Responsive Wettability Research Articles

Topographical Analysis of Human Enamel after Phosphoric Acid Etching and Er,Cr:YSGG Laser Irradiation.

Introduction: Dental hard and soft tissues have been successfully removed by using the Er,Cr:YSGG laser, but there is a controversy about using lasers over conventional tooth surface preparation for bonding aesthetic restoration. Surface roughness and wettability in response to Er,Cr:YSGG laser irradiation are essential properties for restoration longevity. Methods: Fifty-one intact human premolars removed in orthodontic treatment were included in this study and divided into three groups (n=17). The first group (G1) was the control without surface treatment, (G2) was treated with 37% phosphoric acid for 15 seconds, and (G3) was treated with the Er,Cr:YSGG laser using the following parameters: 2 W or 3 W at 20 Hz, 10% air and water ratio using the MZ6 laser tip. The standardization of laser irradiation was accomplished by a computerized numerical control unit. The surface of the samples was evaluated by using a light microscope, profilometer, atomic force microscopy (AFM), SEM, and wettability tests. Results: The SEM examination revealed that the lased enamel surface was clean, irregular, and devoid of a smear layer, while the acid etch surface was relatively smooth and covered with a smear layer. The surface roughness of the lased enamel surface was significantly higher than that of other groups, according to the results of the profilometer as well as the AFM tests. The wettability test showed that the lased enamel surface recorded a significant reduction in the contact angle in comparison to the other groups. Conclusion: It can be concluded that the Er,Cr:YSGG laser can be used as an alternative and safe method to the acid-etching technique for surface treatment.

Temperature-responsive peristome-structured smart surface for the unidirectional controllable motion of large droplets

The manipulation of fast, unidirectional motion for large droplets shows important applications in the fields of fog collection and biochemical reactions. However, driving large droplets (>5 μL) to move directionally and quickly remains challenging due to the nonnegligible volume force. Herein, we fabricated a scalable, bionic peristome substrate with a microcavity width of 180 μm using a 3D printing method, which could unidirectionally drive a large water droplet (~8 μL) at a speed reaching 12.5 mm/s by temperature-responsive wettability. The substrate surface was grafted with PNIPAAm, which could reversibly change its wettability in response to temperature, thereby enabling a temperature-responsive smart surface that could regulate droplet movement in real-time by changing the temperature. A series of temperature-responsive smart patterns were designed to induce water transport along specific paths to further realize controllable droplet motion with the antibacterial treatment of predesignated areas. The ability to achieve temperature-responsive unidirectional motion and dynamic control of droplet movement could allow programmable fluidic biosensors and precision medical devices.A temperature-responsive smart surface was produced to control the unidirectional motion of large droplets between spreading and pinning movement by changing the surface wettability.

Thermodynamic expression of surface reconstruction impact on surface wettability

In this work we demonstrated noticeable change in the surface wettability in response to environmental changes for self-assembled monolayers (SAM) of functional alkanethiols as a result of the orientation of surface polar groups as well as the permeation of the environmental phase into the SAM surface region with the aid of sum frequency generation spectroscopy and quartz microcrystal balance. Yet the revealed surface reconstruction caused unexpectedly subtle change in SAM surface energy (within ± 8 %) due to checks and balances of the dispersive and polar components of surface energy. By introducing the work of wetting as the difference between the work of adhesion of a fluid on a solid and its surface tension, here we managed to consistently express surface reconstruction impact in SAM surface wettability as an exponential function of the relative change in work of wetting for the wetting fluid. Furthermore, we also succeeded in harnessing the relative change ratio of the work of wetting of water to that of oil to demarcate surface polar groups, which are > 1 for weakly polar groups (e.g., Br and pyrrole), <1 for small, highly polar groups (e.g., OH, NH2 and COOH), and environmentally sensitive for large, highly polar groups (e.g., H2PO3).

