Local dynamic mechanical properties in model free-standing polymer thin films

Yoshimoto, Kenji; Jain, Tushar; Nealey, Paul F.; Pablo, Juan J. de

doi:10.1063/1.1873732

Cited by 79 publications

(90 citation statements)

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“…Nonequilibrium molecular dynamics simulations using a coarsegrained polymer model showed that compliant layers form near the free surfaces of glassy thin films. 27 These authors also calculated that the ratio of the surface layer thickness increased to more than half of the entire film thickness as the temperature approached the T g of the bulk polymer. 27 Although two studies of the structural and physical properties of simulated, glassy polymer nanofibers have been reported to date, mechanical properties of such fibers have not been calculated.…”

Section: Introductionmentioning

confidence: 99%

“…27 These authors also calculated that the ratio of the surface layer thickness increased to more than half of the entire film thickness as the temperature approached the T g of the bulk polymer. 27 Although two studies of the structural and physical properties of simulated, glassy polymer nanofibers have been reported to date, mechanical properties of such fibers have not been calculated. 28,29 However, experimental studies of amorphous polymer thin films suggest that the stiffnesses of PS or poly(methyl methacrylate) (PMMA) thin films of thickness <40 nm on poly(dimethylsiloxane) (PDMS) substrates, as inferred from elastic buckling of the adhered films, are significantly less than those of bulk counterparts.…”

Section: Introductionmentioning

confidence: 99%

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Mechanical Properties of Glassy Polyethylene Nanofibers via Molecular Dynamics Simulations

2009

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The extent to which the intrinsic mechanical properties of polymer fibers depend on physical size has been a matter of dispute that is relevant to most nanofiber applications. Here, we report the elastic and plastic properties determined from molecular dynamics simulations of amorphous, glassy polymer nanofibers with diameter ranging from 3.7 to 17.7 nm. We find that, for a given temperature, the Young's elastic modulus E decreases with fiber radius and can be as much as 52% lower than that of the corresponding bulk material. Poisson's ratio ν of the polymer comprising these nanofibers was found to decrease from a value of 0.3 to 0.1 with decreasing fiber radius. Our findings also indicate that a small but finite stress exists on the simulated nanofibers prior to elongation, attributable to surface tension. When strained uniaxially up to a tensile strain of ε = 0.2 over the range of strain rates and temperatures considered, the nanofibers exhibit a yield stress σ y between 40 and 72 MPa, which is not strongly dependent on fiber radius; this yield stress is approximately half that of the same polyethylene simulated in the amorphous bulk.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mechanical Properties of Glassy Polyethylene Nanofibers via Molecular Dynamics Simulations

2009

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“…29 An unentangled polymer melt confined between two repulsive walls was studied using MD simulations, and the reduction in T g upon decreasing film thickness was explained by the faster chain dynamics due to the presence of the smooth walls. [30][31][32] Yoshimoto et al 33 employed nonequilibrium MD simulations using a coarse grained polymer model to show that mechanically soft layers are formed near the free surfaces of glassy thin films and that T g also decreased as the film thickness decreased.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulation of Size-Dependent Structural and Thermal Properties of Polymer Nanofibers

2007

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We present the results of molecular dynamics (MD) simulations of amorphous polymer nanofibers to study their size-dependent properties. The fibers consist of chains that mimic the prototypical polymer polyethylene, with chain lengths ranging between 50 and 300 carbons (C50 to C300). These nanofibers have diameters in the range 1.9 to 23.0 nm. We analyzed these nanofibers for signatures of emergent behavior in their structural and thermal properties as a function of diameter. The mass density at the center of all fibers is constant and comparable to that of the bulk polymer. The surface layer thickness ranges from 0.78 to 1.39 nm for all fibers and increases slightly with fiber size. The calculated interfacial excess energy is 0.022 ( 0.002 J/m 2 for all of the nanofibers simulated. The chains at the surface are more confined compared to the chains at the center of the nanofiber; the latter acquire unperturbed dimensions in sufficiently large nanofibers. Consistent with experiments and simulations of amorphous polymer films of nanoscale thickness, the glass transition temperature of these amorphous nanofibers decreases with decreasing fiber diameter, and is independent of molecular weight over the range considered.

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“…This is a reasonable model considering that the molecular structure and dynamics at the surface of a film can be different from that in the bulk. 2,10,11 The modulus of the surface layer can be either greater (hard surface) or less (soft surface) than the bulk modulus. Here, we take the thickness and modulus of the surface layer to be constant for a given material system.…”

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confidence: 99%

Elastic Moduli of Ultrathin Amorphous Polymer Films

et al. 2006

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The elastic moduli of ultrathin poly(styrene) (PS) and poly(methylmethacrylate) (PMMA) films of thickness ranging from 200 nm to 5 nm were investigated using a buckling-based metrology. Below 40 nm, the apparent modulus of the PS and PMMA films decreases dramatically, with an order of magnitude decrease compared to bulk values for the thinnest films measured. We can account for the observed decrease in apparent modulus by applying a composite model based on the film having a surface layer with a reduced modulus and of finite thickness. The observed decrease in the apparent modulus highlights issues in mechanical stability and robustness of sub-40 nm polymer films and features.

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Local dynamic mechanical properties in model free-standing polymer thin films

Cited by 79 publications

References 20 publications

Mechanical Properties of Glassy Polyethylene Nanofibers via Molecular Dynamics Simulations

Mechanical Properties of Glassy Polyethylene Nanofibers via Molecular Dynamics Simulations

Molecular Dynamics Simulation of Size-Dependent Structural and Thermal Properties of Polymer Nanofibers

Elastic Moduli of Ultrathin Amorphous Polymer Films

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