Natural Surface Films Research Articles

Enhanced corrosion resistance of magnesium-neodymium alloy in simulated concrete pore solution by predesigned corrosion product

The natural surface films on Mg alloys can’t provide enough corrosion protection in aqueous solutions compared to those on Al alloys and Ti alloys. In this study, a strategy is proposed for corrosion protection of Mg alloys by transforming corrosion products into protective coatings. Here, a magnesium-neodymium alloy is immersed in potassium dihydrogen phosphate solution at 50 °C for 4 h. Following this simple corrosion process, a layer of uniform MgHPO4.3 H2O coating with a thickness of about 20 µm is formed on the Mg alloy. Electrochemical test and long-term immersion test reveal that this coating significantly improves the corrosion resistance of the Mg-Nd alloy in Cl--containing simulated concrete pore solution. In summary, it indicates that some corrosion products can be designed to be transformed into protective coatings, providing new technical insights pertaining to the corrosion protection of magnesium alloys.

Towards Automatic Recognition of Wakes Generated by Dark Vessels in Sentinel-1 Images

The recognition of wakes generated by dark vessels is a tremendous and interesting challenge in the field of maritime surveillance by Synthetic Aperture Radar (SAR) images. The paper aims at assessing the detection performance in different scenarios by processing Sentinel-1 SAR images along with ground truth data. Results confirm that the Radon-based approach is an effective technique for wake-based detection of dark vessels, and they lead to a deeper understanding of the effects of different sea and wind conditions. In general, the best applicative scenario is a marine image characterized by homogeneous sea clutter; the presence of natural surface film or strong transition from low wind speed areas to more windy zones worsen the detection performance. Nonetheless, the proposed approach features dark vessel detection capabilities by identifying their wakes, without any a priori knowledge of their positions.

Evolution of natural sea surface films: a new quantification formalism based on multidimensional space vector

Spatial and temporal variability of natural surfactant sea surface film structural parameters were evaluated from force-area isotherms, film pressure-temperature isochors, dynamic surface tension-time relations performed on samples collected in Baltic Sea shallow coastal waters. The film structure state was postulated as a 10-D dimensionless vector created from the normalized thermodynamic, adsorptive, and viscoelastic film parameters. The normalization procedure is based on the concept of self-corresponding states known in thermodynamics. The values taken by all the reduced parameters indicated a significant deviation from the reference ideal-2D gas behavior. The exhibited deviations of the surface parameters from the background values of the same thermodynamic state of each film were independent on the film-collecting procedure, sample solvent treatment, and temperature. The structural similarity was expressed quantitatively as a (Cartesian, street, and Czebyszew) distance between two vectors of the analyzed film and the standard one from the database, and appeared to be related to environmental conditions, surface-active organic matter production, and migration in the studied coastal sea region. The most distinctive parameters differing the films were y, Mw and Eisoth, as established from Czebyszew function application. The proposed formalism is of universal concern and could be applied to any natural water surfactant system (seawater, inland water, rain water, and snowmelt water).

