Hydrophobic SiO2 Research Articles

Preparation of self-healing superhydrophobic cotton fabric based on silica aerogel for self-cleaning and oil/water separation

Self-healing superhydrophobic coatings with excellent self-cleaning ability have received a lot of attention. A self-healing superhydrophobic cotton fabric was obtained by coating SiO2 aerogel and polydimethylsiloxane (PDMS) on a cotton fabric via the spraying process. Sol-gel reaction and ambient pressure drying (APD) were used to prepare hydrophobic SiO2 aerogel utilizing methyl trimethoxy silane (MTMS) as a precursor and water as a solvent in the presence of surfactant. Spraying a mixture of SiO2 aerogel and polydimethylsiloxane onto cotton fabric created the self-healing superhydrophobic cotton fabric. The surface morphology and chemical composition of superhydrophobic cotton fabrics were characterized respectively. The results showed that the treated cotton fabrics exhibited the superhydrophobic property with water contact angle (WCA) and water shedding angle (WSA) 161.1° ± 0.9° and 4° ± 0.5°, respectively, due to the simultaneous introduction of typical three-dimensional network porous structure caused by SiO2 aerogel and low surface tension PDMS layer on cotton fabrics. The treated cotton fabrics had not only excellent self-cleaning and anti-fouling properties, but also self-healing properties. The treated cotton fabrics showed excellent friction durability and laundering durability attributed to stable and firm PDMS adhesive layer. After 20 laundering cycles, 600 friction cycles or 8 cycles of etching-self-healing, the treated cotton fabrics were still superhydrophobic. The treated cotton fabric manifested desirable oil-water separation performance with a separation efficiency of 96.0%. These durable superhydrophobic fabrics with self-cleaning and liquid repellency may find various potential applications and display promising prospects.

Carbon Nanotube-Fastened Graphene Composites with Bubble-Induced Multireflections for Electromagnetic Interference Shielding with Water Repellence

The use of light and flexible electromagnetic interference (EMI) shielding materials, particularly those considered for water repellence, is crucial in managing radiation pollution for modern electronic devices. However, the limited flexibility, weight, and water repellence of available shields constrain their applications. Herein, we demonstrated the potential of a carbon nanotube-fastened graphene composite film for EMI shielding, whose surface is adhered by a thin hydrophobic SiO2 coating. The reduced graphene with a curve and fastened morphology could be stored and form interconnected bubbles in the interior. Thus, the obtained film with flexibility and a thin thickness presents extremely high EMI shield performance of 76.4 dB due to anomalous multireflections in the interconnected bubbles, essentially different from shields that mainly reflect electromagnetic waves on a surface. In addition, the reliable roughness results in strong adhesion of the hydrophobic coating on a surface and demonstrates stable water repellence, even in severe conductions. The superhydrophobic film is a promising shield that could solve critical pollution for modern electronic devices.

Self-Transportation of Superparamagnetic Droplets on a Magnetic Gradient Slippery Surface with On/Off Sliding Controllability.

Recently, research about droplet self-transportation on slippery surfaces has become a hotspot. However, to achieve on/off sliding control during the self-transportation process is still difficult. Herein, we report a magnetic slippery surface, and demonstrate on/off sliding control during the self-transportation of superparamagnetic droplets. The surface is prepared through integrating a substrate that has a gradient magnetic region with a layer of paraffin infused hydrophobic SiO2 nanoparticles. On the surface, a superparamagnetic droplet is pinned at room temperature (about 25 °C), while it can self-transport directionally as the temperature is increased to about 70 °C. When the temperature is cooled down again, the droplet would return to the pinned state, indicating that on/off sliding control during the self-transportation process can be achieved. Furthermore, based on the excellent controllability, controllable coalescence of two droplets from opposite direction is displayed, demonstrating its potential application in numerous areas.

