Flowing Water Conditions Research Articles

A comprehensive electrochemical evaluation of the corrosion inhibition by sodium silicate on carbon steel

Sodium silicate (SS) is investigated as a sustainable green corrosion inhibitor for carbon steel in saline environment under both static and dynamic flow conditions. Potentiodynamic scans and Electrochemical Impedance Spectroscopy revealed that silica is both highly efficient in static and flowing water conditions (up to 98 and 99% resp.). An increased inhibition efficiency (IE) is seen as a function of silica concentration as a result of decreased defects in the resulting silica film (Mott–Schottky). The film forming behaviour changes at increasing flow speed, producing a more defect-rich structure at both low and high silica concentration, although showing improved IE at intermediate flow speed for low SS concentrations.

Application of multilevel immobilized carbon nanotube/sulfur doped carbon nitride composite photocatalytic coating for Cr6+(aq.) reduction

The difficulty in immobilizing carbon nitride (GCN), and the decrease in sorption capacity and photocatalytic performance after immobilization process have become two major bottlenecks limiting the practical application of carbon nitride in photocatalysis field. Herein, sulfur doped carbon nitride and carbon nanotube composite photocatalysts (CNT/SCN) with high sorption, light harvesting capacity, and reduction efficiency was synthesized by two-step solvothermal method. Furthermore, CNT/SCN composite photocatalytic coating with porous three-dimensional surface morphology was prepared using double liquid phase high speeding spray-deposition method. The coverage rate of CNT/SCN coating was calculated to be 55 %, which was 1.57 times higher than that of GCN coating. The introduction of carbon nanotube (CNT) significantly improved the sorption capacity of photocatalytic coating for hexavalent chromium (Cr6+(aq.)). The reduction efficiency of the composite coating towards Cr6+(aq.) under flowing water conditions was further investigated. The CNT/SCN coating exhibited a high removal efficiency of 84.7 % for Cr6+(aq.) (500 mL, 10 mgL−1) within 8 h, which was 29 times than that of GCN coating. The reduction efficiency of CNT/SCN photocatalytic coating remained above 75 % after three cycles of testing. This research provides theoretical basis and data support for the immobilization application of photocatalysts.

Changes in the level of biofilm development significantly affect the persistence of environmental DNA in flowing water

As one of the powerful tools of species biomonitoring, the utilization of environmental DNA (eDNA) technology is progressively expanding in both scope and frequency within the field of ecology. Nonetheless, the growing dissemination of this technology has brought to light a multitude of intricate issues. The complex effects of environmental factors on the persistence of eDNA in water have brought many challenges to the interpretation of eDNA information. In this study, the primary objective was to examine how variations in the presence and development of biofilms impact the persistence of grass carp eDNA under different sediment types and flow conditions. This investigation encompassed the processes of eDNA removal and resuspension in water, shedding light on the complex interactions involved. The findings reveal that with an elevated biofilm development level, the total removal rate of eDNA gradually rose, resulting in a corresponding decrease in its residence time within the mesocosms. The influence of biofilms on the persistence of grass carp eDNA is more pronounced under flowing water conditions. However, changes in bottom sediment types did not significantly interact with biofilms. Lastly, in treatments involving alternating flow conditions between flowing and still water, significant resuspension of grass carp eDNA was not observed due to interference from multiple factors, including the effect of biofilms. Our study offers preliminary insights into the biofilm-mediated mechanisms of aquatic eDNA removal, emphasizing the need for careful consideration of environmental factors in the practical application of eDNA technology for biomonitoring in natural aquatic environments.

Experimental investigation on grout propagation in poured aggregates for controlling water inrush in tunnels with flowing water

