High Contact Angle Research Articles

The green synthesis of carbon quantum dots (CQDs) and characterization of polycaprolactone (PCL/CQDs) films

The synthesis of photoluminescent carbon quantum dots (CQD) from natural products is one of the most remarkable types of carbon-based nanomaterials due to their small size, high water solubility, nontoxicity, high stability, and excellent biocompatibility. New RC-CQDs have been prepared from natural material (rosehip fruit) via a hydrothermal method. CA-CQDs samples were synthesized from a synthetic carbon source (citric acid) by the same method for comparison with RC-CQDs. The maximum quantum yields of the as-prepared RC-CQDs and CA-CQDs samples were 23.8% and 9.6%, respectively. High-resolution transmission electron microscopy (RTEM) of RC-CQDs revealed a sphere shape with an approximate size of 5 nm, CA-CQDs were greater than 5 nm. Biodegradable polycaprolactone (PCL), which is used in bioengineering applications thanks to its mechanical and biodegradable properties, was used as a polymer matrix in this study. The PCL/RC-CQDs and PCL/CA-CQDs nanocomposite films were produced via liquid phase ultrasonic mixing at different amounts of RC-CQDs and CA-CQDs in PCL matrix (0.3-; 0.5-; 1.2-; 2.0% and 4.0% by weight), while unfilled PCL was also produced for comparison. The structural, mechanical, and biodegradable behaviors of PCL/RC-CQDs nanocomposite films have been investigated to improve the mechanical properties of PCL and increase its potential usability in load-bearing applications. PCL/RC-CQDs-2.0 film gave the maximum tensile strength value (17.65 MPa) with an increment of 27.7% and the highest value of the yield strength 9.02 MPa (an increase of 40.9%) and the highest value of microhardness 4.80 HV0,025 (an increase of 14.8%) were obtained using PCL/RC-CQDs-4.0 film compared with the PCL. The tensile strength and % elongation at break values of the PCL/CA-CQDs-0.3 film decreased by 14.8% and 133.1% compared with the PCL, respectively. The microhardness of the PCL/CA-CQDs-0.3 film was 5.48 HV0,025, increasing by 31.1% in comparison with 4.18 HV0,025, for the PCL. Biodegradability test results showed that films containing RC-CQDs exhibited lower weight loss than the PCL and films containing CA-CQDs. This result was attributed to the amorphous structure, low surface roughness and high contact angle of the RC-CQDs containing films. And also, CA-CQDs made PCL films more hydrophilic according to low contact angle results.

Water resistant paper based on natural rubber latex from Hevea brasiliensis and butyl stearate hydrophobic coating for packaging applications

Sustainable hydrophobic coatings on paper have become increasingly important due to the high demand for environmentally friendly materials. In this study, a novel sustainable hydrophobic coating was developed by combining natural rubber latex (NRL) and butyl stearate (BS). The NRL acts as binder and hydrophobic agent, while the butyl stearate improves the hydrophobicity of the coating. Different coating formulations containing 0–50 wt% BS were applied to the paper using a simple bar-coating method at a constant thickness, and the hydrophobic properties were evaluated by using contact angle, Cobb and water vapour transmission rate (WVTR) measurements. The lowest WVTR value was 3.428 g/cm2. Day, obtained when NRL coated, and WVTR of 4.405 g/cm2.day was obtained with an addition of 50 wt% BS, lower than the uncoated paper (5.485 g/cm2.day). All the formulations promoted a remarkable decrease in water absorption (Cobb30 values decreased from 128 g/m2 to 0.8 g/m2, and Cobb60 values decreased from 134.4 g/m2 to 0.7 g/m2). Results showed that the coating effectively reduced the surface energy of the paper, resulting in a high contact angle of 90.6° and increased hydrophobicity. Furthermore, the NRL and butyl stearate coating demonstrated good mechanical properties, suggesting its potential as a sustainable and effective alternative to synthetic hydrophobic coatings. Overall, this study presents a promising approach for the development of sustainable hydrophobic coatings on paper, which can have significant environmental and economic benefits.

