Decrease In Contact Angle Research Articles

Cold plasma treatment boosts barley germination and seedling vigor: Insights into soluble sugar, starch, and protein modifications

This study investigates the impact of three cold plasma treatments on barley seed germination: direct treatment of dry seeds (DDS), direct treatment of water-soaked seeds (DWS), and indirect treatment of seeds using plasma-activated water (IPAW). Our findings reveal that while DDS maintained the seed's imbibition structures, DWS significantly reduced water uptake. Notably, DWS-treated seeds exhibited a substantial increase in moisture content, potentially leading to an oxygen-deficient environment within the seed. This condition appeared to hinder germination, contrasting with the beneficial effects observed in DDS-treated seeds. Analyses of surface hydrophilicity, phenolic compounds, carbohydrate composition, protein storage and seedling growth were conducted. Interestingly, cold plasma treatment enhanced seed surface hydrophilicity, as evidenced by a decrease in water contact angles, particularly for DWS. We observed specific reductions in flavonoids and total phenolics, alongside shifts in carbohydrate composition, including increased sugar content up to 15.1% (DDS) and 13.5% (DWS), accompanied by a decrease in starch content to 189.00 ± 7.86 mg/g FM for DWS. Protein storage assessments revealed declines in albumin, globulin and prolamin fractions post-CP exposure. Finally, DDS and IPAW treatments markedly improved seedling shoot growth (from two to three-fold), underscoring the potential of these treatments in enhancing barley germination.

Assessing the aging and environmental implications of polyethylene mulch films in agricultural land.

Polyethylene mulch films (MFs) are widely employed in agricultural land to enhance crop yield and quality, but the MF residue causes significant environmental concerns. To promote the sustainable application of MFs, it is essential to assess their fate throughout their service life and understand the underlying degradation mechanisms. In this study, surface-exposed and soil-buried MFs were separately collected from agricultural land in Inner Mongolia, China. The variations in aging performance and corresponding property alterations of MF were thoroughly examined. The results indicated that sunlight exposure considerably hastens MF degradation, whereas buried MFs experience a more moderate aging process due to the inhibitory effects of the dark and anaerobic environment on oxidation. Surface cracking was observed in MF-Light samples as a result of photodegradation, while chemical and moisture interactions with soil caused partial perforation in MF-Soil samples. Relative to the pristine MF, the oxidation, unsaturation, and hydroxylation levels of MF-Light increased to 0.88, 0.35, and 0.73, respectively, with corresponding values for MF-Soil at 0.44, 0.13, and 0.24. The generated oxygen-containing functional groups lead to a decrease in contact angles of MF-Light and MF-Soil, enhancing their hydrophilicity. The aging process of MFs led to a decline in mechanical properties, posing challenges for recycling. Moreover, nearly all phthalate esters (PAEs) were released from MFs, regardless of sunlight exposure or soil burial. The use of MFs also impacted the abundance of soil microbial communities. Specifically, the selected polyethylene MF enriched Actinobacteriota by 75%, while reducing Chloroflexi and Firmicutes by 27% and 45%, respectively.

Microscopic visualization of heterogeneous condensation of water vapor on hydrophilic and hydrophobic particles

Heterogeneous condensation of water vapor on particles is widely used in the fields of atmospheric cloud physics and industrial particulate abatement. Particles surface wettability plays a fundamental role in water vapor condensation, but a microscopic insight of the impact of particles surface wettability on vapor condensation is lacked. Therefore, the Environmental Scanning Electron Microscope (ESEM) is adopted to directly visualize vapor condensation on particles with different surface wettability at a microscopic scale. Firstly heterogeneous condensation of water vapor on the hydrophilic and hydrophobic particles is obtained by the ESEM. The results show that when water vapor condenses on the hydrophilic particles, a spherical cap-shaped embryo first appears and subsequently develops into a spherical droplet to finally wrap the single particle. While on the hydrophobic particles, a spherical cap-shaped embryo will first appear and continue to grow into a spherical droplet to finally detach from the particle. Then the wetting coefficient is introduced to characterize the wetting degree of the droplet on the particle. The wetting coefficient will increase with the decrease of the contact angle, so the wettability of water vapor on the hydrophilic particles is better than that on the hydrophobic particles. Meanwhile based on classical nucleation theory, the geometrical factor and the critical supersaturation will decrease when the contact angle decreases, making it easier for water vapor to condense on the hydrophilic particles. Finally the line tension is investigated to explain the condensation mechanism. On the hydrophilic particles, when the droplet has crossed the equatorial line of the particle, the positive line tension promotes the spreading movement of the droplet over the particle to form a wrapped spherical droplet. Therefore, there is a transition from a spherical cap-shaped embryo before crossing the equatorial line of the particle to a wrapped spherical droplet after crossing the equatorial line. While on the hydrophobic particles, the negative line tension suppresses the spreading movement of the droplet over the particle to form a detached spherical droplet. So there is a transition from a spherical cap-shaped embryo before crossing the equatorial line of the particle to a detached spherical droplet after crossing the equatorial line.

