On the other hand, all self-assembled NP structures which have at least one nanoscale dimension (well-dispersed NPs, one-dimensional strings or two-dimensional sheets) follow another general behavior, but one where the viscosity is much larger. Such unusual viscosity increases have been previously observed in the pioneering experiments of Composto and Winey, but there is currently no available theoretical description that can capture these changes and their effects on polymer crystallization.

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Grafted polymer chains suppress nanoparticle diffusion in athermal polymer melts

Cited by 38 publications

References 50 publications

Fluctuation Effects on the Brush Structure of Mixed Brush Nanoparticles in Solution

Fluctuation Effects on the Brush Structure of Mixed Brush Nanoparticles in Solution

Universal Polymeric-to-Colloidal Transition in Melts of Hairy Nanoparticles

Polymer Spherulitic Growth Kinetics Mediated by Nanoparticle Assemblies

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