Synthetic Surfaces Research Articles

Surface Regularity via the Estimation of Fractional Brownian Motion Index

The recent definition of fractional Brownian motions on surfaces has raised the statistical issue of estimating the Hurst index characterizing these models. To deal with this open issue, we propose a method which is based on a spectral representation of surfaces built upon their Laplace-Beltrami operator. This method includes a first step where the surface supporting the motion is recovered using a mean curvature flow, and a second one where the Hurst index is estimated by linear regression on the motion spectrum. The method is evaluated on synthetic surfaces. The interest of the method is further illustrated on some fetal cortical surfaces extracted from magnetic resonance images as a means to quantify the brain complexity during the gestational age.

Topography and Expansion Patterns at the Biofilm-Agar Interface in Bacillus subtilis Biofilms.

Bacterial biofilms are complex microbial communities which are formed on various natural and synthetic surfaces. In contrast to bacteria in their planktonic form, biofilms are characterized by their relatively low susceptibility to anti-microbial treatments, in part due to limited diffusion throughout the biofilm and the complex distribution of bacterial cells within. The virulence of biofilms is therefore a combination of structural properties and patterns of adhesion that anchor them to their host surface. In this paper, we analyze the topographical properties of Bacillus subtilis’ biofilm-agar interface across different growth conditions. B. subtilis colonies were grown to maturity on biofilm-promoting agar-based media (LBGM), under standard and stress-inducing growth conditions. The biofilm-agar interface of the colony type biofilms was modeled using confocal microscopy and computational analysis. Profilometry data was obtained from the macrocolonies and used for the analysis of surface topography as it relates to the adhesion modes present at the biofilm-agar interface. Fluorescent microspheres were utilized to monitor the expansion patterns present at the interface between the macrocolonies and the solid growth medium. Contact surface analysis reveals topographical changes that could have a direct effect on the adhesion strength of the biofilm to its host surface, thus affecting its potential susceptibility to anti-microbial agents. The topographical characteristics of the biofilm-agar interface partially define the macrocolony structure and may have significant effects on bacterial survival and virulence.

Random deposition with spatially correlated noise (RD-SCN) model: Multi-affine analysis

Abstract We study the random deposition model with long-range spatially correlated noise. In this model the particles deposit in a power-law distance of each other as Δ i , j = i n t [ u − 1 2 ρ ] , where u is chosen randomly over the range (0,1) and ρ is the correlation strength. The results show that the enhancement of ρ exponent is accompanied by the appearance of irregularities and jumps in the height fluctuations. In spite of scaling exponents dependent to correlation strength in other linear and non-linear growth equations, enhancement of the correlation strength, does not change the growth exponent β = 1 / 2 . As the short-range correlations in growth equations result in roughness saturation, the results show that the long-range correlations in this growth model does not saturate the interface width for any system size. The fractal analysis of the height fluctuations performed via the multi-fractal detrended fluctuation analysis (MF-DFA) revealed that the synthetic rough surfaces with ρ = 0 are mono-fractal with the Hurst exponent H = 0.5 . It verifies the un-correlated fluctuations in the simple random deposition model. For the correlation strengths in the range [0,1], the Hurst exponent increases in the range [ 1 2 , 1 ) with a mono-fractal behavior. In the critical exponent of ρ c , multi-affinity is occurred. For ρ > ρ c = 1 the mono-fractal feature of the height fluctuations tends to the multi-affine one and the strength of multi-affinity increases by enhancement of ρ exponent. The results show that the observed multi-affinity is because of deviation from the normal distribution and appearance of correlations among small and large fluctuations.

Surface Modification With Gelatin For Polyurethane Vascular Grafts: A Review

The means for developing synthetic vascular grafts to replace blood vessels is increasing extensively because of the limited supply of autologous vessels. Synthetic polymers as the alternatives still suffer from restenosis and thrombus formation. Natural polymers, on the other hand, are commonly biocompatible and biodegradable, compliment the synthetic ones. Blending, grafting and coating of natural polymers have been proposed to improve surface properties of synthetic polymers. Gelatin is a promising candidate to help improving synthetic vascular grafts surface owing to its ability to promote cell adhesion without promoting platelet aggregation at its surface. In this review, several techniques to incorporate gelatin onto synthetic polymers, mainly polyurethane, for vascular grafts application are summarized, together with the recent updates and potential development in the future.

