Contact Angle Of Water Droplet Research Articles

Investigation of anti-icing, anti-skid, and water impermeability performances of an acrylic superhydrophobic coating on asphalt pavement

Icing asphalt pavement affects driving safety. The purpose of this research is to find a solution to improve the anti-icing performance of asphalt pavement. An acrylic superhydrophobic coating (ASC) on asphalt pavement was prepared from uncured acrylic acid and carbon nanotubes. The contact angle and rolling angle of water droplets on the ASC surface are 155.173° and 4.26°. The icing observation experiment shows that the freezing time of the water droplet on the ASC surface is prolonged by 17% in comparison with that on the asphalt mixture surface. The anti-skid performance test results reveal that the coefficient of friction of the ASC is improved by 5.7% than that of asphalt pavement. The water permeability test results show that ASC can prevent water from penetrating the upper pavement structure, thereby reducing moisture damage. The results of this research indicate that ASC has good potential to improve the anti-icing performance of asphalt pavement.

Superwettable PVDF/PVDF-g-PEGMA Ultrafiltration Membranes.

Poly(vinylidene fluoride) (PVDF) is a common and inexpensive polymeric material used for membrane fabrication, but the inherent hydrophobicity of this polymer induces severe membranes fouling, which limits its applications and further developments. Herein, we prepared superwettable PVDF membranes by selecting suitable polymer concentration and blending with PVDF-graft-poly(ethylene glycol) methyl ether methacrylate (PVDF-g-PEGMA). This fascinating interfacial phenomenon causes the contact angle of water droplets to drop from the initial value of over 70° to virtually 0° in 0.5 s for the best fabricated membrane. The wetting properties of the membranes were studied by calculating the surface free energy by surface thermodynamic analysis, by evaluating the peak height ratio from Raman spectra, and other surface characterization methods. The superwettability phenomenon is the result of the synergetic effects of high surface free energy, the Wenzel model of wetting, and the crystalline phase of PVDF. Besides superwettability, the PVDF/PVDF-g-PEGMA membranes show great improvements in flux performance, sodium alginate (SA) rejection, and flux recovery upon fouling.

Study on selective laser melting 316L stainless steel parts with superhydrophobic surface

An inverted trapezoidal structure was designed, and parts with such structure were fabricated with selective laser melting (SLM) technique. We comparatively studied the contact and sliding angles of water droplets of untreated, natural aging, heat treated and chemically modified parts, to characterize the superhydrophobic characteristics and analyze the wettability transition mechanism. We conducted the electrochemical corrosion test to analyze the anti-corrosion and corrosion resistance mechanism of the parts. We did wear test to study the wear performance of parts and analyze the wear mechanism. The experimental results show that the contact angles of water droplets of parts after aging treatment, heat treatment and chemical modification are 156°, 155° and 160.2°, respectively, only the sliding angle of water droplets of chemical modification is 10°, the rest are over 10°, which implies that chemical composition of surface affects hydrophobicity of parts. Electrochemical corrosion tests show that micro texture can improve the material’s anti-corrosion properties, and the chemically modified parts have strong corrosion resistance. Wear tests show that the micro texture can reduce the material’s friction coefficient. At the load of 500 g, parts with chemical modification was observed superhydrophobicity disappearance after 40 min of wear. The friction coefficient of the chemically modified material is the smallest, 0.2228. After wear process, the surface is covered with fluoride and appears secondary structures. The wear methods are mainly abrasive wear and oxidative wear. The inverted trapezoidal structure has excellent superhydrophobicity, corrosion resistance and abrasion resistance by selective laser melting, providing a new method for manufacturing superhydrophobic parts.