Molecular dynamics simulations of dodecane detachment from hydrophobic SiO2 surfaces in CTAB solutions

The oil detachment from solid surfaces has a major influence on enhanced oil recovery, self-cleaning performance, flotation efficiency, oil/water separation, and so on. In this paper, the mechanism of oil detachment from surfaces of different hydrophobicity was studied via molecular dynamics (MD) simulations. The oil detachment process becomes slower and the oil-solid contact angle is smaller with the increasing hydrophobicity of the silica surface. The simulation results showed that the disordered arrangement of oil molecules facilitated the formation of water channels on hydrophobic surfaces. Then, expansion of water channels becomes the key to oil detachment. The main driving forces are the Coulomb interactions and the H-bond formation between water and surface. The resistances are from hydrophobic effects by which the oil layer couldn’t be detached thoroughly from the hydrophobic surface. Data availability statementThe data that supports the findings of this study are available within the article and its supplementary material.

D-Cysteine Functionalized Superhydrophobic Nanocomposite Coating with Multiple-Action Antibacterial Property and Enhanced Mechanical Durability

In this study, a durable superhydrophobic antibacterial coating was developed by a facile spraying method. A mixture of bisphenol A diglycidyl ether (BADGE) and hydrophobic SiO2 nanoparticles was sprayed on carbon steel to provide a superhydrophobic substrate. D-cysteine (D-cys) functionalized SiO2/dopamine/silver nanoparticles with multilayer core-shell structure were then sprayed on superhydrophobic substrate to enhance antibacterial performance. The results of morphology observation and X-ray photoelectron spectroscopy (XPS) indicated the successful preparation of antibacterial nanoparticles and presented the hierarchical micro/nanostructures of coating surface. The as-prepared coating exhibited superhydrophobicity, with the water contact angle of ~153°. The coating was endowed with good mechanical durability, which maintained the water contact angle of ~150° after 180 cycles in tape-peel tests. The results of electrochemical impedance spectroscopy showed satisfactory corrosion resistance of this coating during 3 days of immersion in 3.5% NaCl solution. Furthermore, the coating showed excellent antibacterial performances against Escherichia coli and Pseudomonas aeruginosa, which benefited from the synergistic actions of low wettability of superhydrophobic surface, bactericidal behavior of Ag nanoparticles, and biofilm inhibition effect of D-cys.

Preparation of waterproof and air-permeable silicalite-1/PDMS/PTFE membrane by casting method for metal-air battery

The electrochemical performance of metal-air batteries is sensitive to environmental humidity. In this paper, waterproof and air-permeable polydimethylsiloxane (PDMS)/polytetrafluoroethylene (PTFE) membranes were prepared for alleviating these issues in metal-air battery. The effects of membrane fillers (hydrophilic SiO2, hydrophobic SiO2, activated carbon, silicalite-1) on the water vapor and air permeability of PDMS membranes were investigated. The results showed that, adding an appropriate amount of silicalite-1 can improve the waterproof and air permeability of PDMS membrane. The silicalite-1/PDMS membrane significantly reduces the running resistance of the battery, and improves the cycle number of Li-air batteries by 130% and that of Zn-air batteries by 43% in the air environment (40% RH, 25°C). The polarization voltage is also significantly reduced, indicating great potential in applications.

A Silicone Resin Coating with Water-Repellency and Anti-Fouling Properties for Wood Protection.

The strong hygroscopicity of wood greatly shortens its service life. Here, a simple impregnation modification approach was used to construct superhydrophobic silicone resin coatings on wood surfaces. Briefly, with hydrofluorosilicone oil (HFSO), tetramethyl tetravinyl cyclotetrasiloxane (V4), and hydrophobic SiO2 from industrial production as raw materials, superhydrophobic wood samples (water contact angle ~160.8°, sliding angle ~3.6°) can be obtained by simply dipping the wood in the HFSO/V4/SiO2 modifier solutions. As a result, the superhydrophobic silicone resin coating constructed on the wood surface still has good water repellency after finger touching, tape peeling, and sandpaper abrasion. When the mass ratio of HFSO to V4 is 2:1, the water absorption of the resulting wood after soaking in water for 24 h is only 29.2%. Further, the resulting superhydrophobic wood shows excellent anti-fouling properties. Finally, we believe that the impregnation modification method proposed in this study can be applied to the protection of cellulose substrates.