Relaxation phase during droplet impact on superhydrophobic surfaces with high contact angle hysteresis

The droplet impact process on a solid surface is divided into a spreading phase where the droplet reaches the maximum deformation followed by a retracting phase. However, in the case of surfaces with high contact angle hysteresis, these two phases are connected by a relaxation phase where the contact angle changes from the advancing to the receding contact angle almost without motion of the contact line. Although the relaxation time can represent a significant part of the total droplet contact time, this relaxation regime has been less explored, especially for superhydrophobic surfaces due to the challenge of designing such surfaces with controlled wetting properties. Here, we show that for superhydrophobic surfaces with large contact angle hysteresis, the relaxation time can be comparable to the spreading and retracting time. Our results indicate that both the contact angle hysteresis and the capillary forces play a major role in defining the relaxation time and that relaxation time scales with the inertial–capillary time when using the droplet relative deformation as the characteristic length scale for this relaxation regime.

Mechanical, antibacterial and cytotoxic characteristics of nanolayered TiNb–Zr–Ta and nitrogen-doped TiNb–Zr–Ta coatings

Titanium and titanium alloy materials are often made as medical implants. Surface properties of titanium medical implants play decisive roles for antibacterial and biological response and tissue biocompatibility. In this study, cathode arc evaporation (CAE) technology was used to deposit TiNb–Zr–Ta and nitrogen-doped TiNb–Zr–Ta coatings with nanostructures on the Ti–6Al–4V dental abutment screws. The deposited coatings were then oxidized at high temperature to produce different oxides on the surface of the coatings. The mechanical properties, antibacterial properties and biocompatibilities of the coatings were analyzed. The effect of coatings on the abutment screw loosening and removal torque between the abutment screw and the pure titanium implant fixture was studied by removal torque measurement. In addition, Staphylococcus aureus (S. aureus) was used for evaluating the antibacterial properties of coatings, and mouse fibroblasts (L929) were used for ISO 10993-5 cytotoxicity analyses to determine whether it had good biocompatibility.Nanolayered structures and multiphases of polycrystalline TiNb–Zr–Ta were obtained by co-deposition of Ta, Zr and TiNb. When small content of N was introduced, the TiNb–Zr–Ta(N) showed a polycrystalline TiNb–Zr–Ta where N atoms entered the metallic lattice at interstitial sites. After oxidation, oxide phases of Ta2O5, TiO2, Nb2O5 and ZrO2 were formed on the surface of TiNb–Zr–Ta and TiNb–Zr–Ta(N). Ta2O5 was obtained on the surface of the coating prior to other oxides such as TiO2, Nb2O5 and ZrO2. The deposited TiNb–Zr–Ta and TiNb–Zr–Ta(N) coatings had high contact angle and exhibited a hydrophobic feature, while the annealed TiNb–Zr–Ta–O and TiNb–Zr–Ta(N)–O showed hydrophilicity. The deposited TiNb–Zr–Ta had similar hardness and Young's modulus values to that of the uncoated Ti–6Al–4V. When N was doped, the TiNb–Zr–Ta(N) had the highest hardness and Young's modulus. The hardness of the annealed TiNb–Zr–Ta(N) coating only decreased slightly due to the small oxide layer of ∼140 nm. Compared with the uncoated Ti–6Al–4V, TiNb–Zr–Ta serial coatings deposited on abutment screws had higher removal torques, which prevented the abutment screw of dental implant from loosening after long-term use. The biocompatibility of TiNb–Zr–Ta serial coatings was similar to that of the uncoated Ti–6Al–4V. In addition, the oxidized TiNb–Zr–Ta and TiNb–Zr–Ta(N) coatings had excellent antibacterial properties. It is speculated that the resulting Ta2O5 of both coatings may inhibit bacterial growth and improve the antibacterial effect. Based on the above advantages, the TiNb–Zr–Ta serial coatings are expected to have the potential to be applied to biomedical implants.

Superhydrophobic and Thermally Conductive Coating for Restraining Corona Loss and Audible Noise of High-Voltage Transmission Lines

In recent years, the number of high-voltage transmission lines has sharply increased with the rapid development of modern industry. However, a corona discharge phenomenon often occurs on the exposed high-voltage transmission lines, leading to energy loss and noise pollution. Herein, we have proposed a facile spraying method to prepare a superhydrophobic and thermally conductive coating to restrain the corona discharge phenomenon of high-voltage transmission lines, with vinyl silicone oil and hydrogen silicone oil as the main materials and modified boron nitride (BN) as a thermal conductive filler. The obtained composite coating exhibited superhydrophobicity, with a high water contact angle of 162°. In addition, the coating also showed a good self-cleaning capability, non-adhesion capability, mechanical stability, and chemical stability. Owing to the construction of the thermally conductive pathways with BN, the thermal conductivity of the coating reached 1.05 W/m·K, which was beneficial to quickly dissipating the heat generated by the current heating effect. Moreover, the corona losses of the positive and negative electrodes under simulated rainy conditions were decreased by 7.43% and 8.05%, respectively. The findings of our work have provided a new strategy to effectively restrain the corona discharge phenomenon of transmission lines, showing great application potential in the field of high-voltage power networks.