Lipid-Bilayer Assemblies on Polymer-Bearing Surfaces: The Nature of the Slip Plane in Asymmetric Boundary Lubrication.

Phospholipid–macromolecule complexes have been proposed to form highly efficient, lubricating boundary layers at artificial soft surfaces or at biological surfaces such as articular cartilage, where the friction reduction is attributed to the hydration lubrication mechanism acting at the exposed, hydrated head groups of the lipids. Here we measure, using a surface force balance, the normal and frictional interactions between model mica substrates across several different configurations of phosphatidylcholine (PC) lipid aggregates and adsorbed polymer (PEO) layers, to provide insight into the nature of such lubricating boundary layers in both symmetric and especially asymmetric configurations. Our results reveal that, irrespective of the configuration, the slip plane between the sliding surfaces reverts wherever possible to a bilayer–bilayer interface where hydration lubrication reduces the friction strongly. Where such an interface is not available, the sliding friction remains high. These findings may account for the low friction observed between both biological and synthetic hydrogel surfaces which may be asymmetrically coated with lipid-based boundary layers and fully support the hydration lubrication mechanism attributed to act at such boundary layers.

Mechanical and Dynamic Behavior of an Elastic Rubber Layer with Recycled Styrene-Butadiene Rubber Granules.

This study evaluates the tensile properties, including the tensile strength and elongation at break, and dynamic behavior, including shock absorption and vertical deformation, of an elastic rubber layer in synthetic sports surfaces produced using waste tire chips containing styrene-butadiene rubber (SBR). The primary variables of the investigation were the number of compactions, resin–rubber granule ratio, and curing conditions, such as aging, the temperature, and the relative humidity. The test results showed an increase in the tensile strength of the elastic rubber layer with recycled SBR as the number of compactions, resin–rubber granule ratio, curing period, and temperature increased, while the elongation at break was affected by the curing temperature and period. Shock absorption and vertical deformation decreased with an increasing resin–rubber granule ratio and number of compactions due to the increased hardness. However, these properties were not significantly affected by the curing conditions. Furthermore, the test results indicated that the curing temperature has a pronounced effect on the tensile properties of the elastic rubber layer, and maintaining the appropriate curing temperature—approximately 50 °C—is a possible solution for improving the relatively low tensile properties of the elastic rubber layer.

Thromboxane Synthesis and Platelet Protein Release During Simulated Extracorporeal Circulation

Platelet secretion induced by certain soluble aggregating agents is associated with thromboxane formation. Activation of platelets by artificial surfaces may involve similar biochemical pathways. Therefore, we monitored platelet release and formation of thromboxane B2. the stable end-product of thromboxane A2, during simulated extracorporeal circulation where contact between blood and synthetic surfaces is extensive. Fresh heparinized human blood was recirculated for 2 hr at 37°C at 1 liter/min in circuits (0.95 sqm) constructed of standard silicone rubber components (0.1 sqm) and a spiral coil membrane oxygenator (0.85 sqm). Within 2 min of recirculation, plasma levels of the platelet-specific protein, low-affinity platelet factor 4 (LA-PF4) rose from <1.5% to 11 % ±3% SEM of that which was released by triton X-100, indicating significant release of platelet α-granule contents. This occurred despite the absence of detectable thromboxane B2 in plasma (<0.5 pmole/ml). Between 2 and 15 min, plasma levels of LA-PF4 increased from 11% to 42% ± 3%, and plasma thromboxane B2 concentrations rose to 3.2 pmole/ml. Subsequently, thromboxane B2 levels continued to rise to 9.8 pmole/ml by 2 hr. Thromboxane B2 was not detected in blood from donors who had ingested aspirin, and the extent of platelet secretion was reduced by about 50% (25% at 2 hr). Thus, although a component of platelet granule release during extracorporeal recirculation appears to be associated with thromboxane synthesis, considerable release of LA-PF4 may occur by thromboxanβ-indβpen-dent pathways.