BackgroundIn recent years, the technology of blocking and grouting of has been widely used in the treatment of groundwater inrush in tunnels in China’s mines. Studies have been carried out on the aggregates pouring under hydrodynamic conditions; however, there is lack of studies of the grout propagation in the pouring aggregate mass, which formed in the earlier stage. This paper presents an experimental investigation of grout propagation in poured aggregates with flowing water, which focused on the second stage, i.e., the grouting stage, after the first stage of aggregates pouring in the salvage of an inundated underground tunnel.ResultsIn this work, a visualized tunnel replica with flowing water was adopted to investigate the main effects of sealing efficiency, water pressure variation, propagation mechanism during grouting in the poured aggregates with different grain sizes and flowing water conditions. A series of experiments with orthogonal array design were carried out, and the propagation of cement/sodium silicate and the change characteristics of fluid pressure in the tunnel were obtained. The results show that the main effects on the sealing efficiency of grouting in poured aggregates with flowing water in a descending order is cement/sodium silicate ratio, relative density of aggregates, particle size distribution of aggregates, and final water pressure difference of both ends of aggregates segment. The cementation form of grouted aggregates has four types; T shape, H shape, O shape and shell shape. The main mode of grout propagation includes three types; permeation filling mode, compaction- permeation mode, and compaction-fracturing mode, which reflects the influence of grain size, density of aggregates and grouting pressure. The variation of water pressure can be divided into four categories; overall ascending type, step ascending type, concave type, and convex type. The curve type mainly depends on water pressure, water flowrate, relative density and grain size of aggregates, gel time, propagation mechanism of grout.ConclusionThe flow rate after grouting has decreased by approximately 60% to 86% compared to that before grouting, bulk hydraulic conductivity decreased by more than 80%, reflecting a great improvement of the sealing efficiency in the grouting stage after the pouring stage. The research on grout propagation in different graded aggregate mass has guiding significance for the design and construction of a rapid disaster treatment after groundwater inrush.

Water flow plays a key role in determining chemical biodegradation in water-sediment systems

Before agrochemicals can be registered and sold, the chemical industry is required to perform regulatory tests to assess their environmental persistence, using defined guidelines. Aquatic fate tests (e.g. OECD 308) lack environmental realism as they are conducted under dark conditions and in small-scale static systems, which can affect microbial diversity and functionality. In this study, water-sediment microflumes were used to investigate the impact of these deficiencies in environmental realism on the fate of the fungicide, isopyrazam. Although on a large-scale, these systems aimed to retain the key aspects of OECD 308 tests. Tests were carried out under both a non-UV light-dark cycle and continuous darkness and under both static and flowing water conditions, to investigate how light and water flow affect isopyrazam biodegradation pathways. In static systems, light treatment played a significant role, with faster dissipation in illuminated compared to dark microflumes (DT50s = 20.6 vs. 47.7 days). In flowing systems (DT50s = 16.8 and 15.3 days), light did not play a significant role in dissipation, which was comparable between the two light treatments, and faster than in dark static microflumes. Microbial phototroph biomass was significantly reduced by water flow in the illuminated systems, thereby reducing their contribution to dissipation. Comprehensive analysis of bacterial and eukaryotic community composition identified treatment specific changes following incubation, with light promoting relative abundance of Cyanobacteria and eukaryotic algae, and flow increasing relative abundance of fungi. We conclude that both water velocity and non-UV light increased isopyrazam dissipation, but the contribution of light depended on the flow conditions. These differences may have resulted from impacts on microbial communities and via mixing processes, particularly hyporheic exchange. Inclusion of both light and flow in studies could improve the extent they mimic natural environments and predict chemical environmental persistence, thus bridging the gap between laboratory and field studies.

Comparison of adhesive joint strength of laser fabricated dimple textured Al–Mg alloy in different environment

Joining of aluminium alloys using adhesives has got tremendous applications in aviation, marines, and unmanned aerial vehicles. Surface preparation plays a crucial role in the adhesive joining of two surfaces. In this research work, the nanosecond fibre laser was used to create dimple-shaped textures on aluminium–Mg alloy (AA5754). Dimple-shaped textures were created under three different atmospheric conditions. Experiments were performed in open-air conditions, under static water conditions, and under flowing water conditions. Texture depths differed by varying the scanning speed of laser beam. Texture pitch was also varied at two different levels, that is 300 [Formula: see text]m and 400 [Formula: see text]m in both texturing directions. Two different scanning speeds of 2.5 and 5 mm/s of the laser beam were investigated. Surface contact angle of each sample was evaluated using a goniometer to measure surface hydrophobicity/ hydrophillicity. Surface roughness and dimensions of dimples were measured using a digital microscope. Scanning electron microscopes were used to evaluate the morphology of textured surfaces. An epoxy-based adhesive (partite) was uniformly spread over textured zones and samples for standard tensile tests were prepared as per ASTM. Shear lap tensile tests were carried out to evaluate the shear lap strength of each joint on a universal testing machine. Surfaces prepared in static water conditions and flowing water conditions resulted in completely different morphology compared to open-air processing. It was observed that dimple patterns fabricated under flowing water conditions had the highest bonding strength among all the three processing environments.