Fluorine-free superhydrophobic surface with micron-nanosized two-tiered structure for self-cleaning, anti-frosting, and anti-icing applications

Superhydrophobic surfaces with micron-nanosized two-tiered structures have huge potential in practical applications. However, the complex preparation process and low-stability of the versatile superhydrophobic surfaces restricted their wide application. Herein, a facile chemical etching process was applied to create a micron-sized rough structure on the 1060 aluminum alloy substrate, and the micron-sized rough structure surface (M-surface) was hydrophobic with a water contact angle of 113.50° ± 2.7°. Then, the M-surface was modified by hydrophobic SiO2 nanoparticles, and a superhydrophobic micron-nanosized two-tiered structure surface (MNSS-TMES/H-SiO2 coating) with a water contact angle of 161.20° ± 2.3° was constructed. The as-prepared MNSS-TMES/H-SiO2 coating can maintain superhydrophobicity after self-cleaning, sand impact, and anti-frosting tests. More importantly, the MNSS-TMES/H-SiO2 coating exhibited superior anti-icing performance and higher defrosting efficiency. The freezing delay time of a water droplet on the MNSS-TMES/H-SiO2 coating was prolonged to 4973.87 s at − 15 °C, and the frost layer on the resultant coating was melting speedily and turned into several isolated spherical water droplets in approximately 20 s. Therefore, the prepared durable fluorine-free superhydrophobic MNSS-TMES/H-SiO2 coating with self-cleaning performance, higher defrosting efficiency, and the ability to delay icing, which has great prospects in practical applications.

Low‐Voltage Electrically Responsive Photonic Crystal Based on Weak‐Polar Colloidal System

AbstractElectrically responsive photonic crystal (ERPC) based on particle electrophoresis is a promising material to construct reflective color displays with low‐power‐consumption and antiglare advantages. However, the high driving voltages for the polar ERPC inevitably cause electrochemical reactions on the electrode, which decreases the stability and reversibility of electrical response. Here, a weak‐polar EPRC composed of hydrophobic SiO2 particles, 1,2‐dichlorobenzene (DCB), and dioctyl sulfosuccinate sodium salt (AOT) is fabricated based on the charge separation by AOT reverse micelles and formation of highly charged particles in DCB. Compared to the polar ERPCs, the SiO2/DCB‐AOT ERPC works at much lower voltages (0.5–1.7 V) and still possesses a wide color tuning range because the weak‐polar solvent applies less screening to the coulombic interactions. The low potential further renders the ERPC good capability against color fading in a strong field and long‐term reversibility during color switching, which addresses the critical concerns for its application in reflective displays.

Designing triple-layer superhydrophobic/hydrophobic/hydrophilic nanofibrous membrane via electrohydrodynamic technique for enhanced anti-fouling and anti-wetting in wastewater treatment by membrane distillation

Developing high-performance membranes for membrane distillation (MD) to treat highly saline industrial wastewater is of great significance. In this work, a superhydrophobic/hydrophobic/hydrophilic triple-layer membrane combining an electrosprayed superhydrophobic top layer, an electrospun hydrophobic nanofibrous intermediate layer and a hydrophilic microporous membrane substrate was fabricated by using electrohydrodynamic techniques. The top superhydrophobic surface possesses a unique surface morphology composing of hydrophobic SiO2-polymer microbeads with nanoscaled protrusions and interconnected thin nanofibers, which contributed to the enhanced water flux for desalination in direct contact MD. By tuning the concentrations of hydrophobic SiO2 nanoparticles and polyvinylidene fluoride-co-hexafluoropropylene for electrospraying the top layer, the triple-layer membrane showed both enhanced anti-fouling and anti-wetting properties due to the reduced liquid-solid contact area and stable Cassie-Baxter state. The triple-layer membrane exhibited stable MD performances when using real seawater and industrial flue gas desulfurization wastewater as the feed solutions, while no obvious fouling and wetting being observed even at 60% water recovery. This study provides an effective approach for fabricating a high-performance triple-layer superhydrophobic/hydrophobic/hydrophilic membrane for potential practical MD applications for industrial wastewater treatment.