Scalable and switchable CO2-responsive membranes with high wettability for separation of various oil/water systems

Smart membranes with responsive wettability show promise for controllably separating oil/water mixtures, including immiscible oil-water mixtures and surfactant-stabilized oil/water emulsions. However, the membranes are challenged by unsatisfactory external stimuli, inadequate wettability responsiveness, difficulty in scalability and poor self-cleaning performance. Here, we develop a capillary force-driven confinement self-assembling strategy to construct a scalable and stable CO2-responsive membrane for the smart separation of various oil/water systems. In this process, the CO2-responsive copolymer can homogeneously adhere to the membrane surface by manipulating the capillary force, generating a membrane with a large area up to 3600 cm2 and excellent switching wettability between high hydrophobicity/underwater superoleophilicity and superhydrophilicity/underwater superoleophobicity under CO2/N2 stimulation. The membrane can be applied to various oil/water systems, including immiscible mixtures, surfactant-stabilized emulsions, multiphase emulsions and pollutant-containing emulsions, demonstrating high separation efficiency (>99.9%), recyclability, and self-cleaning performance. Due to robust separation properties coupled with the excellent scalability, the membrane shows great implications for smart liquid separation.

3D‐Printed Robust Dual Superlyophobic Ti‐Based Porous Structure for Switchable Oil/Water Emulsion Separations

AbstractSmart surfaces with responsive wettability are unstable, and depend upon continuous external stimuli, which limits their widespread application in switchable oil/water emulsions separations. In this study, a Ti‐based 3D porous structure (SLM‐3DTi) is printed using advanced selective laser melting (SLM) technology for the switchable separation of oil/water emulsion. With the assistance of the computer program, porous structure and re‐entrant texture can be easily designed and printed in one step. Without any continuous external stimulus, the wettability of SLM‐3DTi can be reversibly switched between underwater superoleophobicity and underoil superhydrophobicity simply by drying and washing cycles. The SLM‐3DTi achieves switchable surfactant‐stabilized oil‐in‐water emulsion (SSE(o/w)) and surfactants‐stabilized water‐in‐oil emulsion (SSE(w/o)) separation with purity above 99.8% at a flux of more than 2000 L m−2 h−1. In addition, the re‐entrant texture of the SLM‐3DTi surface is formed with the partially melting powder particles on the part contour, which has much stronger mechanical durability than any binder. Furthermore, SLM‐3DTi has excellent corrosion resistance due to the material properties of Ti. More importantly, based on the visualization analysis of the simulation, the mechanism of SLM‐3DTi emulsion separation is further elucidated. Therefore, SLM‐3DTi has broad practical application potential for high‐flux, high‐purity, and switchable oil/water emulsion separation.

Surface properties and bioactivity of PNIPAM-grafted-chitosan/chondroitin multilayers

The thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) is widely applied in the biomedical field particularly as thermoresponsive substrate for culture of cells. To be used as a stimuli-responsive coating for cell culture, combining PNIPAM with glycosaminoglycans might be an effective approach to improve its bioactivity. In this study, chitosan is grafted with PNIPAM moieties (PCHI) possessing a cloud point at 31 ​°C and used as a polycation to fabricate thermoresponsive polyelectrolyte multilayers (PEM) with the bioactive polyanion chondroitin sulfate (CS) at pH 4 by layer-by-layer technique. The in-situ investigation by surface plasmon resonance and quartz crystal microbalance with dissipation monitoring confirms that the formation of PEMs with CS can be achieved despite the bulky structure of PCHI at 25 ​°C. The stability of the PEMs is further improved at physiological pH 7.4 by chemical crosslinking using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide. Moreover, these PEMs exhibit de-swelling and swelling ability with different surface wettability in response to temperature, which triggers the adsorption and desorption of adhesive protein vitronectin on the PEMs. At 37 ​°C, the PEMs containing PNIPAM particularly associated with CS terminal layer supports protein adsorption and consequently enhances cell adhesion using multipotent murine stem cells. Overall, due to improved stability, crosslinked PNIPAM-modified biogenic multilayers are cytocompatible and hold great potential as culture substrate for different tissue cells and application in tissue engineering.