Study of gas-liquid two-phase flow characteristics in hydrate-bearing sediments

The characteristics of gas-liquid two-phase flow in hydrate-bearing sediments (HBS) are critical for natural gas hydrate production. This study experimentally investigates the flow patterns in the presence of hydrates and employs the phase field method for accurate simulations. Additionally, flow pressure differences in a capillary model were analyzed, and the impacts of occurrence patterns, saturation, and wettability of hydrates were investigated by numerical simulation. The results show that flow patterns are predominantly influenced by flow velocity. At high flow rates (Reynolds number >10), different gas-liquid ratios result in a variety of flow patterns, including annular, Taylor, and bubble flow. However, at lower flow rates (Reynolds number <10), the flow pattern consistently manifests as Taylor flow, regardless of gas-liquid ratio variations. Notably, the Jamin effect (a significant pressure differential caused by hydrates within the flow) was observed, which intensifies with increasing hydrate saturation and decreasing contact angle. Pore-filling hydrate patterns, in contrast to grain-coating, exhibit a greater number of gas-liquid interfaces, leading to larger pressure differences and a more evident Jamin effect. These findings aid in understanding the fluid migration in HBS and help estimate the natural gas production capacity.

Experimental investigation of new derived anionic natural surfactant from peanut oil: Application for enhanced oil recovery

Nowadays, there is a growing inclination towards the environmentally friendly and economically viable materials in the field of chemical enhanced oil recovery including the surfactant flooding. This study investigates the performance of a newly developed anionic surfactant derived from peanut oil in enhanced oil recovery (EOR) applications. The validity of the formulated surfactant using the esterification and sulfonation methods was verified through FTIR, 1H NMR, and TGA analytical techniques. According to the outputs of conductivity and surface tension from developed surfactant solutions at 500 and 4000 ppm, the concentration of 2000 ppm was identified as the critical micelle concentration (CMC). Several experimental tests were applied on the surfactant solutions and more specifically at CMC range, such as IFT measurement, wettability estimation, foamability, oil displacement and emulsification. The surfactant solution at CMC (optimal surfactant solution) reduced the IFT from an initial value of 15.5 to 6.8 × 10−2 mN/m at the optimum concentration of formation water (15,000 ppm). Wettability alteration was examined on sandstone and carbonate rock samples, and the optimal surfactant solution successfully altered both rock surfaces from strongly oil-wet to water-wet, resulting in a decrease in contact angle from 144° to 58° on carbonate rock and from 138° to 44° on sandstone rock. In addition, the emulsion test results revealed a significant ability of the peanut surfactant to create emulsions. Examination of microscopic images demonstrated that the emulsion remained stable for approximately 90 days with a high compatibility under high saline conditions. Hence, the developed natural surfactant enabled to displace extra 19.3 % and 15.64 % original oil in place (OOIP) from the sandstone and carbonate core plugs, respectively, with shifting the relative permeability curves towards the lift side.