Fabrication and Characterization of Cu2+-Driven PTFE-Reinforced Artificial Muscle Polymer Membrane for Water Purification and Energy Harvesting Applications.

Ionic polymer membranes have not yet gained widespread practical application in areas such as water purification and energy harvesting due to their high cost and tendency to swell. The present study involved the fabrication of reinforced textile structures composed of polytetrafluoroethylene (PTFE)-reinforced Nafion membranes coated with non-precious metals, copper and silver, as a surface electrode by applying a chemical decomposition technique. Several mechanical, contact angle measurement and dielectric tests were conducted on membranes to evaluate their mechanical, wettability and conductivity properties. From scanning electron microscopy, it is clear that the formation of surface electrodes with uniform dispersion of metal particles. Scratch test reveals the adhesive strength between the coated metal particles and membrane. The silver-activated copper-coated membrane has a high contact angle of 121°. Thus, the fabricated membranes can have good antibacterial and adsorption properties for water treatment. The copper-coated membrane has a high Young's modulus of 779 ± 80 MPa and a tensile strength of 29.1 ± 8 MPa, whereas the elongation at break is more for silver-activated copper-coated samples recorded as 158 ± 4%. The viscoelastic behavior of the membranes was analyzed through dynamic mechanical analysis (DMA). A sharp rise in the storage modulus (E') value of 4.8 × 1010 Pa at ~80 °C at a frequency of 1 Hz on metal surface electrodes signifies an improvement in the strength of the material in comparison to the initial pure membrane. The successful enhancement of conductivity on the membrane surface via chemical deposition on the silver-activated membrane is 1 × 10-4 (S/cm) and holds great potential for facilitating voltage transmission through the tribolayer in the nanogenerators.

Successful Fabrication of Hydrophobic Surfaces of Microstructures Cooperating with Solid-Liquid Nanomaterials on the CuZnPb Alloy Substrate.

For protecting the exquisite structural patterns of such coins, developments of simple preparation methods were explored to achieve good hydrophobic capability and the wear-damage resistance of CuZnPb surfaces. A self-cleaning nanoliquid (SN) was combined with microstructured Ag-dispersed CuZnPb (MAC) to realize good hydrophobicity functions of the SNMAC. This was because the cooperative functions of silver and the SN enhanced the water reunion ability and increased solid-liquid-gas contact areas, leading to high contact angles of SNMAC. Their cooperations produced discrepant forces in their respective areas of the water drops and increased heterogeneous flowing, resulting in a high-angle hysteresis of SNMAC. Subsequently, the wear-damage resistance of the hydrophobic interface was measured in a ball-on-flat tribopair system, and the results showed that sliding injuries made a height distribution of the hydrophobic surface trend toward an equalization, allowing the cooperation of nano-silver, SN, and CuZnPb to form a new-style interface for achieving excellent hydrophobicity, thus producing the highest contact angles of the SNMAC among the as-prepared samples.

Pickering Emulsions and Hydrophobized Films of Amphiphilic Cellulose Nanofibers Synthesized in Deep Eutectic Solvent.