Dual-responsive polyacrylonitrile-based electrospun membrane for controllable oil-water separation

Membrane separation based on smart materials with responsive wettability has attracted great attention due to the excellent performance of controllable oil-water separation. Herein, responsive copolymer originated from N-isopropylacrylamide and 2-(dimethylamino) ethyl methacrylate was synthesized and electrospun with polyacrylonitrile to fabricate smart composite membrane. The introduction of the responsive copolymer endowed the membrane with stimuli-responsive wettability to pH and temperature. Specifically, at the initial state, water was selectively blocked while oil passed through the membrane. After treatment with acidic water or CO2, the reverse separation was realized due to the protonation of the tertiary amine group in the copolymer. Water was selectively passed through the membrane after heat treatment because of the structural change of membrane upon temperature. The developed membrane was able to separate different types of oil-water mixtures and surfactant-stabled emulsions with high efficiency. Additionally, two membranes controlled by temperature and pH were designed to construct a logic AND gate for oil-water separation, and the results demonstrated that only the temperature and acidity of the solution were simultaneously satisfied, the water could flow through the valve combination, and such capability made this smart membrane great potential for remotely controlling the oil-water separation process.

AgNPs-thiols modified PVDF electrospun nanofiber membrane with a highly rough and pH-responsive surface for controllable oil/water separation

To develop a novel membrane with controllable wettability in response to external stimuli for intelligent oil/water separation is always in urgent demand. In this study, a pH-responsive nanofibrous membrane was prepared through the step-by-step modification of polyvinylidene fluoride (PVDF) electrospun nanofiber membrane, including mussel-inspired self-polymerization of polydopamine (PDA), immobilization of silver nanoparticles (AgNPs) and self-assembly of thiols. A rough membrane surface could be formed by the loading of AgNPs, and the subsequent introduction of HS(CH2)11CH3/HS(CH2)10COOH via metal-thiol coordination could endow the membrane with pH-responsive wettability. The surface of the membrane was able to quickly and reversely switch between superhydrophobicity and superhydrophilicity through simply applying pH stimulus at pH 7 and 13, respectively. The membrane can be applied for separating multiphase oil/water mixtures, achieving separation efficiency of over 99.2% for light oil/water mixture and 96.5% for heavy oil/water mixture with a stable flux of around 2500 L/m2·h for water and 11,000 L/m2·h for oil over the 10-cycle separation process. Meanwhile, the membrane exhibited separation efficiency of higher than 99% for all the tested oil-in-water emulsions, and the water flux of the membrane could be effectively recovered by water rinsing. Moreover, the membrane demonstrated a good structural stability against rigorous mechanical abrasion. The pH-responsive membrane could be potentially applied for smart and energy-saving separation and recycle of oil or water from oily wastewater.

Self-Assembled Monolayers of Arylazopyrazoles on Glass and Silicon Oxide: Photoisomerization and Photoresponsive Wettability.

Surface coatings that respond to external influences and change their physical properties upon application of external stimuli are of great interest, with light being a particularly desirable choice. Photoswitches such as azobenzenes have been employed in a range of photoresponsive coatings. One striking change in physical property of many photoresponsive coatings is their responsive wettability upon illumination. In this work, we present photoswitchable self-assembled monolayers based on arylazopyrazoles (AAPs). In solution, AAPs offer significant improvements in terms of the photostationary state, thermal stability, and fatigue resistance. The AAP photoswitch is coupled to triethoxysilanes for an easy, one-step functionalization of glass and silicon oxide surfaces. We show the synthesis of AAP-based silanes and the successful surface functionalization, and we confirm the excellent photoswitchability of the AAPs in a self-assembled monolayer upon alternating irradiation with UV (365 nm) and green (520 nm) light. The self-assembled monolayers are investigated by UV/vis spectroscopy, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and contact angle goniometry. We furthermore investigate the effect of substitution of the AAPs on the photoresponsive wetting behavior and compare this with density functional theory (DFT) calculations of the dipole moments of the AAPs.

