Determination Of Contact Angle Research Articles

Fungal-induced water repellency in sand

Water infiltration into granular soils and the associated pore water pressure increase and reduction in shear strength can trigger landslides, instability of vertical cuts and failure of retaining walls. Water-repellent soils can reduce infiltration to maintain soil suction. Recent research has demonstrated the creation of synthetic water-repellent soils using chemical methods. This paper investigates a biological treatment for creating water-repellent sand by way of the growth of the fungus Pleurotus ostreatus. Water repellency was assessed using: (a) the water drop penetration test; (b) the molarity of ethanol drop test; and (c) the modified sessile drop method with contact angle (θ) determination by way of image analysis. Fungal-induced water repellency was found to be ‘extreme’ (θ > 110°) up to 4 weeks and ‘severe’ (θ > 105°) up to 12 weeks, even with no further supply of moisture or nutrients. A water-repellent layer was formed and maintained in saturated conditions, which is difficult to achieve using chemical methods.

Erratum: “Reliable determination of contact angle from the height and volume of sessile drops” [Am. J. Phys. 87(1), 28–32 (2019)

Erratum: “Reliable determination of contact angle from the height and volume of sessile drops” [Am. J. Phys. <b>87</b>(1), 28–32 (2019)

Using energy balance to determine pore-scale wettability

HypothesisBased on energy balance during two-phase displacement in porous media, it has recently been shown that a thermodynamically consistent contact angle can be determined from micro-tomography images. However, the impact of viscous dissipation on the energy balance has not been fully understood. Furthermore, it is of great importance to determine the spatial distribution of wettability. We use direct numerical simulation to validate the determination of the thermodynamic contact angle both in an entire domain and on a pore-by-pore basis. SimulationsTwo-phase direct numerical simulations are performed on complex 3D porous media with three wettability states: uniformly water-wet, uniformly oil-wet, and non-uniform mixed-wet. Using the simulated fluid configurations, the thermodynamic contact angle is computed, then compared with the input contact angles. FindingsThe impact of viscous dissipation on the energy balance is quantified; it is insignificant for water flooding in water-wet and mixed-wet media, resulting in an accurate estimation of a representative contact angle for the entire domain even if viscous effects are ignored. An increasing trend in the computed thermodynamic contact angle during water injection is shown to be a manifestation of the displacement sequence. Furthermore, the spatial distribution of wettability can be represented by the thermodynamic contact angle computed on a pore-by-pore basis.

Alignment of functionalized multiwalled carbon nanotubes in forward osmosis membrane support layer induced by electric and magnetic fields

A novel aligned polyphenylensulfone (PPSU)/cellulose acetate phthalate (CAP)/functionalized multiwalled carbon nanotube (FMWCNT) membrane support was prepared for forward osmosis (FO) application. The effect of applying the electric and/or magnetic fields on the horizontal and vertical alignment of FMWCNTs within PPSU/CAP membrane supports was investigated in detail. Field emission scanning electron microscopy (FESEM) confirmed the alignment of FMWCNTs under combined electric and magnetic fields. Furthermore, energy dispersive X-ray (EDX) spectroscopy, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, Raman spectroscopy, tensile test, thermogravimetric analysis (TGA), and water contact angle determination were conducted to further characterize the obtained samples. The performance of the obtained supports was studied in terms of pure water flux (PWF) and consequently, the vertically aligned nanocomposite membrane support prepared with 0.8 wt% FMWCNT, aligned under 0.6 kV/cm electric field followed by 2 T magnetic field demonstrated almost 6 times higher PWF in comparison with the unaligned one.

Relating nanofiltration membrane morphology to observed rejection of saccharides

Nanofiltration for the fractionation of uncharged solutes has become more interesting in recent times, due to the goal of valorizing side-streams and by-products of the food industry. Since the membranes suitable for this purpose are mainly utilized for demineralization processes, the specifications given by the manufacturer are insufficient for the prediction of the rejection of uncharged solutes. Nine membranes with a molecular weight cut-off between 150 and 1000 Da were investigated showing differences in their rejection of fructose at a transmembrane pressure difference ΔpTM of 1.0 MPa. These values were correlated with the root-mean-square roughness Sq and apparent pore size dap determined by atomic force microscopy, while the determined contact angle Θ did not influence the rejection. Thereby, a correlation between membrane morphology and rejection behavior was established.

