Molecular mass dependence of point-to-set correlation length scale in polymers

Hanson, Ben; Pryamitsyn, Victor; Ganesan, Venkat

doi:10.1063/1.4745481

Cited by 3 publications

(4 citation statements)

References 55 publications

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“…Figure b compares Δ T vs h eff with Δ T vs h , where it is seen that the h eff values for polymer confinement effects to become noticeable (30–50 nm) are generally larger and closer to the length scales typically reported in thin film studies. The critical h eff values also fall within the limit of 20 R g of the host polymer suggested by recent computer simulations …”

Section: Resultssupporting

confidence: 75%

“…Molecular simulations by Ganesan et al 42 reported that much smaller surface-to-surface distances between nanoparticles are needed in PNCs to produce quantitatively similar effects on T g as in polymer thin films, which is consistent with our findings. A more concrete understanding of this point is possible by using an analogy to fluid flow in porous particle beds to compute the effective separation between flat plates, h eff = (D eff /3)[(1 − ϕ eff )/ϕ eff ], 43 required to achieve the same flow resistance. Here D eff and ϕ eff are the nanoparticle diameter and volume fraction, including the polymer brush height (Δ), respectively.…”

Section: Resultsmentioning

confidence: 99%

“…The critical h eff values also fall within the limit of 20R g of the host polymer suggested by recent computer simulations. 43 Keddie et al 37,44 proposed an empirical relation T g (h) = T g,Bulk [1 − (A/h) δ )], where A represents a characteristic length and δ is the exponent, to fit the decreasing T g values with decreasing thickness for poly(styrene) and PMMA films on nonattractive substrates. The authors suggested that on the surface of the glassy film, a liquidlike layer exists, which causes on overall reduction in the T g (h).…”

Section: Resultsmentioning

confidence: 99%

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Multiscale Dynamics of Polymers in Particle-Rich Nanocomposites

et al. 2016

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We report on the dynamics of entangled polymers in polymer–nanoparticle composites (PNCs) with moderate and high particle loadings. Using composites comprised of poly(ethylene glycol) (PEG)-tethered silica (SiO2) nanoparticles and poly(methyl methacrylate) (PMMA), we show by means of small-angle X-ray scattering (SAXS) analysis that the nanoparticles are uniformly dispersed over a range of particle concentrations. From oscillatory shear rheology measurements, we find that the time–temperature superposition (TTS) principle holds for these SiO2-PEG/PMMA PNCs up to a particle concentration ϕG ≈ 11% where the materials begin to exhibit soft glassy rheological properties. At particle concentrations below ϕG, we take advantage of TTS to create dynamic maps for PNCs that span time scales ranging from fast segmental motions to slow terminal relaxation of polymer chains. These maps reveal that at low ϕ and depending on the host polymer (PMMA) molecular weight (M w), hairy nanoparticles may either speed up or slow down terminal relaxation of the host. In contrast, at high ϕ, nanoparticles slow down polymer dynamics on intermediate and long time scales, irrespective of the host polymer M w. The slowdown coincides with particle concentrations at which the mean interparticle spacing lies below the equilibrium tube diameter of the entangled PMMA host and is thought to reflect the onset of confinement dynamics of polymer chains in PNCs. Studies of PNCs in the confinement regime reveal important analogies between glassy attributes of 3D-confined polymer chains in nanocomposites with those of polymer thin films supported on attractive substrates.

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Section: Resultssupporting

confidence: 75%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Multiscale Dynamics of Polymers in Particle-Rich Nanocomposites

et al. 2016

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“…Both research fields are linked by the long tradition to receive information about length scales of glassy dynamics from confined liquids [5][6][7]. To avoid spurious liquid-matrix interactions, recent simulation studies pinned appropriate fractions of particles of a bulk liquid so as to obtain confining matrices consisting of the same type of particles as the confined liquid [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. While the strong slowdown of dynamics near interfaces is accompanied by a substantial perturbation of the structure for most matrices, the slower dynamics occurs in an unperturbed structure for such neutral matrices [18,26,31].…”

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confidence: 99%

Slow Water Dynamics near a Glass Transition or a Solid Interface: A Common Rationale

Klameth

Vogel

2015

J. Phys. Chem. Lett.

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Performing molecular dynamics simulations, we investigate the enormous slowdowns of water dynamics when approaching a glass transition or a solid interface. We show that both effects can be described on common grounds within a theoretical framework, which was recently proposed by Schweizer et al. and considers coupled local hopping and elastic distortion. For confined water, we correctly describe the variation of the α-relaxation time, τα, as a function of both temperature and position with respect to the interface. Exploiting our knowledge of a cooperative length scale ξ(T) from the confinement studies, we quantitatively rationalize the glassy slowdown, τα(T), and the Stokes-Einstein breakdown of bulk water. For both confined and bulk liquid, variations of the α-relaxation time are intimately related to changes of the cage-rattling amplitude.

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Static and dynamic length scales in supercooled liquids: Insights from molecular dynamics simulations of water and tri-propylene oxide

Klameth

Henritzi

Vogel

2014

The Journal of Chemical Physics

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We perform molecular dynamics simulations to study static and dynamic length scales in molecular supercooled liquids, in particular, water. For a determination of these scales, we use equilibrium configurations and pin appropriate subsets of molecules so as to obtain random matrices, cylindrical pores, and slit confinements. Static length scales ξ(s) are determined by analyzing overlap correlation functions for various fractions of pinned molecules or distances to the confining walls. For water in all confinements and for propylene oxide trimers in random geometry, a linear increase of ξ(s) with inverse temperature is found. Dynamic length scales ξ(d) are determined by analogous analysis of fraction-dependent or position-resolved correlation times of structural relaxation. While ξ(d) continuously grows upon cooling in the cylindrical and slit confinements, we find no evidence for a temperature dependence in random matrices, implying that molecular dynamics in parsed volumes is qualitatively different from that in bulk liquids. Finally, we study possible connections between the growth of the static and dynamic length scales and the slowdown of the structural relaxation of the supercooled bulk liquids. For water, we observe a linear relation between ln τ(α) and ξ(s)²/T in the whole accessible range down to the critical temperature of mode-coupling theory, T(c). In the weakly supercooled regime, the same relation holds also for ξ(d), as obtained from cylindrical and slit confinements, but deviations from this behavior are observed near T(c). The results are discussed in connection with random first-order theory and experimental studies of liquid dynamics in nanoscopic confinements and binary mixtures.

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Molecular mass dependence of point-to-set correlation length scale in polymers

Cited by 3 publications

References 55 publications

Multiscale Dynamics of Polymers in Particle-Rich Nanocomposites

Multiscale Dynamics of Polymers in Particle-Rich Nanocomposites

Slow Water Dynamics near a Glass Transition or a Solid Interface: A Common Rationale

Static and dynamic length scales in supercooled liquids: Insights from molecular dynamics simulations of water and tri-propylene oxide

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