Investigation of Gas Diffusion Layer Degradation in Polymer Electrolyte Fuel Cell Via Chemical Oxidation

The gas diffusion layer (GDL) is a key part of the membrane electrolyte assembly and is critical for the transport of fuel, oxygen and water. The GDL is made up of two layers: macroporous substrate (MPS) and microporous layer (MPL) (1). To achieve the hydrophobicity required for water management, the two layers are typically treated with polytetrafluoroethylene (PTFE) (2). In many long-term experiments, it has been observed that GDL degradation, such as carbon corrosion and PTFE loss, leads to a deterioration of water management, conductivity and mass transport (3).To solve this durability problem, a thorough and in-depth understanding of the GDL degradation mechanism is required. In this study, GDLs are subjected to an accelerated stress test to investigate degradation by chemical oxidation. GDLs are soaked in Fenton's reagent for 24 hours. The hydrophobic properties of pristine and soaked GDLs are compared based on contact angle measurements, thermogravimetry and scanning electron microscopy. In addition, the chemical composition of the solutions before and after the immersion test is analyzed using a total organic carbon analyzer and an ion chromatograph. The results show that the hydrophobicity of GDL exposed to Fenton reagent is decreased by 5 and 4 degrees for the MPL and the MPS respectively. Fig 1. depicts a decrease in surface contact angle, which is associated with surface oxidation and PTFE deterioration.AcknowledgementThis research work is performed under the project AlpeDHues (AlpeDHues / FFG 889328) which is supported by the Austrian Research Promotion Agency (FFG).References C. Csoklich, R. Steim, F. Marone, T. Schmidt and F. Büchi, ACS Applied Materials & Interfaces, 13, 9908–9918 (2021).A. Ozden, S. Shahgaldi, X. Li and F. Hamdullahpur, Progress in Energy and Combustion Science, 74, 50–102 (2019).Y. Yang, X. Zhou, B. Li and C. Zhang, Applied Energy, 303, 117688 (2021). Figure 1

Relationship Between Residual Saturations and Wettability Using Pore-Network Modeling

Summary The relationship between residual saturation and wettability is critical for modeling multiphase processes like enhanced oil recovery, CO2 sequestration, and geologic storage of hydrogen. The wetting state of a core is often quantified through Amott indices, which are estimated from the ratio of the saturation fraction that flows spontaneously to the total saturation change that occurs due to spontaneous flow and forced injection. Observations from traditional coreflooding experiments show a minimum in the trends of residual oil saturation (Sor) around mixed-wet conditions. Amott indices, however, provide an average measure of wettability because of their intrinsic dependence on a variety of factors such as the initial oil saturation, aging conditions, rock heterogeneity, etc. Thus, the use of Amott indices could potentially cloud the observed trends of residual saturation with wettability. Using pore-network modeling (PNM), we show that Sor varies monotonically with the contact angle, which is a direct measure of wettability. That is, for fixed initial oil saturation, the Sor decreases monotonically as the reservoir becomes more water-wet (decreasing contact angle). Further, the calculation of Amott indices for the PNM data sets shows that a plot of the Sor vs. Amott indices also shows this monotonic trend, but only if the initial oil saturation is kept fixed. Thus, for the cases presented here, we show that there is no minimum residual saturation at mixed-wet conditions as wettability changes. In this research, we employ a numerical approach to quantify trends of Sor against the traditional definition of wettability. Through the analysis of our numerical work and literature experiments, we find that under isolated conditions (constant initial saturation), linear trends exist between Sor and wettability. This can have important implications for low salinity waterflooding, water-alternating-gas enhanced oil recovery, or CO2 sequestration where the effects of wettability are critical to understand phase trapping.

Characterization and in vitro bioactivity evaluation of polyvinyl alcohol incorporated electro spun chitosan/ fluor apatite nanofibrous scaffold for bone tissue engineering

In this study, polyvinyl alcohol/chitosan/fluor apatite scaffolds with different concentrations of polyvinyl alcohol of 0.075 g ml−1 and 0.1 g ml−1, respectively named A and B fabricated by electrospinning method to use in tissue engineering. By examining the scaffolds by FE-SEM, an appetite layer formation which was on the scaffold surface was clearly observable. Increasing the concentration of polyvinyl alcohol from 0.075 g ml−1 to 0.1 g ml−1 in the nanofibrous scaffolds improved degradation characteristic with an optimized value of 26 ± 2 and 42 ± 1 % after 28 days, respectively. The mean diameter of fibers both scaffolds was 405 nm and 212 nm, respectively. Furthermore, the percentage of porosity in both scaffolds was calculated as 84% and 91%, separately. The level of hydrophilicity of the scaffolds was measured by the dynamic contact angle method. Moreover, the increase in the percentage of polyvinyl alcohol led to the decrease in the average contact angle in scaffold A and scaffold B from 90° to 70°, respectively. The results of bone marrow culture test with MG-63 (NCBI C555) cell on the surface of scaffolds demonstrated not cytotoxicity in the resulting scaffolds as well as a suitable substrate for the adhesion and growth of the cells. According to our findings, the electrospun fluorapatite-incorporated-chitosan/polyvinyl alcohol scaffold could provide a new nanocomposite for biomedical applications.