Investigation of High Voltage Anodic Plasma (HVAP) Ag-DLC Coatings on Ti50Zr with Different Ag Amounts

The paper presents the investigation of a series of silver-incorporated diamond-like carbon (Ag-DLC) coatings with increasing Ag content on Ti50Zr and deposited using high voltage anodic plasma (HVAP). The coatings surface properties were analyzed with scanning electron microscope (SEM), atomic force microscope (AFM), and contact angle determinations. Electrochemical tests were performed in Afnor artificial saliva and evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy. Based on these properties, comparisons of coatings performance were linked with the amount of deposited Ag. Increasing the Ag content led to the increase of the corrosion resistance and to the decrease of the forces exhibited on the surface. The hydrophobic character of the coating with the highest Ag amount could prevent thrombosis, thus suggesting its possible use for medical implants.

Physical and Antibacterial Properties of Peppermint Essential Oil Loaded Poly (ε-caprolactone) (PCL) Electrospun Fiber Mats for Wound Healing.

The aim of this study was to fabricate and characterize various concentrations of peppermint essential oil (PEP) loaded on poly(ε-caprolactone) (PCL) electrospun fiber mats for healing applications, where PEP was intended to impart antibacterial activity to the fibers. SEM images illustrated that the morphology of all electrospun fiber mats was smooth, uniform, and bead-free. The average fiber diameter was reduced by the addition of PEP from 1.6 ± 0.1 to 1.0 ± 0.2 μm. Functional groups of the fibers were determined by Raman spectroscopy. Gas chromatography-mass spectroscopy (GC-MS) analysis demonstrated the actual PEP content in the samples. In vitro degradation was determined by measuring weight loss and their morphology change, showing that the electrospun fibers slightly degraded by the addition of PEP. The wettability of PCL and PEP loaded electrospun fiber mats was measured by determining contact angle and it was shown that wettability increased with the incorporation of PEP. The antimicrobial activity results revealed that PEP loaded PCL electrospun fiber mats exhibited inhibition against Staphylococcus aureus (gram-positive) and Escherichia coli (gram-negative) bacteria. In addition, an in-vitro cell viability assay using normal human dermal fibroblast (NHDF) cells revealed improved cell viability on PCL, PCLPEP1.5, PCLPEP3, and PCLGEL6 electrospun fiber mats compared to the control (CNT) after 48 h cell culture. Our findings showed for the first time PEP loaded PCL electrospun fiber mats with antibiotic-free antibacterial activity as promising candidates for wound healing applications.

Understanding surface and interface properties of modified Ti50Zr with nanotubes

The present work is a presentation of new results about the properties of nanostructures fabricated on Ti50Zr alloy surface in the context of the new trend in dentistry to extend Zr use as an alternative for Ti restorative works in the oral cavity. As a novelty, the present manuscript promotes a nanotubular Ti50Zr surface as a better choice than other TixZr alloys with and without modified nanostructured surfaces. The discussed modified nanostructured surfaces on Ti50Zr are mixtures of Ti and Zr nanotubes oxides fabricated via two steps anodizing and an ultrasonication stage between them leading to a nano cavities structure. The final surface nanotubes texture is able to improve mechanical properties and antibacterial effect. The surface characteristics were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), contact angle and atomic force microscopy (AFM) roughness determinations. Besides SEM and XRD characterization, the AFM extended investigation, developing more knowledge about adhesive and nano-mechanical properties, is a new approach, involving also the inverse Hall-Petch effect, in understanding surface and interface, able to introduce more performance in bio-applications.

Robust Contact Angle Determination for Needle-in-Drop Type Measurements.

One of the main approaches for contact angle determination using sessile drops with a missing apex (e.g., because of the presence of the needle tip) is the polynomial drop-profile fitting method. The major disadvantage of this fitting procedure is that the derived contact angle is highly sensitive to the polynomial order and the number of pixels involved in the actual fit. In the present work, an easily implementable method is introduced to effectively tackle these drawbacks. Instead of fitting the drop-profile itself, the polynomial fitting is applied to the difference between the drop profile and the circumcircle, independently for both sides of the drop. The derivative value of this difference at the contact point is used to correct the slope obtained analytically from the circumcircle. It is shown that this approach allows the robust determination of the contact angle with high (≤0.6°) accuracy in a straightforward manner, and the results are not affected by the actual contact angle, drop volume, or the resolution of the captured image. Validation of this new approach is also given in the contact angle range of 20°–150° by comparing the results to the values calculated by the Young–Laplace fit.