Study of photodegradation and wetting behavior on synthesis oxides of tin (stannous and stannic)

Amongst the varieties of metal oxides, tin oxides semiconducting are particularly interesting because of their promising nature as catalyst, energy harvesting, water purification, electronics device and space applications. In this study, three synthesized methods (air thermal oxidation, aqueous and non-aqueous) were adopted to explore the properties and application of stannous oxide (SnO) and stannic oxide (SnO2). Tin oxide materials were characterized through different techniques such as scanning electron microscopy (SEM), ultraviolet visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy and photoluminescence. The optical microscopy and electron microscopy images show the morphology of the tin oxide. The percentage of tin and oxygen from the elemental analysis was ~ 55% and 44 wt% respectively. FTIR spectra confirmed the Sn–O functional from the vibration peak. XRD pattern shows the prominent diffraction peak which indicates the state of oxidation of tin oxide and crystallinity. A photodegradation activity was tested in the tin oxide sample with methylene blue to explore how tin oxide surface features absorb the integrity of a dye and degrade in the presence of sunlight. The tin oxide solution emits green fluorescence in the UV light, depending upon its concentration. The water droplet contact angle measured on the tin oxide film which was experimentally observed as 69°. The theoretically wetting behavior was also studied on a tin oxide with the effect of substrate by molecular dynamics. The results suggest that material can be utilized as a photo-catalyst, drug delivery and thin-film application of solar cells.

Biodiesel flames as a unique pyrolyzing carbon source for the synthesis of hydrophobic carbon films

We report the rapid single-step flame synthesis of hydrophobic carbon layers (C-layers) on the surface of stainless-steel (SS) substrates using vaporized biodiesel as the fuel. A co-flow canola methyl ester/air diffusion flame is used to generate a hydrophobic monolayer on the surface of the metal substrate upon its insertion into the reaction zone. Carbon deposition on the surface of the SS substrates varies by changing the SS disk’s position in the post-flame, and by varying its exposure time. The thickness and mass of the flame-formed monolayer varied depending on the substrate’s insertion point into the flame. However, the variation of mass did not significantly impact the C-layer’s uniformity or hydrophobicity. We hypothesize that a small “inner-cone” of the biodiesel flame along with a high soot propensity can result in an ideal medium to form uniform hydrophobic C-layers of unique hierarchical surface structure. This is supported by introducing SS substrates in methane/air flames formed using the same co-flow burner. The hydrophobic property of the carbon deposits was quantified by measuring the contact angle of water droplets placed on the film’s surface. A water droplet drop test was conducted on the flame-formed hydrophobic layers to study their wettability property.

Wettability, water absorption and water storage in rosette leaves of the dragon tree (Dracaena draco L.)

Main conclusionLeaf surfaces of Dracaena draco are wettable and can absorb water. The thick, basal leaf part could act as a water reservoir that changes in volume with plant hydration.Rosettes of leaves of Dracaena draco play an important role in directing fog water through leaf axils into the stem tissues, where it can be stored for further use. However, how water is intercepted and collected by the leaves remains unclear, especially since leaf blade surfaces are considered hydrophobic. Based on the observations of D. draco individuals growing in Spain and in glasshouse conditions in Poland, we hypothesised that their long leaves (~ 70 cm) are able to absorb water along the whole leaf blade, but leaf age affects this process. We used water droplet contact angle measurements, anatomical analyses of leaf cross sections along the age gradient and dye tracer experiments to test this hypothesis. The data showed that the leaf surfaces of D. draco are wettable. In general, the mature leaves of the rosette are more wettable than the young ones. Water can be absorbed both through the adaxial and abaxial surfaces. The hydrenchyma is not uniformly distributed along the leaf, it is especially abundant towards the leaf base where it forms a massive water reservoir, which changes in volume depending on plant water status. The results of these studies shed light on the role of rosettes in water absorption by D. draco, and broaden our understanding of the functioning of this vulnerable species.