Biocompatibility, anti-hemolytic, and antibacterial assessments of electrospun PCL/collagen composite nanofibers loaded with Acanthophora spicifera extracts mediated copper oxide nanoparticles

Research in the advancement of wound dressings strives to address specific issues related to infections, speed up the healing process, and enhance patient wellness, all of which will lead to improved wound care procedures. This study investigates the synthesis and characterization of electrospun Polycaprolactone (PCL)/Collagen (Col) nanofibers incorporated with Acanthophora spicifera extracts mediated copper oxide nanoparticles (CuO NPs) and to evaluate their biocompatibility, anti-hemolytic properties, and antibacterial efficacy. The synthesized copper oxide nanoparticles were spherical and 58 ± 17 nm in size as evidenced by the field emission scanning electron microscopy. The fiber diameter of PCL, PCL/Col, PCL/Col/CuO 1%, PCL/Col/CuO 2%, and PCL/Col/CuO 5% was found to be 373 ± 141 nm, 281 ± 46 nm, 221 ± 57 nm, 173 ± 40 and 162 ± 47 nm respectively. Contact angle measurements revealed that the addition of copper oxide nanoparticles into Polycaprolactone/Collagen nanofibers resulted in a decrease in water contact angle from 86.9° to 50.8°. The biocompatibility of the composite nanofibers was evaluated in vitro using mouse fibroblast cells. The results established that copper oxide-imbued nanofibers were non-toxic and biocompatible. The hemolytic index for PCL/Col, PCL/Col/CuO 1%, PCL/Col/CuO 2%, and PCL/Col/CuO 5% scaffolds was 0.91 ± 0.14, 0.76 ± 0.14, 1.21 ± 0.19, and 1.52 ± 0.08 % respectively which was below the permissible value. Furthermore, the PCL/Col/CuO 5% nanofibers exhibited bactericidal properties against Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, and Escherichia coli. These findings suggest the potential applications of copper oxide-infused nanofibers in various biomedical fields, including tissue engineering, antimicrobial coatings, and wound healing.

Wetting and swelling behaviour of N-acetylated thin chitosan coatings in aqueous media

Chitosan nanocoatings (thickness range of 120–540 nm) were produced on glass, zinc and silicon substrates with dip-coating and spin coating techniques to study their pH-dependent wetting and swelling behaviour. The coatings were N-acetylated with the methanolic solution of acetic anhydride to increase the degree of acetylation from 36 % to 100 % (according to ATR-FTIR studies). The measured contact angles of Britton–Robinson (BR) buffer solutions (pH 6.0, 7.4 and 9.0) were lower on the acetylated surfaces (ca. 50°), than that of their native counterparts (ca. 70°) and does not depend on the pH. Contrary, contact angles on the native coating deteriorated 10°-15° with increasing the pH. In addition, for native coatings, the decrease of the contact angles over time also showed a pH dependence: at pH 9.0 the contact angle decreased by 7° in 10 min, while at pH 6.0 it decreased by 13° and at a much faster rate. The constraint swelling of the coatings in BR puffer solutions was studied in situ by scanning angle reflectometry. The swelling degree of the native coatings increased significantly with decreasing pH (from 250 % to 500 %) due to the increased number of protonated amino groups, while the swelling degree of acetylated coatings was ca. 160 % regardless of the pH. The barrier properties of the coatings were studied by electrochemical tests on zinc substrates. The analysis of polarization curves showed the more permeable character of the acetylated coatings despite the non-polar character of the bulk coating matrix. It can be concluded that in the case of native coatings, 49 % of the absorbed water is in bound form, which does not assist ion transport, while in the case of acetylated coatings, this value is only 33 %.

