Thin Water Layer Research Articles

“Reptational” Movements of Single Synthetic Polymer Chains on Substrate Observed by in-Situ Atomic Force Microscopy

Vital “reptational” movements of isolated synthetic polymer chains on a substrate were imaged by atomic force microscopy (AFM) in the tapping mode. The isotactic poly(methyl methacrylate) molecules deposited on mica have long flexible chains that reptated on the substrate like snakes (caterpillar-like) along their chain directions in humid air. The thin water layer adsorbed on the substrate accelerated these movements. Possible tip scan effects on the observed movements were evaluated and found to be small mainly based on the following points: (1) the directions and time scales of the movements were not related to those of the scan, (2) the movements of the chains during interruption of the scan were similar to the movements during scanning, and (3) the movements were also observed in the frequency modulation mode (namely, “noncontact” mode) in which the tip force acting on the chains is significantly smaller than that in the tapping mode. The dynamic information about single polymer chains will stimulate new insights into the understanding of polymers, especially in surface phenomena, such as adhesion, wetting, and friction, and is also essential for fabricating advanced nanomaterials based on polymers.

Dimethylsulfide and major sulfur compounds in a stratified coastal salt pond

We conducted a diurnal study of gradients of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), dimethylsulfoxide (DMSO), and bacterial numbers in a stratified coastal salt pond (Salt Pond, Falmouth, Massachusetts). Microlayer samples were collected with a surface skimmer, a partially submerged rotating glass cylinder that allows the collection of a thin layer of water by adherence to the drum. All sulfur compounds and bacteria increased toward the water surface, with a diurnal signal in DMSP and DMSO. Fractionation of DMSP and DMSO in dissolved (d) and particulate (p) pools revealed that any trend in DMSP was due to the p fraction, and trends in DMSO originated from the d fraction. Photoeffects are important for the distribution of DMSPp and DMSOd. In Salt Pond, the production of DMSP is probably linked to photosynthesis, and photooxidation is of greater importance to the production of DMSO than is biological oxidation.

Nanofriction Mechanisms Derived from the Dependence of Friction on Load and Sliding Velocity from Air to UHV on Hydrophilic Silicon

This paper examines friction as a function of the sliding velocity and applied normal load from air to UHV in a scanning force microscope (SFM) experiment in which a sharp silicon tip slides against a flat Si(100) sample. Under ambient conditions, both surfaces are covered by a native oxide, which is hydrophilic. During pump-down in the vacuum chamber housing the SFM, the behavior of friction as a function of the applied normal load and the sliding velocity undergoes a change. By analyzing these changes it is possible to identify three distinct friction regimes with corresponding contact properties: (a) friction dominated by the additional normal forces induced by capillarity due to the presence of thick water films, (b) higher drag force from ordering effects present in thin water layers and (c) low friction due to direct solid–solid contact for the sample with the counterbody. Depending on environmental conditions and the applied normal load, all three mechanisms may be present at one time. Their individual contributions can be identified by investigating the dependence of friction on the applied normal load as well as on the sliding velocity in different pressure regimes, thus providing information about nanoscale friction mechanisms.

A surface mass balance model for the Greenland Ice Sheet

A surface mass balance model aimed at being coupled to a Global Circulation Model (GCM) for future climate prediction is described and tested for the Greenland Ice Sheet. The model builds on previous modeling designed to be forced by automatic weather station data, and includes surface energy balance as well as processes occurring near the surface such as water percolation and refreezing. Surface albedo is calculated with a new scheme that differentiates the timescale for aging of wet and dry snow and incorporates the effect of a thin layer of water and/or fresh snow at the surface. The model was driven with automatic weather station data from two sites located in the ablation zone in the Kangerlussuaq area (West Greenland), and calculated reasonable annual mass balance values (within 10% in seven out of eight cases) for four individual and consecutive years (1998–2001), using both measured and calculated albedo. This implies that the albedo parameterization is adequate and climate feedbacks affecting the mass balance are well captured. The model was then applied to a distributed 20‐km‐resolution grid covering the whole ice sheet, and forced with 10 years of the European Centre for Medium‐range Weather Forecast (ECMWF) reanalysis (ERA‐40) data. With the aim of coupling the model to a GCM, this study focuses on the ability to model the interannual variability in mass balance rather than to assess the present state of balance of the ice sheet. Modeled spatial and temporal wet zone extent compares well with information derived from passive microwave satellite data.