Facile preparation and strong adhesive strength of honeycomb polyurethane films with small pore diameter

AbstractWith the continuous development of bionics, such as, geckos and virginia creeper with both superhydrophobic and super‐adhesive, the surface wetting and super‐adhesive properties of various porous materials have attracted extensive attention of the scientific and medical communities. Here, the honeycomb polyurethane (PU) porous films with strong adhesion were successfully prepared by microphase separation method and the effects of growth parameters on their microstructure and adhesive strength to ice were investigated. It was found that a high relative humidity (e.g., 100%) and a low solution concentration (e.g., 2%) facilitated the formation of ordered honeycomb PU porous films, and as‐prepared PU pores with average pore diameter as small as 5 μm are better ordered and more uniform than these in related documents. Although the contact angle of water droplets on the surface of PU porous films increased from the premodification value of 85–130° to more than 160° after surface modification with polydopamine (PDA), the corresponding rolling angle remained approximately constant (180°), indicating that the surface of PU porous films has strong adhesion similar to geckos and virginia creeper. Furthermore, at lower temperature, the PU porous films exhibited the high adhesive strength of 142.13 kPa on ice, which was strongly dependent on the porous microstructures and surface compositions. The improved adhesive behavior to ice of honeycomb PU porous films modified with PDA provides new strategies for surface modification of materials and potential applications in medical domain.

Preparation of a Flexible Superhydrophobic Surface and Its Wetting Mechanism Based on Fractal Theory

Substrates of superhydrophobic surface are important for their application. Preparation of a flexible superhydrophobic surface has drawn more and more attention. In this work, a flexible substrate was made using a semi-curing spray method to obtain a flexible superhydrophobic surface with excellent abrasion resistance on the surface of a room temperature vulcanized silicone rubber. Results show that under a bending condition, excellent superhydrophobic properties are still maintained. The Cassie-Baxter model and Wenzel model can be used to estimate the static water contact angle for regular roughness surfaces. There are few numerical theoretical models to predict contact angle or wetting mode for irregular micro-nanostructures superhydrophobic surfaces. The fractal theory can be used to transform the equation of Wenzel model and obtained the fractal wetting theory suitable for fractal structures on irregular rough surfaces. However, this fractal-wetting model cannot be applied to Cassie-Baxter state, which is always suitable for superhydrophobic surfaces. A new method was developed to calculate the static water contact angle of water droplets in the Cassie-Baxter model state. Using image identification and split surface method, a new model is constructed based on the fractal theory. Experimental data for water contact angles on flexible superhydrophobic surface with SiC/CNTs micro-nanostructures is agreement with the simulated values.

The origin of microscopic spheres on the exoskeleton of the woodlouse Porcellionides pruinosus (Crustacea: Isopoda) and their effect on its hydrophobicity

The dorsal surface of the woodlouse Porcellionides pruinosus is covered with minute spheres, providing its characteristic powdered appearance. Little has been known about their composition and formation. A previously suggested function of these structures was to increase the hydrophobicity of the cuticular surface. We studied the ultrastructure, composition and formation of the spheres as well as tested whether they affect the hydrophobicity of the cuticle. We determined the composition of the spheres with histochemistry and scanning electron microscopy after applying various chemicals. We studied the process of their formation with transmission electron microscopy and assessed the hydrophobicity of the cuticle by measuring contact angles of water droplets with its surface. Our results show that the spheres are largely organic. They contain proteins and glycoproteins or possibly polysaccharides without detectable amounts of lipids. By studying the formation of the spheres we established that they are epicuticular structures. They are deposited early in the premolt stage of the molt cycle around branching extensions of epidermal cells. The sphere-covered cuticle of P. pruinosus is more hydrophobic than the cuticle with experimentally removed spheres as well as the scale-covered cuticle in a related species.