7th International Symposium on Gas Transfer at Water Surfaces

The 7th International Symposium on Gas Transfer at Water Surfaces was held 18-21 May 2015 in Seattle, Washington. These symposia, which have occurred approximately every five years since 1983, bring together the international scientific and engineering community investigating the mechanisms, parameterizations, and applications of gas transfer at water surfaces. The focus in part is on the physical processes that govern the gas flux, which include air entrainment (by breaking waves, flow over hydraulic structures, or direct injection), turbulence (generated by mechanical agitation, wind, wave breaking, rainfall, or currents), and the effect of natural and synthetic surfactants. Of equal importance to the treatment of the forcing mechanisms are the discussions on how to model or parameterize air-water gas transfer relevant to biogeochemical cycling on global, regional, and local scales. Furthermore, because the mechanisms controlling the gas flux also govern the air-sea flux of heat and momentum, the conference is attended by many studying a wide range of air- and water-side mixing processes that occur at or near the ocean surface. This provides opportunities for crossfertilization of ideas between the classical air-sea interaction community and those focused on biogeochemical cycling.The first symposium was held at Cornell University, Ithaca, New York in 1983 [1]. The second symposium took place in Minneapolis in 1990 [2] and the third symposium was held at the University of Heidelberg in Heidelberg, Germany in 1995 [3]. The fourth symposium took place in Miami in 2000 [4] and the fifth symposium was held in Liège, Belgium in 2005 in conjunction with the 37th International Liège Colloquium on Ocean Dynamics [5]. The sixth symposium was held in Kyoto, Japan in 2010 [6].Gas transfer at air-water interfaces encompasses a wide variety of research, including fundamental fluid dynamics, biogeochemistry, and oceanography across a range of spatial and temporal scales. For example, the exchange of greenhouse gases between the atmosphere and natural bodies of water is critical to characterize and quantify global climate change. The establishment of a regular series of international symposia with a periodicity of five years was motivated by the increasing societal interest in the consequences of gas transfer at air-water interfaces, the size and productivity of the research community, and the wide geographic distribution of active researchers. The symposium has established a reputation as an important and influential venue for presenting and disseminating research progress to the community. The five-year period between gatherings ensures that significant progress since the last occurrence will be reported.The research problems involve extremely challenging and complex issues associated with turbulent flow over a wide range of spatial and temporal scales that include the effects of wind and currents, breaking waves, rainfall, and two-phase flow effects due to the presence of bubbles generated by breaking waves and raindrops. The complexity is increased by the occurrence of both natural and anthropogenic surface films, which can modify the chemical and physical characteristics of the interface. The challenge of understanding gas transfer and the effect of gas exchange on biogeochemistry has led to the need for multidisciplinary, collaborative efforts and the development of a wide variety of innovative observational and experimental techniques. As many dedicated past attendees can attest, the symposia have fostered productive and long-lasting collaborations that have made new and pivotal contributions over the past three decades.

Elastic Properties of Natural Sea Surface Films Incorporated with Solid Dust Particles: Model Baltic Sea Studies

Floating dust-originated solid particles at air-water interfaces will interact with one another and disturb the smoothness of such a composite surface affecting its dilational elasticity. To quantify the effect, surface pressure (Π) versus film area (A) isotherm, and stress-relaxation (Π-time) measurements were performed for monoparticulate layers of the model hydrophobic material (of μm-diameter and differentiated hydrophobicity corresponding to the water contact angles (CA) ranging from 60 to 140°) deposited at surfaces of surfactant-containing original seawater and were studied with a Langmuir trough system. The composite surface dilational modulus predicted from the theoretical approach, in which natural dust load signatures (particle number flux, daily deposition rate, and diameter spectra) originated from in situ field studies performed along Baltic Sea near-shore line stations, agreed well with the direct experimentally derived data. The presence of seawater surfactants affected wettability of the solid material which was evaluated with different CA techniques applicable to powdered samples. Surface energetics of the particle-subphase interactions was expressed in terms of the particle removal energy, contact cross-sectional areas, collapse energies, and so forth. The hydrophobic particles incorporation at a sea surface film structure increased the elasticity modulus by a factor K (1.29–1.58). The particle-covered seawater revealed a viscoelastic behavior with the characteristic relaxation times ranging from 2.6 to 68.5 sec.

Properties of natural microlayers on Australian freshwater storages and their potential to interact with artificial monolayers

Microlayers are natural surface films derived from hydrophobic organic compounds that form on most lakes and streams. Holarctic brown-water lakes have been most commonly studied, with Australian research limited to marine microlayers. Artificial monolayers based on long-chain fatty alcohols have been applied to freshwater storages to reduce evaporative loss. As a water conservation strategy, monolayer technology was not widely adopted because of variable field performance. However, the role of natural microlayers in reducing monolayer performance has not previously been investigated. In the present study, microlayer and subsurface samples from six water storages in Queensland were characterised for water-quality indices, including biochemical oxygen demand, permanganate index and ultraviolet light absorbance. Microlayer enrichment in south-eastern Queensland is comparable to or higher than that in holarctic lakes. The results indicated that microlayer compounds have the potential to disrupt monolayers in at least the following three ways: as substrates for microbes capable of degrading monolayer compounds, as chromophores accelerating photodegradation, and as impurities disrupting the molecular packing required to reduce evaporative loss. The knowledge gained from studying natural microlayers can also be used to benchmark novel monolayer compounds, to minimise their environmental impact on freshwater ecosystems.

