Thin Water Film Research Articles

Effects of Salinity and the Extent of Water on Supercritical CO2-Induced Phlogopite Dissolution and Secondary Mineral Formation

To ensure the viability of geologic CO2 sequestration (GCS), we need a holistic understanding of reactions at supercritical CO2 (scCO2)-saline water-rock interfaces and the environmental factors affecting these interactions. This research investigated the effects of salinity and the extent of water on the dissolution and surface morphological changes of phlogopite [KMg2.87Si3.07Al1.23O10(F,OH)2], a model clay mineral in potential GCS sites. Salinity enhanced the dissolution of phlogopite and affected the location, shape, size, and phase of secondary minerals. In low salinity solutions, nanoscale particles of secondary minerals formed much faster, and there were more nanoparticles than in high salinity solutions. The effect of water extent was investigated by comparing scCO2-H2O(g)-phlogopite and scCO2-H2O(l)-phlogopite interactions. Experimental results suggested that the presence of a thin water film adsorbed on the phlogopite surface caused the formation of dissolution pits and a surface coating of secondary mineral phases that could change the physical properties of rocks. These results provide new information for understanding reactions at scCO2-saline water-rock interfaces in deep saline aquifers and will help design secure and environmentally sustainable CO2 sequestration projects.

Effects of fundamental processing parameters on the durability of sol-gel-derived silica thin films in water

Effects of fundamental processing parameters on the durability of sol-gel-derived silica thin films in water

Durable Antifog Films from Layer-by-Layer Molecularly Blended Hydrophilic Polysaccharides

Mechanically durable, long-lasting antifog coatings based on polysaccharides were developed using a layer-by-layer (LBL) assembly process. The unique properties of these coatings are a result of a molecular-level blending of the polysaccharides, with multilayers containing chitosan and carboxymethyl cellulose providing the best overall properties. The antifog properties resulted from a strong interaction between the polar and H-bonding elements of the assembled polymers and water molecules and the concomitant formation of thin films of water. Environmental scanning electron microscopy (ESEM) studies confirmed that fogging coatings are decorated with light scattering, micrometer-sized droplets of water whereas antifogging coatings remain droplet free. To improve the mechanical durability of the multilayer films on substrates, the surface was modified via self-assembly of epoxy-functionalized silane molecules. Cross-linking chemistry was then applied to improve the mechanical robustness of the LBL films on various surfaces. These films were characterized using several techniques: optical profilometery (PL), spectroscopic ellipsometry (EL), contact angle goniometry (CA), and atomic force microscopy (AFM). The antifog properties of the films were evaluated by several tests under different environmental conditions. This work demonstrates that the unique water-adsorbing properties of polysaccharides can be exploited to create permanent antifog properties, which may be useful for various applications.

Salt matrix voltammetry: Microphase redox processes at ammonium chloride | gold | gas triple phase boundaries

Electrochemical processes at the electrode | ammonium chloride salt crystal | gas triple phase boundary are detected under the condition that (i) microscopic contact points of salt crystals to a suitable working electrode are formed and (ii) the relative humidity level is adjusted to allow sufficient surface ion conduction in a thin water film within the salt matrix. In this preliminary report, redox systems such as Fe(CN)63−/4−, hydroquinone/benzoquinone, decamethylferrocene+/0, ferrocenedimethanol+/0, and Cu2+/+/0 are investigated embedded into an ammonium chloride salt matrix (by mechanical grinding) and then brought into contact with a macroscopic gold disc electrode. Voltammetric current responses are demonstrated consistent with the processes in the microphase formed at the salt | electrode | gas triple phase boundary. Copper metal electro-deposition is observed. Direct electrochemistry of dioxygen from the gas phase at the salt crystal | gold electrode contact is observed and gas sensing applications are proposed.

