Bound Polymer Layer in Nanocomposites

Jouault, Nicolas; Moll, Joseph; Meng, Dong; Windsor, Kendra; Ramcharan, Stacy; Kearney, Clare; Kumar, Sanat K.

doi:10.1021/mz300646a

Cited by 166 publications

(234 citation statements)

References 25 publications

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“…We note that the thickness of the so-called bound layer (type 1 chains) increases with aggregate size (SI Appendix, Fig. S11), similar to previous work (40,41), which could also enhance the bridging effect-increase N 3 /N polymer -by increasing the effective bridging region volume relative to the total volume of the composite (42); however, the precise effect of boundary layer thickness on the different composite systems is not clear. Conversion of "slippery" adsorbed (type 1) chains into type 3 chains has been shown, specifically in samples (nearly identical to ours) where limited interaction between the polymer and fillers is present (19,43).…”

Section: Significancesupporting

confidence: 80%

Nanoparticle amount, and not size, determines chain alignment and nonlinear hardening in polymer nanocomposites

Varol

Meng

Hosseinkhani

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Polymer nanocomposites-materials in which a polymer matrix is blended with nanoparticles (or fillers)-strengthen under sufficiently large strains. Such strain hardening is critical to their function, especially for materials that bear large cyclic loads such as car tires or bearing sealants. Although the reinforcement (i.e., the increase in the linear elasticity) by the addition of filler particles is phenomenologically understood, considerably less is known about strain hardening (the nonlinear elasticity). Here, we elucidate the molecular origin of strain hardening using uniaxial tensile loading, microspectroscopy of polymer chain alignment, and theory. The strain-hardening behavior and chain alignment are found to depend on the volume fraction, but not on the size of nanofillers. This contrasts with reinforcement, which depends on both volume fraction and size of nanofillers, potentially allowing linear and nonlinear elasticity of nanocomposites to be tuned independently.nanocomposites | nonlinear elasticity | strain stiffening | polymer bridging | polymer chain alignment M any synthetic and natural materials around us increase their elastic modulus upon large deformation after initial softening-a phenomenon that is known as work or strain hardening, which is critical to their function. In ductile polymer materials, the strain-hardening behavior is essential for their functional lifetime, resilience, and toughness-all key parameters of their practical uses-because these materials repetitively bear large loads (1, 2). Many industrial and consumer polymeric materials are composites, in which (hard) nanoscale inorganic particles, or fillers, are blended with polymer matrices to tailor their mechanical properties. In preparing such nanocomposites, filler−filler and filler−matrix interaction, filler dispersion, and polymer properties all affect the linear (low strain) and nonlinear (high strain) mechanical response in nontrivial ways (3). Although a massive volume of work has attempted to clarify the mechanism of reinforcement (increased linear elasticity) at low strain and of nonlinear strain softening (the Payne and Mullins effects) at medium strain, a comparatively much smaller body of work exists that focuses on the mechanism of strain hardening in polymer composite materials.In analogy to rubber elasticity at large deformations, strain hardening in polymer composites is typically attributed to the increasing resistance to deformation of extended and oriented polymer chains (4-7). However, it has been shown that polymer chain alignment during strain hardening is strongly affected by dispersing fillers within the host polymer matrix (8-10). To account for these observations, one needs to establish the relation between the macroscopically observed strain hardening and the microscopic chain alignment that is affected by the presence of fillers.The connection between chain alignment and strain hardening in glassy polymer composites is purported to occur because the fillers act as "entanglement attractors." In this...

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Section: Significancesupporting

confidence: 80%

Nanoparticle amount, and not size, determines chain alignment and nonlinear hardening in polymer nanocomposites

Varol

Meng

Hosseinkhani

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…It is experimentally known that the bound layer thickness is dependent on the (spherical) NP diameter, increasing from ≈1 nm for a NP diameter of ∼10 nm to 4-5 nm for flat surfaces. 142 However, there is currently no theoretical understanding of the bound layer thickness, its temporal stability, and the effect of NP shape. The consequences of the bound layer on nanocomposite mechanical properties and how these are affected by both equilibrium (e.g., interactions) and nonequilibrium (casting solvent, rate of evaporation, temperature) factors also remain open.…”

Section: A Modeling Variations In Np Sizementioning

confidence: 99%

Perspective: Outstanding theoretical questions in polymer-nanoparticle hybrids

Kumar

Ganesan

Riggleman

2017

The Journal of Chemical Physics

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171

143

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This topical review discusses the theoretical progress made in the field of polymer nanocomposites, i.e., hybrid materials created by mixing (typically inorganic) nanoparticles (NPs) with organic polymers. It primarily focuses on the outstanding issues in this field and is structured around five separate topics: (i) the synthesis of functionalized nanoparticles; (ii) their phase behavior when mixed with a homopolymer matrix and their assembly into well-defined superstructures; (iii) the role of processing on the structures realized by these hybrid materials and the role of the mobilities of the different constituents; (iv) the role of external fields (electric, magnetic) in the active assembly of the NPs; and (v) the engineering properties that result and the factors that control them. While the most is known about topic (ii), we believe that significant progress needs to be made in the other four topics before the practical promise offered by these materials can be realized. This review delineates the most pressing issues on these topics and poses specific questions that we believe need to be addressed in the immediate future. Published by AIP Publishing. [http://dx

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“…Due to attractive interactions, polymer chains physically adsorb to the NP's surface and form an "adsorbed bound layer" with a series of loops, trains and tails [8][9][10][11][12], which has an average thickness proportional to the polymer radius of gyration (R g ) [8,13]. These adsorbed chains form an dynamic interfacial layer (DIL), which has distinct segmental mobility and other properties [7,[14][15][16][17][18][19][20][21][22][23], and is believed to directly correlate with many advanced macroscopic properties of PNCs [3,5].…”

mentioning

confidence: 99%