Switchable Surface Wettability Research Articles

Intelligent Wearable Graphene Nano‐Electronics with Switchable Surface Wettability Capabilities for Autonomous Sweat Enrichment‐Purification‐Analysis

AbstractSweat wearable biosensors facilitate continuous monitoring of individuals’ in‐depth body physiological state with real‐time and molecular‐level insight. However, limited detection accuracy and sensitivity resulted from insufficient amount of sweat sampling and impurities interferences still hinder their practical applications. Here, a miniature wearable skin‐interfaced intelligent graphene nano‐electronic (SIGN) patch employing a novel Janus membrane integrated surface wettability switchable microfluidic module with autonomous sweat sampling and purification capabilities is presented for in situ analysis of sweat biomarkers. Due to the asymmetric surface energy distribution characteristics of the microfluidic surfaces, rapid, directional transport of sufficient amount of sweat to the Janus membrane is achieved. The Janus membrane purifies the sweat sample and transport the sample to the sensing surface autonomously, thus eliminating impurities interferences and enhancing the sensing performance. An ultra‐flexible bio‐receptor functionalized graphene transistor for accurately monitoring sweat biomarkers such as lactate, with outstanding signal reproducibility and good long‐term (over 1 month) stability, and a signal processing unit are employed incorporating with the microfluidic module. In practical wearing tests, the SIGN patch enables the continuous measuring of sweat lactate levels for volunteers during exercises and intelligently providing a preliminary diagnostic assessment on their exercise intensity successfully, suggesting its potential commercialization prospects.

Switchable superlyophobic CoAl-layered double hydroxide (LDH)-based mesh membranes for separation of various oil/water systems and removal of soluble organic pollutants

Switchable surface wettability has attracted tremendous attention owing to its potential applications, but it is still thorny to construct under-liquid dual superlyophobic surfaces for reversible separation of emulsified oil/water mixtures and treatment of complex oily wastewater. In this work, a CoAl-LDH-based mesh membrane was prepared for switchable separation of emulsified oily wastewater. The interpenetrating CoAl-LDH nanosheets were grown on the stainless steel mesh (SSM) forming a micro-/nano hierarchical structure via a hydrothermal method, which endows the membrane with under-liquid dual superlyophobicity. The obtained CoAl-LDH membrane exhibited switchable separation capability for both oil/water mixtures and oil/water emulsions with high fluxes and efficiencies (99.7%). In addition, the CoAl-LDH membrane could not only separate but also photodegrade the oil-in-water (O/W) emulsions containing soluble organic pollutants. Interestingly, after introducing a ZnO nanorod layer, the LDH/ZnO membrane exhibited progressive removal efficiency (99%) and photodegradation efficiency (＞99%) for methylene blue (MB). The cycled and harsh condition tests also confirmed the stability and robustness of the prepared membranes. The excellent separation performance and photocatalytic property endow the membranes appealing to practical oil/water separation and oily wastewater treatment.

Wettability-modulated ordered mesoporous carbon electrodes for electrocatalytic reactions involving gases

Herein, a series of ordered mesoporous carbon (OMC) electrodes with switchable surface wettability were developed. These electrodes are favorable for water electrolysis at high current densities and increase the production of H2O2 in the oxygen reduction reaction. The hydrophilic OMC electrodes can promote the oxygen evolution reaction performance by separating O2 bubbles promptly. The hydrophobic OMC electrodes provide a directional diffusion channel for O2 transport to improve the efficiency of O2 utilization. The hydrophobic OMC electrode is used for green synthesis of H2O2 with a production rate of 48.1 mmol gcat−1 h−1, Faraday efficiency of 86.3%, and minimum energy consumption of 3.07 kWh kg−1. The constructed electro-Fenton system reached 87% and 73% removal rate of rhodamine B and methyl orange within 60 min, respectively. The hydrophilic/hydrophobic electrodes are expected to have an important function in electrocatalytic reactions involving gases.

