Reassessment of Solidification in Fluids Confined between Mica Sheets

Zhu, Yunhua; Granick, Steve

doi:10.1021/la035155+

Cited by 95 publications

(99 citation statements)

References 30 publications

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“…Yet, various experimental studies in the literature reported a strong dependence of the mechanical response of the liquid under investigation on the (very slow) approach rate of the cantilever (*Å /s) [17,21]. A qualitatively similar dependence was reported in SFA experiments [10]. We suspect that this dependence is related to the rather large lateral dimensions of the confinement region in these experiments:…”

Section: Discussionsupporting

confidence: 74%

“…This again implies, that the exact tip shape will have a significant effect on the measured damping. Finally, we would like to comment on an alternative way of characterizing the ''rheological'' properties of the confined films, as it is frequently studied in experiments as well [10,53]. By calculating the Fourier transform of the force-autocorrelation function, we can extract the conservative and the dissipative response of the system for the entire spectrum of frequencies.…”

Section: Discussionmentioning

confidence: 99%

“…While this behavior of the conservative forces is well understood and has also been reproduced for nanoscale contacts in early Atomic Force Microscopy (AFM) experiments [8], the dissipative behavior of nano-confined liquid films is heavily debated. In the SFA community, slightly different measurement techniques for nominally identical systems produced highly incompatible experimental results with interpretations ranging from confinement-induced solidification [9] or a glassy response [10] to bulk-like dynamics for liquid films of even just a few molecular layers thickness [11][12][13]. SFA measurements are limited to film thicknesses of integer numbers of molecular layers due to a mechanical (''jump-to-contact'') instability.…”

Section: Introductionmentioning

confidence: 99%

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Can Confinement-Induced Variations in the Viscous Dissipation be Measured?

et al. 2012

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Liquids confined to molecular scales become anisotropic and often show pronounced self-organization such as layering. Although this effect is well accepted, it is still debated if confinement induces measurable changes of viscous friction. We use molecular dynamics to address this issue by simulating a Lennard-Jones liquid confined between a solid cylinder and an atomically smooth surface. The simulations reproduce the well-established variations of normal force, density, and diffusivity with the distance between wall and cylinder. We find high diffusivity and low density when the numbers of layers is in between integers. This observation seems to contradict most experimental results on the effective damping between atomic force microscope tips and substrates when interpreting them within continuum hydrodynamics used to connect liquid viscosity and diffusivity. This contradiction is resolved by directly extracting the damping that the tip experiences, which we achieve by using the fluctuationdissipation theorem; as in experiment, we find local minima in the damping near integer numbers of molecular layers and maxima in between. These variations correlate with distinct structural changes in the microscopic order of the fluid. We reconfirm that constitutive equations valid at macroscopic scales cannot be used to interpret confined liquids and finally conclude that viscous friction displays measurable, non-monotonic behavior with the degree of confinement.

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Section: Discussionsupporting

confidence: 74%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Can Confinement-Induced Variations in the Viscous Dissipation be Measured?

et al. 2012

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“…Specifically, the confined phase is buried between two solid mica walls with just a few layers of material contained in this region, which has thus far made it impossible to directly observe the structure. Moreover, the discovery of platinum nanoparticles on the mica surfaces in some experiments 10,11 led to a reexamination of previously published results, with the conclusion that some experimental findings were potentially compromised 12 .…”

Section: Introductionmentioning

confidence: 99%

Confined fluid and the fluid-solid transition: Evidence from absolute free energy calculations

et al. 2012

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The debate on whether an organic fluid nanoconfined by mica sheets will undergo a fluid-tosolid transition as the fluid film thickness is reduced below a critical value has lasted over two decades. Extensive experimental and simulation investigations have thus far left this question only partially addressed. In this work we adapt and apply absolute free energy calculations to analyze the phase behavior of a simple model for nanoconfined fluids, consisting of spherical Lennard-Jones (LJ) molecules confined between LJ solid walls, which we use in combination with grand canonical molecular dynamics simulations. Absolute Helmholtz free energy calculations of the simulated nanoconfined systems directly support the existence of order-disorder phase transition as a function of decreasing wall separation, providing results in close agreement with previous experiments and detailed atomistic simulations.

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“…Recently, a sharp transition was found as a function of compression rate in several liquids, where the liquid shows liquid-like characteristics at slow compression rate but solid-like peaks in relaxation times when compressed above a critical speed [12,18,20]. This observation may depend on a critical lateral system size, for example the size of the confining tip in the case of atomic force microscopy (AFM) measurements [21][22][23].…”

mentioning

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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Reassessment of Solidification in Fluids Confined between Mica Sheets

Cited by 95 publications

References 30 publications

Can Confinement-Induced Variations in the Viscous Dissipation be Measured?

Can Confinement-Induced Variations in the Viscous Dissipation be Measured?

Confined fluid and the fluid-solid transition: Evidence from absolute free energy calculations

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

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