Translational diffusion of cumene and 3-methylpentane on free surfaces and pore walls studied by time-of-flight secondary ion mass spectrometry

Mobility of molecules in confined geometry has been studied extensively, but the origins of finite size effects on reduction of the glass transition temperature, T(g), are controversial especially for supported thin films. We investigate uptake of probe molecules in vapor-deposited thin films of cumene, 3-methylpentane, and heavy water using secondary ion mass spectrometry and discuss roles of individual molecular motion during structural relaxation and glass-liquid transition. The surface mobility is found to be enhanced for low-density glasses in the sub-T(g) region because of the diffusion of molecules on pore walls, resulting in densification of a film via pore collapse. Even for high-density glasses without pores, self-diffusion commences prior to the film morphology change at T(g), which is thought to be related to decoupling between translational diffusivity and viscosity. The diffusivity of deeply supercooled liquid tends to be enhanced when it is confined in pores of amorphous solid water. The diffusivity of molecules is further enhanced at temperatures higher than 1.2-1.3 T(g) irrespective of the confinement.

Einfluss der Wurzeln auf das Wasserspeichervermögen hydromorpher Waldböden | Significance of roots for soil water storage capacity of hydromorphic forest soils

In this study we investigated the significance of roots for the water storage capacity of hydromorphic forest soils in the northern Pre-Alps of Switzerland. Irrigation experiments were conducted on 1 m2 plots with high initial soil water content. A total of 67 horizons were investigated for water content variations using time domain reflectometry (TDR). The data was processed using a physically based model, which assumes gravity-driven and viscosity-controlled water flow along pore walls in the form of thin water films. The model calculates the contact length (L) between mobile water and the stationary parts of the soil water system in the horizontal plane. L characterises porosity which is effectively involved in water flow. A multiple linear regression analysis of all investigated horizons, including root density, bulk density and texture as predictors for L, demonstrated that the root density had the best explanatory value for L (R2 = 0.63). Thus, it can be assumed that increases in root density increase water storage capacity. Considering the extent of hydromorphicity in horizons, the relationship between root density and contact length was only significant in topsoils and hydromorphic subsoils. An increase of root density by 50% in hydromorphic subsoils would increase short-time water storage capacity from 0.03 to 0.05 m3/m3, while higher root densities in topsoils did not increase water storage capacities. To improve the water retention potential of flood protection forests on hydromorphic soils, we suggest promoting deep-rooting species which are able to sustain anaerobic periods in soils.

Case Study: Dynamic Modulus Characterization of Naturally Occurring Bituminous Sands for Sustainable Pavement Applications

──────────────── ─────── Abstract: Oil sand is a generic name given to naturally occurring deposits of bituminous sand materials that are mined for crude oil production. These materials are currently used as subgrade materials of temporary and permanent roads in oil sand fields. The presence of high bitumen content makes oil sand materials problematic for field operations of off-road haul trucks and shovels during the warm spring and summer months. The behavior of oil sand materials is primarily dependent upon stress states, temperature, and the rate of loading or frequency. To effectively account for temperature and loading frequency, dynamic modulus is the preferred material property to characterize bituminous materials. In this paper, dynamic modulus is determined for three types of oil sand materials with natural bitumen contents of 8.5, 13.3, and 14.5% by weight using cyclic load triaxial test procedure. All the three oil sand samples were compacted close-to-field densities and then tested at two temperatures and three loading frequencies (related to field trafficking speeds) at different stress states. Based on the test results, dynamic modulus was modeled as a power function of the applied stress states and temperature. Using all the test data obtained from the three oil sand samples, unified dynamic modulus characterization models were successfully developed to account for stress state, bitumen content, and temperature. The proposed model can be calibrated for field practical use to estimate modulus and deformation behavior of these oil sand materials for their sustainable use in pavement applications. 2 Oil sands, sometimes called as tar sands, are natural deposits of bituminous sand materials that are rich in bitumen content to the extent that oil can be extracted from these deposits. Oil sands are found worldwide. The largest and most thoroughly studied deposits are located in Canada, United States, and Venezuela. The Alberta Province in Canada has the world's largest deposit of oil sands. Oil sand surface mining involves excavation to remove the overburden and providing access to the mineral sands below it using haul trucks and shovels. In situ, the oil sand deposits are predominantly quartz sand surrounded by a thin film of water and fines, with bitumen filling the pore spaces between the sand grains. The quartz sand, silt, and clay, i.e., inorganic materials of the oil sand composition normally constitutes about 80% by weight, with bitumen and water constituting about 15 and 5%, respectively (1). Oil sand materials are currently used as construction materials of temporary and permanent roads in oil sand fields for operating large capacity haul trucks and shovels. These materials often exhibit stress dependent, viscoelastic, and plastic behavior under off-road construction and mining equipment. Field studies have shown that the modulus and deformation behavior of oil sands are primarily dependent upon the