Novel hydrophobic PVDF membranes prepared by nonsolvent induced phase separation for membrane distillation

Polyvinylidene fluoride (PVDF) was used for membrane preparation using the nonsolvent induced phase separation (NIPS). In this paper, the effect of the polymer concentration in the dope solution and the nonsolvent bath composition is widely investigated. In particular, the effect of increasing concentrations of ethanol in the coagulation bath on the morphology and characteristics of the membranes, as well as on their performance in membrane distillation of pure water and a brine was evaluated. FESEM analysis, coupled with contact angle determination highlighted different coagulation paths that allowed to obtain superhydrophobic membranes at higher ethanol concentrations. Moreover, the polymer concentration had major effects on the overall porosity and pore size of the membrane. By tuning the membrane preparation conditions, it was possible to obtain membranes that showed great distillate flux as well as a complete salt rejection during the vacuum membrane distillation tests.

Osteogenic Differentiation of Mesenchymal Stem Cells with Silica-Coated Gold Nanoparticles for Bone Tissue Engineering.

Multifunctional nanofibrous scaffolds for effective bone tissue engineering (BTE) application must incorporate factors to promote neovascularization and tissue regeneration. In this study, silica-coated gold nanoparticles Au(SiO2) were tested for their ability to promote differentiation of human mesenchymal stem cells (hMSCs) into osteoblasts. Biocompatible poly-ε-caprolactone (PCL), PCL/silk fibroin (SF) and PCL/SF/Au(SiO2) loaded nanofibrous scaffolds were first fabricated by an electrospinning method. Electrospun nanofibrous scaffolds were characterized for fiber architecture, porosity, pore size distribution, fiber wettability and the relevant mechanical properties using field emission scanning electron microscopy (FESEM), porosimetry, determination of water contact angle, measurements by a surface analyzer and tabletop tensile-tester measurements. FESEM images of the scaffolds revealed beadless, porous, uniform fibers with diameters in the range of 164 ± 18.65 nm to 215 ± 32.12 nm and porosity of around 88–92% and pore size distribution around 1.45–2.35 µm. Following hMSCs were cultured on the composite scaffolds. Cell-scaffold interaction, morphology and proliferation of were analyzed by FESEM analysis, MTS (3-(4,5-dimethyl thiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt) and CMFDA (5-choromethyl fluorescein acetate) dye assays. Osteogenic differentiation of MSCs into osteogenic cells were determined by alkaline phosphatase (ALP) activity, mineralization by alizarin red S (ARS) staining and osteocalcin expression by immunofluorescence staining. The results revealed that the addition of SF and Au(SiO2) to PCL scaffolds enhanced the mechanical strength, interconnecting porous structure and surface roughness of the scaffolds. This, in turn, led to successful osteogenic differentiation of hMSCs with improved cell adhesion, proliferation, differentiation, mineralization and expression of pro-osteogenic cellular proteins. This provides huge support for Au(SiO2) as a suitable material in BTE.

Nanotubes and nano pores with chitosan construct on TiZr serving as drug reservoir

Taking into account that modified and non modified TiZr alloys have a chance as alternatives for Ti as implant materials, this paper is focused on the elaboration and characterization of TiZr hybrid nanostructures (nanopores and nanotubes) loaded with gentamicin (GS) and covered with chitosan. FT-IR analysis permitted structure and corresponding bands identification. Scanning electronic microscopy (SEM) was used for morphology analysis and nanostrucure dimensions evaluations. The surface analysis was completed with roughness measurements, contact angle determinations and surface energy evaluations. The amount of drug released in both cases was measured using ultraviolet–visible spectroscopy (UV/Vis). The in-vitro drug release profile was applied to three kinetic mathematical models (Korsmeyer-Peppas, Peppas-Sahlin and Linder-Lippold). Using the experimental data on the three simulation models, the Lindner-Lippold was found to be the best suited for the transport mechanism dominated by Fickian diffusion. It was observed that the same quantity of gentamicin (approx. 95%) will be released in 10 days from nanopores and in 21 days from nanotubes, establishing in both cases longer term release as an expression of better targeted treatment of bone and osteomyelitis.