Polyelectrolyte Functionalisation of Track Etched Membranes: Towards Charge-Tuneable Adsorber Materials.

Porous adsorber membranes are promising materials for the removal of charged pollutants, such as heavy metal ions or organic dyes as model substances for pharmaceuticals from water. Here, we present the surface grafting of polyethylene terephthalate (PET) track-etched membranes having well defined cylindrical pores of 0.2 or 1 µm diameter with two polyelectrolytes, poly(2-acrylamido glycolic acid) (PAGA) and poly(N-acetyl dehydroalanine) (PNADha). The polyelectrolyte functionalised membranes were characterised by changes in wettability and hydraulic permeability in response to the external stimuli pH and the presence of Cu2+ ions. The response of the membranes proved to be consistent with functionalisation inside the pores, and the change of grafted polyelectrolyte macro-conformation was due to the reversible protonation or binding of Cu2+ ions. Moreover, the adsorption of the model dye methylene blue was studied and quantified. PAGA-grafted membranes showed an adsorption behavior following the Langmuir model for methylene blue.

Bioinspired Metal-Intermetallic Laminated Composites for the Fabrication of Superhydrophobic Surfaces with Responsive Wettability.

Hundreds of copper and titanium foils were applied to prepare biomimetic metal-intermetallic laminated composites by diffusion bonding. The cross sections of the obtained diffusion bonded bulks were etched selectively with FeCl3 solution to get regular microarray structures. This kind of microstructure was controlled accurately and promptly by simple parameter adjustment. The etched surfaces were modified with 1-dodecanethiol, and the water contact angles (WCAs) were measured. The relationship between the microstructure and wettability of the achieved material was discussed, and the reason for the anisotropic wettability was also analyzed. Then etched surfaces were anodized in different electrolyte solutions to obtain different nanostructures. The morphology and chemical compositions of the surfaces were analyzed. The surfaces with CuO nanostructures by modification show superhydrophobicity with self-cleaning, on which the WCA and water sliding angle are 160.9° and 0.8°, respectively. The surfaces with TiO2 nanostructures without modification show ultraviolet light-responsive wettability. After modification with 11-mercaptoundecanoic acid and 1-decanethiol, the surfaces also exhibit pH-responsive wettability. The superhydrophobic surfaces with responsive wettability have potential applications in biotechnology and microfluidics.

Bioinspired textile with dual-stimuli responsive wettability for body moisture management and signal expression

A smart bioinspired loofah textile with biosafe wettability shows high directional liquid transport capacity and the ability to identify liquids with different pH values.

Bioinspired superwetting surfaces for biosensing

AbstractInspired by nature, scientists and researchers have studied the wetting behaviors on various creatures and mimicked their structures to fabricate diverse functional superwetting materials. As one kind of emerging application, the bioinspired superwettable surfaces used for biosensing have been aroused wide interests. In this review, we summarized the recent developments of bioinspired superwettable surfaces in the field of biosensing. In the first part, superwettable creatures in nature, namely, superhydrophobic self‐cleaning lotus leaf, high‐adhesion superhydrophobic rose petal, amphiphobic springtail, patterned wetting desert beetles, slippery pitcher plant, were introduced. In sequence, we successively described the special wetting models of superhydrophobicity, superamphiphobicity, responsive wettability, patterned wettability, and slipperiness. Then, biosensing applications based on the respective patterned wettable, superhydrophobic, responsive wettable, and slippery substrates that were combined with the common detection approaches (colorimetry, fluorescence, surface‐enhanced Raman scattering (SERS), electrochemistry) were shown in detailed. At last, an insight of remaining challenges and future development for bioinspired superwetting materials applied in biosensing was provided.

Electroresponsive Polyelectrolyte Brushes Studied by Self-Consistent Field Theory.