Surface hydrophobicity-hydrophilicity switching induced interface heat and water transfer enhancement for high-efficiency solar steam generation

Beyond photothermal conversion, the surface wettability of light-absorbing materials should be also determinative to the efficiency of solar-driven interfacial steam generation (SISG). Herein, by modifying hydrophobic Cu nanoparticles (NPs) with a hydrophilic carbon (C) shell, hydrophilic Cu@C core–shell NPs were successfully fabricated and used for constructing evaporation films for SISG. In comparison to the film constructed with Cu NPs, the evaporation films constructed with Cu@C core–shell NPs exhibit much increased SISG efficiency, reaching 94.6% as high. Except for the localized surface plasmon resonance (LSPR) effect of Cu NPs ensuring the excellent photothermal conversion, it is experimentally and theoretically revealed that the surface wettability switching from hydrophobicity to hydrophilicity, as induced by C coating, is beneficial to heat transfer at the solid/liquid interface and water transport at the evaporative surface, thus improving the thermal-evaporation conversion performance for efficient SISG. However, the further thickened C shells would weaken the LSPR effect and hinder the interface heat and water transfer, leading to the decreased photothermal and thermal-evaporation conversion efficiencies, and thus the lowered SISG performances. This demonstration gives an alternative and promising access to the rational design of photothermal materials featured with switchable surface wettability ensuring interface heat and water transfer enhancement for efficient SISG.

Smart and durable pH-responsive superhydrophobic fabrics with switchable surface wettability for high-efficiency and complex oil/water separation

The oily wastewater has posed a great threat to the environment and human health, and the oil-water mixture is complex and diverse. Therefore, it is crucial to develop a smart and efficient oil/water separation material. In this paper, random polymers containing carboxyl groups were synthesized for surface-modifying hydrophilic SiO2 nanoparticles. Polydimethylsiloxane (PDMS) was then used as the adhesive to fix the modified SiO2 nanoparticles firmly on the fabric surface endowing the fabric with a robust hydrophobic effect. The modified SiO2 nanoparticles not only made the fabric obtain a rough structure but also caused the fabric to have the effect of switchable wettability under the stimulation of pH. In addition, the prepared fabric maintained good mechanical durability and chemical stability after the mechanical abrasion, ultraviolet irradiation, and organic solvent treatment. Interestingly, under the stimulation of pH, the smart fabric could controllably separate different oil/water mixtures (including heavy oil/water and light oil/water) with excellent separation efficiency and high flux even after 20 cycles of separation process. Meanwhile, the pH-responsive fabric material successfully separated light oil/water/heavy oil three-phase oil/water mixture and different kinds of emulsions. Therefore, the prepared pH-responsive superwetting fabric has a broad application prospect in the field of dealing with complex oil/water mixing systems.

Biomimetic superwetting CuSx–based composite mesh for wastewater treatment: Reversible oil/water separation, photocatalytic degradation and photothermal sterilization

Water pollutants, often containing insoluble oils, soluble dyes, and pathogenic bacteria in wastewater, have threatened ecosystem security and human health, making great challenges for water purification and wastewater treatment. Considering the variety and complexity of water pollutants in wastewater, the development of a versatile material for complex wastewater cleanup with one single-step procedure is highly desirable. Herein, a biomimetic superwetting CuSx-based composite mesh is constructed as a versatile platform for all-in-one water purification. In this procedure, the hierarchical micro/nanoscale CuSx structures are controllably generated on Cu mesh surface via a single-step solvothermal process, endowing CuSx-based composite mesh with special switchable surface wettability, efficient photocatalytic capability and excellent photothermal antibacterial activity. Owing to its special switchable surface wettability, this superwetting CuSx-based composite mesh firstly demonstrates the reversible oil/water separation with high separation efficiency, robust durability and good reusability. Moreover, such superwetting CuSx-based composite mesh simultaneously reveals the efficient photodegradation towards organic dye contaminants and the enhanced photothermal antibacterial properties against Escherichia coli and Staphylococcus aureus in water under light illumination. With respect to these features, this superwetting CuSx-based composite mesh can simultaneously clean up those complex contaminants from wastewater, showing the promising potential in advanced water purification and wastewater treatment.

