Unusual High-Frequency Mechanical Properties of Polymer-Grafted Nanoparticle Melts

Jhalaria, Mayank; Cang, Yu; Huang, Yucheng; Benicewicz, Brian C.; Kumar, Sanat K.; Fytas, George

doi:10.1103/physrevlett.128.187801

Cited by 17 publications

(23 citation statements)

References 43 publications

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“…The PMMA chain conformation and surface mobility, which impact interparticle interactions, are different in the bold and core–shell particles infiltrated with PDMS. Change of the PMMA packing can impact c eff as recently reported in the case of polymer grafted SiO 2 . However, this delicate conformation issue merits a detailed study in the future.…”

Section: Resultsmentioning

confidence: 70%

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Origin of the Acoustic Bandgaps in Hypersonic Colloidal Phononics: The Role of the Elastic Impedance

et al. 2022

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How phonons propagate in nanostructures determines the flow of elastic and thermal energy in dielectric materials. However, a reliable theoretical prediction of the phonon dispersion relation requires experimental verification both near to and far from the Brillouin zone of the nanostructure. We report on the experimental hypersonic phonon dispersion of hard (SiO 2 ) and soft (polymer) fcc colloidal crystals infiltrated in liquid polydimethylsiloxane with different elastic impedance contrast using Brillouin light spectroscopy. We discuss the distinct differences with first-principles full elastodynamic calculations involving a multiple-scattering theory. Interparticle contacts strongly impact the long-wavelength speed of sound and the nature of the particle vibration resonance-induced hybridization hypersonic bandgap. The absence of the order-induced Bragg bandgap in SiO 2 and its presence in soft opals cannot be fully accounted for by the theory, limiting its predictive power. Bridging the elasticity of the two colloidal crystals with suitable SiO 2 core–shell (polymer) particles reveals an unprecedented crossover behavior in the dispersion relation. In view of many conversational parameters, the control tuning of phonon propagation in soft matter-based hypersonic phononics remains challenging.

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Section: Resultsmentioning

confidence: 70%

“…Change of the PMMA packing can impact c eff as recently reported in the case of polymer grafted SiO 2 . 48 However, this delicate conformation issue merits a detailed study in the future.…”

Section: Resultsmentioning

confidence: 99%

Origin of the Acoustic Bandgaps in Hypersonic Colloidal Phononics: The Role of the Elastic Impedance

et al. 2022

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“…Overall, the ICPM predicts both modulus and toughness that are in good agreement with the finer-grained CG-MD models at the respective graft lengths. Furthermore, Figure c shows a comparison of the bulk modulus of matrix-free PGNs as a function of the volume fractions of the NP cores from ICPM simulations and a recent experimental measurement . The experimental data is based on polymethacrylate (PMA) in the glassy high-frequency regime at comparable volume fractions and employing larger (8 nm, as opposed to 2 nm) silica NPs.…”

Section: Resultsmentioning

confidence: 99%

“…The error bars in CG-MD simulations are standard deviations from 9 trials of CG-MD systems with different initial coordinates and velocities. (c) Comparison of the bulk modulus of matrix-free PGNs as a function of volume fractions of nanoparticle cores from the ICPM (red squares) and experimental measurements (green triangles) by Jhalaria et al…”

Section: Resultsmentioning

confidence: 99%

“…Recent experimental studies have identified several unique features of matrix-free PGN assemblies compared with the traditional polymer nanocomposites. These include the ability to form very stiff films with exceptional ordering of nanoparticles, the formation of amorphous films with extraordinary slow relaxations governed by colloidal jamming, superior impact resistance at high strain rates due to ductile unravelling of grafted chains, and unusual transport properties due to interfacial relaxation mechanisms near nanoparticle surfaces and graft interfaces. − Recent advances in experiments have extensively examined various material properties of matrix-free PGN composites such as chain conformations, dynamics, glass transition, and mechanical properties . However, understanding the molecular mechanisms underpinning these emergent behaviors remains extremely challenging with experimental techniques.…”

Section: Introductionmentioning

confidence: 99%

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Implicit Chain Particle Model for Polymer-Grafted Nanoparticles

Pal

Keten

2023

Macromolecules

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Matrix-free nanocomposites made from polymer-grafted nanoparticles (PGN) represent a paradigm shift in materials science because they greatly improve nanoparticle dispersion and offer greater tunability over rheological and mechanical properties in comparison to neat polymers. Utilizing the full potential of PGNs requires a deeper understanding of how polymer graft length, density, and chemistry influence interfacial interactions between particles. There has been great progress in describing these effects with molecular dynamics (MD). However, the limitations of the length and time scales of MD make it prohibitively costly to study systems involving more than a few PGNs, even with bead−spring coarse-grained models. Moreover, it remains unclear how to properly address shortcomings of these models in describing the rate-dependent constitutive response of polymers in a chemistry-specific fashion. Here, we address some of these challenges by proposing a new modeling paradigm for PGNs using a strain-energy mapping framework involving potential of mean force (PMF) calculations. In this approach, each nanoparticle is coarse grained into a representative particle with chains treated implicitly, namely, the implicit chain particle model (ICPM). Using a chemistry-specific coarse-grained molecular dynamics (CG-MD) model of poly(methyl methacrylate) as a testbed, we derive the effective interaction between particles arranged in a close-packed lattice configuration by matching bulk dilation and compression strain-energy densities up to failure. We establish an iterative optimization scheme to fine tune PMFs in the ICPM to accurately match the stress−strain behaviors during dilation and compression tests. The strain-rate dependence of the mechanical work done is quantified to reveal that the interparticle potential can be expressed with a strain-rate-dependent energy well depth that culminates in a simple power-law Cowper−Symonds strain hardening model. Given the aggressive degree of coarse graining (∼1:10 000) involved, the scope and limitations of the ICPM are cautiously discussed. Overall, the ICPM increases the computational speed by approximately 5−6 orders of magnitude compared to the CG-MD models. This novel framework is foundational for particle-based simulations of PGNs and their blends and accelerates the understanding and predictions of emergent properties of PGN materials.

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Free Standing Dry and Stable Nanoporous Polymer Films Made through Mechanical Deformation

et al. 2023

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A new straight forward approach to create nanoporous polymer membranes with well defined average pore diameters is presented. The method is based on fast mechanical deformation of highly entangled polymer films at high temperatures and a subsequent quench far below the glass transition temperature Tg. The process is first designed generally by simulation and then verified for the example of polystyrene films. The methodology does not need any chemical processing, supporting substrate, or self assembly process and is solely based on polymer inherent entanglement effects. Pore diameters are of the order of ten polymer reptation tube diameters. The resulting membranes are stable over months at ambient conditions and display remarkable elastic properties.

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Unusual High-Frequency Mechanical Properties of Polymer-Grafted Nanoparticle Melts

Cited by 17 publications

References 43 publications

Origin of the Acoustic Bandgaps in Hypersonic Colloidal Phononics: The Role of the Elastic Impedance

Origin of the Acoustic Bandgaps in Hypersonic Colloidal Phononics: The Role of the Elastic Impedance

Implicit Chain Particle Model for Polymer-Grafted Nanoparticles

Free Standing Dry and Stable Nanoporous Polymer Films Made through Mechanical Deformation

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