Concentrated perchlorate at the Mars Phoenix landing site: Evidence for thin film liquid water on Mars

NASA's Phoenix mission, which landed on the northern plains of Mars in 2008, returned evidence of the perchlorate anion distributed evenly throughout the soil column at the landing site. Here, we use spectral data from Phoenix's Surface Stereo Imager to map the distribution of perchlorate salts at the Phoenix landing site, and find that perchlorate salt has been locally concentrated into subsurface patches, similar to salt patches that result from aqueous dissolution and redistribution on Earth. We propose that thin films of liquid water are responsible for translocating perchlorate from the surface to the subsurface, and for concentrating it in patches. The thin films are interpreted to result from melting of minor ice covers related to seasonal and long‐term obliquity cycles.

Adsorption of Nonionic Surfactants (CnEm) at the Silica−Water and Cellulose−Water Interface

The adsorption of nonionic surfactants to the silica-water and cellulose-water interfaces was studied using optical reflectometry (OR) and soft-contact atomic force microscopy imaging. The polyethylene oxide alkyl ethers C(14)E(6) and C(16)E(8) were shown to readily adsorb to both interfaces. The kinetics of the adsorption process as well as the equilibrium surface excess was determined using OR. In agreement with previous studies, the short headgroup surfactant C(14)E(6) adsorbed to a greater extent than the longer headgroup surfactant C(16)E(8) on silica. This trend was also observed for the cellulose-water interface. The structure of the adsorbed surfactant layer above the critical surface aggregation concentration (csac) was visualized using the soft contact imaging technique for both interfaces. On the silica surface, the layer structure for both surfactants mostly showed spherical aggregates, however, with some elongation into rods being more prevalent for C(14)E(6). Similar structures were observed on the cellulose surface, but imaging was more difficult due to the soft gel-like nature of the cellulose thin film in water. This suggests that these surfactants adsorb in a cooperative fashion above the critical micelle concentration (cmc) with a similar interaction between surfactant headgroup and surface for both silica and cellulose. No evidence was seen for the penetration of surfactant molecules into the cellulose surface or any solubilization of the interface.

Structure and stability of thin water films on quartz surfaces

We investigated thin water films on quartz (0001) surfaces using first-principles density functional theory calculations. Interfacial structure and energetics were studied through a layer-by-layer deposition. From monolayer to multilayer, the low energy state configurations and adsorption sites show a transition due to formation of a highly stable bilayer membranelike structure. The water adsorption energy on a quartz surface coated by this membrane is of typical hydrogen bond strength for both dry and fully hydroxylated surfaces. The interactions between the surface and the water films are short-ranged due to shielding of the bilayer.

Development of a Colloidal Lithography Method for Patterning Nonplanar Surfaces

A colloidal lithography method has been developed for patterning nonplanar surfaces. Hexagonal noncontiguously packed (HNCP) colloidal particles 127 nm-2.7 μm in diameter were first formed at the air-water interface and then adsorbed onto a substrate coated with a layer of polymer adhesive ∼17 nm thick. The adhesive layer plays the critical role of securing the order of the particles against the destructive lateral capillary force generated by a thin film of water after the initial transfer of the particles from the air-water interface. The soft lithography method is robust and very simple to carry out. It is applicable to a variety of surface curvatures and for both inorganic and organic colloidal particles.

Enhancement of solar still performance using a reciprocating spray feeding system—An experimental approach

It is well-established that minimizing water depth is one of the most vital key features to enhance the performance of solar stills. Accordingly, the performance of most recent attempts and proposed ideas tackling this point is limited. Thus, this work introduces a new approach that permits governing the water depth as desired and simultaneously evades all previous experienced interrelated implications through creating a thin re-established film of saline water on a particular manner in the solar still. This has been performed by feeding the saline water into the still through a controlled transverse reciprocating spraying system on the form of fine droplets to spread on the top surface of a corrugated steeped shape absorber of solar still. The application of the saline water thin film with the very low warming up period on this way has numerous significant advantages on the still performance. Consequently, the present approach has undergone a systematic study to examine its anticipated validity in real practice and to optimize its performance at various varying operating conditions. The performance results at any operating conditions reveal extraordinary superiority over those obtained from other recent stills by other investigators. Instead, an optimum operating condition could be identified. At then, an accumulated productivity of 6.355 l/m 2 over only 10 working hours at high efficiency of 77.35% was gained. Similarly, the hourly productivity profiles exhibited good uniformity along the representative testing hours of the daytime with relatively high average values. These findings are a result of improving the performance along the whole daytime and, particularly, on the morning hours. This indicates the high response of the still to the increase of the solar radiation leading to the rapid heating up on launching phases. In addition, the performance distributions at various operating conditions showed slight deviations. This emphasizes the flexible, consistent and robust characteristics encountered with this approach that fold on many practical benefits.