A bio-inspired green method to fabricate pH-responsive sponge with switchable surface wettability for multitasking and effective oil-water separation

Smart oil-water separation materials with stimuli-responsive wettability surfaces have attracted wide attention. In this paper, a novel, simple and low-cost method is developed to prepare a pH-responsive melamine sponge (MS) with switchable wettability. This approach involves the hydrophobic modification of hexadecyltrimethoxysilane (HDTMS) on the MS surface modified by polydopamine (PDA) and the Michael addition reaction and Schiff base reaction between 12-aminododecanoic acid (NH2(CH2)11COOH) and PDA. Hydrophobic/oleophilic HDTMS and pH-triggered NH2(CH2)11COOH enable the functionalized sponge to repeatedly switch between the two extreme wettability under different pH environments. Benefiting from the excellent 3D porous surface structure and smart wettability, the as-prepared sponge can be applied in the on-demand separation of various oil-water mixtures by adsorption or filtration with a separation efficiency over 98.5% and high absorption capacity of 72.7–161.3 g·g−1. With the assistance of pump-driven, continuous adsorption separation can be achieved in two cases by utilizing the wettability transformation. Moreover, in an alkaline solution, the sponge can quickly release most of the absorbed oil, showing a controllable desorption process. This smart wettability material with simple preparation and green has application potential in controllable oil-water separation and on-demand oil-spills treatment.

Multifunctional Silica-Modified Hybrid Microgels Templated from Inverse Pickering Emulsions.

Microgels are regarded as soft colloids with environmental responsiveness. However, the majority of reported microgels are inherently hydrophilic, resulting in aqueous dispersions, and only used in water-based applications. Herein, we reported an efficient method for hybridization of poly(N-isopropylacrylamide) microgel by coating hydrophobic silica nanoparticles on their surface. The resultant hybrid microgel had switchable surface wettability and could be dispersed in both aqueous and oil phases. Meanwhile, the coated hydrophobic silica nanoparticles solved the difficulty in redispersing microgels caused by particle aggregation and film formation during the drying process, providing a significant advantage in dried storage. Furthermore, the introduction of hydrophobic silica nanoparticles endowed the hybrid microgel with a variety of applications, including cargo encapsulation, active release induced by emulsion reversion, and trace water absorption.

Smart Titanium Wire Used for the Evaluation of Hydrophobic/Hydrophilic Interaction by In-Tube Solid Phase Microextraction.

Evaluation of the hydrophobic/hydrophilic interaction individually between the sorbent and target compounds in sample pretreatment is a big challenge. Herein, a smart titanium substrate with switchable surface wettability was fabricated and selected as the sorbent for the solution. The titanium wires and meshes were fabricated by simple hydrothermal etching and chemical modification so as to construct the superhydrophilic and superhydrophobic surfaces. The micro/nano hierarchical structures of the formed TiO2 nanoparticles in situ on the surface of Ti substrates exhibited the switchable surface wettability. After UV irradiation for about 15.5 h, the superhydrophobic substrates became superhydrophilic. The morphologies and element composition of the wires were observed by SEM, EDS, and XRD, and their surface wettabilities were measured using the Ti mesh by contact angle goniometer. The pristine hydrophilic wire, the resulting superhydrophilic wire, superhydrophobic wire, and the UV-irradiated superhydrophilic wire were filled into a stainless tube as the sorbent instead of the sample loop of a six-port valve for on-line in-tube solid-phase microextraction. When employed in conjunction with HPLC, four kinds of wires were comparatively applied to extract six estrogens in water samples. The optimal conditions for the preconcentration and separation of target compounds were obtained with a sample volume of 60 mL, an injection rate of 2 mL/min, a desorption time of 2 min, and a mobile phase of acetonile/water (47/53, v/v). The results showed that both the superhydrophilic wire and UV-irradiated wire had the highest extraction efficiency for the polar compounds of estrogens with the enrichment factors in the range of 20–177, while the superhydrophobic wire exhibited the highest extraction efficiency for the non-polar compounds of five polycyclic aromatic hydrocarbons (PAHs). They demonstrated that extraction efficiency was mainly dependent on the surface wettability of the sorbent and the polarity of the target compounds, which was in accordance with the molecular theory of like dissolves like.