Analysis of element accumulation in cell wall attached and intracellular particles of snow algae by EELS and ESI

Snow algae frequently occur in alpine and polar permanent snow ecosystems and have developed adaptations to their harsh environment, where extreme temperature regimes high irradiation and low nutrient levels prevail. They live in a unique microhabitat, namely the liquid water between snow crystals. The predominant form appears as ‘red snow’ and in polar environment also ‘green snow’ frequently occurs. Light microscopy showed that most cells are densely covered by non-biotic particles of so far unknown composition. As snow normally contains very low amounts of nutrients, introduced mainly airborne like dust and precipitation, the inorganic particles at the surface of the snow algae may be important for their survival.By using electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI), we investigated element distribution in ultrathin sections of snow algae from different polar (Svalbard, 5ma.s.l., 79°N and maritime Antarctic, King George Island, 10ma.s.l., 62°S) and alpine habitats (2400–3100ma.s.l. Tyrol) for the present study. It turned out that the main elements of the cell wall attached particles are Si, Al, Fe and O independently from the origin of the snow algae. Interestingly, the same elements were also found in vacuolar compartments inside the cells. These vacuoles contain electron dense granules or crystals and are frequently found to be connected to the cortical cytoplasm. This finding suggests an uptake mechanism of the respective elements by pinocytosis. Co-transport of toxic aluminium together with silicon may be unavoidable as the inorganic nutrient uptake of the snow algae is limited to the thin water layer between the ice crystals. However, formation of insoluble aluminium silicates may serve as detoxification mechanism.

Molecular dynamics simulations of ice growth from supercooled water

The kinetics of ice growth on the secondary prismatic plane and the basal plane {0001} is studied by Molecular Dynamics simulations. The simulation system initially consists of a slab of ice in contact with a layer of water on one side, and vacuum on the other side. The remaining surface of the water layer is also facing vacuum. The time evolution of the system shows the crystallization of the liquid water and the evaporation of very few molecules at the free surfaces. The ice vapour interfaces are wet on both sides by identical thin layers of liquid water, strongly suggesting that the system has reached its equilibrium state. To analyse the results, we have developed a new method to discriminate whether a molecule belongs to the ice lattice or is in liquid state. Using this method to monitor the number of ice molecules as a function of time, we find that the freezing is much faster on the prismatic plane than on the basal plane. For the prismatic plane, irregularities in the surface of the solid phase are observed during the growing period contrasting with a smooth interface on the basal plane at all times. We studied three different temperatures and found that the rate of crystallization decreases with temperature for the prismatic plane, while no conclusive behaviour was found for the basal plane growth.

Acoustic scattering by a metallic tube with a concentric solid polymer cylinder coupled by a thin water layer. Influence of the thickness of the water layer on the two Scholte–Stoneley waves

The problem of a plane acoustic wave scattered by a layered cylinder submerged in water is considered. This cylinder consists of a tube made of aluminum with a solid Lucite cylinder concentrically fitt inside it. These two components are coupled by a thin layer of water. A particular investigation is made on the influence of the thickness of the water layer on the presence of the bending wave A on the tube and the Scholte–Stoneley wave on the cylinder. The presence of these waves is examined in the function of the varying water layer thickness: two special cases are discussed. First, for a layer thickness greater than the tube thickness, it is shown that both the A wave on the aluminum tube and the Scholte–Stoneley wave on the Lucite cylinder are generated. Second, for a thickness much smaller than the tube thickness, a different wave is generated, which is a combination of both waves. These two cases are experimentally verified in a setup that employs a short pulse method.