Research on Contamination-Resistant SiO2 Optical Thin Films in a Vacuum Environment

The Contamination resistance of SiO2 optical films prepared by using sol-gel method was investigated and improved in this research. FDTS (1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane) was used to modify SiO2 thin films. Fourier Transform Infrared Spectrometer (FT-IR) and X-ray photoelectron spectroscopy (XPS) were used to evaluate the components on surface of the SiO2 thin films. The optical properties and hydrophobicity were also measured. The results show that the SiO2 thin film modification with FDTS causes −OH groups to be replaced by organic groups containing fluorine. The transmittance peak of SiO2 thin film changes, and the surface contact angle of water droplets on the SiO2 film increases from 35° to 107° after surface modification with FTDS. After the SiO2 thin films had been put in a vacuum environment for 24 hours, the peak transmittance of the modified SiO2 film under the same conditions is reduced to 0.14%, which is less than 3.17% of the unmodified film. The peak transmittance of the modified SiO2 thin films is also improved.

The influence of selected treatment parameters with atmospheric plasma on the treatment process and wood wettability

The paper presents the use of low-temperature plasma, generated in the air at atmospheric pressure, for treatment of wood surfaces to improve their wettability. For this purpose, a dielectric barrier discharge plasma device with a floating electrode configuration was used. The density and homogeneity of the plasma discharge, formed between the isolated high voltage electrodes and the surface of the spruce (Picea abies (L.) Karst.) and beech (Fagus sylvatica L.) wood, was shown to be highly dependent on the size of the gap between the electrode and wood. Topography measurements using a confocal laser microscope showed that exposure of wood to plasma causes changes on its surface at the sub-microscopic level. Measurements of the contact angles of water droplets and water-based coating showed the improved susceptibility to wetting of treated surfaces. Differences in surface wettability were also detected depending on the selected machining parameters: type of wood, workpiece feed speed, the distance between the electrodes, the distance between the electrodes and workpiece, and workpiece thickness.

Effect of Partial Oxidation Rubber on Hydrophilicity of Cement Composites

The purpose of this study was to observe the effect of partially oxidized rubber powder on cement hydration. The experiment first pulverized the rubber and then put it into a reactor with a low oxygen concentration for partial oxidation. The surface functional groups of the rubber particles before and after the reaction were observed by Fourier Transform Infrared Spectroscopy (FT-IR). The area integral ratio of S-O to C-H3 in the FT-IR spectrum was used as the indicator of partial oxidation results. Finally, the rubber particle after the reaction was added to cement to prepare a cement paste, and its effect on the hydration reaction of the cement was observed by FT-IR, scanning electronic microscope (SEM), optical microscope (OM). SEM images also showed that such sample had very dense C-S-H structure. It confirmed that this composite had the hydrophobic property by observing the contact angle of water droplets on this composite surface.

Solar reduced graphene oxide coated sponge for oil and organic solvent adsorption studies

In this work, we have synthesized solar reduced graphene oxide (SRGO)by facile, fast and cost effective technique. The as-prepared SRGO was coated on polyurethane sponge and used for oil adsorption from the oil-water interface. The material was characterized by x-ray diffraction spectroscopy and scanning electron microscopy for structural, surface and morphological analysis. Further the hydrophobicity of the graphene coated sponge was investigated by measuring the contact angle of water droplet with the graphene coated sponge. The graphene coated sponge demonstrates strong hydrophobicity along with oleophilic property. SRGO coated sponge shows high adsorption and achieves equilibrium in few seconds. Highest adsorption capacity has been obtained for tetrahydrofuran, which is 65.67 g/g. SRGO coated sponge prepared could be a desirable material for cleanup of oil spills in sea.

Evaluation of dispersion of MWCNT/cellulose composites sheet using electrical resistance 3D-mapping for strain sensing

Carbon nanomaterials including, but not limited to, carbon nanotubes (CNTs) and graphene have attracted considerable attention due to their nanoscale electrical conductivity. Flexible sensors have experienced a growing demand due to several potential applications, such as personalized health monitoring and robots. In this study, CNT/cellulose composite sheets were manufactured using spray methods for flexible sensors. MWCNTs were ultrasonically dispersed in an acetone solvent and flexible plain paper was used as a substrate on which the CNT suspension was sprayed. At the end of the coating process, to remove the acetone solvent, the specimens were dried in an oven. Electrical resistance (ER) three-dimensional-mapping and optical observation were used to confirm and evaluate the dispersion of CNTs on the paper. To access the wettability of CNT/cellulose sheets, the changes of static contact angle of distilled water droplets on the sheets were measured. The critical point of the CNT coating numbers was determined using the ER method as well as the change of wettability using the static contact angle measurements.