Fish-scale nickel mesh with switchable wettability for efficient oil/water separation

In the daily life of human beings, sewage discharge and oil spill accidents occur from time to time. New types of controllable oil/water separation interface materials have received more attention. In this study, we proposed a simple and environmentally friendly method to prepare a Nickel filter with switchable wettability. The final product is prepared by high temperature calcination and soaked with stearic acid ethanol solution. The prepared filter screen has selective separation performance for oil/water mixture with switchable surface wettability between superhydrophobic and superhydrophilic. The separation efficiency is higher than 99.50%, and the flux rate is as high as 46.25 L m−2s−1 for water-removing process and 40.22 L m−2s−1 for oil-removing process. The wettability conversion of the membrane can be achieved through heating treatment and soaking treatment, and it still has good oil/water separation performance. After 20 times of cycles, the separation efficiency remains unchanged, and the flux remain above 40.06 L m−2s−1 for oil removal and 36.81 L m−2s−1 for water removal process. The results show that the prepared nickel filter screen has good practical application prospects such as water reclamation and oil spill treatment.

Biotemplated Fabrication of a Multifunctional Superwettable Shape Memory Film for Wearable Sensing Electronics and Smart Liquid Droplet Manipulation.

Wearable superwettable surfaces with dynamic tunable wettability and self-healability are promising for advanced wearable electronics, whereas have been rarely reported. Herein, a flexible superhydrophobic shape memory film (SSMF) with switchable surface wettability and high strain sensitivity has been conveniently fabricated. The surface topography of the SSMF can be finely adjusted by a reversible stretching (bending)/recovery way, which makes it feasible to control the surface-switchable adhesive superhydrophobicity by simple body movements, demonstrating great advantages in selective droplet manipulation and smart control of droplet movement. Moreover, benefitting from the hierarchical micro/nanostructures and outstanding sensing performance, the flexible SSMFs with good adaptivity and durability can serve as smart wearable sensors attached to human skin to achieve full-range and real-time detection of human motions and intelligent control of Internet of Things. More interestingly, the unique dynamic dewetting property enables the sensors to work in a humid environment or rainy days. Overall, this work successfully integrates dynamic tunable superwettability into design of intelligent wearable electronics with multifunctions. The obtained SSMF-based wearable surface with dynamic dewetting properties reveals great potential in versatile application fields such as liquid-repellent electronics, wearable droplet manipulators, and all-weather intelligent actuators.

Wettability Switchable Membranes for Separating Both Oil-in-water and water-in-oil emulsions

Separation membranes with switchable wettability show great potential in the efficient treatment of both oil-in-water and water-in-oil emulsions. There still remain some critical challenges to prepare these membranes by a facile procedure and to elucidate the wettability response mechanism reasonably. Herein, commercial polypropylene membranes are endowed with switchable surface wettability by a simple co-deposition method of tannic acid and diethylenetriamine. The as-fabricated membrane surfaces are hydrophilic due to water immersion but hydrophobic after ethanol treatment. This hydrophilicity-hydrophobicity translation can repeat cyclically by water/ethanol treatments without losing the surface wettability. DFT simulations are used to calculate the solvation free energies of tannic acid in water and ethanol, respectively, to illustrate the chemical mechanism of the hydrophilicity-hydrophobicity translation. The results are in accordance with UV–vis spectra of the polyphenol in both solvents. The wettability switchable membranes show great potential in separating both oil-in-water and water-in-oil emulsions with excellent efficiency (98%). Moreover, the driving force for the separation processes can be an applied pressure of 0.1 MPa or merely the gravity of emulsions.

Highly stable superamphiphobic material with ethanol-triggered switchable wettability for high-efficiency on-demand oil–water separation

A large quantity of oil spills occurred have greatly endangered the natural environment and human survival health. Super-wetting materials with switchable wettability provide a good way to solve these problems efficiently and have been paid more and more attention. In this paper, we have successfully prepared an ethanol-triggered and highly stable superamphiphobic material with a switchable surface wettability by using zinc oxide (ZnO) particles and organic silane (PFDS) via a simple coating method. The superamphiphobic material can maintain high oil-repellent and water-repellent performances under various harsh conditions. Most importantly, the superamphiphobic material demonstrates the switchable wettability by ethanol treatment. In view of this fresh mechanism, it can separate various oil–water mixtures on-demand with high separation efficiency and flux. Surprisingly, the mixtures of highly corrosive liquids and oils can also be separated. In addition, the material also has excellent self-cleaning and anti-fouling capabilities and low surface adhesion, which can effectively avoid the pollution of pollutants in the air. All these advantages show that the as-prepared material can play a vital function in solving the related severe conditions of marine oil pollution and industrial wastewater.

