Monotonic Damping in Nanoscopic Hydration Experiments (original) (raw)
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The Journal of Chemical Physics, 2013
A three-dimensional interaction force mapping experiment was carried out on a muscovite mica surface in an aqueous solution using a high-resolution and low-thermal drift frequency-modulation atomic force microscope. By collecting oscillatory frequency shift versus distance curves at the mica/solution interface, complicated hydration structures on the mica surface were visualized. Reconstructed two-dimensional frequency shift maps showed dot-like or honeycomb-like patterns at different tip-sample distances with a separation of 0.2 nm with each other, which agree well to the water molecule density maps predicted by a statistical-mechanical theory. Moreover, site-specific force versus distance curves showed a good agreement with theoretically calculated site-specific force curves by a molecular dynamics simulation. It is found that the first and second hydration layers give honeycomb-like and dot-like patterns in the two-dimensional frequency shift images, respectively, corresponding to the lateral distribution function in each layer.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2010
Noncontact atomic force microscopy ͑AFM͒ using frequency modulation ͑FM͒ detection allows atomic resolution to be obtained in vacuum on a variety of insulating surfaces and molecular deposits. This technique has recently been extended to liquid environments, and, in addition to atomic scale contrast, FM-AFM in liquid allows measurement of ordered liquid layers above surfaces. The role of water and ions in biological processes is of great interest and in order to localize fluorescently tagged structures, such as proteins, optical microscopy combined with AFM provides an invaluable tool. Thus, to take advantage of the wealth of optical identification techniques available in biology, the AFM must be coupled to an optical microscope. Such systems are commercially available, but mechanical noise due to vibrations is a major concern compared with the compact, specialized instruments used to measure hydration structure to date. In this article the authors demonstrate, through both modeling and measurement, that hydration structure can be measured on such a commercial "bio-AFM," despite the additional noise sources present in these instruments and that with the addition of a bandpass filter and amplifier it can be done "out-of-the-box" using only commercial electronics and tips. Thus, hydration structure measurements are accessible to virtually any laboratory with such a system.
Hydration forces: Observations, explanations, expectations, questions
Current Opinion in Colloid & Interface Science, 2011
The hydration force between large molecules or large surfaces is built on weak perturbation of many solvent molecules. The structure of the surface sets boundary conditions on solvent while structural forces within the solvent set the range. For this collection of essays, we focused on forces between surfaces at nanometer separations. It is instructive to distinguish primary hydration, the binding of water and perturbation within a few layers, from secondary hydration related to redistribution of solutes. The subject is still basically empirical, lacking satisfactory theory and sufficient measurement.
Visualizing water molecule distribution by atomic force microscopy
The Journal of Chemical Physics, 2010
Hydration structures at biomolecular surfaces are essential for understanding the mechanisms of the various biofunctions and stability of biomolecules. Here, we demonstrate the measurement of local hydration structures using an atomic force microscopy system equipped with a low-noise deflection sensor. We applied this method to the analysis of the muscovite mica/water interface and succeeded in visualizing a hydration structure that is site-specific on a crystal. Furthermore, at the biomolecule/ buffer solution interface, we found surface hydration layers that are more packed than those at the muscovite mica/water interface.
Nonlinear dynamics of the atomic force microscope at the liquid-solid interface
Physical Review B, 2012
The measurement of intermolecular forces at the liquid-solid interface is key to many studies of electrochemistry, wetting, catalysis, biochemistry, and mechanobiology. The atomic force microscope (AFM) is unique in its ability to measure and map these forces with nanometer resolution using the oscillating sharp tip of an AFM cantilever. These surface forces are only measured by observing the changes they induce in the dynamics of the resonant AFM probe. However, AFM cantilever dynamics at this interface can be significantly different when compared to air/vacuum environments due to the nature of nanoscale forces at the interface and the low-quality factors in liquids. In this work, we study the nonlinear dynamics of magnetically excited AFM microcantilevers on graphite and mica immersed in deionized water, high-concentration buffers, and methanol. By combining theory and experiments, a wealth of nonlinear dynamical phenomena such as superharmonic resonance, hysteretic jumps, and multimodal interactions are demonstrated and their dependence on hydration/solvation forces is clarified. These results are expected to aid ongoing efforts to link liquid-solid interface properties to cantilever dynamics and lead to accurate interpretation of data from experiments.
