Green processing via surface diffuse atmospheric plasma to enhance the dyeing performance on polylactic acid fabric.

Poor dyeing performance has been a major defect of polylactic acid (PLA) fibers, which is caused by the lack of active chemical groups in PLA, and hinders the widespread use of this biodegradable material. Most of the existing chemical modification methods are not environmentally friendly and produce effluents. Herein, we report a green, efficient and continuous method to process PLA fibers via surface diffuse atmospheric plasma for the improvement of its hydrophilicity and dyeing performance. PLA fibers were processed via atmospheric plasma for grafting oxygen-containing functional groups, such as carboxyl, to achieve hydrophilicity and, meanwhile, strengthen the binding interactions with various dye molecules via covalent bonds, ionic bonds, or hydrogen bonds. In addition, different mechanisms of improving the dyeing performance on plasma-modified PLA fibers with different kinds of dyes have been discussed. This approach of material modification involves no chemical additives and has high processing efficiency, showing the potential applicability of green treatment to products in various fields.

Confined Water Dominates Ion/Molecule Transport in Hydrogel Nanochannels.

Current artificial nanochannels rely more on charge interactions for intelligent mass transport. Nevertheless, popular charged nanochannels would lose their advantages in long-term applications. Confined water, an indispensable transport medium in biological nanochannels, dominating the transport process in the uncharged nanochannels perfectly provides a new perspective. Herein, we achieve confined-water-dominated mass transport in hydrogel nanochannels (HNCs) constructed by in situ photopolymerization of acrylic acid (PAA) hydrogel in anodic alumina (AAO) nanochannels. HNCs show selectivity to Na+ transport and a high transport rate of molecules after introducing Na+/Li+, compared with other alkali metal ions like Cs+/K+. The mechanism given by ATR-FTIR shows that the hydrogen-bonding structure of confined water in HNCs is destabilized by Na+/Li+, which facilitates mass transport, but is constrained by Cs+/K+, resulting in transport inhibition. This work elucidates the relationship between confined water and mass transport in uncharged nanochannels while also presenting a strategy for designing functional nanochannel devices.

Interfacial Water-Dictated Oil Adhesion Based on Ion Modulation.

Oil adhesion on ionic surfaces is ubiquitous in organisms and natural environments and is generally determined by surface chemical component and texture. However, when adhesion occurs, water molecules at the solid-liquid interface, acting as a bridge not only influenced by the structure and composition of the solid surface but also interacting with the neighboring oil molecules, play a crucial role but are always overlooked. Herein, we investigate the oil adhesion process on a carboxyl-terminated self-assembled monolayer surface (COOH-SAM) in ionic solutions and observe the interfacial water structure via surface-enhanced Raman scattering (SERS) in this system. It is found that the lower the tetracoordinated water content, the stronger the oil adhesion. Compared to monovalent ions, the strengthened binding of multivalent ions to the COOH-SAM surface makes the interfacial water more disordered, which eventually leads to a stronger oil adhesion. Notably, the amount of oil adhesion decreases with an increase in the thickness of the interfacial water region. The interfacial water-dictated oil adhesion has been demonstrated in capillary to simulate the water-driven oil recovery, providing a molecular-level explanation for enhanced oil recovery from low salinity water flooding and also indicating potential applications in intelligent microfluidic and seawater desalination.

Barnacle inspired high-strength hydrogel for adhesive.

Barnacle exhibits high adhesion strength underwater for its glue with coupled adhesion mechanisms, including hydrogen bonding, electrostatic force, and hydrophobic interaction. Inspired by such adhesion mechanism, we designed and constructed a hydrophobic phase separation hydrogel induced by the electrostatic and hydrogen bond interaction assembly of PEI and PMAA. By coupling the effect of hydrogen bond, electrostatic force and hydrophobic interaction, our gel materials show an ultrahigh mechanical strength, which is up to 2.66 ± 0.18 MPa. Also, benefit from the coupled adhesion forces, as well as the ability to destroy the interface water layer, the adhesion strength on the polar materials can be up to 1.99 ± 0.11 MPa underwater, while that of the adhesion strength is about 2.70 ± 0.21 MPa under silicon oil. This work provides a deeper understanding of the underwater adhesion principle of barnacle glue. Furthermore, our bioinspired strategy would provide an inspiration for the fabrication of high mechanical gel materials, and the rapid strong adhesive used in both water and organic solvents.