Underwater laser texturing for enhanced adhesive joint bonding strength of Al-Mg alloy

In this research work, nanosecond pulsed fiber laser texturing was performed on Aluminum-Mg alloy (AA5754). Effect of laser texturing as a surface pre-treatment method in adhesive bonding process was investigated in details. Laser texturing was performed in under open air condition, under static water condition and under flowing water conditions. Grid shaped textures were fabricated on Al-Mg alloy work-pieces. The geometrical parameters of grid texturing were varied at two levels. Pitch of the lines were kept at 300 and 400 μm in both horizontal as well as vertical directions. Scanning speed of laser texturing process was also varied at two levels that is 2.5 and 5 mm/s. Total four experiments were conducted in each atmospheric conditions. Surface roughness and water contact angle of each surface was evaluated. Surfaces were also characterized using scanning electron microscope. Lap shear strength of each samples were evaluated using a universal tensile testing machine (UTM). Failed surfaces were analyzed to investigate the mode of failure. It was observed that the textures created in flowing water conditions resulted in cohesive mode of failure while samples fabricated in open air and in under static water conditions failed in adhesive and mixed mode respectively. Samples prepared in flowing water conditions resulted in higher lap shear strengths compared to static water, open air, and plain surfaces.

Does swimming activity influence gas bubble trauma in fish?

AbstractTotal dissolved gas (TDG) supersaturation from sources such as hydroelectric dams can cause harmful bubble growth in the tissues of aquatic animals, known as gas bubble trauma (GBT). Locomotion is known to exacerbate bubble growth in tissues during decompression under certain conditions (such as in diving animals), possibly because of increased bubble nucleation. As with decompression sickness, GBT is caused by the supersaturation of tissues with gas, and thus we hypothesize that locomotion promotes bubble nucleation in the tissues of fish exposed to TDG supersaturation. Many previous laboratory studies have tested the effects of TDG on fish exposed to low‐velocity, non‐directional flow, whereas fish in field conditions are exposed to higher‐velocity flows and are likely more active. Therefore, it is important to understand the effects of locomotion on GBT to apply laboratory results to active fish in field conditions. We exposed rainbow trout (Oncorhynchus mykiss) to either control (100% TDG) or TDG supersaturation (123% TDG) in either static or flowing water conditions (1.8 Bl/s) and recorded time to 50% loss of equilibrium (LOE). We observed no statistically significant difference in time to 50% LOE between flow conditions. Given the lack of statistically significant difference between static and flowing water, our findings indicate that results from GBT experiments on rainbow trout in non‐directional flow are applicable to more active individuals.

Plugging efficiency of pouring aggregates through multiple boreholes into an inundated tunnel to prevent groundwater inrush disasters

This paper presents an experimental investigation of the plugging efficiency of aggregate pouring through multiple boreholes under flowing water conditions into an inundated mine tunnel. Aggregate pouring into an inundated mine tunnel has been widely used and constitutes the premise for the salvage of flooded underground mines through further grouting. However, corresponding in-depth research is relatively limited due to the concealment of underground engineering. A visual experimental setup for aggregate pouring into a tunnel replica was built based on the theory of similarity between sediment movement and slurry pipeline transportation. Four factors, each with four levels, including the aggregate particle size (0.25–0.5, 0.5–1, 1–2 and 2–5 mm), distance between boreholes (0.5, 0.75, 1 and 1.5 m), initial water flow rate (0, 1.5 × 10−2 m/s, 2.4 × 10−2 m/s and 3 × 10−2 m/s) and tunnel inclination (0°, 3°, 5° and 8°) were selected in orthogonal experiments to investigate the plugging efficiency. Range and variance analysis of the four-level orthogonal array experimental results indicated that the factors influencing the plugging efficiency, varying between 83.96 and 98.15%, could be ranked in descending order as the initial water flow rate, aggregate particle size, distance between boreholes and tunnel inclination. The former two factors yielded a more significant influence than that of the latter two factors. The measured water pressure difference ranging from 16 to 32% between the front and back ends of the formed aggregate mass in the pouring process indicated that there remained a high resistance to water flow, even if the aggregate mass was not capped but reached a certain length. Plugging criteria for aggregate pouring into horizontal and inclined tunnels were then proposed. Moreover, the optimal distance between boreholes to form an effective bulkhead was determined, which could be defined as the distance between boreholes when the aggregate mass exhibits the fastest build-up and the plugging capacity is reached.