The influence of polycaprolactone content on the surface properties of polyurethane networks

AbstractThe aim of this work was to examine the influence of polycaprolactone (PCL) as a soft segment (SS) on the surface properties of polyurethane networks (PUNs). Five PUNs with different SS content (from 10 to 50 wt%) were prepared using Boltorn® aliphatic hyperbranched polyester of the second pseudo generation and isophorone diisocyanate as components of hard segments. The structure, hydrophobicity, wettability, and swelling behavior of these PUNs were investigated. Primarily, the obtained results showed that properties of prepared PUNs strongly depend on the content of SS that is, PCL. It has been established that the increase of SS content reduced the degree of hydrogen bonding in PUNs. Also, the increase of the SS content in PUNs induced appearance of more pronounced microphase separated morphology, better hydrophobicity and non‐wetting with diiodomethane. Simultaneously, the increase of the SS content led to the decrease of contact angles with formamide, and surface free energy of the prepared PUNs. These PUNs show good surface properties that are required for their potential application such as coatings.

A seed and bridge layer method for inkjet printing of narrow traces on receding ink-substrate combinations

Inkjet printing of electronic materials is of interest for digital printing of flexible electronics and sensors, but the width of the inkjet-printed lines is still large, limiting device size and performance. Decreasing the drop volume, increasing the drop spacing, and increasing the ink-substrate contact angle are all approaches by which the line width can be lowered, however these approaches are limited by the nozzle geometry, ink coalescence and bead instabilities, and contact angle hysteresis, respectively. Here we demonstrate a novel approach for stable inkjet printing of very narrow lines on ink-substrate combinations with a high contact angle, utilizing the de-wetting of the ink due to the decreased contact angle hysteresis. After printing and drying an initial layer of disconnected seed drops of silver nanoparticle ink, we print an additional layer of bridging drops of the same ink in between the dried seed drops. The bridging drops expand to touch the dried seed drops and then retract into a line, due to the pinning of the wet ink on the dried seed ink but not on the substrate, forming a continuous silver trace. The trace width is decreased from 60 μm with a traditional printing approach down to 12.6 μm with this seed-bridge approach. The electrical conductivity of the silver trace is similar to that of a conventionally printed trace. Due to poor adhesion on the print substrate, the trace was transferred to a separate polymer substrate with a simple hot-pressing procedure, which preserves the electrical conductivity of the trace.

Transparent and Superhydrophilic Flexible Protein Films with Antifogging and Self-Cleaning Attributes.

Cyanoglycoside-modified flexible protein films, exhibiting a high level of transparency of ≈46 to 83%, were successfully prepared from lysozyme and glycerol with varying amounts of amygdalin (20, 40, and 60%) using water as a solvent. The increasing percentage of amygdalin leads to a drastic improvement of the hydrophilicity of the surface with a decrease in the water contact angle to 5.6°, resulting in superhydrophilicity. The increasing percentage of amygdalin led to a significant improvement in the surface's hydrophilicity, resulting in a reduced water contact angle of 5.6° and achieving superhydrophilicity. This superhydrophilic characteristic is particularly relevant to the excellent antifogging and self-cleaning properties of the resulting protein films. In addition to enhanced flexibility, the films also exhibited considerably improved thermal stability with a 40% loading of amygdalin in the protein solution. The superior mechanical, optical, and thermal properties of amygdalin-modified films are due to the strong hydrogen bonding with the peptides of lysozyme, as evidenced by the disappearance of amide bands in the cured protein films. Therefore, these transparent protein films, with their antifogging and enhanced thermal stability properties, can be potentially used for different packaging and coating applications.

Fractal model of spontaneous imbibition in low-permeability reservoirs coupled with heterogeneity of pore seepage channels and threshold pressure

Spontaneous imbibition (SI) is an important mechanism for enhancing oil recovery in low-permeability reservoirs. Due to the strong heterogeneity, and the non-Darcy flow, the construction of SI model for low-permeability reservoirs is extremely challenging. Commonly, traditional SI models based on single or averaged capillary tortuosity ignore the influence of heterogeneity of pore seepage channels and the threshold pressure (TP) on imbibition. Therefore, in this work, based on capillary model and fractal theory, a mathematical model of characterizing SI considering heterogeneity of pore seepage channels is established. On this basis, the threshold pressure was introduced to determine the pore radius at which the wetted phase can displace oil. The proposed new SI model was verified by imbibition experimental data. The study shows that for weakly heterogeneous cores with permeability of 0–1 mD, the traditional SI model can characterize the imbibition process relatively accurately, and the new imbibition model can increase the coefficient of determination by 1.05 times. However, traditional model has serious deviations in predicting the imbibition recovery for cores with permeability of 10–50 mD. The new SI model coupling with heterogeneity of pore seepage channels and threshold pressure effectively solves this problem, and the determination coefficient is increased from 0.344 to 0.922, which is increased by 2.68 times. For low-permeability reservoirs, the production of the oil in transitional pores (0.01–0.1 μm) and mesopores (0.1–1 μm) significantly affects the imbibition recovery, as the research shows that when the heterogeneity of pore seepage channels is ignored, the oil recovery in transitional pores and mesopores decreases by 7.54% and 4.26%, respectively. Sensitivity analysis shows that increasing interfacial tension, decreasing contact angle, oil–water viscosity ratio and threshold pressure will increase imbibition recovery. In addition, there are critical values for the influence of these factors on the imbibition recovery, which provides theoretical support for surfactant optimization.