Ultrastructural features of the double capsulated connective tissue around silicone prostheses.

The implantation of breast prostheses for both aesthetic and reconstructive purposes has been growing exponentially in the last 20 years. Safety and prosthesis lifespan are majorly debated issues in relation to the correlated long-term complications. Mainly the periprosthetic capsule that develops around the implant is often the cause of complications and particularly for macrotextured silicone breast implants. Some reports have tried to elucidate the mechanism by which macrotextured silicone implants undergo damage and cause double capsule formation. In this study, we investigated the morphological characteristics of double capsule of macrotextured implants surgically removed from patients. With the use of microscopy techniques, this work analyzed the newly formed tissue observed in the interaction between synthetic and biological surfaces.

Numerical Simulation for Rock Fracture Viscoelastic Creep under Dry Conditions

In many rock engineering projects such as hydrocarbon extraction and geothermal energy utilization, the hydraulic and mechanical behavior of rock fractures significantly affects the safety and profitability of the project. In field conditions, the hydraulic and mechanical behavior of rock fractures changes with time (the rock fractures creep), and this creep is not negligible even under dry conditions. In addition, creep is strongly affected by the rock fracture surface geometry. However, there is not much literature systematically studying the effect of surface geometry on rock fracture creep under dry conditions. This paper presents the results of a numerical study considering the effect of surface geometry on rough fracture viscoelastic deformations. An in-house numerical code has been developed to simulate the viscoelastic deformation of rough fractures. In addition, another numerical code has been developed to generate synthetic rough fracture surfaces by systematically changing the surface roughness parameters: the Hurst exponent, mismatch length, and root mean square roughness. The results indicate that by increasing the Hurst exponent or decreasing the mismatch length or decreasing the root mean square roughness, the fracture mean aperture decreases, and the contact ratio (number of contacting cells/total number of cells) increases faster with time.

Enhanced GPR data interpretation to estimate in situ water saturation in a landfill

Research was completed to show that using the complex refractive index model (CRIM) to interpret GPR data can improve the estimation of in situ water content of the waste in the landfill. Literature shows that the Topp equation is normally used to analyse GPR data, despite the fact it fails to consider porosity and other properties of the landfill material or soil that can affect the electromagnetic properties of the material. The application of (CRIM) overcomes these limitations and more. Previously measured field GPR data were reanalyzed with CRIM and supported by synthetic GPR data to show that CRIM provides a better prediction of the water content of the landfill material.Further enhancement of GPR data interpretation was implemented by optimizing the frequency of the GPR scan and determining the ideal offset separation distance between the transmitter and the receiver using sensitivity tests. The sensitivity tests were based on synthetic 2D surface based-reflection GPR data sets generated by MATLAB®. The sensitivity results showed that the optimum frequency was 1 GHz, with an ideal offset distance of 0.75 m. After using the optimized values, it was possible to obtain a percentage of error of 1% between modelled water saturation and GPR measured water saturation.

Efficient removal of diclofenac from surface water by the functionalized multilayer magnetic adsorbent: Kinetics and mechanism