Herein, a dual-functioning deep eutectic solvent system based on triethylmethylammonium chloride and imidazole was harnessed as a swelling agent and a reaction medium for the esterification of cellulose with n-octyl succinic anhydride (OSA). The modified or amphiphilic cellulose nanofibers (ACNFs), synthesized using three different OSA-to-anhydroglucose unit molar ratios (0.5:1, ACNF-1; 1:1, ACNF-2; and 1.5:1, ACNF-3), were further converted into nanofibers with degree of substitution (DS) values of 0.24-0.66. The ACNFs possessed a lateral dimension of 4.24-9.22 nm and displayed surface activity due to the balance of hydrophobic and hydrophilic characteristics. The ACNFs made stable aqueous dispersions; however, the instability index of ACNF-3 (0.51) was higher than those of ACNF-1 (0.29) and ACNF-2 (0.33), which was attributed to the high DS-induced hydrophobicity, causing the instability in water. The amphiphilic nature of ACNFs promoted their performance as stabilizers in oil-in-water Pickering emulsions with average droplet sizes of 4.85 μm (ACNF-1) and 5.48 μm (ACNF-2). Self-standing films of ACNFs showed high contact angles for all the tested DS variants (97.48-114.12°), while their tensile strength was inversely related to DS values (ACNF-1: 115 MPa and ACNF-3: 49.5 MPa). Aqueous dispersions of ACNFs were also tested for coating fruits to increase their shelf life. Coatings improved their shelf life by decreasing oxygen contact and moisture loss.

A facile and cost-effective fabrication of robust carbon black-based superhydrophobic coatings on aluminum alloy

Frozen contamination, including ice and frost, on the key surface of systems or facilities, can lead to serious problems and substantial financial losses. Superhydrophobic materials with high water contact angle (CA) and low sliding angle (SA) are potentially effective as anti-icing and self-cleaning materials. Herein, we present an inexpensive and durable superhydrophobic material prepared by combining carbon black (CB) and epoxy resin (EP) with polydimethylsiloxane (PDMS) via facile spraying. The as-prepared superhydrophobic material named PDMS@CB has excellent water repellence, and its water CA and SA can reach 171.5° and 4.6°, respectively. PDMS@CB characteristics are systematically investigated via field-emission scanning electron microscopy, laser scanning confocal microscopy, atomic force microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. PDMS@CB exhibits satisfactory chemical and thermal stability. After being dragged for a length of 800 cm, the CAs remain above 150° and the SAs remain below 10° for PDMS@CB, indicating the excellent durability of the material. Furthermore, the superhydrophobicity of PDMS@CB renders the material outstanding anti-icing and photothermal de-icing characteristics. PDMS@CB also exhibits excellent self-cleaning performance under the pollution caused by the daily liquid contaminants.

Stable and impalement-resistant superamphiphobic coatings enabled by phase-separated adhesive for anti-adhesion of viscous liquids with low surface tension

Superamphiphobic coatings have great potential in various fields but surfer from weak mechanical stability, low impalement resistance and poor repellency to viscous liquids with low surface tension. Here, we report stable and impalement-resistant superamphiphobic coatings enabled by phase-separated adhesive for anti-adhesion of viscous liquids with low surface tension. By fluorination of silica (F-silica) nanoparticles and solvent induced phase separation of an adhesive, a homogeneous suspension was obtained, which could be readily used for preparing superamphiphobic coatings via spray-coating. The effects of phase separation degree and adhesive/F-silica mass ratio on superamphiphobicity, impalement resistance and mechanical stability of the coatings were studied. The coatings have a hierachical micro-/nanostructure and numerous perfluorodecyl groups on the surface. Thus, the coatings show excellent static and dynamic superamphiphobicity, e.g., high contact angles, low sliding angles, high maximum release height, short solid-liquid contact time and large bouncing height for various liquids with high viscosity and low surface tension. The coatings also show excellent mechanical stability, good chemical and temperature stability. Furthermore, the coatings are applicable onto diverse substrates and could be easily scaled-up.

Freezing Characteristics of a Water Droplet on a Multiscale Superhydrophobic Surface.

Superhydrophobic surfaces have the potential to retard ice formation owing to their super water-repellant nature arising from high static contact angle and low contact angle hysteresis. Most of the previous studies have focused on patterned surfaces with mono-scaled prismatic structures. In contrast, the freezing behavior on multiscaled rough superhydrophobic surfaces that are of practical significance is relatively little studied. This article presents, for the first time, the freezing dynamics of a water droplet interacting with multiscale fractal superhydrophobic surfaces which validates well with experimental measurements. It is shown that the dual effects of increased contact angle and poor interfacial conduction due to trapped air cavities within the roughness features of the superhydrophobic surface lead to increasing freezing time with increasing surface hydrophobicity, determined as a function of the fractal surface parameters. A comparison of the freezing dynamics of sessile droplets of identical contact angle on a smooth versus a rough superhydrophobic surface shows that interfacial asperity thermal resistance contributes to over 14% increase in the freeze time. It is further shown that by tailoring the multiscale characteristics, the freeze time may be increased by up to 7-fold compared to freezing on a smooth surface. The application of the numerical model to studying ice formation on several practical superhydrophobic surfaces of a range of metallic materials and fabrication methods is also discussed, which offers guidelines for the design of anti-icing surfaces in practice.