Wettability alteration of oil-wet carbonate surface induced by self-dispersing silica nanoparticles: Mechanism and monovalent metal ion's effect

Various analysis methods including IR, SEM, contact angle determination and spontaneous imbibition experiments were used to investigate the mechanism of wettability alteration of oil-wet carbonate surface by silica nanoparticles (NPs) in the present study. Stable silica nanofluids were first studied through zeta potential measurement. Results show that there is an optimal sonication time interval (5 h) for the preparation of SiO2 nanofluid after the magnetic stirring treatment in this work. The addition of NaCl can decrease the dispersion stability of SiO2 nanofluids. Both IR and SEM results show that the originally water-wet silica NPs are adsorbed on the calcite surface, making the surface water-wet. The role of sodium ions is to compress the electric double layer, giving the nanoparticle (NP) an opportunity to access the palmitic acid molecules. The palmitic acid molecules are replaced by the NPs through competitive adsorption. The longer the contact time, the better the performance of wettability alteration of oil-wet carbonate rock by the nanofluid. The contact angle decreases as the NPs concentration increases. Among the metal ions in the formation water, Na+ ion is closest to the solid surface, making Na+ ion have a great influence on wettability change of oil-wet carbonate surface by silica NP. Na+ ions in the solution can neutralize some negatively charged portion of the carbonate surface, making the adsorption amount of silica NPs on the solid surface increase. Thus, wettability alteration of oil-wet carbonate surface by SiO2 NPs is improved in the presence of Na+ ions. During the spontaneous imbibition experiments, silica NPs are adsorbed on rock surface and gradually form a wedge film in the contact area of the three-phase (oil-water-solid). In this case, structural disjoining pressure is generated due to the presence of electrostatic repulsion and Brownian motion of silica NPs. When the structural disjoining pressure is stronger than the oil droplet adhesion, the contact area of oil droplet on the solid surface gradually decreases, making the oil droplet eventually peel off from the rock surface.

Surfactin application for a short period (10/20s) increases the surface wettability of sound dentin.

The aim of this study was to evaluate the effect of spreading the lipopeptide surfactin, for short time (10/20s), on dentin wettability. Study groups were surfactin: 2.8; 1.4; 0.7; 0.35; and 0.175mg/mL and a control group that received no treatment. Dentin discs (4mm height) were prepared and polished with 600-grit SiC paper. Contact angle determinations were carried out after microbrush spreading of surfactin on dentin specimens for, respectively, 10 and 20s. Excess liquid was removed, and after 60s, the specimens were analyzed in a goniometer using the sessile drop method to measure the contact angle. Results were analyzed by two-way ANOVA (concentration × time) and t student, with α = 0.05. Lower contact angles were obtained for surfactin (0.7mg/mL) spread for 10s. However, no statistical difference was observed for surfactin (2.8mg/mL) applied during 20s. Higher contact angles were observed for surfactin (0.7mg/mL) spread for 20s. In conclusion, dentin wettability is dependent on spreading time and surfactin concentration.

Preparation and characterization of styrene-butadiene-styrene membrane incorporated with graphene nanosheets for pervaporative removal of 1,2,4-trimethylbenzene from water.

In the present study, novel styrene-butadiene-styrene (SBS) membranes were prepared by the addition of graphene (Gr) nanosheets to the casting solution and were utilized in the pervaporative separation of a dilute solution of 1,2,4-trimethylbenzene (1,2,4-TMB) as a volatile organic compound (VOC) in water. Several characterizations such as field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), mechanical tensile test, and determination of water contact angle and swelling degree were conducted to investigate the properties of the prepared membranes. The results showed that with the addition of Gr the membrane thermal stability and hydrophobicity were increased while there was an optimum Gr loading to achieve the highest elastic modulus and tensile strength. Moreover, it was found that by increasing the Gr concentration up to 0.5 wt. %, the separation factor and pervaporation separation index (PSI) were increased by 250% and 43% compared to pure SBS membrane and reached 930 and 545 kg/m2h, respectively.

Improving Wood Resistance to Decay by Nanostructured ZnO-Based Treatments

In this study, the maple wood surface was coated with nanostructured zinc oxide, grown on the surface by using a hydrothermal process, and furtherly treated with shellac varnish. Samples obtained both after ZnO treatment and after the final varnish application were characterized by different techniques, i.e., X-ray diffraction (XRD), scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS), micro-FTIR with attenuated total reflectance (μ-ATR-FTIR), chromatic variation measurements, and contact angle determinations. Analytical results showed that the wood surface was covered by quite a homogeneous array of inorganic nanoparticles and that the natural resin forms a regular film over the ZnO nanostructures. An accelerated aging test was used to evaluate the protecting effectiveness of the treatments towards UV-induced decay of wood material. After the test, wood treated with ZnO and with the shellac/ZnO combination underwent a considerably lower chromatic change if compared to the untreated wood, suggesting an enhanced resistance of the treated maple to the decay due to light exposition. The presence of nanostructured ZnO protects from decay not only the wood substrate but also the shellac film. A microbiology test showed that growth of fungal species, e.g., common mold, is prevented on the wood surface treated with ZnO or with shellac/ZnO, indicating that the nanostructured zinc oxide also provides an effective protection from biodeterioration. The coating obtained by consecutive application of nanosized ZnO particles and shellac varnish combines the excellent aesthetical features and water repellence of the traditional finish with the protecting effectiveness of the nanostructured inorganic component.