Evolution of natural sea surface film structure as a tool for organic matter dynamics tracing

The paper contains the results of natural film experiments carried out on inland waters in the Dead Vistula catchment area during 2000–2002 using the integrated Langmuir trough–Wilhelmy plate system. The static film parameters result from the generalized scaling procedures applied to the surface pressure-area isotherms and surface pressure–temperature isochores. They appear to reflect in a quantitative and sensitive way the film composition ( A lim, M w, E isoth), film solubility and the miscibility of its components (via R, Δ S c and y factors), kinetic mobility of surfactant molecules ( β s, π k), and its surface concentration ( π eq, Γ eq). There is a reason to suggest that certain classes of film-forming components or “end-members” may dominate the static and dynamic surface properties. Variation in the surface rheological parameters of source-specific surfactants is postulated to reflect organic matter dynamics in natural waters and were measured for the Dead Vistula river, its tributaries and the adjacent sea coastal area. The obtained results demonstrate that natural films are o complex mixture of biopolymeric molecules covering a wide range of solubilities, surface activities and molecular masses with a complex interfacial architecture. For the first time, the apparent solvent polarity effect on the structure and surface parameters of ex-situ formed natural sea microlayer films was quantitatively evaluated by means of the author's scaling procedures applied to unique Brewster angle microscopy and Langmuir trough isotherm data on Mediterranean Sea samples obtained by others.

Air Pollution: Urban Grime Recycles Toxics

Grime clinging to windows and other surfaces in cities may be an unrecognized source of toxic nitrogen oxide (NOx) pollutants that can damage lung tissue, according to research in the 1 June 2007 issue of Environmental Science & Technology. Atmospheric chemist James Donaldson and colleagues at the University of Toronto found that when sunlight strikes grime, inactive nitrogen compounds may be transformed into active forms that become airborne. This view challenges the long-standing notion that nitrogen compounds trapped in grime (also known as urban surface film) are washed away by rain and are no longer available to produce ozone and smog. The combustion of fossil fuels by automobiles and power plants forms NOx, which combines with volatile organic compounds to produce smog. Donaldson and colleagues observed that nitrogen compounds sequestered in urban surface films seemed to disappear faster than could be explained by rain washing them away into soil or groundwater. To test this idea, Donaldson’s team coated slides with a few key chemicals found in grime and exposed them to gaseous nitric acid. This main form of nitrogen is considered to be an atmospheric end product; it sticks to windows, where it is assumed to be inert. When the slides were irradiated with visible light, nitric acid was removed, likely converted to nitrogen dioxide, nitric oxide, and nitrous acid—all major players in ozone and smog formation. The discovery suggests that “nitrogen oxides are being recycled and are not lost as people have thought,” Donaldson says. He plans to repeat the experiment with actual grime scraped from dirty windows to verify whether sunlight releases NOx from complex natural urban surface films. These films are composed of several broad classes of chemicals, some with hundreds of identified compounds, according to research published in volume 63, issue 1 (2006) of Chemosphere. If the initial results hold up, computer models of urban air quality may need to be adjusted to account for this overlooked supply of photochemically activated compounds. “This is not the first suggestion that nitric acid can be recycled back into photochemically active forms in the gas phase,” says Barbara Finlayson-Pitts, a professor of chemistry at the University of California, Irvine. “Renoxification” reactions were proposed back in the 1990s, and Finlayson-Pitts’s own group has done work in this area. However, she adds, “The idea that chemistry on the surfaces of buildings plays a significant role in the chemistry of the atmosphere has not been given much attention,” and Donaldson’s study nicely illustrates that it could prove to be critically important for developing accurate computer models of air pollution.