Hydrophilic/Hydrophobic SiO2 Nanoparticles Enabled Janus‐Type Paper through Commercial Glaco Spraying and Air‐Plasma Treatment

AbstractFunctional paper‐based microdevices have been receiving wide attention in the research areas of microfluidic chips, soft actuators, etc. This work introduces the design and fabrication of a Janus‐type paper in which one side of the paper remains hydrophilic and the other side is hydrophobic. Such Janus‐type paper is prepared by directly spraying hydrophobic Glaco solutions and following air plasma treatment. The former treatment can cover the paper fibers with numerous hydrophobic SiO2 nanoparticles. Through optimizing the fabrication parameters of the air plasma, it can penetrate the filter paper in a controllable depth, resulting in effectively regulating the hydrophobic particles into hydrophilic ones. Thereafter, the antirotation and interfacial stability of the Janus paper are investigated. Finally, a liquid storage and contamination‐free analysis devices are demonstrated on the Janus‐type paper platform. Noting that the commercially nonfluoride coating (Glaco) and mature plasma instrument together make the fabrication method simple, rapid, users/environmental‐friendly, and mass‐produced. The method provides a new route to fabricate Janus‐type paper for potential multifunctional applications in microfluidic chips and smart actuators, and may open up new avenue to prepare Janus films in a simple/rapid way.

Durable superhydrophobic polyvinylidene fluoride membranes via facile spray-coating for effective membrane distillation

Membrane wetting and fouling substantially limits application and deployment of membrane distillation process. Designing high-performance superhydrophobic membranes offers an effective solution to solve the challenge. In this work, a highly durable superhydrophobic surface (water contact angle of 170.8 ± 1.3°) was constructed via a facile and rapid spray-coating of extremely hydrophobic SiO2 nanoparticles onto a porous polyvinylidene fluoride (PVDF) substrate for membrane distillation. The superhydrophobic membrane coated by fluorinated SiO2 nanoparticles exhibited a superior physicochemical stability in a wide range of extreme environments (i.e., NaOH, HCl, hot water, rust water, humic acid solution, ultrasonication, and high-speed water scouring). During 8-h continuous membrane distillation desalination experiment, the coated superhydrophobic membrane experienced a consistently stable water vapor flux (ca. 19.1 kg·m−2·h−1) and desalination efficiency (99.99 %). Additionally, such a stable superhydrophobicity endowed the spray-coated PVDF membrane to overcome membrane wetting and fouling during membrane distillation of highly saline solutions containing foulants (i.e., humic acid and rust). Results reported in this study provides a useful concept and strategy in facile construction of robust superhydrophobic membranes via spray-coating for effective membrane distillation.

Vibrational spectroscopic evaluation of hydrophilic or hydrophobic properties of oxide surfaces

AbstractHerein, we evaluated the hydrophilic or hydrophobic surface properties of various oxides using vibrational spectroscopy, such as FT‐IR (mid‐IR) and near‐IR spectroscopy. Pristine SiO2 showed hydrophobic properties because H2O molecules weakly interacted with the hydroxyl groups via hydrogen bonding. Furthermore, the hydrophobic SiO2 adsorbed less toluene, as a hydrophobic probe molecule. In case of the alkyl‐groups‐modified SiO2, H2O molecules were barely adsorbed on the surface even in air, confirming the water‐repellent property. The TiO2 and Al2O3 surfaces adsorbed larger amounts of H2O than did pristine SiO2, indicating hydrophilic properties, because the Ti4+ and Al3+ sites play an essential role in strong interactions with H2O molecules via coordinative adsorption. Furthermore, the hydrophilic TiO2 and Al2O3 showed a high affinity to toluene, indicating oleophilic (affinity to oil or non‐polar compounds) properties, because the aromatic compounds were adsorbed on the cation sites by cation‐π interaction. Moreover, MgO reacted with H2O molecules to yield Mg(OH)2, indicating a greater hydrophilicity than TiO2 or Al2O3. Based on the considerations, when evaluating the hydrophilic or hydrophobic properties of oxide surfaces, the hydroxyl groups and the cation sites on the surface must be considered.