Contact Angle Determination on Hydrophilic and Superhydrophilic Surfaces by Using r-θ-Type Capillary Bridges.

To avoid the restrictions of the captive bubble and the Wilhelmy plate techniques, a method was introduced for contact angle measurements under equilibrium conditions. It enables to determine even ultralow contact angles with high precision without prewetting the investigated surface because in this case, the capillary bridge of the test liquid is formed from a pendant drop and used as a probe. The contact angle is determined from the measured capillary force and liquid bridge geometry by using Delaunay's analytical solution. The method was experimentally proved to be valid. As a demonstration, contact angles less than 1° were measured with the uncertainty down to 0.1° on lightly corroded glass surfaces. Moreover, a new observation was obtained in complete wetting situations: the receding contact line starts to advance again during the increase of the bridge length. The contact angle is much lower in this readvancing phase compared to the advancing and receding values because the contact line finds prewetted surface in front of itself. Further advantage of the method is that the existing contact angle goniometers can be developed further into the presented measurement setup.

Preparation and Corrosion Resistance of 304 Super-hydrophobic Stainless-Steel Surface

Super-hydrophobic stainless-steel surface (SHSSS) was prepared by simple chemical etching method using ferric chloride ethanol solution and nutmeg acid ethanol solution as etching and modification solution respectively. Characterization analyses, including water contact angle (WCA) determination, Fourier-transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and electrochemical workstation were performed on SHSSS.The stainless steel etched with ferric chloride (20 wt%) ethanol solution for 1 h, modified with nutmeg acid, and obtained super-hydrophobic properties (WCA = 151.6 °). Furthermore, the SHSSS has satisfactory chemical stability and corrosion resistance. The surface can maintain super-hydrophobicity within 3.5 wt% NaCl solution of 2 days. The corrosion inhibition efficiency calculated by the fitting parameters of Tafel polarization curve is 81.8%.

Microwave-assisted preparation of biodegradable, hemocompatible, and antimicrobial neem gum–grafted poly (acrylamide) hydrogel using (3)2 factorial design

The objective of the study was to prepare neem gum polysaccharide graft copolymers of acrylamide (NGP-g-Am) using 3 factorial design. Prepared NGP-g-Am’s hydrogels were characterized using UV-visible spectroscopy, FTIR spectral analysis, SEM images, contact angle determination, biodegradability, hemocompatibility, and pH-dependent swelling ability. NGP-g-Am showed more swelling index in all the media like double distilled water, 1 N NaOH, and 0.1 N HCl than native form. Data obtained through soil burial biodegradation studies were showed t90% for neem gum polysaccharide (NGP) and NGP-g-Am (N1), 9 and 28 days, respectively. Findings of the Lee-White test for blood clotting time showed the longest clotting time (15.39 ± 0.53 min) for NGP-g-Am (N5) as compared with that for the uncoated glass surface (2.05 ± 0.93 min). Thrombus formed during studies were found to be significantly more in case of uncoated glass surface as compared with N (0.47 ± 0.23 mg), N1 (0.29 ± 0.08 mg), N2 (0.30 ± 0.13 mg), N5 (0.29 ± 0.11 mg), N7 (0.29 ± 0.07 mg), and N9 (0.28 ± 0.13 mg). Structure-based docking studies predict that binding of ligands to TLR-4 receptors is significantly more responsible for the antimicrobial effect of both NGP and NGP-g-Am.

Reliable determination of contact angle from the height and volume of sessile drops

Contact angle is an important parameter in characterizing the wetting properties of fluids. For this reason, accurate measurement of the contact angle at liquid-solid interfaces is of great importance in industrial and scientific applications. The most common method for measuring the contact angle is to obtain it directly from the profile of a sessile drop. Though convenient, this method suffers from certain inherent drawbacks. Here, we describe an alternative method that uses the height and volume of a sessile drop as constraints to construct its profile by numerical integration of two parametric differential equations. The integration yields, self consistently, the average value of the contact angle along the entire contact line as well as the footprint radius of the drop and its crown radius of curvature. As a test case, the new method is used to obtain the contact angle of pure water on two different substrates, Teflon and Lucite. For each substrate, four drops ranging in volume from 10. to 40 μl are used. The computed contact angles are consistent across the four different drop sizes for each substrate and are in good agreement with the literature values.