Lubrication by molecularly thin water films confined between nanostructured membranes

We use molecular dynamics simulations to study thermal sliding of two nanostructured surfaces separated by nanoscale water films. We find that friction at molecular separations is determined primarily by the effective free energy landscape for motion in the plane of sliding, which depends sensitively on the surface character and the molecular structure of the confined water. Small changes in the surface nanostructure can have dramatic effects on the apparent rheology. Whereas porous and molecularly rough interfaces of open carbon nanotube membranes are found to glide with little friction, a comparably smooth interface of end-capped nanotubes is effectively stuck. The addition of salt to the water layer is found to reduce the sliding friction. Surprisingly, the intervening layers of water remain fluid in all cases, even in the case of high apparent friction between the two membranes.

Effect of Micro-Area pH Value on Formation of Different Rust Phases of Weathering Steel in Initial Corrosion Period

The formation of protective rust layer of atmospheric corrosion resistance was discussed for weathering steel. The rust layers of experimental steels were made by using an accelerating industrial atmospheric corrosion test of dry-wet cyclic immersion. Furthermore XRD were used to measure and analyze the rust layers. The initial corrosion processes below thin water film were observed and the changes of micro-area pH value were measured. The results are as follows: The corrosion processes of P-RE weathering steel are obviously different from those of carbon steel. The surface of P-RE weathering steel rapidly forms α-FeOOH and the micro-area pH value is above 5, 4 during the initial corrosion period. While the component of the rust layer for the carbon steel is mainly Fe 3O 4 and the microarea pH value is below 3.8.

Spontaneous formation of water droplets at oil-solid interfaces.

We report observations of spontaneous formation of micrometer-sized water droplets within micrometer-thick films of a range of different oils (isotropic and nematic 4-cyano-4'-pentylbiphenyl (5CB) and silicone, olive and corn oil) that are supported on glass substrates treated with octadecyltrichlorosilane (OTS) and immersed under water. Confocal imaging was used to determine that the water droplets nucleate and grow at the interface between the oils and OTS-treated glass with a contact angle of approximately 130 degrees. A simple thermodynamic model based on macroscopic interfacial energetic arguments consistent with the contact angle of 130 degrees, however, fails to account for the spontaneous formation of the water droplets. zeta-potential measurements performed with OTS-treated glass (-59.0 +/- 16.4 mV) and hydrophobic monolayers formed on gold films (2.0 +/- 0.7 mV), when combined with the observed absence of droplet formation under films of oil supported on the latter surfaces, suggest that the charge of the oil-solid interface promotes partitioning of water to the interfacial region. The hydrophobic nature of the OTS-treated glass promotes dewetting of water accumulated in the interfacial region into droplets (a thin film of water is seen to form on bare glass). The inhibitory effect on droplet formation of both salt (NaCl) and sucrose (0.1-500 mM) added to the aqueous phase was similar, indicating that both solutes lower the chemical potential of the bulk water (osmotic effect) sufficiently to prevent partitioning of the water to the interface between the oil and supporting substrates. These results suggest that charged, hydrophobic surfaces can provide routes to spontaneous formation of surface-supported, water-in-oil emulsions.

Potential of Mean Force for K+in Thin Water Films on Cleaved Mica

The atomically smooth surface of cleaved K(+)-mica is a common substrate for investigations of various phenomena at the mineral-water interface. In this study, K(+) inner-sphere adsorption above tetrahedral substitutions in the mica structure is found to be more favorable than that in mica's ditrigonal cavities for both dehydrated and hydrated cleaved mica. The activation energy necessary to transfer K(+) from the inner-sphere adsorption state to the outer-sphere adsorption state, in which K(+) can presumably migrate parallel to the surface, is calculated to be 45-48 kJ/mol on hydrated cleaved mica. The K(+) desorption state is predicted to be >13 A above the mica surface.