TiO2 reinforced high-performance epoxy-co-polyamide composite coatings

Epoxy-based protective coatings for outdoor and marine applications are commonly used to protect metals and alloys, and architectural elements against the environmental impact. An epoxy-co-polyamide (EP-PA) polymer is synthesized by reacting pre-polymers: epoxy and polyamide resins. TiO2 nanoparticles of different sizes are embedded into EP-PA copolymer to form composite coatings on the Teflon substrate, referred to as EP-PA/TiO2. TiO2 content is varied from 0.1 to 1.0 wt.% and the electrical, thermal, and mechanical performance of composites is analyzed. Both EP-PA polymer and EP-PA/TiO2 composite coatings are characterized by FTIR spectroscopy and electron microscopy. EP-PA/TiO2 composites exhibit a uniform distribution of individual TiO2 nanoparticles in the EP-PA matrix at low TiO2 content, while some aggregates are observed at the higher TiO2 content. The size effect of TiO2 nanoparticles is also demonstrated by clear differences in the surface topography, size distribution, extent of agglomeration, and surface roughness of the EP-PA/TiO2 composites. TiO2 nanoparticles have lower surface energy and therefore, increase the hydrophobic character of the composite coatings that is revealed by the increasing water droplet contact angle. The surface resistivity of EP-PA/TiO2 composites decreased with the increasing TiO2 content, while thermal degradation temperatures are improved by 100 K (15.7 %) compared to neat EP-PA polymer. The mechanical properties such as yield strength and Young’s modulus are also enhanced by 56.9 % and 32.7 %, respectively at 1.0 wt.% TiO2 loading, while the toughness of EP-PA/TiO2 composites is comparable to the neat polymer. The remarkable enhancement in the hydrophobic character, electrical conductivity, thermal stability, and mechanical performance of EP-PA/TiO2 composites at low TiO2 content (1.0 wt.%) is achieved by the small size, high surface area, and excellent dispersion of nanoparticles in the polymeric matrix. The simultaneous improvement in properties suggests EP-PA/TiO2 composites useful as protective coatings for a variety of applications in the harsh environment.

Evaluation of Material Properties of Acetylated Medium Density Fiberboard (MDF)

This study examined the material properties of MDF manufactured using acetylated pinus radiata fibers against moisture and compared the properties with the fiberboard quality standards of KS F 3200. Since acetylated MDF shows very low moisture content, water absorption and thickness swelling than the quality standards, it is expected to have an excellent dimensional stability. The bending strength in wetting condition of the acetylated MDF reached approximately 70% of the bending strength in dry condition, making it suitable for the quality standards. The internal bond of the acetylated MDF in the wetting condition was higher than the minimum internal bond of the quality standards in the dry condition, showing a good water resistance. Since the water droplet contact angle of the acetylated MDF is larger than that of untreated MDF, it is determined that it contributes in improving the water resistance due to the low wettability.

Fluorocarbon versus hydrocarbon organosilicon surfactants for wettability alteration: A molecular dynamics approach

This paper presents a theoretical model based on molecular dynamics to represent and explain the experimental measurements of water droplet contact angles on fluorocarbon and hydrocarbon organosilicon surfactants of different chain lengths. In addition to the contact angles, we evaluated the distribution of the surfactants on the surface (surface density, packing degree, density profile, and coating thickness) and the interaction energies (surfactant–surfactant, surfactant–water, and water–water) to better understand the effect generated by the differences in the molecular structure of the surfactants. We found that the surface densities of the fluorocarbon surfactants were lower than those of hydrocarbon surfactants. This is because fluorocarbon chains are more rigid and because the attractive interaction energy between CF chains is less than that between CH chains because the fluorine–fluorine repulsive electrostatic interactions are stronger than the corresponding hydrogen–hydrogen interactions. The wettability alteration resulted from the modified surface–water interactions. The initial state was hydrophilic (water angle contact of 24°), produced by the high interaction energy between water and the silica surface. Upon application of surfactant, the surface–water interaction energies were considerably lowered, generating hydrophobic surfaces, with water angles contact between 87° and 99°.