Developing robust and effective adsorbent for removing ubiquitous pharmaceutical diclofenac (DCF) from the aquatic environment is vitally important for environmental safety. Hence, a novel chitosan-based multilayer adsorbent (FCS-PD) with magnetic separation ability and surface functionality was successfully assembled, which had countless potential for removing contaminants from water. A series of instrumental technologies were performed to demonstrate the physicochemical properties of FCS-PD. Its adsorption performance toward DCF removal was comprehensively evaluated in synthetic water and surface water. The effects of microplastics, inorganic ions and humic acid on the adsorption were investigated. The maximum adsorption capacity of FCS-PD was calculated as 434.78 mg/g under neutral conditions, exhibiting superior adsorption performance than most reported adsorbents. The DCF in surface water was practically removed at low concentration (50 μg/L). FCS-PD presented a multistage kinetics controlled by chemisorption and intraparticle diffusion, which was emphasized by the pseudo-second-order kinetic and intra-particle diffusion analysis. After five cycles of adsorption and regeneration, the adsorption capacity only decreased by 9.9%, indicating the satisfactory regeneration of FCS-PD. The analysis of high-resolution X-ray photoelectron spectroscopic (XPS) and Fourier transform infrared spectroscopy (FTIR) revealed that the quaternary ammonium groups on the outer layer and the amino and hydroxyl groups on the chitosan layer are involved in the capture of DCF under electrostatic force and hydrogen bonding.

Selective CO2 electrocatalysis at the pseudocapacitive nanoparticle/ordered-ligand interlayer

Enzymes feature the concerted operation of multiple components around an active site, leading to exquisite catalytic specificity. Realizing such configurations on synthetic catalyst surfaces remains elusive. Here, we report a nanoparticle/ordered-ligand interlayer that contains a multi-component catalytic pocket for high-specificity CO2 electrocatalysis. The nanoparticle/ordered-ligand interlayer comprises a metal nanoparticle surface and a detached layer of ligands in its vicinity. This interlayer possesses unique pseudocapacitive characteristics where desolvated cations are intercalated, creating an active-site configuration that enhances catalytic turnover by two orders and one order of magnitude against a pristine metal surface and nanoparticle with tethered ligands, respectively. The nanoparticle/ordered-ligand interlayer is demonstrated across several metals with up to 99% CO selectivity at marginal overpotentials and onset overpotentials of as low as 27 mV, in aqueous conditions. Furthermore, in a gas-diffusion environment with neutral media, the nanoparticle/ordered-ligand interlayer achieves nearly unit CO selectivity at high current densities (98.1% at 400 mA cm−2). The complex, multi-component environments found in enzymes induce high catalytic specificity, but are difficult to achieve in synthetic catalysts. Now, researchers report a catalyst comprising a dynamic, ordered layer of ligands above a nanoparticle surface that creates a pocket to facilitate CO2 electroreduction.

Bioaccessibility of potentially toxic metals in soil, sediments and tailings from a north Africa phosphate-mining area: Insight into human health risk assessment

The risk assessment of phosphate mining/processing industrial activities on the environment and human health is crucial to properly manage and minimize the risks over time. In this work, we studied the inhalation and dermal bioaccessibility of potentially toxic metals (PTM) in different particle-size fractions of urban soil, sediments and tailings from Gafsa-Metlaoui phosphate mining area, to assess afterwards the non-carcinogenic (NCR) and carcinogenic (CR) risks for the health of local citizens and workers constantly exposed to airborne particulate matter (PM) originating from these sources of contamination. Samples were separated in particle-size fractions by centrifugation and consecutive cycles of sedimentation and decanting. The pseudo-total concentrations and bioaccessible fractions of PTM were extracted by aqua regia and in vitro bioaccessibility tests, respectively. Both sediments and tailings showed higher-than-background concentrations of PTM (mainly Cd, Zn and Cr), with a tendency to accumulate these metals in fine particles (<10 μm). In urban soil, only Cd was above the background concentration. The bioaccessibility of PTM via inhalation was significantly higher in artificial lysosomal fluid (ALF) than in simulated epithelial lung fluid (SELF): basically, Cd was the most bioaccessible metal (relative bioaccessibility up to 80%), followed by the medium-to-high bioaccessible Zn (47%), Pb (46%) and Cu (39%), and the least bioaccessible Cr (16%). In synthetic skin surface liquid (NIHS 96-10), only Cd was bioaccessible at worrying extent (20–44%). On the basis of US.EPA risk assessment, the exposure to PTM bioaccessible fractions or pseudo-total concentrations would not cause serious NCR and CR risks for human health. Significant health risks (Hazard Index >1 and CR > 10−4), especially for children, can occur if ingestion route is also considered. The findings underline the need for adequate protection of contaminated soil, sediments and mine tailings laying nearby urban agglomerates, to reduce the health risks for inhabitants and workers of Gafsa-Metlaoui mining area.