Failure of Au-coated metallic bipolar plates for fuel cell in a 3-kW stack under the new European driving cycle

The studies on coating materials and their failure modes are significant for promoting the commercialization of metallic bipolar plates (BPPs) in proton exchange membrane fuel cells. Here in this work, the influence of simulative operation condition in automobile on the degradation of gold (Au)-coated 316 L BPPs is systematically investigated using New European Driving Cycle (NEDC) in a 3-kW stack for 5000 h. The original stack showed 36% decay after 5000 h while negligible change on ohmic resistance (3–5 mΩ) is surprisingly found, indicating the stable interface between aged BPPs and membrane electrode assembly (MEA). However, 15% voltage loss is found in a reassembled single cell using aged BPP and fresh MEA, indicating the degradation of BPPs indeed. Further short stack matching testing and microscopic analysis reveal the well matching state and unobstructed conductivity between BPPs and MEA in the original stack, while it would be broken during reassembly (the high-frequency resistance has increased by about 2 times). The postmortem analysis on degraded BPPs indicates the failure mode of coating including the aggregation of the Au, the growth of oxides and gradual coverage of Au. The failure of coating not only results in the increase of interfacial contact resistance (ICR) from 5.4 mΩ cm2 to 137.8 mΩ cm2 and decrease of contact angle from 63.5° to 0° in some severely corroded region, but also has significant impact on the mass transport due to increased surface roughness. Especially, the formed passive layer is found to be dissolved at high potential, leading to the ion precipitation risk. These results provide guidance for optimizing coating materials, operation conditions, and assembly procedures in the future.

Numerical simulation of Marangoni flow around a growing hydrogen bubble on a microelectrode

In this work, a numerical model for Marangoni flow around a growing hydrogen bubble on a microelectrode is developed and validated. The growth of the bubble is implemented using a body-fitted moving mesh method that moves the bubble interface based on the production of hydrogen at the cathode. The dissolved hydrogen that is produced at the cathode diffuses into the bubble. The geometry of the bubble is a spherical cap with a pinned contact line and a decreasing contact angle as the bubble grows larger. There are two cases: (1) a case in which the bubble grows on a microbubble carpet that grows during the evolution of the bubble, and (2) a case in which the carpet thickness is negligible. The purpose of this model is to simulate and investigate thermocapillary Marangoni convection during almost the entire bubble lifetime (nucleation and detachment are not included).We validate the model with data from two experiments reported in literature (Massing et al. 2019; Bashkatov et al. 2022; Bashkatov, 2022). The evolution of the bubble radius, the temperature profile around the bubble, and the profile of the Marangoni velocity, which is tangential to the bubble surface at 5 μm from the bubble, near the lower half of the bubble are accurately predicted. For the case with a bubble carpet, we investigated models with a growing carpet and fixed carpet thickness. We found that for a given bubble size the Marangoni velocity reduces with increasing carpet thickness.Stagnant bubble models are less complicated and computationally cheaper than the growing bubble model. For the case without a carpet, we compare the growing bubble model with two stagnant bubble models: one using constant current and another one using a transient current. A stagnant bubble model is recommended if the growth rate drb/dt<0.05uM where drb/dt is the instantaneous bubble growth rate and uM the average Marangoni velocity at the bubble interface. This is the case at a relatively late stage of the bubble evolution. At the early stage of the bubble evolution, the absence of bubble growth dynamics in the stagnant bubble models appears to have an effect on the velocity profile and the pressure part of the hydrodynamic force.

