Preface

Findley, W. N.; Lai, James S.; Onaran, K.

doi:10.1016/b978-0-7204-2369-3.50003-5

Cited by 61 publications

(50 citation statements)

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“…The interpretation of this phenomenon depends on the conceptual model used to analyze the obtained data. Commonly used models are simple viscoelastic equivalent models [24], especially the Kelvin-Voigt (KVM) and the Maxwell (MM) models, which are combinations of one purely elastic and one purely viscous element in either a parallel or a series configuration. These models roughly correspond to either a solid-like (KVM) or a liquid-like (MM) system.…”

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confidence: 99%

Squeeze-out dynamics of nanoconfined water: A detailed nanomechanical study

Khan

Hoffmann

2015

Phys. Rev. E

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In this study, we present a detailed analysis of the squeeze-out dynamics of nanoconfined water confined between two hydrophilic surfaces measured by small-amplitude dynamic atomic force microscopy (AFM). Explicitly considering the instantaneous tip-surface separation during squeezeout, we confirm the existence of an adsorbed molecular water layer on mica and at least two hydration layers. We also confirm the previous observation of a sharp transition in the viscoelastic response of the nanoconfined water as the compression rate is increased beyond a critical value (previously determined to be about 0.8 nm/s). We find that below the critical value, the tip passes smoothly through the molecular layers of the film, while above the critical speed, the tip encounters "pinning" at separations where the film is able to temporarily order. Pre-ordering of the film is accompanied by increased force fluctuations, which lead to increased damping preceding a peak in the film stiffness once ordering is completed. We analyze the data using both Kelvin-Voigt and Maxwell viscoelastic models. This provides a complementary picture of the viscoelastic response of the confined water film.

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Squeeze-out dynamics of nanoconfined water: A detailed nanomechanical study

Khan

Hoffmann

2015

Phys. Rev. E

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“…22 A more accurate description of the viscoelastic behavior can be obtained by studying the dependence of the relaxation rate on strain levels and of the creep rate on stress levels. 30 For linear viscoelastic materials, the relaxation/creep rate does not depend on the strain/stress level, and instead is characterized by a constant value. In contrast, nonlinear viscoelastic behavior is strongly dependent on the strain/stress level.…”

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confidence: 99%

“…3] confirm the time-dependent behavior typical of viscoelastic materials. 30 2012) change their alignment, becoming less oriented, breaking van der Waals forces, and creating new tube-tube interactions. 23 Such behavior can be compared to the conformational changes observed in polymer chains.…”

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confidence: 99%

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Nonlinear viscoelasticity of freestanding and polymer-anchored vertically aligned carbon nanotube foams

Lattanzi

Raney

Nardo

et al. 2012

Journal of Applied Physics

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Vertical arrays of carbon nanotubes (VACNTs) show unique mechanical behavior in compression, with a highly nonlinear response similar to that of open cell foams and the ability to recover large deformations. Here, we study the viscoelastic response of both freestanding VACNT arrays and sandwich structures composed of a VACNT array partially embedded between two layers of poly(dimethylsiloxane) (PDMS) and bucky paper. The VACNTs tested are ∼2 mm thick foams grown via an injection chemical vapor deposition method. Both freestanding and sandwich structures exhibit a time-dependent behavior under compression. A power-law function of time is used to describe the main features observed in creep and stress-relaxation tests. The power-law exponents show nonlinear viscoelastic behavior in which the rate of creep is dependent upon the stress level and the rate of stress relaxation is dependent upon the strain level. The results show a marginal effect of the thin PDMS/bucky paper layers on the viscoelastic responses. At high strain levels (ɛ = 0.8), the peak stress for the anchored CNTs reaches ∼45 MPa, whereas it is only ∼15 MPa for freestanding CNTs, suggesting a large effect of PDMS on the structural response of the sandwich structures

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“…In this case, the magnitude of complex modulus jE*j is proportional to the ratio of stress to strain. 24 Figure 2(b) is a plot of jE*j normalized by that at f ¼ 0.01 Hz as a function of f. It is clearly seen that the relative value of jE*j follows a single power law, which has been commonly measured at local regions of single cells 25 and in a whole single cell that was largely deformed during stretching. 26 In the present experiments, cell deformation was ca.…”

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confidence: 99%