Hydrophobic–Hydrophilic Interactions of Water with Alkanethiolate Chains from First‐Principles Calculations

The interaction of water with alkanethiolate chains is studied from first principles. A detailed analysis is performed by optimizing the structure of small water clusters, one-dimensional water chains, and ordered and disordered thin water layers adsorbed on hydroxyl(OH)- and methyl(CH3)-terminated alkanethiol monolayers. The hydrophilic/hydrophobic character of these two different substrates is investigated by means of an energetic analysis combined with hydrogen-bond counting. On the hydrophilic OH-terminated alkanethiol surface, zigzag, one-dimensional water chains and disordered thin water layers are the energetically favored structures. The ab initio results can be used to determine the optimal value of the empirical parameters characterizing a suitable force field to be used in classic molecular dynamics simulations.

Numerical simulation of glass fogging and defogging

A numerical procedure for the prediction of fogging and defogging phenomena is presented. The simulation involves the solution of an air flow field along a cold solid surface, the evaluation of the unsteady conduction through the solid itself, and a model for the heat and mass transfer within the thin water layer on the fogged surface. A suite of routines for the unsteady simulation of the water layer evolution is coupled with an equal order finite element Navier Stokes solver and a finite volume conduction code. The procedure is fully independent of the numerical details of the solid and fluid domain solvers. Two different coupling approaches may be followed: A loose one, where the Navier Stokes solution is used only for a steady state estimate of the heat transfer coefficient, or a close one, where the Navier Stokes, conduction and water layer codes are iterated simultaneously. The latter is required for the problem of natural convection, where temperature (and thus the energy balance of the water layer) and flow field are coupled. The water layer is modelled as a collection of closely packed tiny droplets, leaving a portion of dry area among them. The effect of the contact angle is taken into account, and physical assumptions allow to define the local ratio between wet and dry surface for both the fogging and defogging process. As a case study, a comparison with experimental data for a complete fogging and defogging cycle of a glass lens in natural convection is presented.

A Multi-Index GEM Technique and Its Application to the Southwestern Japan/East Sea

Abstract This paper demonstrates a new gravest empirical mode (GEM) technique that constructs multi-index lookup tables of temperature (T) and specific volume anomalies (δ) using historical hydrocasts as a function of three indices: round-trip travel time (τ) from sea floor to the surface, sea surface temperature, and pressure. Moreover, the historical hydrocasts are separated into non-mixed-layer (NML) and mixed-layer (ML) groups, and a single GEM field is constructed for each group. This is called the MI-GEM technique. The appropriate dates for MI-GEM fields are determined by the monthly distribution of the number of NML and ML profiles in the historical hydrocasts, which are also well correlated with the strength of the winds during the 2 yr of observations. The T and δ profiles that are determined by this MI-GEM technique capture 92% and 88% of the T and δ variances in the depth range of 0–200 db. These values reduce by about one-third of the unexplained error variance of the residual GEM, which was recently developed and applied to the optimal interpolated τ data in the southwestern Japan/East Sea (JES) by Mitchell et al. Comparisons with the in situ CTD casts demonstrate that the MI-GEM technique almost always produces improved full water column profiles of T and δ. Whereas the residual GEM estimates had exhibited qualitatively erroneous features like T inversions in the near–surface layer and too thin or thick intermediate water layers in some regions, the MI-GEM estimates avoid those problems, which were inherent to the residual GEM technique in the southwestern JES.

Charge transfer through interfacial water inside an STM junction

Charge transfer through thin layers of water between an STM tip and an Au surface has been investigated by using a scanning tunneling microscopy (STM) technique at a relative humidity of 95%. The plateau currents were found to appear at separations larger than several Å where the current decay stops. The polarity dependence of the electrochemical currents was not observed with STM junction between an Au tip and an Au surface, which was observed with STM junction between a Pt/Ir tip and an Au surface. The plateau currents at H 2O saturation were measured to be 10–20% higher than those at D 2O saturation at bias voltages above |0.4| V. The results were rationalized in terms of the electrochemical currents originating mostly from the processes of OH − (OD −) or H 2O (D 2O) on the positive surface with different conductivity between H 2O and D 2O.