Systematic error of microwave scatterometer wind related to the basin‐scale plankton bloom

Chlorophyll‐a concentration derived from satellite ocean color sensor are compared with coincident wind speed difference between microwave scatterometer QuikSCAT product and reanalysis product from the National Center for Environmental Prediction over global oceans. The objective is to explore if a natural surface film, which originates in biological productivity, causes the underestimation of surface wind in scatterometer measurement by damping the small capillary wave through the surface tension. The wind speed difference (Reanalysis wind – QuikSCAT wind) is found to correlate positively with chlorophyll‐a over the biologically highly productive areas, especially from intra‐seasonal to seasonal time scales, indicating the surface film effect. The wind speed difference increases from ∼−1 m s−1 to ∼0.5 m s−1 as chlorophyll‐a increases from ∼0.1 mg m−3 to ∼3 mg m−3, which is comparable with the results of previous laboratory experiments with artificial oil.

First evidence for the detection of natural surface films by the QuikSCAT scatterometer

For the first time it is demonstrated that with the QuikSCAT scatterometer it is possible to detect natural surface films resulting from enhanced biological activity in the ocean. It is shown for two regions in the Norwegian and Baltic Sea that areas of strongly reduced Normalized Radar Cross Section (NRCS) are associated with areas of enhanced chlorophyll‐a concentration as evidenced by quasi‐simultaneously acquired SeaWiFS data. This result has two implications. Firstly, it opens up the possibility to map globally natural surface film coverage using QuikSCAT data. Secondly, it demonstrates that in ocean areas with high biological activity the presence of natural surface films can give rise to significant errors in wind vector retrieval when using the current QuikSCAT wind retrieval algorithm.

Structural and thermodynamic signatures of marine microlayer surfactant films

Natural surface film experiments in inland waters and shallow offshore regions of the Baltic and Mediterranean Seas were carried out in the time period 1990–1999 under calm sea conditions using a novel device for sampling and force-area studies. The sampler-Langmuir trough-Wilhelmy filter paper plate system ‘cuts out’ an undisturbed film-covered sea area to perform π-A studies without any initial physico-chemical sample processing. The limiting specific area A lim (2.68–31.57 nm 2/molecule) and mean molecular mass M w (0.65–9.7 kDa) of microlayer surfactants were determined from the 2D virial equation of state applied to the isotherms. Enthalpy ΔH and entropy ΔS t of the 2D first-order phase transitions were evaluated using the Clausius-Clapeyron equation applied to the isotherms. Miscibility of film components and film structure evolution is expressed by the scaling exponent y adopting the 2D polymer film scaling theory. The stress-relaxation measurements revealed a two-step relaxation process at the interface with characteristic times τ 1=1.1–2.8 and τ 2=5.6–25.6 seconds suggesting the presence of diffusion-controlled and structural organisation relaxation phenomena. The obtained results suggest that natural films are a complex mixture of biomolecules covering a wide range of solubilities, surface activity and molecular masses with an apparent structural organisation exhibiting a spatial and temporal variability.

Mesoscale variability in the Alboran Sea: Synthetic aperture radar imaging of frontal eddies

In autumn 1992 the entire Alboran Sea (western Mediterranean) was sampled by the Spanish R/V García del Cid. The incoming jet of Atlantic water, its associated meandering front, and the two big anticyclonic gyres were described from conductivity‐temperature‐depth (CTD) and acoustic Doppler current profiler (ADCP) data. Smaller‐scale eddies were also observed. Additionally, 36 ERS‐1 synthetic aperture radar (SAR) scenes were obtained from mid‐September to mid‐October. The SAR images capture these features when wind conditions are suitable. The current shear is mainly depicted as narrow lines of low backscatter because of the damping of waves by natural surface films. These lines delineate the northern border of both gyres and the beginning of the alongslope Algerian current at the eastern limit of the Alboran Sea. ADCP observations confirm that lines on SAR imagery follow the direction of the surface currents. The two gyres present high backscatter values in their center, while their frontal boundaries appear modulated by the variation of the marine atmospheric boundary layer stratification due to the surface thermal front. SAR has observed small spiral eddies that were not evidenced by the almost contemporaneous but too coarse CTD in situ sampling. Good spatial correspondence between radar‐detected and in situ‐measured structures occurs when comparing SAR images to the surface dynamic topography, rather than strictly surface water characteristics.