Investigation on grouting diffusion in inclined fracture with flowing water conditions

Investigation on grouting diffusion in inclined fracture with flowing water conditions

Vertical migration of cesium in weathered granite soil under flowing water condition depending on Cs concentration and states of dissolved organic matter

After the accident at the Fukushima Daiichi nuclear power plant in Japan, the migration of radioactive cesium (Cs) in soils has become a crucial issue since this can negatively affect human health and the surrounding environment. Dissolved organic matter (DOM) may have different influences on Cs migration in soils depending on Cs adsorption sites with different selectivity. It is unclear how DOM affects the rapid migration of Cs in soils under flowing water conditions during rainfall events. This study evaluated the effects of DOM on Cs migration in weathered granite soil depending on Cs adsorption sites by conducting laboratory experiments under different DOM conditions and Cs concentrations in the liquid phase.Cs concentration can affect the fraction of Cs adsorbed onto differently selective sites, and DOM can have different influences on Cs migration in the soil accordingly. Under condition of high-Cs concentration, the DOM adsorbed on the soil reduced Cs migration due to increasing Cs electrostatic adsorption to less selective sites in the soil. Meanwhile, under low-Cs concentration, the DOM adsorbed on the soil enhanced Cs migration because the DOM on the soil decreased the Cs adsorption to highly selective sites. Furthermore, DOM in the liquid phase detached the Cs adsorbed on the less selective sites and enhanced Cs migration in the soil, regardless of the Cs concentration.

NMR-based investigation on deterioration characterization of gypsum breccia in surrounding rock undergoing flow-by wetting-drying cycles

In underground engineering, many geological hazards caused by the cyclic actions of wetting and drying occur under flowing water conditions. Understanding the evolution of the strength and pore structure characteristics of some environmentally sensitive surrounding rocks under these conditions is critical for maintaining the long-term stability of tunnels. In this study, the deterioration characteristics of gypsum breccia in the surrounding rock of an anonymous tunnel in Shanxi under the flow-by wetting-drying cycles were investigated. After being treated by wetting-drying cycles with different flow conditions (0 and 10 l/h), the evolution characteristics of the pore structure of gypsum breccia were characterized using the nuclear magnetic resonance (NMR) technique. The relationship between the P-wave velocities and the pore characteristics of gypsum breccia was studied. The results showed that the water flow would accelerate the deterioration process of gypsum breccia in the wetting-drying process. The microstructure damage of gypsum breccia was induced by the combined action of the wetting-drying cycles and water flow. There was a significant correlation between the attenuation of P-wave velocity and the development of the pore structure of gypsum breccia. The study can provide references for the engineering design of tunnels in gypsum breccia.

Behavioural response of downstream migrating European eel (Anguilla anguilla) to electric fields under static and flowing water conditions

Like many other species of diadromous fish, the European eel (Anguilla anguilla) is threatened by entrainment at hydropower intakes and resultant injury and mortality during passage through turbines. Historically, physical screens have been installed to prevent European eel access to intakes but these are not wholly effective and can incur high costs of construction and maintenance, especially when regulations require screen retrofits with increasingly fine mesh. There is interest in the use of potentially less expensive behavioural guidance methods to block or guide eel movements. Electric barriers have been developed to guide several species of fish, but information relating to their effectiveness for European eel is limited. In this study, two experiments were conducted to quantify the response of downstream migrating adult (silver-phase) European eel to electric fields and the effectiveness of electricity to block movements. First, a static water tank was used to identify the field strengths (Vcm−1) required to induce threshold responses for three key behaviours (twitch, loss of orientation and tetany) across three different pulsed direct current (PDC) electric waveforms (single pulse-2 Hz, double pulse-2 Hz and single pulse-10 Hz) (Experiment 1). Second, a recirculatory flume was used to investigate how avoidance responses (acceleration, change in orientation and rejection) differed between two water velocity regimes [0.5 ms−1 and 1.0 ms−1] and two field strengths [≈ 0.15 Vcm−1 and ≈ 0.3 Vcm−1] identified during the first experiment (Experiment 2). In Experiment 1, lower electric field strengths were needed to elicit tetany under the single pulse-10 Hz and single pulse-2 Hz compared to the double pulse-2 Hz waveform, but there was no effect of waveform for the other behaviours. In Experiment 2, avoidance was less frequent (31.4%) under the high compared with the low (74.5%) velocity, but electric field strength did not influence the response exhibited. This study provides insights into the potential use of electric fields to deter European eel. The effectiveness of electric barriers to block downstream migrating eel are likely limited at higher water velocities.