Green Synthesis of a Carbon Quantum Dots-Based Superhydrophobic Membrane for Efficient Oil/Water Separation.

The efficient separation of oil and water is a significant challenge worldwide due to the increasing frequency of industrial oily wastewater. Previous work by our group utilizes biological metal-organic framework-based superhydrophobic (S.P) textile fabric for oil/water separation. However, this system is limited due to the low mechanical stability, so there is a need for producing a more robust S.P membrane for oil/water separation. In this study, we report on the synthesis of carbon quantum dots (CQD) from banana leaves via a hydrothermal process and their application in producing a robust S.P coating on textile fabric for oil/water separation. The CQDs were characterized using various techniques including TEM, XRD, absorbance spectroscopy, and the BET method. The TEM images showed that the CQDs were circular in shape with a size of 4.4 nm, while the XRD micrograph indicated that the CQDs were crystalline in nature. The UV-vis graph showed a peak at a wavelength of 278 nm, suggesting strong absorption in the ultraviolet region. The BET-specific surface area of the prepared CQDs is 845 m2/g, with a pore volume of 0.33 cm3/g, and a mean pore diameter of 1.62 nm. We examined the surface wettability, morphology, composition, oil absorption capacity, oil/water separation performance, flux rate, chemical stability, and mechanical stability of the S.P membrane. Our findings indicate that the developed CQD-based S.P membrane possesses excellent S.P properties, displaying high water contact angles of 163° and low water sliding angles of 1°. The membrane demonstrated superior oil absorption capacity, separation efficiency, and flux rate towards three different oils-petroleum ether, n-hexane, and silicone oil. Petroleum ether has the highest separation efficiency (99.5%), and flux rate (13,500 L m-2 h-1), while silicone oil has the lowest. However, silicone oil has the highest absorption capacity (218.9 g/g) and petroleum ether has the lowest (194.8 g/g). For the absorption capacity and separation efficiency, a one-way ANOVA test was conducted. The statistical analyses revealed significant differences in absorption capacity and separation efficiency for the three oils, highlighting the efficacy of the superhydrophobic membrane for tailored oil/water separation. Additionally, the S.P membrane exhibited good mechanical (the membrane maintains its superhydrophobicity until an abrasion length of 850 cm) and chemical stability (the membrane maintains its superhydrophobicity in pH range 1-13), withstanding abrasion and immersion in solutions of varying pH values. The CQD-based S.P membrane shows great potential as a promising material for oil/water separation applications, with excellent performance and stability under various environmental conditions.

An experimental study on the impact of Boger and Newtonian droplets on spherical surfaces

This study examined the impact of Boger droplets on spherical surfaces, considering the various properties of liquids and surfaces for the first time. The experimental setup involved spheres with three different diameters composed of hydrophilic and hydrophobic surfaces. The main innovative aspect of the present study lies in the examination of the effects of rheological properties including elasticity, elongational viscosity, and the first normal stress difference on the impact of Boger droplets on solid surfaces via stress analysis. For this purpose, the results of the impact of Boger droplets are compared to the impact of equivalent Newtonian droplets with the same viscosity and surface tension coefficient. The research also explored the influences of Weber number, diameter ratio, and surface wettability on the dynamic behaviors of viscoelastic droplets during the spreading and receding stages. The results suggested that increasing the Weber number increases the maximum spreading factor of the droplets. A smaller diameter ratio required more time to reach this factor. The surface wettability significantly affected the receding phase, while its effect on the spreading stage was minimal. Droplets exhibited more retraction on surfaces with higher contact angles. The Newtonian fluids showed greater spreading and retraction than viscoelastic fluids with the same viscosity, highlighting the influence of fluid elasticity. It is shown that the normal stress caused by extensional viscosity during droplet spreading is significantly higher than the normal stress difference resulting from shear deformation, showing different behaviors between these two types of stress concerning droplets.