End-grafting of polyelectrolyte chains to conducting substrates offers an opportunity to fabricate electro-responsive surfaces capable of changing their physical/chemical properties (adhesion, wettability) in response to applied electrical voltage. We use a self-consistent field numerical approach to compare the equilibrium properties of tethered strong and weak (pH-sensitive) polyelectrolytes to applied electrical field in both salt-free and salt-containing solutions. We demonstrate that both strong and weak polyelectrolyte brushes exhibit segregation of polyions in two populations if the surface is oppositely charged with respect to the brush. This segregation gives rise to complex patterns in the dependence of the brush thickness on salt concentration. We demonstrate that adjustable ionization of weak polyelectrolytes weakens their conformational response in terms of the dependence of brush thickness on the amplitude of the applied voltage.

Cellulosic sponges with pH responsive wettability for efficient oil-water separation

To obtain efficient oil-water separation materials with responsiveness, cellulosic porous materials with switchable wettability in response to pH changes were developed by reacting cellulose acetoacetate sponges with alkylamines of varying carbon chain length via dynamic covalent enamine bonds. The resulting sponges reversibly changed between being superhydrophilic (θwater = 0°) and highly hydrophobic (maximal θwater = 146°) under suitable pH conditions while maintained the favorable porous structures. Notably, the functionalized sponges exhibited high and selective oil absorption capacity (40–80 g/g) and satisfying desorption ability of 80%, and could efficiently separate oil-water mixtures and emulsions with extremely high efficiency (> 99%) in a controllable manner. With the three-dimensional micro/nano porous structure, switchable wettability and intrinsic environmentally friendliness, the pH responsive cellulosic sponges developed here hold great potential in controllable oil-water separation and oily wastewater purification.

Bioinspired Slippery Lubricant-Infused Surfaces With External Stimuli Responsive Wettability: A Mini Review.

Responsive slippery lubricant-infused surfaces (SLIS) have attracted substantial attention because of the high demand of fundamental research and practical applications, such as controllable liquid-repellency, intelligent, and easy-to-implement wettability switching. In this review, advanced development of responsive slippery surfaces is briefly summarized upon various external stimuli, including stress, electrical field, magnetic field, and temperature. In addition, remaining challenge and prospect are also discussed.

Superhydrophobicity-memory surfaces prepared by a femtosecond laser

Superhydrophobicity-memory surface that can transform its surface morphology and wettability in response to heat was successfully prepared by using femtosecond laser to directly induce hierarchical micropillar array on the surface of a thermal-responsive shape-memory polymer (SMP). When the resultant surface was pressed by an external load to make the micropillars lean to one side, the superhydrophobicity would weaken caused by the deformation of the micro/nanoscale structures. Interestingly, the original surface morphology and wettability could recover just through a simple heating process due to the excellent macro/microscopic shape-memory effect of such polymer. Even after 10 cycles of pressing-heating treatments, the surface was also able to re-obtain its original ultralow-adhesive superhydrophobicity. In addition to the restorable property, the superhydrophobicity of the as-prepared surface was very stable since the laser-induced microstructure on the SMP could withstand various harsh treatments/environments, such as sandpaper abrasion, tape peeling, UV irradiation, and the immersion in different pH solutions. The superhydrophobicity-memory surface was successfully used as a rewritable platform for directional liquid transportation. It is anticipated that the laser-induced hierarchical micropillars with superhydrophobicity-memory property will have significant applications in tunable wettability, liquid/droplet manipulation, and chemical engineering.

Design of Active Interfaces Using Responsive Molecular Components.

Responsive interfaces are interfaces that show a defined and reversible change in physical properties in response to external stimuli. Typically, responsive interfaces result from the immobilization of responsive molecular components at the interface that translate a nanoscale signal into a macroscopic effect. Responsive interfaces can also be obtained if the topology of the interface can be reversibly changed using an external stimulus. As the surface of any material is its connection to the environment, responsive interfaces provide opportunities for interactive materials which are not only able to change properties upon demand, but also sense their environment and act autonomously. The application of responsive molecular components at interfaces, however, requires chemical and physical compatibility with the material surface of interest, posing a challenge not least in the retention of the responsive functionality. The state of the art in "active" interfaces which display responsive wettability, permeability, or adhesion is discussed, with a particular emphasis on microscale and nanoscale patterning since patterned interfaces can give rise to unique material properties. Finally, perspectives in the development of responsive interfaces, as well as promising approaches for bypassing the most prominent challenges are discussed.