Effects of the dissolved organic matter on Cs transport in the weathered granite soil

It is important to understand the migration of Cesium (Cs) in soils, particularly after the nuclear power plant accident at Fukushima Dai-ichi, Japan. Dissolved organic matter (DOM) is one of factors affecting the migration of Cs in soils under flowing water conditions. We investigated the effect of DOM on the migration of Cs adsorbed to the clay planar site via laboratory column experiments. The sequence of DOM application had a significant influence on Cs transport in the soil. When DOM was applied concurrently with or prior to Cs application, the DOM adsorbed on to the clay planar site adsorbed onto the soil solid surface and enhanced Cs adsorption; consequently, it slowed Cs migration in the soil. In particular, in the case of DOM loaded prior to the application of Cs solution, a noticeable delay in Cs migration was observed. On the other hand, when DOM was applied to the soil where the Cs solution had been previously applied, the DOM desorbed Cs from the soil. DOM in liquid phase enhanced the migration of Cs through the formation of binding to organic matter. Majority of Cs affected by DOM was the exchangeable fraction that adsorbed to the clay planar site. In other words, DOM attached to the soil would adsorb Cs as a easily exchangeable form and depress migration of Cs. On the other hand, DOM in the soil solution may up take adsorbed Cs from the soil and enhanced the transport in the form of Cs bound to DOM.

Surface modification of titanium alloy using hBN powder mixed dielectric through micro-electric discharge machining

In the present study, hard, wear, and corrosion resistance coating is deposited on titanium alloy with hexagonal boron nitride powder (avg. size 70 nm) suspended in deionized water by micro-electro discharge coating process. The influence of input process parameters on surface integrity, wear properties, and corrosion resistance is studied. XRD analysis of coating surface shows the presence of phases such as BN, Al2O3, TiN, TiAlN, TiO, and CuO. Micro-hardness of the coating surface increases by five times as compared to titanium alloy (parent material). At the parameter settings of 60 V, 0.7 duty factor, and 12 g/l, the maximum deposition rate of 5.65 ± 0.1 × 10−4 g/min and recast layer thickness of 13.1 μm is obtained. Pin on disk wear test results reveal the reduction of wear rate of the coated surface to one-fourth of that of the base material. The average coefficient of friction (COF) for the deposited BN surfaces reduces to 0.26 from 0.4 (substrate material). Corrosion resistance of the coated surface is found to be 1.24 μm/year in flowing water conditions and 1.07 μm/year in stagnant water whereas for the parent material it is 5.92 μm/year in flowing water condition and 4.89 μm/year for stagnant water condition.

Correction of metabolic parameters and unit process performance data. Part I. derivation of equations

An understanding of the dynamics of oxygen consumption by the culture animal is needed to properly design and operate an aeration system. In commercial production systems, oxygen consumption rates are typically determined under flowing water conditions. A simple mass balance on a flow-through system results in the following equation in terms of mg oxygen/(kg fish h):Oxygen Consumption=-flowmass of fish(Ctin-Ct)+rearing volumemass of fishdCdtThe formula commonly used to estimate oxygen consumption is biased because it only considers the first term. The error in the oxygen consumption rate depends primarily on the rate of change of oxygen within the rearing unit (dC/dt) and is larger when the oxygen consumption rate has a significant variation with time. This same lag response can also bias other metabolic rates (carbon dioxide, ammonia, solids) and the computation of performance and efficiencies of unit processes such as biofilters and solids removal processes.While a number of approaches have been developed to correct oxygen consumption rates for the impact of this hydraulic lag, their accuracy has never been evaluated in any comprehensive manner and in many cases, their derivation is entirely lacking. To better understand their assumptions and limitations, the derivation of these correction approaches (and several new methods) have been clearly and comprehensively developed in this article. Without this background information, it is difficult to understand the differences between the approaches and their potential limitations. In companion paper, the accuracy of the correction equations and analysis assumptions will be evaluated.

Biomimetics: Highly Permeable Skin Patch with Conductive Hierarchical Architectures Inspired by Amphibians and Octopi for Omnidirectionally Enhanced Wet Adhesion (Adv. Funct. Mater. 13/2019)

In article number 1807614, Changhyun Pang and co-workers report highly air-permeable, water-drainable, and reusable skin patches with enhanced omnidirectional peel resistance and pulling adhesion, inspired by the toe pads of tree frogs and convex cups in the suckers of octopi. The patch can be utilized as flexible electrodes by coating reduced graphene oxides to monitor electrocardiography signals without delamination on skin in sweaty and even flowing water conditions.