A mathematical approach to improving the representation of surface water–groundwater exchange in the hyporheic zone

AbstractIt is well known that land surface topography governs surface–groundwater interactions under some circumstances and can be separated in a Fourier-series spectrum that provides an exact analytical solution of both the surface and the underlying three-dimensional groundwater flows. We evaluate the performance of the current Fourier fitting process by testing on different scenarios of synthetic surfaces. We identify a technical gap and propose a new version of the approach which incorporates the spectral analysis method to help identify the statistically significant frequencies of the surface to guide the refinement and mesh. Our results show that spectral analysis is the method that can help improve the accuracy of representing the surface, thus further improving the accuracy of predicting the bedform-driven hyporheic exchange flows.

Anti-Myeloma Drug Melflufen Inhibits RANKL-Stimulated Osteoclastogenesis By Suppressing Proliferation of CD14+ Precursor Cells

Background Melflufen (melphalan flufenamide) is a first-in-class peptide-drug conjugate (PDC) that targets aminopeptidases and rapidly releases alkylating agents into tumor cells. Osteolytic lesions are a hallmark of multiple myeloma and occur in almost all MM patients, causing severe bone pain and pathological fractures. Previous reports indicate that melphalan enhances osteoclastogenesis. On other other hand, melflufen is able to suppress proliferation of malignant myeloid cells including osteoclast precursors, monocytes. In the present study we therefore evaluated the direct effects of melflufen and melphalan on human osteoclastogenesis using cultured peripheral blood CD14+ monocytes. Methods CD14+ osteoclast precursors were isolated from peripheral blood. Osteoclastogenesis was stimulated by adding RANKL and M-CSF to CD14+ osteoclast precursors and assessed by tartrate-resistant acid phosphatase (TRAP) staining using para-nitrophenyl phosphate (PNPP). Osteoclastic activity was assessed by two assays. First, TRAP activity was measured by quantification of resorption pits on osteo assay synthetic surface made of crystalline calcium phosphate coating mimicking living bone material. Second, collagen degradation was quantified by release of C-terminal telopeptide of type I collagen (CTx) from mineralized bone slices. The proliferation of mature osteoclasts and their precursors in the presence of melflufen and melphalan was assessed using cytotoxicity assays. RNA isolated from osteoclast precursors and mature osteoclasts was subject to gene expression analysis by microarray. Results Melflufen inhibited RANKL-induced osteoclast formation at 1 µM concentration, while 25 µM melphalan was needed to initiate osteoclastogenesis inhibition. However, only extremely high concentrations of melflufen (10 µM) and melphalan (100 µM) affected mature osteoclasts and their TRAP activity. Cytotoxicity assays have demonstrated that melflufen, but not melphalan, can inhibit proliferation of monocytes, osteoclast progenitor cells, at clinically relevant concentrations. When added during osteoclastogenesis, melflufen has significantly inhibited TRAP phosphatase activity on crystalline calcium phosphate-coated surface at 1 µM, whereas 25 µM of melphalan was required to achieve the same effect. As for collagen degradation, the addition of 1 µM melflufen completely suppressed the CTx fragment release. In a parallel assay, 10 µM of melphalan was necessary to produce the same effect. Noteworthy, we did not observe any positive effect of melphalan on osteoclastogenesis or proliferation of osteoclasts. Gene expression analysis showed that mature osteoclasts express higher levels of bone lytic genes ACP5/TRAP, CTSK, MMP2, MMP7, and MMP9. In addition, CD276 and PDCD1LG2 mRNAs encoding B7 family immune checkpoint molecules B7-H3 and PD-L2 are also strongly up-regulated upon osteoclastogenesis. Discussion Myeloma patients often suffer from severe bone pain associated with osteolytic bone lesions. These lesions are the result of excessive osteoclastogenesis induced by multiple myeloma in the bone marrow microenvironment. Moreover, this process creates an immunosuppressive microenvironment since osteoclasts express immune checkpoint molecules known to negatively control activity of T lymphocytes (PD-L2, B7-H3) and NK cells (B7-H3). In this study, we have shown that a novel anti-myeloma PDC melflufen efficiently inhibits osteoclastogenesis and associated collagen degradation and bone resorption when used at clinically relevant concentrations. Melphalan could also induce a reduction of bone resorption and collagen release, however high and clinically irrelevant concentrations were necessary to obtain these effects. Given these results, it is plausible that melflufen-treated MM patients might achieve a reduction in bone pain, and this should be assessed in more detail in the follow-up studies. Also, elimination of immunosuppressive osteoclasts by melflufen may provide a synergistic effect between melflufen and immunotherapy while treating MM patients. This hypothesis is currently being tested in clinical trials. Disclosures Byrgazov: Oncopeptides AB: Current Employment. Gullbo:Theradex: Current Employment; Oncopeptides AB: Consultancy, Current Employment, Current equity holder in publicly-traded company. Slipicevic:Oncopeptides AB: Current Employment. Lehmann:Oncopeptides AB: Current Employment, Current equity holder in publicly-traded company. Larsson:Oncopeptides AB: Current equity holder in publicly-traded company. Fryknäs:Oncopeptides AB: Research Funding.