Interaction of Polysaccharides with Lipid Monolayers

The interactions of model neutral lipids such as lecithin and dipalmitoyl phosphatidylcholine (DPPC), and of the positively charged lipid dioctadecyl dimethyl ammonium bromide (DOMA) with neutral (dextrans) and acidic polysaccharides (carrageenans and xanthan), representing the hydrophilic solutes occurring in natural aquatic systems, have been monitored electrochemically and by monolayer techniques. Surface pressure-area (π-A) and surface potential-area (ΔV-A) isotherms have been measured. The values for compressibility of mixed films and the dipol moments (effective dipole moment μT and polar head group dipole moment μα) have been calculated from π-A and Δ V-A isotherms, respectively. In electrochemical experiments lipid-coated mercury electrodes have been used. The influence of polysaccharides on the monolayers structure has been studied by capacitance measurements and by using an electrochemical probe (redox processes of cadmium) with phase-sensitive ac voltammetry. The results presented here are part of more general studies of the interaction of organic solutes naturally occurring in the aquatic systems with hydrophobic lipids at different phase boundaries. These investigations are of great importance for the interfacial properties of mixed monolayers and for understanding the influence of hydrophilic and hydrophobic substances on the physicochemical properties of natural surface films.

Application of 2D polymer film scaling theory to natural sea surface films

The polymer film scaling theory was applied, by measuring the high-frequency limit of the surface modulus E 0 as a function of the surface pressure P [ E 0 = yP, where y = 2ν (2ν − 1) and ν is the critical exponent of the excluded volume], to natural marine surface films. An increase in y from < 3.5 through ∼ 8 to over 10 indicating “good”, Θ, and “poor” solvent behaviour, respectively of the interfacial system is also correlated with the structure transition in the multicomponent film beginning from a homogeneous mixed monolayer, through a heterogeneous film with surface-active substances segregated into patches or domains to at least a vertically layered structure at the interface, and it is believed to hold for natural sea surface films. The scaling exponent y is a complex function of environmental factors affecting the film structure (bulk concentration of a surfactant, pH, ionic strength and composition of the subphase, temperature, locations of sampling site and film collection procedures).

Adhesion force and the character of surfaces immersed in seawater

A new method to measure adhesion force, or that force that holds surfaces in molecular contact, is used to quantify the effect of natural surface films on adhesion between surfaces immersed in seawater. Results of measurements demonstrate that bacterial films significantly modify surface adhesion and that the resulting interfacial force is nearly independent of bulk material composition. Where surfaces are hydrophilic and of similar surface charge, as is typical of surfaces in seawater, formation of bacterial films should cause a marked increase in adhesion force. A reduction in adhesion force observed for surfaces in seawater of low biological activity is attributed to adsorption of a surface active conditioning film, while a further reduction in adhesion force sometimes observed under bloom conditions remains unexplained. A broad range of adhesion forces corresponding to different sites on a surface can be understood in terms of surface microheterogeneity. Adhesion force measurements may be key for understanding steady state aggregate size, the timing of the sinking of blooms, and formation of oxygen-minimum layers. Understanding the nature of surfaces immersed in seawater is essential to understanding particle aggregation and disaggregation and the effects that these processes have on sedimentation of particulate matter in the ocean. The dynamics of particles in seawater has been the subject of many experimental and theoretical treatments in the

Natural surface film studies in shallow coastal waters of the Baltic and Mediterranean Seas