Cellulose nanofiber assisted dispersion of hydrophobic SiO2 nanoparticles in water and its superhydrophobic coating

It is challenging to build a superhydrophobic coating with aqueous dispersions since hydrophobic substances are usually dispersed in pure organic or water/organic mixed solvents. In this study, hydrophobic SiO2 nanoparticles were dispersed in water assisted with cellulose nanofiber (CNF) and the superhydrophobic surface was manufactured by coating a waterborne dispersion composed of CNF, hydrophobic SiO2 nanoparticles and methyltrimethoxysilane (MTMS). It was found that the dispersion of SiO2 in water can be improved by CNF. Meanwhile, the coated paper surface retained its hydrophobicity after 10 abrasion cycles due to the adhesion of the coating surface promoted by MTMS. When SiO2 content over 0.25 wt%, the coated paper surface displayed a superhydrophobic property, and the moisture absorption decreased to 31–34%. The contact angle of the coating surface was 162°, the contact angle hysteresis was 1.96° and the rolling contact angle was 1.33° when SiO2 content was 1 wt%.

Optimized preparation of thermal insulation hydrophobic SiO2 aerogel based on orthogonal design method

Optimized preparation of thermal insulation hydrophobic SiO2 aerogel based on orthogonal design method

Relationship between hydrophobicity and drag reduction of SiO2/HLR-Si coatings

The one-step spraying deposition method using hydrophobic SiO2 and fluorine-silicone resin (HLR-Si) was adopted in this paper to prepare the hydrophobic micro-nanoscale hierarchical structure on the surface of the test sample. Scanning electron microscopy and atomic force microscopy were used to characterize the surface morphology of the coating, and the contact angle meter was employed to evaluate the surface wettability. The content of hydrophobic silica produced on the hydrophobic performance of the coating was studied, and the relationships between hydrophobic performance and drag reduction performance were investigated. Results show that the one-step spraying deposition method is a simple and efficient technique for coating preparation. The maximum contact angle of SiO2/HLR-Si coating is 163°, and the sliding angle is only 1.8°. Compared with the 96° pure HLR-Si resin coating, the maximum drag reduction rate of the prepared superhydrophobic coating is 23.4%. Furthermore, the water resistance increases with the contact angle when the contact angle is less than 150°, while the drag reduction effect is improved with the increase of the contact angle when the contact angle is larger than 150°. However, the effect of drag reduction disappears when the rotation speed is excessively high. Finally, results verified that the air film captured by the superhydrophobic surface can reduce the water resistance through the method of artificial air supplement.

Preparation of Waterproof and Air-Permeable Membrane by Water Surface Spreading Method for Metal-Air Battery

The electrochemical performance of metal–air batteries is sensitive to environmental humidity, which significantly limits its wide application in an air environment. In this paper, a waterproof and breathable polydimethylsiloxane (PDMS) composite membrane has been successfully synthesized by the water spreading method for metal–air batteries. The effects of spreading times and fillers (hydrophobic SiO2 and silicalite-1) on the water vapor and air permeability of the PDMS membrane were investigated. The results demonstrate that increasing the spreading times and adding an appropriate amount of hydrophobic SiO2 can improve the waterproof quality and air permeability of the PDMS membrane. The optimized membrane was assembled into a metal–air battery, and the effects of the membrane on the running resistance, cycle number, and polarization voltage of the battery were evaluated. The hydrophobic SiO2–PDMS membrane significantly reduces the running resistance of the battery and improves the cycle number of lithium–air batteries by 25% and that of zinc–air batteries by 100% in an air environment (40% RH, 25 °C). The polarization voltage is also significantly reduced, indicating great potential in applications.