Atomic-level viscosity distribution in the hydration layer
Physical Review Letters , 2019
Viscosity of the solvation structures is crucial for the development of energy-efficient biochemical and electrochemical devices. Elucidating their subnanoscale distributions can cause the formation of a sustainable energy society. Here, we visualize the three-dimensional damping distribution on a CaCO3 surface composing binary ion species using ultra-low-noise frequency-modulation atomic force microscopy. With the support from molecular dynamics simulation, we found a strikingly large damping at the calcium sites, which demonstrates the capability of this methodology to visualize molecular-scale viscosity in the hydration layers, which will expedite the evolutions of various functional devices.
Hydration Force in the Atomic Force Microscope: A Computational Study
Biophysical Journal, 1998
Using a hard sphere model and numerical calculations, the effect of the hydration force between a conical tip and a flat surface in the atomic force microscope (AFM) is examined. The numerical results show that the hydration force remains oscillatory, even down to a tip apex of a single water molecule, but its lateral extent is limited to a size of a few water molecules. In general, the contribution of the hydration force is relatively small, but, given the small imaging force (ϳ0.1 nN) typically used for biological specimens, a layer of water molecules is likely to remain "bound" to the specimen surface. This water layer, between the tip and specimen, could act as a "lubricant" to reduce lateral force, and thus could be one of the reasons for the remarkably high resolution achieved with contact-mode AFM. To disrupt this layer, and to have a true tip-sample contact, a probe force of several nanonewtons would be required. The numerical results also show that the ultimate apex of the tip will determine the magnitude of the hydration force, but that the averaged hydration pressure is independent of the radius of curvature. This latter conclusion suggests that there should be no penalty for the use of sharper tips if hydration force is the dominant interaction between the tip and the specimen, which might be realizable under certain conditions. Furthermore, the calculated hydration energy near the specimen surface compares well with experimentally determined values with an atomic force microscope, providing further support to the validity of these calculations.
Nanotechnology, 2010
We determine conservative and dissipative tip-sample interaction forces from the amplitude and phase response of acoustically driven atomic force microscope (AFM) cantilevers using a non-polar model fluid (octamethylcyclotetrasiloxane, which displays strong molecular layering) and atomically flat surfaces of highly ordered pyrolytic graphite. Taking into account the base motion and the frequency-dependent added mass and hydrodynamic damping on the AFM cantilever, we develop a reliable force inversion procedure that allows for extracting tip-sample interaction forces for a wide range of drive frequencies. We systematically eliminate the effect of finite drive amplitudes. Dissipative tip-sample forces are consistent with the bulk viscosity down to a thickness of 2-3 nm. Dissipation measurements far below resonance, which we argue to be the most reliable, indicate the presence of peaks in the damping, corresponding to an enhanced 'effective' viscosity, upon expelling the last and second-last molecular layer.
Surface Science, 2002
At room temperature and under ambient conditions, due to the adsorption, a water film is always present on silica surfaces. If the surface is investigated with a scanning probe method in Contact mode, this causes the formation of a meniscus between the tip and the surface. This liquid neck generates additional capillary forces between the nano-tip and the surface. In dynamic mode, due to the action of the oscillating tip on the surface, the mechanical response of the adsorbed water layers can induce additional dissipation that is probed through the phase variations of the oscillator. In the present work, we analyze by dynamic force microscopy the growth of a water film on a silica surface as a function of time. The silica sample is first cleaned and heated at 420 • C, then is exposed to dry conditions. The influence of the water film is checked with the dynamic mode by using intermittent contact and noncontact situations. To describe the experimental observations, additional dissipation is taken into account when the tip approaches the surface. The results of the fits allow the evaluation of the dissipation induced by the attractive interaction between the tip and the silica surface related to the adsorption of water molecules on surface as a function of time.
Chemical Physics Letters, 2003
We have measured the force acting on neutral tips as function of distance to hydrophobic surfaces in aqueous solutions. The unusually large magnitude of this force is attributed to an electrostatic response of the aqueous fluid structure (hydration layer). The exchange of a volume of this region with a dielectric permittivity int by the tip with a dielectric constant tip is responsible for the tip attraction when it is immersed in the hydration layer. Hydrophobic hydration layers, characterized by a variable dielectric permittivity profile, have measured widths of 4and4 and 4and8 nm for hydrophobic silicon and CTAB monolayer covering mica surfaces, respectively.