Natural surface film experiments in shallow offshore waters of the Baltic and Mediterranean Seas were carried out in 1990 and 1991 under calm sea conditions, using a novel device for sampling and studies of monolayer properties [ Pogorzelski, 1992a, Review of Scientific Instruments, 63(7), 3773–3776 ]. The sampler “cuts out” an undisturbed film-covered region, 8 cm in thickness, to perform force-area measurements of untreated water samples. Intercomparisons of the isotherm features for water samples from 0.5 m depth and those collected by the sampler, at the same location and time, have indicated significant differences. The selected film parameters (elasticity modulus, film homogeneity represented by the filling factor, isotherm reversibility, the mechanical energy transfer through surface films from isotherm hysteresis measurements, and film formation rate) are subjected to large seasonal and spatial variability. Averaged natural film signatures found in the Baltic and Mediterranean and reported by others ( Pelinovsky and Talipova, 1990, SAS films on the sea surface, SSSR Academy of Sciences) for the Black Sea differ significantly from each other.

Isotherms of natural sea surface films: A novel device for sampling and properties studies

A double-walled submersible sea surface film sampler which ‘‘cuts out’’ an undisturbed film-covered area has been built for force-area isotherm studies of untreated water samples. Preliminary results on static and dynamic surface properties of naturally formed films present in coastal zones of the Baltic Sea are presented and discussed in reference to water samples collected in a bottle (depth of 20 cm) at the same site and time, which in turn significantly differ from each other. The new sampler also allows a few statements of oceanographic relevance on the film homogeneity (i.e., film filling factor) and the energy transfer through surface films from isotherm hysteresis measurements.

Modulation of the Spectra of Short Gravity Waves by Sea Surface Films: Slick Detection and Characterization with a Microwave Probe

Abstract Organic sea surface films are often indicators of surface and subsurface processes that influence their formation and their spatial and temporal distribution. The films modify the physics of the sea surface and influence remotely sensed optical and microwave imagery. Natural sea surface films have been detected, charted, and characterized by measurements of the short-gravity spectra of wind waves during three experimental periods, one in the Sicilian Channel, and two in the Gulf of Maine. Wind wave spectra with and without organic films were measured in situ with a microwave probe. These spectra were analyzed to characterize the elasticity moduli of the wave modulating films using a recently developed theory. Theory and experiment are in good agreement. It has been demonstrated that the microwave probe can detect the presence of sea surface films and their visco-elastic properties by the measurement of their wave-modulating effects. The data collected by this system can possibly be further interp...

Natural surface films on GeS

Natural surface films on GeS

A new method to evaluate expansion/compression stress—strain properties of surface films of biological surfactants

Surface films exhibit time-dependent behavior when undergoing rapid deformations. This is particularly true of extracts of the pulmonary alveolar lining layer. Stress—relaxation is characteristic of both fluids and solids (viscoelastic). In this study, material properties characterizing the responses of surface films relevant to alveolar lining layer function are evaluated by simple extension, or compression, stress—relaxation using models modified from those used on rubber polymers. This enables the time-dependent behavior of viscoelastic materials undergoing simple extension, or compression, stress—relaxation to be analyzed in a new way, yielding several material properties as functions of time (i.e. viscosity, elasticity, compressibility and relaxation time) simply, within the same experiment. The new method was applied to both synthetic (dipalmitoylphosphatidylcholine) and natural (pulmonary lavage) surface films. Precise data obtained by several other, more cumbersome methods agreed well with that obtained in a single, less cumbersome, experiment with our method. Our results show that during surface expansion the natural film has lower elastance, though relaxation time of both films is similar. The synthetic film has greater resistance to deformation (dilatational viscosity). When compressed to levels above the point of film collapse both materials initially behave similarly. The synthetic film becomes more rigid over time. Compression to levels below the point of film collapse causes elastance to increase greatly in both materials while elastance is significantly larger in the natural film. This strongly suggests that under high compression the configurations of the surfaces are dissimilar.