Fog basking by Namib Desert weevils

Namib Desert darkling beetles (Onymacris unguicularis) capture water droplets from fog using a highly specialized behavior called “fog basking”. This has applications in biomimetics (the study of biology-inspired technology, which can be utilized to solve complex human problems). In short, synthetic surfaces that mimic the external texture of fog-dependent organisms can be used to extract water from the atmosphere, thereby helping to address the critical and growing human demand for water in arid regions. In April 2019, my colleagues and I visited a site within the Namib Sand Sea approximately 18.7 km due east of the Atlantic seaboard, near Walvis Bay. At the time, heavy fog was being carried over the dunes by a westerly breeze. Near the base of a large sand dune, we encountered several clumps of dune grass (Stipagrostis sabulicola) and observed many Namib Desert weevils (Leptostethus marginatus) clinging head-down about halfway up the grass stems. All of the weevils had drops of water collecting within the pits on their wing cases and thoraxes from the fog. The surface architecture of the weevils, characterized by concave impressions of pits and grooves, is nearly opposite from that of the darkling beetles, distinguished by bumpy convex features. This observation could stimulate biomimetic research and further advances in developing artificial surfaces that can capture water from atmospheric sources.

Assessment of High‐Resolution Dynamical and Machine Learning Models for Prediction of Sea Ice Concentration in a Regional Application

AbstractIn this study, the potential for sea ice concentration prediction using machine‐learning methods is investigated. Three different sea ice prediction models are compared: one high‐resolution dynamical assimilative model and two statistical machine‐learning models. The properties of all three models are explored, and the quality of their forecasts is compared. The dynamical model is a state‐of‐the‐art coupled ocean and sea ice ensemble‐prediction system with assimilation. The observations assimilated are high‐resolution sea ice concentration from synthetic aperture radar (SAR) and sea surface temperature from infrared instruments. The machine‐learning prediction models are a fully convolutional network and a k‐nearest neighbors method. These methods use several variables as input for the prediction: sea ice concentration, sea surface temperature, and 2‐m air temperature. Earlier studies have applied machine‐learning approaches primarily for seasonal ice forecast. Here we focus on short‐term predictions with a length of 1–4 weeks, which are of high interest for marine operations. The goal is to predict the future state of the sea ice using the same categories as traditional ice charts. The machine‐learning forecasts were compared to persistence, which is the assumption that the sea ice does not change over the forecasting period. The machine‐learning forecasts were found to improve upon persistence in periods of substantial change. In addition, compared to the dynamical model, the k‐nearest neighbor algorithm was found to improve upon the 7‐day forecast during a period of small sea ice variations. The fully convolutional network provided similar quality as the dynamical forecast. The study shows that there is a potential for sea ice predictions using machine‐learning methods.