Effect of plasma treatment of wood fiber on the wettability, dynamic mechanical and thermal properties of polypropylene composite panels

This work evaluates the effect of plasma treatment on the wettability, dynamic mechanical and thermal properties of compression-molded composite panels produced from wood fiber (WF) and polypropylene (PP). Initially, WF was treated with different plasma durations (60, 120, and 180 s radiation). Afterward, the contact angle, moisture uptake, storage modulus, loss modulus, damping loss, and weight loss of the specimens prepared from untreated and plasma-treated were evaluated. Results revealed that the plasma treatment facilitates the interactions between WF and PP, and increases the adhesion properties. Compared with the lowest contact angle of 74.8° for the untreated specimens, the highest contact angle was found in the treated specimens around 79.06°, 81.29°, and 82.7°, using 60 and 15 using 180 s plasma radiations. Furthermore, the water absorption of the specimens reduced as a result of plasma treatment. The plasma-treated specimens demonstrated better molecular restriction and larger dynamic modulus than the unmodified ones. The tan δ peak signifying the glass transition temperature of composites shifted to a higher temperature, in the presence of plasma treatment. It was noted that the thermal stability of the composite panels produced from plasma-treated wood was remarkably improved.

Preparation of superhydrophobic sponge and its application in oil-water separation and treatment of polymer-containing wastewater.

At present, the application prospect of superhydrophobic materials in oil-water separation, an-tibacterial and other aspects have attracted more and more attention. However, preparing a simple and low-cost superhydrophobic material remains a challenge. Using acetone as solvent, candle soot, silver/silica nanoparticles and polydimethylsiloxane were uniformly mixed to form a mixed solution, and the superhydrophobic sponge was successfully prepared by spraying method. The results show that the superhydrophobic sponge has high water contact Angle (162°) and excellent oil-water separation efficiency, which can realize effective treatment of polymerized wastewater. In addition, the superhydrophobic sponge showed better antibacterial properties on the surface of Escherichia coli and Staphylococcus aureus. In this work, a simple way to prepare superhydro-phobic oil-water separation material is proposed. The preparation process is green, the material is easy to obtain, and it is expected to be widely used in practical production.

Influence of bio-inspired surface texture of additively manufactured 17-4 PH stainless steel adherends on the strength of adhesively bonded joints

The bonding potential of as-printed additively manufactured stainless steel is largely unknown, and the use of additional hierarchical bio-inspired surface texture has not yet been explored or characterized. In this study, it is demonstrated with the use of Selective Laser Melting (SLM) that a hierarchy of three surface features at different length scales can greatly improve the shear strength of metal-metal adhesive joints. The intrinsic stochastic texture of the SLM as-printed surface showed a high contact angle and a mixed failure with a dominance of adhesive failure. However, enhancing the as-printed surface with the Tree Frog (TF) and Fish Scale (FS) bio-inspired textures produced super-wetting surfaces, significantly improving the shear strength due to the synergistic effect of mechanical interlocking and physical adsorption adhesion mechanisms, resulting in mixed failure. The results indicated that the interfacial bonding performance was in line with the super-wetting behavior and was higher for the samples with a hierarchy of three surface features. The highest increase in bond strength was found for the tree frog hierarchical hexagonal texture (+70% compared to the as-printed texture). In contrast, abrasion of the as-printed surface with P1000-grit paper significantly reduced the surface roughness and increased the water contact angle, resulting in the lowest shear strength.

Durable Co(OH)2/stearic acid-based superhydrophobic/superoleophilic nanocellulose membrane for highly efficient oil/water separation and simultaneous removal of soluble dye

The discharge of industrial oily wastewater is threats to the environment. A long-lasting Co(OH)2/stearic acid (STA)-based superhydrophobic/superoleophilic nanocellulose-based membrane (SSNM) for extremely effective oil/water and simultaneous removal of soluble dye was created to offer solutions to this problem. The mechanical durability of the prepared Co(OH)2/STA-based SSNMs was reinforced by depositing Co(OH)2 and STA on the cellulose fibers. The Co(OH)2/STA-based SSNM shows a high water contact angle of 164 ± 2° and an oil contact angle of ∼0°, exhibiting excellent superhydrophobicity and superoleophilicity. With good usage stability, high separation efficiencies (>94.0%) and high separation fluxes (>130 L·m−2·h−1) were achieved for four oils. The separation flux and efficiency of N-hexane did not change obviously after repeated separation. Furthermore, it exhibited reliable photocatalytic ability, which contributed to the reduction of organic contamination. As a result, Co(OH)2/STA-based SSNM shows strong potential for practical applications such as oil/water separation and photocatalytic degradation of organic pollutants.