Enhancing water transport performance of gas diffusion layers through coupling manipulation of pore structure and hydrophobicity

The water discharge capacity of gas diffusion layer (GDL) is a key factor for improving the performance of proton exchange membrane fuel cells (PEMFCs) at high current density. In this study, the hydrothermal decoration approach is employed to enhance the hydrophobicity of a commercial GDL and is compared with the immersion method. The hydrophobic SiO2 particles are homogeneously deposited on the carbon fiber of the GDL via hydrothermal decoration (HD-GDL). In contrast, the hydrophobic SiO2 only partially coats the carbon fiber in the top and bottom regions of the GDL during the immersion (IM-GDL). The surface roughness and diameter of fibers increase when the surface morphology of fibers changes from grooves (CR-GDL) to coating (IM-GDL) and particles (HD-GDL). The breakthrough pressure is higher and the liquid water saturation ratio is lower for HD-GDL than that for CR-GDL and IM-GDL. Multi-scale numerical simulations show that the enhanced water transport velocity is due to the enlarged fiber diameter, whereas the decreased liquid water saturation ratio is due to the coupled effects of enhanced fiber hydrophobicity and enlarged fiber diameter. The improved water discharge capacity of the GDL induced by hydrothermal decoration can be employed to enhance the water management performance of PEMFCs.

Fabrication of superhydrophobic P(VDF-HFP)/SiO2 composite film for stable radiative cooling

Daytime radiative cooling that cools down an object by reflecting solar light and radiating heat simultaneously is expected to be a promising technology for dissipating heat without any energy consumption. However, radiative cooling materials’ solar reflection and infrared emissivity will be affected by the rain or dust pollution, therefore reducing the cooling performance under outdoor environments. A superhydrophobic radiative cooling composite film with hydrophobic SiO2 embedded in poly(vinylidene fluoride-co-hexafluoropropene) was proposed via phase separation technology. The SiO2 particles not only imparted to the film porous micro-nano tier rough structure to enhance the surface hydrophobicity, but also improved the mid-infrared emissivity of the film. As a consequence, the as-prepared film achieved 10.3 °C cooling under direct sunlight with convective heat reduced by transparent polyethylene film, and excellent superhydrophobicity with water contact angle greater than 160° and sliding angle close to 0°. Moreover, the cooling performance and superhydrophobicity of the film changed little after immersion in different pH solution and long-time exposure to UV irradiation. Importantly, the obtained film demonstrated great self-cleaning property making it hardly to be contaminated in outdoor environments, which is significant for sustainable applications.

Improving the mechanical performance of P(N‐hydroxymethyl acrylamide/acrylic acid/2‐acrylamido‐2‐methylpropanesulfonic acid) hydrogel via hydrophobic modified nanosilica

AbstractHydrogels with high mechanical strength are essential for its most industrial applications. In this work, the hydrophobic SiO2nanoparticles (M‐SiO2NPs) modified with octadecyltrimethoxysilane were used as physical crosslinker to toughen the mechanical properties of hydrogels. The solution of monomers containing M‐SiO2NPs, N‐hydroxymethyl acrylamide (NHAM), acrylic acid (AA), 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS), was polymerized to prepare a P(NHAM/AA/AMPS)‐based composite hydrogel without any chemical cross‐linker. The composition and microstructure of the hydrogel were carefully studied with Fourier transform infrared spectroscopy and scanning electron microscopy. The mechanical properties of the hydrogel were investigated through compressive and tensile tests. Dynamic swelling tests were carried out at different pH values (1.0–12.0) and salinity (2000–20,000 mg/L) to study the acid resistance, alkali resistance, and salt resistance of the hydrogel. The obtained results showed that the hydrogel exhibited excellent mechanical performance, which was attributed to the unique 3D network formed by the hydrogen bond between M‐SiO2NPs and polymer as well as the hydrophobic association effect between the hydrophobic chains of M‐SiO2NPs. Furthermore, the hydrophobic association effect was enhanced when contacting with salt, acid, and alkali solutions, thus endowing the hydrogel with intensified salt resistance and wider acid–base adaptability range.