Percolation model of interfacial effects in polymeric glasses

Lipson, Jane E. G.; Milner, Scott T.

doi:10.1140/epjb/e2009-00324-y

Cited by 83 publications

(82 citation statements)

References 21 publications

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“…Systematic coarse-grained molecular dynamics (CGMD) simulations 29,30 have recently aimed to elucidate the effects of interfacial energy and intermolecular cohesive forces on local and average glass transition temperatures in supported PMMA films using atomistically informed potentials. 31 These studies revealed that the average T g in a supported thin film increases linearly with the energy of attraction to the substrate up to a plateau value; that local deviations from bulk T g extend tens of nanometers into the film, in agreement with both experimental results 32 and theoretical treatments; 33,34 and that the effects of confinement and free surfaces are stronger for rubbery films than for glassy films, which is useful to interpret controversial findings on polymers that can show either appreciation or depreciation of T g depending on confinement conditions. However, studies have shown that the confinement effect extends beyond changes in T g .…”

Section: Introductionsupporting

confidence: 59%

Anisotropy of Shear Relaxation in Confined Thin Films of Unentangled Polymer Melts

2015

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The anisotropic shear relaxation functions of confined thin films of unentangled polymer melts are measured via nonequilibrium step−strain simulations of in-plane and outof-plane shear using the finitely extensible, nonlinear-elastic (FENE) model. We show that the classical Rouse model unsurprisingly fails to predict the thin-film relaxation functions in response to out-of-plane shear, due in part to non-Gaussian conformation statistics in the dimension perpendicular to the sub/superstrate. Using an alternate empirical model for the outof-plane response, we quantify decreases in the plateau modulus G ⊥ P , relaxation time λ ⊥ , and viscosity η ⊥ and an increase in the logarithmic relaxation rate r ⊥ as functions of film thickness, and we discuss these anisotropic changes in stress-relaxation properties in terms of structural/conformation changes on the microscopic level, namely the relative contraction and non-Gaussian quality of polymer conformations in the dimension normal to the substrate and the resulting phenomenon of cooperative relaxation. We then incorporate these into a semiempirical extension to the Rouse model which closely predicts our computational results and which will be useful for further study of polymer thin films.

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Section: Introductionsupporting

confidence: 59%

Anisotropy of Shear Relaxation in Confined Thin Films of Unentangled Polymer Melts

2015

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“…[ 18 ] Finally, study of near-interface dynamic modifi cations in thin fi lms and nanocomposites has emphasized the role of spatially and temporally correlated dynamics [40][41][42][43][44][45][46] in supercooled liquids. [2][3][4]7,23,[31][32][33][34][45][46][47] These diverging explanations raise the question of whether any more universal mechanism underlies nearinterface alterations in segmental dynamics in all of these systems. David S. Simmons is an Assistant Professor of Polymer Engineering at the University of Akron, where his work focuses on computationally-driven design of polymers with targeted glass formation, mechanical, and transport behavior.…”

Section: Introductionmentioning

confidence: 99%

An Emerging Unified View of Dynamic Interphases in Polymers

Simmons

2015

Macro Chemistry & Physics

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The properties of nanostructured polymeric materials reflect the presence of a dynamic interphase in which polymer segmental dynamics, glass formation, mechanics, and transport properties are altered from their bulk states. Examples include nanoconfinement effects on polymer nanofilms, reinforcement effects in polymer nanocomposites and filled rubbers, formation of a rigid amorphous fraction in semicrystalline polymers, and observation of suppressed‐mobility domains around ionic aggregates in ionomers. Whereas many of these phenomena have been viewed as emerging from system‐specific mechanisms, here recent work is highlighted that contributes to an emerging unified understanding of the dynamic interphase in all of these systems. This view suggests that the size scales of dynamic interphases in polymers are generally determined by the scale of cooperative rearrangements intrinsic to relaxation dynamics in supercooled glass‐forming liquids. It also implicates alterations in local segmental rattling as playing a central role in the dynamic interphase, and it suggests that near‐interface modifications in dynamics exhibit a general dependence on the interfacial work of adhesion and the relative high‐frequency moduli of the interface‐adjacent domains.

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“…26 However, this hypothesis for the origins of nanoconfinement should be taken caution because the length scale of a single CRR near T g is about 1 ∼ 4 nm, [27][28][29][30] which is much smaller than the length scale of the onset of nanoconfinement that can be as large as 100 nm for polymers. 1,2,4,5,8,19 A large amount of experimental, 3-10 simulation, 12,13,25,[31][32][33][34] and theoretical efforts [35][36][37][38][39][40][41] had been devoted to investigate the variations of T g of polymers in confinement. But there is still no consensus on the T g variation of polymers with different chain stiffness in confinement.…”

Section: Introductionmentioning

confidence: 99%

The glass transition of polymers with different side-chain stiffness confined in free-standing thin films

Xie

Huang

2015

The Journal of Chemical Physics

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The effect of confinement on the glass transition temperature Tg of polymeric glass formers with different side chain stiffness is investigated by coarse-grained molecular dynamics simulations. We find that polymer with stiffer side groups exhibits much more pronounced Tg variation in confinement compared to that with relatively flexible side groups, in good agreement with experiments. Our string analysis demonstrates that the polymer species dependence of dynamics can be described by an Adam-Gibbs like relation between the size of cooperatively rearranging regions and relaxation time. However, the primary effect of changing side-group stiffness is to alter the activation barrier for rearrangement, rather than string size. We clarify that free-surface perturbation is the primary factor in determining the magnitude of Tg variation for polymers in confinement: It is more significant for polymers having higher Tg and results in much more pronounced reduction of surface Tg and then the overall Tg of the polymers.

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Percolation model of interfacial effects in polymeric glasses

Cited by 83 publications

References 21 publications

Anisotropy of Shear Relaxation in Confined Thin Films of Unentangled Polymer Melts

Anisotropy of Shear Relaxation in Confined Thin Films of Unentangled Polymer Melts

An Emerging Unified View of Dynamic Interphases in Polymers

The glass transition of polymers with different side-chain stiffness confined in free-standing thin films

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