A facile and versatile route to functional poly(propylene) surfaces via UV-curable coatings

A convenient UV-curable coatings assisted surface functionalization strategy is presented to convert commodity Poly(propylene) (PP) films into diverse functional materials. To ensure a covalent integration between PP surface and functional UV-curable coatings, 3-(trimethoxysilyl) propyl acrylate (TMSPA) was functionalized on the surface of oxidized PP film. Two distinct UV-curable coatings differing primarily in the chemical nature of monomers were separately tethered on the surface of TMSPA functionalized PP films. The monomers applied in this study include 1H,1H,2H,2H-heptadecafluorodecyl acrylate (HFDA) and 2-isocyanatoethyl methacrylate (ICEMA). The use of HFDA as monomer resulted in PP film with fluorinated surface chemical nature, which would be attractive for applications desiring low surface energy, low dielectric constant, low flammability, low refractive index, and superior chemical resistance. Employing ICEMA monomer as part of UV-curable mixture resulted in PP film offering a high density of surface isocyanate groups (–NCO) that could be conveniently conjugated to a variety of amines to give a range of functional surfaces. For proof of concept, the –NCO groups on the surface of PP film were conjugated with amine terminated polyethylene glycol to give PP film that exhibited antifouling nature. In a separate experiment, the surface –NCO groups were conjugated to 2-aminoethanesufonic acid (AESA) to fabricate an anionic PP surface capable of effectively interacting with cationic species. The conjugation of surface –NCO groups with l-lysine imparted pH responsive wettability switching behaviour to the surface of PP film. Finally, poly(ethylene imine) (PEI) was conjugated to surface –NCO groups and the resulting surface PEI moieties were used as reducing and stabilizing agent to synthesize catalytically active gold nanoparticles (AuNPs) confined to the surface of PP film. All the surface functionalization's were fully corroborated by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), water contact angle (WCA) goniometry, and scanning electron microscopy (SEM). Considering the potential for incorporation into the existing industrial processes and resourcefulness of the surface functionalization via UV-curable coatings, we envision that the herein reported strategy holds an excellent potential to transform commodity PP films into a wide range of specialty materials for diverse applications at large scale.

Smart nonwoven fabric with reversibly dual-stimuli responsive wettability for intelligent oil-water separation and pollutants removal

This work presents the first fabrication of smart nonwoven fabric (DSR-CZPP) with extraordinary reversible double-stimulus responsive wettability, where carboxyl groups of cellulose nanocrystals/zinc oxide (CNC/ZnO) nanohybrids deposited on fabric surface can bond with hydroxyl group of the PDMAEMA-b-PHEMA-b-PMAAAB triblock polymer brushes that was prepared by using methyl methacrylate (HEMA), dimethylaminoethyl methacrylate (DMAEMA) and methacrylamide-azobenzene monomer (MAAAB) via reversible addition–fragmentation chain transfer (RAFT). The peculiar reversible double-stimulus responsive wettability of the DSR-CZPP can be modulated by triggering hydrophilic/hydrophobic transitions and lipophilic/oleophobic transitions under dual-stimulations of pH and UV light irradiation. The special molecular structure of the triblock polymer brushes enabled DSR-CZPP to intelligent modulation of oil-water separation under the control of "UV & pH double switch", meanwhile CNC/ZnO simultaneously can induce the photocatalytic degradation of organic dyes. Moreover, DSR-CZPP can have high removal ratios of various pollutants, such as metal ion (Cu2+) and toxic organic solvent (silicone oil, acetone and chloroform). This smart and multifunctional fabric shows great potentials for treating complicated polluted water from most industrial fields.