MODIFICATION OF DIAMOND SURFACE DURING PHOTOLITHOGRAPHY, PLASMA-CHEMICAL CLEANING, AND MAGNETRON DEPOSITION

An influence of the conventional planar technology of the semiconductor surface treatment operations (photolithography, plasma-chemical surface cleaning in radio frequency low-pressure oxygen discharge, and thin metal films growth) on monocrystalline diamond surface topography and roughness is investigated. It is preliminary shown that photolithography without the plasma cleaning and magnetron deposition of an aluminum film do not induce any diamond surface changes which could be found by the optical profilometry, electron and optical microscopy. However, as a result of the lithography some organic contaminants can decrease the adhesion of the aluminum film and have to remove from the surface. Further, the influence of the above-listed surface treatment operations separately and in combinations on the synthetic diamond surface is investigated. It is found that an even short oxygen plasma cleaning during 5 min with a low bias power of 20 W leads to etching the grooves on the diamond surface The depth of the etching grooves varies by more than an order of magnitude in different experiments (0.3 - 19 nm), and by 10-20% within the same substrate under the influence of the poorly controlled external factors. Also, oxygen plasma treatment changes its secondary electron emission coefficient. Deposition of aluminum film after plasma cleaning does not induce noticeable changes in the diamond surface topography. The quality of diamond surface polishing (in “hard” of “soft” direction), the diamond’s type (IIa or IIb) as well as producing method (HPHT or homoepitaxial CVD) do not affect the result of grooves formation.

Fouling of nanofiltration membranes based on polyelectrolyte multilayers: The effect of a zwitterionic final layer

In this work, we investigate the effect of membrane surface chemistry on fouling in surface water treatment for polyelectrolyte multilayer based nanofiltration (NF) membranes. The polyelectrolyte multilayer approach allows us to prepare three membranes with the same active separation layer, apart from a difference in surface chemistry: nearly uncharged crosslinked Poly(allylamine hydrochloride) (PAH), strongly negative poly(sodium 4-styrene sulfonate) PSS and zwitterionic poly(2-methacryloyloxyethyl phosphorylcholine-co-acrylic acid) (PMPC-co-AA). Initially, we study foulant adsorption for the three different surfaces (on model interfaces), to demonstrate how a different surface chemistry of the top layer affects the subsequent adsorption of five different model foulants (Humic Acids, Alginates, Silica Nanoparticles, negatively and positively charged Proteins). Subsequently, we study fouling of the same model foulants on our polyelectrolyte multilayer based hollow fiber NF membranes with identical surface chemistry to the model surfaces. Our results show that nearly uncharged crosslinked PAH surface generally fouls more than strongly negatively charged PSS surface. While negative BSA adsorbs better on PSS, probably due to charge regulation. Overall, fouling was mainly driven by electrostatic and acid-base interactions, which led, for both PAH and PSS terminated membranes, to flux decline and changes in selectivity. In contrast, we demonstrate through filtration experiments carried out with synthetic and real surface water, that the bio-inspired zwitterionic phosphatidylcholine surface chemistry exhibits excellent fouling resistance and thus stable performance during filtration.

A vision-based approach for rolling contact fatigue evaluation in twin-disc tests on a railway wheel steel

ABSTRACT A vision-based experimental methodology was developed for monitoring the surface state evolution of specimens during twin-disc rolling contact tests, aimed at providing information for identifying the damage phenomena. The system is based on a high-speed camera and three laser pointers for illuminating the specimen surface. Images of the specimen surface are acquired and processed, allowing the definition of synthetic surface state indexes, as well as the section profiles of the surface. The vision system was applied to alternated dry–wet rolling–sliding contact tests on railway wheel steel specimens, highlighting its effectiveness in the damage evaluation. The potential of the section profile reconstruction as a tool for surface topology analysis was shown.