Structural Relaxation of Vapor-Deposited Water, Methanol, Ethanol, and 1-Propanol Films Studied Using Low-Energy Ion Scattering

Glassy thin films of water, methanol, ethanol, and 1-propanol were prepared by deposition from the gas phase at 20 K. Relaxation of their surface and bulk structures was investigated by measuring temperature evolutions of H(+), H(-), and total yields in low-energy H(2)(+) scattering. The surface structure of a methanol film changes at temperatures of about 20 K below the glass transition temperature (T(g) = 103 K) because of enhanced diffusivity of molecules at the surface. Both surface and bulk structures change at around T(g) for ethanol, but the structure of the 1-propanol film is unchanged at temperatures higher than T(g), indicating that the vapor-deposited 1-propanol glass is more stable than the liquid-quenched one. These behaviors strongly suggest that the configurations of molecules in the vapor-deposited glass differ significantly from those in the liquid-quenched glass and that the aliphatic-chain length plays an important role in structural relaxation. The surface (bulk) structure of the water film changes gradually (is invariant) across T(g), suggesting that the relaxation and glass transition processes differ significantly between those of water and alcohols.

The Charge of Solid–Liquid Interfaces Measured by X‐Ray Standing Waves and Streaming Current

Measurements of ion distributions at a charged solid-liquid interface using X-ray standing waves (XSW) are presented. High energy synchrotron radiation (17.48 keV) is used to produce an XSW pattern inside a thin water film on a silicon wafer. The liquid phase is an aqueous solution containing Br and Rb ions. The surface charge is adjusted by titration. Measurements are performed over a pH range from 2.2-9, using the native Si oxide layer and functional (amine) groups as surface charge. The Debye length, indicating the extension of the diffuse layer, could be measured with values varying between 1-4 nm. For functionalized wafers, the pH dependent change from attraction to repulsion of an ion species could be detected, indicating the isoelectric point. In combination with the measurement of the streaming current, the surface charge of the sample could be quantified.

Electron emission from amorphous solid water induced by passage of energetic protons and fluorine ions.

Absolute doubly differential electron emission yields were measured from thin films of amorphous solid water (ASW) after the transmission of 6 MeV protons and 19 MeV (1 MeV/nucleon) fluorine ions. The ASW films were frozen on thin (1-microm) copper foils cooled to approximately 50 K. Electrons emitted from the films were detected as a function of angle in both the forward and backward direction and as a function of the film thickness. Electron energies were determined by measuring the ejected electron time of flight, a technique that optimizes the accuracy of measuring low-energy electron yields, where the effects of molecular environment on electron transport are expected to be most evident. Relative electron emission yields were normalized to an absolute scale by comparison of the integrated total yields for proton-induced electron emission from the copper substrate to values published previously. The absolute doubly differential yields from ASW are presented along with integrated values, providing single differential and total electron emission yields. These data may provide benchmark tests of Monte Carlo track structure codes commonly used for assessing the effects of radiation quality on biological effectiveness.

Ecology of Plant and Free-Living Nematodes in Natural and Agricultural Soil

Nematodes are aquatic organisms that depend on thin water films to live and move within existing pathways of soil pores of 25-100 mum diameter. Soil nematodes can be a tool for testing ecological hypotheses and understanding biological mechanisms in soil because of their central role in the soil food web and linkage to ecological processes. Ecological succession is one of the most tested community ecology concepts, and a variety of nematode community indices have been proposed for purposes of environmental monitoring. In contrast, theories of biogeography, colonization, optimal foraging, and niche partitioning by nematodes are poorly understood. Ecological hypotheses related to strategies of coexistence of nematode species sharing the same resource have potential uses for more effective biological control and use of organic amendments to foster disease suppression. Essential research is needed on nematodes in natural and agricultural soils to synchronize nutrient release and availability relative to plant needs, to test ecological hypotheses, to apply optimal foraging and niche partitioning strategies for more effective biological control, to blend organic amendments to foster disease suppression, to monitor environmental and restoration status, and to develop better predictive models for land-use decisions.