Effect of Surface Modification with Na Lauryl Sulfate on The Water-Uptake and Release Properties of Na Tripolyphosphate-Cross Linked Chitosan Beads

In this study we evaluated the effect of Na Lauryl sulfate (SLS) on the water-uptake and release properties of Na Tripolyphosphate (TPP)-cross linked chitosan beads. Chitosan beads were prepared by dropping riboflavin-loaded, chitosan (CS) solution into a curing medium composed of either an aqueous solution of TPP, SLS or a combination of these solutes. The resultant beads were characterized in terms of their size, drug encapsulation efficiency, water uptake properties by gravimetry and image analysis. Drug release properties of the prepared beads were studied using USP Apparatus 1 in media with different pH and ionic strength. Composites (CS/TPP, CS/SLS, and CS/TPP/SLS) were also evaluated using DSC, FTIR and contact angle measurements. Encapsulation efficiency was found to be 93%, 93.2% and 93.1% for CS/TPP, CS/SLS, and CS/TPP/SLS beads respectively and did not show any dependence on the composition of the curing medium for riboflavin. FTIR data suggested the presence of electrostatic interactions between positively charged amine group of CS and the negatively charged TPP and SLS. Drug release from the prepared beads was prolonged with CS/SLS beads releasing the drug faster than CS/TPP beads. The slowest drug release was observed in the case of CS/TPP/SLS beads. Drug release from the different types of beads was pH-dependent with the fastest release observed in 0.1 N HCl. Gravimetric water uptake was highest for CS/SLS beads followed by CS/TPP and CS/TPP/SLS respectively. Swelling study using image analysis showed a similar trend to the gravimetric water uptake results. The drug release and water uptake results could be explained by the effect of SLS on the wettability of the beads and the ability of the release medium to hydrate them which was confirmed by the high contact angle between water and CS/TPP/SLS composites.

Superhydrophobic polytetrafluoroethylene/polyvinylidene fluoride coating for passive daytime radiative refrigeration

Passive daytime radiation refrigeration (PDRR) is a new type of refrigeration that requires no extra energy consumption and also cools objects by reflecting radiant heat from sunlight and mid-infrared wavelengths. However, the properties of ordinary radiative refrigerative (RR) materials are degraded by surface dust accumulation during use. In this work, superhydrophobic radiative refrigerative (SRR) polytetrafluoroethylene/polyvinylidene fluoride (PTFE/PVDF) coating was prepared by one-step spraying method with PTFE as white pigment, PVDF as binder, and N, N-dimethylacetamide (DMAC) as solvent. The PTFE/PVDF coating (containing 20 wt% of PTFE) exhibits synergistic effect with high water contact angle (CA, 153.7°), low water sliding angle (SA, 7.7°), high solar reflectivity (SR, 93.7%), and high infrared emissivity (IE, 93.3%). Under a clear sky and direct sunlight, the coating achieves a RR temperatures of 5.8 °C (shielding convection heat) and 5.3 °C (without shielding convection heat) respectively under two measurement conditions. In addition, the coating exhibits excellent self-cleaning properties that can automatically remove dust accumulated on the surface with the assistance of rainfall, thus maintaining its RR performance for a long time. More importantly, the mechanical robust self-cleaning function also provides excellent corrosion resistance and anti-UV aging ability. The PTFE/PVDF SRR coating developed in this work is simple to fabricate, can be applied over a large area, and has good durability, which is conducive to promoting the practicalization of RR coatings.

Natural superhydrophobic surfaces and recent advances in synthetic superhydrophobic surfaces: A review

This review uses modern technologies to discuss the hydrophobicity mechanism of various natural surfaces found and studied in recent decades and their chemical components and delicate surface structure. It also contains many invent inspired by lifelike superhydrophobic characters, and tons of human living has been solved with the help of these applications. Also, the theories of how low hysteresis is induced by high contact angle devoted to the ability of water-repellent, drag reduction, and self-cleaning of a bunch of natural creatures are presented along with their characteristics. Besides, some of the recent fast, eco-friendly fabrication methods of superhydrophobic are discussed with the application of superhydrophobic surfaces in industry. Furthermore, the problems and challenges currently facing how to make the fabrication methods of the superhydrophobic characters better fit the industrial manufacture.