Fabrication of switchable surface wettability with UV-triggered on cotton fabric

A series of switchable wettability cotton fabrics were fabricated with inorganic oxide nanoparticles (TiO2 or Al2O3) modification of stearic acid (STA). By adjusting the additive amount of binary of inorganic oxide nanoparticles, five kinds of samples were obtained. These cotton fabrics were fully characterized, and all the samples possessed superhydrophobic surface. Under the UV irradiation, the photoresponsive materials TiO2 could alter the fabrics wetting state, but the STA modified UV inactive Al2O3 nanoparticles could remain the superhydrophobicity of samples. The changed wettability fabrics recovered the superhydrophobicity after heating, and the switchable wettability of the samples was maintained even after several UV irradiation/heating cycles.

On-demand oil/water separation enabled by magnetic super-oleophobic/super-hydrophilic surfaces with solvent-responsive wettability transition

Materials with common super-wettability are always restricted either by the pores fouling by oil (super-hydrophobicity/super-oleophilicity), or by the formation of hydration layer in advance (super-hydrophilicity/underwater super-oleophobicity) during oil water separation. To resolve this problem, super-oleophobic/super-hydrophilic surfaces were fabricated by introducing magnetic nanoparticles, short-chain fluorine groups and hydrophilic-induced units into the 2D or 3D substrates. Wettability formation mechanism was systematically investigated by combining theoretical calculation with characterization of surface micro-morphology and chemical composition. Surfaces with the uncommon super-wettability exhibited excellent anti-oil fouling ability, and can be directly used for oil water separation in way of “water removing”. Moreover, a solvent-responsive wettability transition strategy was proposed, which can reversibly convert the super-oleophobic/super-hydrophilic surfaces into super-oleophilic/underoil super-hydrophobic surfaces within 10 s. Then, free light or heavy oil/water separation and demulsification of oil-in-water emulsions and water-in-oil emulsions were achieved through the switchable surface wettability toward water and oil. Furthermore, the super-wettability of as-prepared samples are almost unchanged even after the test of immersion in pH = 1 acid and pH = 14 alkali solution for 48 h and 100 cycles of successive cyclic compression. Hence, these unique advantages of the super-oleophobic/super-hydrophilic surfaces are promising for multitasking and highly efficient oil water separation and demulsification.

Fast Modulation of Surface Amphiphobicity/Amphiphilicity via Bidirectional Substitution between Perfluorinated Surfactants and Polyanions throughout Pre-Assembled Polyelectrolyte Multilayers

In the present work, we demonstrate a bidirectional substitution between perfluorooctanoate (PFO) surfactants and polyanions throughout the pre-assembled polyelectrolyte multilayers (PEMs) for a rapid modulation of surface wettability between amphiphobicity and amphiphilicity. Upon incubation of the PEMs made of alternating deposition of poly(diallyldimethylammonium) (PDDA) and poly(styrenesulfonate) (PSS) in PFO solutions at concentrations above or around its critical micelle concentration, the majority (ca. >75%) of PSS molecules throughout the PDDA/PSS PEMs can be substituted by PFO anions within 10 s, generating PFO-substituted PDDA/PSS (PFO-PDDA/PSS) films. This effective substitution of PSS polyanions in PDDA/PSS PEMs by PFO anions is suggested by the mechanism that the stability of PDDA/PFO complexes is higher than that of PDDA/PSS PEMs. Furthermore, PFO anions all the way through the PFO-PDDA/PSS films can be reversibly substituted by PSS polyanions, while the substitution efficiency depends on the ionic strength of the PSS solutions. The processes of bidirectional and reversible substitution between PFO anions and PSS polyanions throughout the PDDA/PSS films can be repeated at least 10 times accompanied with a negligible change in the film thickness and surface morphology. The surface wettability study reveals that the PFO-PDDA/PSS films are amphiphobic with water and oil contact angles (CAs) of 114 ± 2 and 64 ± 2°, respectively, while PSS-substituted PFO-(PDDA/PSS) films are amphiphilic with water and oil CAs of 6 ± 1 and 0°, respectively. These novelties of the films enable switchable surface wettability simply by dipping the PDDA/PSS film-coated objects into PFO solutions for 2 s or PSS solutions for 30 s.