Surface Reactions of Carbon Dioxide at the Adsorbed Water−Iron Oxide Interface

Despite the fact that carbon dioxide is an abundant atmospheric gas with profound environmental implications, there is little information on the reaction of carbon dioxide at the adsorbed water-oxide interface. In this study, the chemistry of carbon dioxide at the adsorbed water-iron oxide interface is investigated with FTIR spectroscopy. As shown here, the thin water layer on the iron oxide surface plays an important role in the surface chemistry of carbon dioxide. In particular, adsorbed water enhances CO(2) uptake, undergoes isotope exchange with CO(2) in O(18)-labeled experiments, and influences the chemical nature of the predominant adsorbed product on the surface from bicarbonate to carbonate. The resultant thin water film is acidic in nature from the reaction of CO(2). The IR spectrum recorded of adsorbed carbonate at the adsorbed water-iron oxide interface is remarkably similar to that at the bulk liquid water-iron oxide interface. Since reactions in thin water films estimated to be approximately 2 layers will play a role in a number of environmental processes, it is essential to understand the chemistry of these "wet" interfaces with atmospheric gases.

Hydrogen entry into steel during atmospheric corrosion process

Hydrogen entry and permeation into iron were measured by an electrochemical method during atmospheric corrosion reaction. The hydrogen permeation was enhanced on passive films because the hydrogen adsorption increased by the hydrogen evolution mechanism which is different from that on a bear iron surface. The permeation rate during a wet and dry corrosion cycle showed a maximum in the drying process depending upon the surface pH and the corrosion potential. The pollutant such as Na 2SO 3 which decreases the pH and the corrosion potential causes an increase in the permeation rate. The mechanism of the change in the permeation rate during the wet and dry cycles is explained by the polarization diagram of the electrode covered by thin water layer.

Molecular dynamics simulation of a thin water layer evaporation and evaporation coefficient

This work investigates the evaporation of a thin water layer into vacuum using molecular dynamics simulations based on TIP4P model for intermolecular potential. The results of simulation reveal micro-scale physical phenomena near the liquid–vapor interface such as evaporation, condensation, recoil after evaporation or condensation, and molecular exchanges. The simulations show that the hydrogen bond has a significant effect on the molecular behavior near the interface and may reduce the evaporation coefficient. This study also demonstrates that the combination of molecular dynamics simulations and the classical Schrage model may provide an elegant methodology to determine the evaporation coefficient of water at different temperatures or corresponding saturation pressures.

Properties of physisorbed water layers on gold revealed in a FEM study

Field emission study of thin water layers was performed to examine their properties and their changes after application of a high electric field. Comparison of field emission characteristics of water layers adsorbed on clean tungsten and gold-covered tungsten suggested that, whereas water molecules adsorbed on tungsten are oriented by oxygen atoms towards the metal surface, water layer on gold-covered tungsten has amorphous character with no preferential orientation. Both heated and non-heated layers are heavily influenced by applied high electric field strengths ( F ≈30 MV/cm). Decrease of the work function and of the voltage needed for a constant emission current during successive increase of the electric field was tentatively interpreted in terms of chemical and morfological changes of the water layer due to the field dissociation and solvation.

Ice formation in Saharan dust over central Europe observed with temperature/humidity/aerosol Raman lidar

Three gravity‐wave‐induced clouds and a glaciating altocumulus layer were continuously monitored with lidar at Leipzig, Germany, on 21 November 2003. The midtropospheric clouds formed in Saharan dust at heights from 3.5 km (−9°C) to 6.5 km (−27°C). Distinct ice formation in the altocumulus was triggered by the gravity wave. For the first time, an aerosol/cloud study presents height profiles of temperature, water vapor mixing ratio, relative humidity, dust, and cloud optical properties (volume extinction and backscatter coefficients, lidar ratio, depolarization ratio) within the same air column, solely derived from lidar data. The three gravity‐wave‐induced clouds did not show any sign of ice formation. The aged dust particles below 4.5‐km height were probably partly coated and mixed with hygroscopic material and thus deactivated concerning ice nucleation. Ice crystals were generated in isolated air parcels at the cloud edges of a young, optically thin altocumulus layer between 5‐ and 6.5‐km height. An aged altocumulus deck composed of a geometrically thin liquid water layer at cloud top and an extended ice crystal layer (ice virga) was observed 2 hours later in the same height range. Strong ice formation occurred in the altocumulus during the downdraft induced by the gravity wave. Contact freezing was probably the main reason for the observed ice formation on dust particles. Ice depolarization ratios were relatively low with values from 10 to 15% in the altocumulus and indicate plate‐like crystals.