Effect of NH4Cl on the microstructure, wettability and corrosion behavior of electrodeposited Ni–Zn coatings with hierarchical nano/microstructure

In this study, nickel‐zinc (Ni–Zn) superhydrophobic coatings with a hierarchical nano/microstructure were deposited through a two-step electrodeposition process on the copper substrate. The effect of adding NH4Cl crystal modifier concentration on the composition, surface morphology, roughness and wettability of coatings were evaluated by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM), laser confocal scanning microscopy (LCSM) and contact angle measurements. Additionally, the corrosion behavior of selected coatings was investigated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques. The results showed that adding NH4Cl could affect the composition and surface morphology of the Ni–Zn coatings. A transition from a Zn-rich Ni–Zn coatings with polyhedral shape to the Ni-rich Ni–Zn coatings with hierarchical nano/mico-conical structure was taken place through adding NH4Cl as a crystal modifier. The Ni–Zn coating prepared with 400 g·L−1 NH4Cl showed superhydrophobic behavior with the highest water droplet contact angle of ~155°. The confocal microscopy results confirmed this coating has the highest roughness and power spectral density (PSD) values at entire spatial frequencies. In addition, the superhydrophobic coatings exhibited higher corrosion resistance compared to the other coatings.

Picosecond laser surface modification of aluminum oxide with fish-scale structures for cell culture

The surface modification of a layer substrate has received attention for many biomedical applications (e.g., tissue engineering and biosensing). Under an in situ control, we proposed a strategy for surface modification of hard and brittle ceramics with ultrafast laser pulses for cell culture. A type of ultrafast laser based on the picosecond pulse technique was employed to ablate the surface of a pristine aluminum oxide (Al2O3) substrate. The surface of the formed reproducible micro-nanostructures indicated the fish-scale structures, which was analyzed under different laser ablation conditions. Subsequently, the SV40 T-antigen human embryonic kidney 293 (HEK293T) cells were cultured on the laser-ablated Al2O3 substrates. These microstructures and nanostructures can enhance cell proliferation response. The surface effect played a crucial role, by which the surface roughness (Ra) and contact angle (CA) of water droplets on the ablated Al2O3 substrate increased with the increasing laser fluence. The formed fish-scale structures were formed by the parameters of laser ablation where the structural characteristics of the Al2O3 substrate can be remained in the ultrafast laser process. The presented process provides a simple support for developing ablated structures on the Al2O3 substrate for cell culture.

Starch nanoparticles produced via acidic dry heat treatment as a stabilizer for a Pickering emulsion: Influence of the physical properties of particles

To evaluate the effect of the starch particle size on the stability of a Pickering emulsion, starch particles with various mean diameters were prepared using dry heat treatment under mildly acidic conditions. As addition level of acid increased, mean diameter of starch particles decreased from 23,100 to 15.7 nm, and contact angle of water droplet on the starch film increased from12 to 42.7°. Confocal microscopy revealed that a cohesive layer of starch particles with diameter of 28.6 nm surrounded the oil droplets, which may stabilize the emulsion. For starch particles smaller than 33.5 nm, the emulsion stability index increased up to approximately 95 % when starch content was higher than 9.1 %. For 16.7 % starch content, starch particles (< 33.5 nm) could form a stable emulsion with oil content of up to 61 %. For the emulsion stabilized by starch with 28.6 nm, it was stable when subjected to heating and freeze-thawing treatment.