Functionalized Superwettable Fabric with Switchable Wettability for Efficient Oily Wastewater Purification, in Situ Chemical Reaction System Separation, and Photocatalysis Degradation.

In view of the increasing serious water environmental and human health issues caused by oily wastewater, functional superwetting materials with controllable wettability, high durability, and scale preparation methods are highly desired for efficient oil/water separation. In this respect, a pH-responsive multifunctional fabric with switchable surface wettability, favorable mechanical durability, and self-repairing property has been developed via decorating the modified TiO2 nanoparticles of special surface compositions onto the fabric surface. By virtue of the intelligent surface wettability, the resulted superwettable fabric can be used for controllable separation of multiple oil/water mixtures, particularly the complicated oil/water/oil ternary mixtures, showing excellent separation efficiency and high filtration flux even under extreme pH conditions, which is comparable to most of the commercial and currently reported functionalized membranes. Simultaneously, the negative pressure-driven, continuous, high-speed, and highly efficient in situ purification of large volumes of oily wastewater is successfully achieved based on the resulted superwettable fabric. More importantly, with the as-prepared superwettable fabric as the filtration membrane, the continuous in situ separation of the synthetic oily product from the corresponding chemical reaction systems is well performed without interruption of the reaction, demonstrating outstanding merits of simplifying procedures, saving operation time, and increasing product yield. In addition, it is worth noting that the alkali-treated superhydrophilic fabric presents superior photocatalysis self-cleaning performance for various water-soluble organic pollutants. These unique advantages of the functionalized smart superwettable fabric ensure that it can be competent in multifarious relevant challenging settings, indicating a broad prospect for diverse practical applications, especially the oily wastewater treatment and multiple industrial operation optimizations.

A fully bio-based composite coating with mechanical robustness and dual superlyophobicity for efficient two-way oil/water separation

Recently, two-way oil/water separation materials bearing both “water-removing” and “oil-removing” functions are of great interest for treating environmental water pollution. Despite having switchable surface wettability, these materials are generally designed to possess superhydrophilicity in air, which, standing on the viewpoint of thermodynamics, is unstable and easy to lose the superwetting property. Concerning the full exploitation of sustainable biomass resources, herein, we use soy protein and ramie fiber to fabricate a cross-linked biocomposite whose amphiphilicity can be tuned by introducing a low surface-energy agent, octadecylamine. The resultant composite can be used as a coating for stainless steel meshes, preparing stably hydrophobic surface in air as well as achieving dual superlyophobicity under liquid that is required for efficiently separating light and heavy oils from water. Furthermore, a high separation efficiency is acquired for both light oil/water and heavy oil/water mixtures during cyclicusage. Notably, the fully bio-based coating displays high resistance against mechanical abrasion and harsh chemical corrosions (acid, alkaline, and salt) without losing high separation efficiency, indicating the potential application of such material in oily wastewater treatment.

Polydopamine as a Versatile Adhesive Layer for Robust Fabrication of Smart Surface with Switchable Wettability for Effective Oil/Water Separation

A smart material with switchable surface wettability is highly desired for the practical application in removing oil from oily wastewater. In this work, we developed a robust and simple method to f...

CO2-Responsive Cellulose Nanofibers Aerogels for Switchable Oil-Water Separation.

Cellulose nanofibers (CNFs) aerogels with controllable surface wettability were prepared by grafting poly( N, N-dimethylamino-2-ethyl methacrylate) (PDMAEMA) polymer brushes via surface-initiated atom-transfer radical polymerization. After grafting PDMAEMA polymer, the surface of the aerogel was hydrophobic. However, in the presence of CO2, the surface of the aerogel gradually changes from hydrophobic to hydrophilic. The porous structure and CO2-responsiveness of PDMAEMA brushes within the CNFs aerogels allowed for the on-off switching of the oil-water mixture separation process. These CNFs aerogels were recyclable and displayed attractive separation efficiency for oil-water mixture and surfactant-stabilized emulsions. Furthermore, the switchable surface wettability holds an advantage of avoiding oil-fouling, which will greatly improve its recyclability.