Effect of wettability on the impact force of water drops falling on flat solid surfaces

Drops falling on substrates with varying wettability exhibit distinct morphologies. However, the relation between the impact force exerted by a water drop and the substrate wettability has not been thoroughly explored. In this paper, we investigate the effect of contact angle (ranging from 40° to 180°) on the impact force of water drops, along with the spreading diameter, rim height, and retracting velocity. Our attention is focused to the inertial regime with the Weber number ranging from 30 to 100, which enables us to rationalize the dynamic relations and to correlate the kinematics of the drop with the impact force through scaling analysis. We find that substrate wettability has insignificant effect on the first force peak, which arises mainly from the momentum change during the initial impact. However, it does influence the second force peak, which originates from the momentum change in the flow redirecting from the radial inward direction to the vertical direction, accompanied by a column-shape Worthington jet. The second peak force gradually diminishes as the contact angle decreases, until it becomes indistinguishable below 40°, while the time at which the second peak force emerges is delayed.

Reactively-sputtered super-hydrophilic ultra-thin titania films deposited at 120 °C

Abstract We investigate super-hydrophilic TiO2 (titania) films for concentrated solar-thermal power applications. Reactive magnetron sputtering has been used to deposit 8 to 12 nm thick titania thin films onto borosilicate microscope glass slides, low-Fe extra-clear architectural glass, or Si(100) wafers with a 500 nm thick thermal SiO2 layer. The effects of deposition temperature and O2 fraction of the O2/Ar working gas were investigated. We demonstrate the importance of the O2 fraction for obtaining optically transparent, super-hydrophilic (contact angle below 1°) thin films. In particular, we show that as the O2 fraction increases, contact angle decreases, obtaining super-hydrophilic titania thin films at deposition temperatures as low as 120 °C. Our work enables to develop low thermal budget cost-efficient industrial synthesis processes, paving the way for commercial applications.

Surface Roughness-Induced Changes in Important Physical Features of CoFeSm Thin Films on Glass Substrates during Annealing.

Co60Fe20Sm20 thin films were deposited onto glass substrates in a high vacuum setting. The films varied in thickness from 10 to 50 nm and underwent annealing processes at different temperatures: room temperature (RT), 100, 200, and 300 °C. Our analysis encompassed structural, magnetic, electrical, nanomechanical, adhesive, and optical properties in relation to film thickness and annealing temperature. X-ray diffraction (XRD) analysis did not reveal characteristic peaks in Co60Fe20Sm20 thin films due to insufficient growth-driving forces. Electrical measurements indicated reduced resistivity and sheet resistance with increasing film thickness and higher annealing temperatures, owing to hindered current-carrier transport resulting from the amorphous structure. Atomic force microscope (AFM) analysis showed a decrease in surface roughness with increased thickness and annealing temperature. The low-frequency alternating current magnetic susceptibility (χac) values increased with film thickness and annealing temperature. Nanoindentation analysis demonstrated reduced film hardness and Young's modulus with thicker films. Contact angle measurements suggested a hydrophilic film. Surface energy increased with greater film thickness, particularly in annealed films, indicating a decrease in contact angle contributing to this increase. Transmittance measurements have revealed intensified absorption and reduced transmittance with thicker films. In summary, the surface roughness of CoFeSm films at different annealing temperatures significantly influenced their magnetic, electrical, adhesive, and optical properties. A smoother surface reduced the pinning effect on the domain walls, enhancing the χac value. Additionally, diminished surface roughness led to a lower contact angle and higher surface energy. Additionally, smoother surfaces exhibited higher carrier conductivity, resulting in reduced electrical resistance. The optical transparency decreased due to the smoother surface of Co60Fe20Sm20 films.

Ultrafast laser texturing to improve wettability of polyimide (Kapton) films

Aim of this study is investigating the possibility of increasing the wettability of polyimide Kapton thin films by laser texturing. The laser textured surfaces were characterized through the water contact angle measurement and the surface tension evaluation; morphological and topological analyses were performed by scanning electron microscopy and atomic force microscope, respectively. As main outcome, it was found that laser texturing increases the wettability with respect to the untreated material with a decrease of contact angle of more than 20 %. In addition, the ultrashort pulse laser induced, on the material, LIPSS structures oriented in the direction of the polarization plane.