Macro-, micro- and nano-investigations on 3-aminopropyltrimethoxysilane self-assembly-monolayers

Here we report X-ray Photoelectron Spectroscopy (XPS), Secondary Ion Mass Spectrometry (SIMS) and Atomic Force Microscopy (AFM) studies of 3-aminopropyltrimethoxysilane (APTMS) film on a silicon oxide substrate. It was intended to verify the structure at macro-, micro- and nano-levels of the self-assembled monolayers obtained to identify the factors affecting possible film defects and to optimise the deposition technique. A method, involving the removal of the native SiO 2 surface layer by a HF/NH 4F solution followed by the generation of a new layer of silicon oxide by a NH 4OH–H 2O 2 solution, was preferred. The N(1s) XPS maps highlighted good macroscopic film homogeneity confirming a complete coating of the substrate. SIMS analyses involving depth profiles for both positive (H +, O +, Si +, C +) and negative (H −, O −, CN −, C 2 −) secondary ions and chemical maps for H −, O −, CN − ions indicated a high molecular order for the APTMS chains and suggested the presence of a thin water layer adsorbed at the surface of the self-assembled film. An approximate APTMS thickness estimate was also provided by Stopping Range of Ions in Matter calculations. AFM investigations carried out on several areas of the samples showed flat and regular surfaces.

Imaging the substructure of antibodies with tapping‐mode AFM in air: the importance of a water layer on mica

Monoclonal antibodies (immunoglobulin G; IgG) against the N-terminal domain of the A subunit of DNA gyrase have been imaged using tapping-mode atomic force microscopy under ambient conditions on hydrophilic mica surfaces. The familiar tri-nodal submolecular resolution of IgG (i.e. 50-kDa resolution) has been achieved when operating the microscope with the tip predominantly in the attractive force regime. Under common laboratory conditions of about 40% relative humidity, the resolution of this substructure was not achieved owing to motion of the antibodies on the surface and/or image distortion from tip-sample instabilities. Reproducible imaging of the tri-nodal antibody substructure was achieved by desiccating the samples for extended periods of time (1 week or more) before imaging. This effect is attributed to the presence of a humidity-dependent thin water layer (a few molecules or nanometres thick), which has been observed previously using the surface force apparatus and scanning polarization force microscopy. Desiccation of the mica surfaces allowed enough water to be removed from the mica surface to prevent this effect. Degradation in the image quality over the imaging period of an hour or two was observed, owing to re-adsorption of water under the ambient laboratory conditions.

Laboratory studies of stratified convection with multiple states

A simplified box model of the cooling of a salt-stratified ocean has been constructed in the laboratory to test a theory that predicts multiple equilibria if certain conditions exist. An isothermal basin of water had a thin layer of fresh water over salt water. Beside this was a smaller basin connected to the large basin by horizontal tubes at the top, middle and bottom. The small basin was cooled from above. If the top tube has more flow resistance than the bottom tubes, theory indicates that as cooling temperature T* is made colder, there is a sudden transition between two flow states. The velocities in the tubes jump to greater values, while salinity and temperature in the small basin jump to another value. These multiple states are found in the laboratory experiments along with some states that oscillate. Laboratory measurements and layered model calculations for hysteresis and the jump of temperature and salinity agree qualitatively, but there is only rough quantitative agreement.

Quasi-two-dimensional turbulence on the polar beta-plane: laboratory experiments

Results from a new series of experiments on turbulent flows decaying in a thin layer of water with a free surface in a rotating circular container are presented. The flows are generated electromagnetically using a regular array of permanent magnets. The Particle Image Velocimetry method is used to determine the velocity and vorticity fields in the flow. The experimental results demonstrate the formation of a polar vortex and jets perturbed by stationary Rossby waves in experiments with higher values of the beta parameter. Blocking events similar to those occurring in the Earth's atmosphere were observed in the laboratory flows. The Two-dimensional energy spectra of the flow demonstrate anisotropy in the space of the azimuthal and total wavenumbers. The One-dimensional energy spectra are characterized by a peak at the Rhines wavenumber.