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

Beer, Sissi de; Otter, Wouter K. den; Ende, Dirk van den; Briels, Willem J.; Mugele, Friedrich Gunther

doi:10.1007/s11249-011-9905-4

Cited by 14 publications

(16 citation statements)

References 54 publications

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“…Caution should however be exerted when comparing AFM and the MD results since the MD simulations presented here do not take into account the fact that the interfacial liquid is effectively confined between the calcite surface and the AFM tip under typical imaging conditions. Recent MD simulation studies have shown that under confinement, the liquid can exhibit substantial changes in its viscoelastic properties and molecular dynamics, 57 and induce ion-specific structures. 58 The good correspondence between the trends derived from AFM and the present MD simulations results suggests that AFM can nevertheless capture the main features of the 'non-confined' interface.…”

Section: Discussionmentioning

confidence: 99%

Direct Visualization of Single Ions in the Stern Layer of Calcite

et al. 2013

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Calcite is among the most abundant minerals on earth and plays a central role in many environmental and geochemical processes. Here we used amplitude modulation atomic force microscopy (AFM) operated in a particular regime to visualize single ions close to the (1014) surface of calcite in solution. The results were acquired at equilibrium, in aqueous solution containing different concentrations of NaCl, RbCl, and CaCl(2). The AFM images provide a direct and atomic-level picture of the different cations adsorbed preferentially at certain locations of the calcite-water interface. Highly ordered water layers at the calcite surface prevent the hydrated ions from directly interacting with calcite due to the energy penalty incurred by the necessary restructuring of the ions' solvation shells. Controlled removal of the adsorbed ions from the interface by the AFM tip provides indications about the stability of the adsorption site. The AFM results show the familiar "row pairing" of the carbonate oxygen atoms, with the adsorbed monovalent cations located adjacent to the most prominent oxygen atoms. The location of adsorbed cations near the surface appears better defined for monovalent ions than for Ca(2+), consistent with the idea that Ca(2+) ions remain further away from the surface of calcite due to their larger hydration shell. The precise distance between the different hydrated ions and the surface of calcite is quantified using MD simulation. The preferential adsorption sites found by MD as well as the ion residence times close to the surface support the AFM findings, with Na(+) ions dwelling substantially longer and closer to the calcite surface than Ca(2+). The results also bring new insights into the problem of the Stern and electrostatic double layer at the surface of calcite, showing that parameters such as the thickness of the Stern layer can be highly ion dependent.

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Section: Discussionmentioning

confidence: 99%

Direct Visualization of Single Ions in the Stern Layer of Calcite

et al. 2013

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“…Whether that scenario also extends to the much larger tipsubstrate separations studied here is not clear. At larger separations, thermal fluctuations as well as the tip geometry on a larger scale may lead to increased disorder [68][69][70] and, thus, prevent the crystalline arrangement found at smaller separations.…”

Section: E Solvation Force and Distance-dependent Dissipationmentioning

confidence: 99%

Atomic force microscopy of confined liquids using the thermal bending fluctuations of the cantilever

et al. 2013

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We use atomic force microscopy to measure the distance-dependent solvation forces and the dissipation across liquid films of octamethylcyclotetrasiloxane (OMCTS) confined between a silicon tip and a highly oriented pyrolytic graphite substrate without active excitation of the cantilever. By analyzing the thermal bending fluctuations, we minimize possible nonlinearities of the tip-substrate interaction due to finite excitation amplitudes because these fluctuations are smaller than the typical 1 Å, which is much smaller than the characteristic interaction length. Moreover, we avoid the need to determine the phase lag between cantilever excitation and response, which suffers from complications due to hydrodynamic coupling between cantilever and fluid. Consistent results, and especially high-quality dissipation data, are obtained by analyzing the power spectrum and the time autocorrelation of the force fluctuations. We validate our approach by determining the bulk viscosity of OMCTS using tips with a radius of approximately 1 μm at tip-substrate separations >5 nm. For sharp tips we consistently find an exponentially decaying oscillatory tip-substrate interaction stiffness as well as a clearly nonmonotonic variation of the dissipation for tip-substrate distances up to 8 and 6 nm, respectively. Both observations are in line with the results of recent simulations which relate them to distance-dependent transitions of the molecular structure in the liquid.

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“…It shows a reasonably constant profile of the elastic modulus with the tip size. The slight increase toward higher radii may be the result of jamming of the molecules during squeeze-out more likely for larger tips [41]. However, more experimental efforts are required to pinpoint the mechanism behind it.…”

Section: Resultsmentioning

confidence: 99%

Young’s modulus of nanoconfined liquids?

Khan

Hoffmann

2016

Journal of Colloid and Interface Science

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In material science, bioengineering, and biology, thin liquid films and soft matter membranes play an important role in micro-lubrication, ion transport, and fundamental biological processes. Various attempts have been made to characterize the elastic properties, such as Young's modulus, of such films using Hertz theory by incorporating convoluted mathematical corrections. We propose a simple way to extract tip-size independent elastic properties based on stiffness and force measurement through a spherical tip on a flat surface. Using our model, the Young's modulus of nanoconfined, molecularly-thin, layers of a model liquid TEHOS (tetrakis 2-ethylhexoxy silane) and water were determined using a small-amplitude AFM. This AFM can simultaneously measure the stiffness and forces of nanoscale films. While the stiffness scales linearly with the tip radius, the measured Young's modulus essentially remains constant over an order of magnitude variation in the tip radius. The values obtained for the elastic modulus of TEHOS and water films on the basis of our method are significantly lower than the confining surfaces' elastic moduli, in contrast with the uncorrected Hertz model, suggesting that our method can serve as a simple way to compare elastic properties of nanoscale thin films as well as to characterize a variety of soft films. In addition, our results show that the elastic properties (elastic modulus) of nanoconfined liquid films remain fairly independent of increasing confinement.

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

Cited by 14 publications

References 54 publications

Direct Visualization of Single Ions in the Stern Layer of Calcite

Direct Visualization of Single Ions in the Stern Layer of Calcite

Atomic force microscopy of confined liquids using the thermal bending fluctuations of the cantilever

Young’s modulus of nanoconfined liquids?

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