Interfacial Properties of Polymer Nanocomposites: Role of Chain Rigidity and Dynamic Heterogeneity Length Scale

Cheng, Shiwang; Carroll, Bobby; Lu, Wei; Fan, Fei; Carrillo, Jan‐Michael Y.; Martin, Halie; Holt, Adam P.; Kang, Nam‐Goo; Bocharova, Vera; Mays, Jimmy W.; Sumpter, Bobby G.; Dadmun, Mark; Sokolov, Alexei P.

doi:10.1021/acs.macromol.6b02816

Cited by 133 publications

(140 citation statements)

References 57 publications

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“…The perturbed layer length discussed in the previous section is generally not directly measurable in experiment. We thus explore an alternative "mean interfacial length", L int , motivated by recent dielectric spectroscopy measurements that extract it [54,55]. We use the criterion τ α (z = L int )/τ α,bulk = C to define this length scale, but consider the practical experimental sensitivity situation where the long range, but very low amplitude, tail of the mobility gradient due to elastic field cutoff effect is not probed.…”

Section: B Practical Interfacial Layer Thicknessmentioning

confidence: 99%

Influence of Longer Range Transfer of Vapor Interface Modified Caging Constraints on the Spatially Heterogeneous Dynamics of Glass-Forming Liquids

Phan

Schweizer

2019

Macromolecules

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Based on the Elastically Collective Nonlinear Langevin Equation (ECNLE) theory of bulk relaxation in glass-forming liquids, and our recent ideas of how interface-nucleated modification of caging constraints are spatially transferred into the interior of a thick film, we present a force-based theory for dynamical gradients in thick films with one vapor interface that includes collective elasticity effects. Quantitative applications to the foundational hard sphere fluid and polymer melts of diverse fragilities are presented. We predict a roughly exponential spatial variation of the total activation barrier which is non-perturbatively modified to ∼ 10 particle diameters into the film. This leads, to leading order, to the prediction of a reduced alpha relaxation time gradient of a double exponential form characterized by a nearly constant spatial decay length, in qualitative accord with simulations. The relaxation acceleration at the surface grows exponentially with increasing packing fraction or decreasing temperature. The rate of increase with cooling of the alpha time strongly weakens upon approaching the vapor interface, with the top two layers remaining liquid-like down to ∼ 80 − 85% of the bulk glass transition temperature. These spatially heterogeneous changes of the temperature variation of the alpha time result in a large and long range gradient of the local glass transition temperature. An average interfacial layer thickness relevant to ensemble-averaged dielectric and other experiments is also computed. It is predicted to be rather large at the bulk glass transition temperature, decreasing roughly linearly with heating. Remarkably, to leading order the ratio of this layer-averaged interfacial relaxation time to its bulk analog is, to leading order, invariant to chemistry, volume fraction and temperature and of modest absolute magnitude. Spatially inhomogeneous power law decoupling of the alpha relaxation time from its bulk value is predicted, with an effective exponent that decays to zero with distance from the free surface in a nearly exponential manner, trends which are in qualitative accord with recent simulations. This behavior and the double exponential alpha time gradient are related, and can be viewed as consequences of an effective quasi-universal factorization of the total barrier in films into the product of its bulk temperature dependent value times a function solely of location in the film.

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Section: B Practical Interfacial Layer Thicknessmentioning

confidence: 99%

Influence of Longer Range Transfer of Vapor Interface Modified Caging Constraints on the Spatially Heterogeneous Dynamics of Glass-Forming Liquids

Phan

Schweizer

2019

Macromolecules

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“…Moreover, the dynamics of the polymer chains close to the particle surface appears to be slowed down by confinement. [12][13][14][15][16][17] Because the mechanical response of these chains is stiffer than that in the bulk, the confined polymer chains form rigid polymer bridges connecting the particles within the sample.…”

Section: Introductionmentioning

confidence: 99%

Role of Glassy Bridges on the Mechanics of Filled Rubbers under Pressure

et al. 2020

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In this study, we address the question of the equivalent role of the pressure and temperature on the mechanical properties of highly filled elastomers. It is well known that in polymer matrixes, the equivalence of temperature and pressure results from free volume variations. Our measurements performed on phenylated polydimethylsiloxane (PDMS) chains filled with silica particles show that a temperature-pressure superposition property is still observed in both linear and nonlinear regimes in these systems. However, the temperature-pressure equivalence involves coefficients that are two orders of magnitude larger than those in non-reinforced matrixes. We suggest that the mechanical response of the filled elastomers is controlled by the shape of the rigid network made by fillers that are connected by rigid polymer bridges. In this frame, we provide quantitative evidence that the macroscopic behavior of reinforced elastomers is controlled by the variation in the degree of the confinement of polymer chains between particle surfaces.

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“…This densely bound layer weakens the interfacial interactions between miscible adsorbed‐matrix chains, whereas, the adsorbed chains with less rigidity prefer to form loops and would interact better with matrix trains that will enhance the dynamic properties. Moreover, the interfacial layer thickness was shown to substantially increase with polymer rigidity . The local stiffness (rigidity) of a polymer chain is defined by Flory's characteristic ratio, C ∞ , and it is calculated as 10.0 for poly(2‐vinylpyridine) (P2VP), 7.0 for PMMA, 2.4 for Poly(Bisphenol A carbonate) (PC) and 5.6 for PEO.…”

Section: Introductionmentioning

confidence: 99%

Role of adsorbed chain rigidity in reinforcement of polymer nanocomposites

Yang

Hassan

Akcora

2018

J Polym Sci B Polym Phys

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The thermomechanical behavior of polymer nanocomposites is mostly governed by interfacial properties which rely on particle-polymer interactions, particle loading, and dispersion state. We recently showed that poly(methyl methacrylate) (PMMA) adsorbed nanoparticles in poly(ethylene oxide) (PEO) matrices displayed an unusual thermal stiffening response. The molecular origin of this unique stiffening behavior resulted from the enhanced PEO mobility within glassy PMMA chains adsorbed on nanoparticles. In addition, dynamic asymmetry and chemical heterogeneities existing in the interfacial layers around particles were shown to improve the reinforcement of composites as a result of good interchain mixing. Here, the role of chain rigidity in this interfacially controlled reinforcement in PEO composites is investigated. We show that particles adsorbed with less rigid polymers improve the mechanical properties of composites.

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Interfacial Properties of Polymer Nanocomposites: Role of Chain Rigidity and Dynamic Heterogeneity Length Scale

Cited by 133 publications

References 57 publications

Influence of Longer Range Transfer of Vapor Interface Modified Caging Constraints on the Spatially Heterogeneous Dynamics of Glass-Forming Liquids

Influence of Longer Range Transfer of Vapor Interface Modified Caging Constraints on the Spatially Heterogeneous Dynamics of Glass-Forming Liquids

Role of Glassy Bridges on the Mechanics of Filled Rubbers under Pressure

Role of adsorbed chain rigidity in reinforcement of polymer nanocomposites

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