Neptunium(V) transport in granitic rock: A laboratory scale study on the influence of bentonite colloids

In the present study neptunium(V) uptake by crystalline granitic rock (Kuru Grey granite) and the role of stable and mobile bentonite colloids (MX-80) on the migration of neptunium(V) was investigated. Two different experimental setups were utilized, batch-type experiments under stagnant conditions and column experiments under flowing water conditions. The uptake of 10−6 M neptunium(V) by 40 g/L crushed granite in 10 mM NaClO4 was found to be pH-dependent, whereas neptunium(V) uptake by MX-80 bentonite colloids (0.08–0.8 g/L) was pH-independent up to a pH-value of approximately 11. Column experiments were conducted in the presence and absence of colloids at two pH values (pH = 8 and 10) and two flow rates (0.3 and 0.8 mL/h) in 10 mM NaClO4. The injected neptunium(V) concentration was 2 × 10−4 M and the colloid concentration ranged from 0.08 to 0.32 g/L. The properties of the flow field in the columns were investigated with a conservative chloride tracer, at the same two flow rates of 0.8 and 0.3 mL/h. The resulting breakthrough curves were modeled using the analytical solution of advection–matrix diffusion equation. A tailing of neptunium(V) breakthrough curves in comparison to the conservative tracer was observed, which could be explained by a slightly higher retardation of neptunium(V) in the column caused by sorption on the granite. The sorption was in general lower at pH 8 than at pH 10. In addition, the tailing was almost identical in the absence and presence of MX-80 bentonite colloids, implying that the influence of colloids on the neptunium(V) mobility is almost negligible.

Highly Permeable Skin Patch with Conductive Hierarchical Architectures Inspired by Amphibians and Octopi for Omnidirectionally Enhanced Wet Adhesion

AbstractAmphibian adhesion systems can enhance adhesion forces on wet or rough surfaces via hexagonal architectures, enabling omnidirectional peel resistance and drainage against wet and rough surfaces, often under flowing water. In addition, an octopus has versatile suction cups with convex cup structures located inside the suction chambers for strong adhesion in various dry and wet conditions. Highly air‐permeable, water‐drainable, and reusable skin patches with enhanced pulling adhesion and omnidirectional peel resistance, inspired by the microchannel network in the toe pads of tree frogs and convex cups in the suckers of octopi, are presented. By investigating various geometric parameters of microchannels on the adhesive surface, a simple model to maximize peeling strength via a time‐dependent zig‐zag profile and an arresting effect against crack propagation is first developed. Octopus‐like convex cups are employed on the top surfaces of the hexagonal structures to improve adhesion on skin in sweaty and even flowing water conditions. The amount of reduced graphene oxide nanoplatelets coated on the frog and octopus‐inspired hierarchical architectures is controlled to utilize the patches as flexible electrodes which can monitor electrocardiography signals without delamination from wet skin under motion.

Functionality and chemical stability of plasma polymer films exhibiting a vertical cross-linking gradient in their subsurface

Preserving the amount of amine groups in a plasma polymer film (PPF) immersed in water is crucial for biomedical applications such as, e.g., bio-sensing or tissue engineering. In this study, nanometer thick PPFs were deposited on a substrate by activation of NH3/C2H4 gaseous mixtures in a low pressure plasma. In particular, plasma deposition conditions were adjusted during film growth to create a vertical gradient in amine group functionality and cross-linking degree extending over a few nanometers of the PPF near its surface. As a result of the vertical gradient structure, undesired changes in wettability, in chemical composition, in surface charge and in topology of the ’gradient’ NH2-PPF were strongly reduced as observed over one week in water. In comparison, ‘conventional’ coatings, i.e. deposited at constant plasma conditions yielding the same chemical composition as the top layer of the gradient structure, revealed distinct surface restructuring effects. Albeit oxidation of the coatings was found to be inevitable, the gradient structure significantly decreased these aging effects of the NH2-PPF. To further highlight the benefits of the stabilizing structure in the coating's subsurface, investigations were carried out under flowing water conditions demonstrating the reduced degradation of the NH2-PPFs with vertical cross-linking gradient for realistic conditions.