Strong Anchoring of Hydrogels through Superwetting-Assisted High-Density Interfacial Grafting.

Strong adhesion of hydrogels on solids plays an important role in stable working for various practical applications. However, current hydrogel adhesion suffers from poor interfacial bonding with solid surfaces. Here, we propose a general superwetting-assisted interfacial polymerization (SAIP) strategy to robustly anchor hydrogels onto solids by forming high-density interfacial covalent bonds. The key of our strategy is to make the initiator fully contact solid surfaces via a superwetting way for enhancing the interfacial grafting efficiency. The designed anchored hydrogels show strong bulk failure with a high breaking strength of ≈1.37 MPa, different from weak interfacial failure that occurs in traditional strategies. The strong interfacial adhesion greatly enhances the stability of hydrogels against swelling destruction. This work opens up new inspirations for designing strongly anchored hydrogels from an interfacial chemistry perspective.

One-pot method for preparation of capsaicin-containing double-network hydrogels for marine antifouling.

Marine biofouling which interferes with normal marine operation and also causes huge economic loss has become a worldwide problem. With the development of society, there is an urgent need to develop non-toxic and efficient anti-fouling strategies. Capsaicin is an environmentally friendly antifouling agent, but controlling the stable release of capsaicin from the coating is still a challenge to be solved. To achieve long-lasting antifouling property, in this work, we incorporate a derivative of capsaicin N-(4-hydroxy-3-methoxybenzyl)acrylamide (HMBA) to prepare double network (DN) hydrogels and make HMBA a part of the polymer network. Polyvinyl alcohol (PVA) has good hydrophilicity, and as a soft and ductile network, acrylamide (AM) and HMBA can polymerize to generate a rigid and brittle network. By adjusting the content of HMBA in the DN hydrogels, we can obtain a PVA-PAHX hydrogel with high mechanical strength, low swelling rate, and excellent antifouling effect, which provides a feasible way for the practical application of a hydrogel coating in long-term marine antifouling.

Spontaneous Freezing of Water between 233 and 235 K Is Not Due to Homogeneous Nucleation.

The spontaneous freezing of microdroplets around 233 K has long been regarded as the occurrence of homogeneous ice nucleation. The corresponding temperature has been directly regarded as the homogeneous ice nucleation temperature, which is an intrinsic character of water. However, many recent investigations indicate that the spontaneous freezing may be still induced by surfaces of the water microdroplets or the residual impurities inside. Therefore, it is highly desired to reveal with solid evidence the exact origin of the spontaneous freezing. Here we show with no ambiguity that the spontaneous freezing between 233 and 235 K is actually triggered by the surface of microdroplets, as the nucleation rate is found to be proportional to the surface area of droplets, via systematically investigating the freezing of water droplets with varying sizes under various cooling rates followed by a new approach in data analysis. The conclusion is further consolidated by published experimental data from other groups when using our data analysis approach. This study is critical for understanding the sources of "no-man's land" and features of homogeneous nucleation, as well as studying the structure and properties of deeply supercooled liquid water.

Nickel-Catcher-Doped Zwitterionic Hydrogel Coating on Nickel-Titanium Alloy Toward Capture and Detection of Nickel Ions.

Nickel-titanium (NiTi) alloys show broad applicability in biomedical fields. However, the unexpected aggregation of bacteria and the corrosion of body fluid on NiTi-based medical devices often lead to the leakage of nickel ions, resulting in inevitable allergic and cytotoxic activities. Therefore, the capture and detection of nickel ions are important to avoid serious adverse reactions caused by NiTi-based medical devices. Herein, we presented a nickel ion capture strategy by the combination of zwitterionic hydrogels as anti-bacteria layers and carbon disulfide (CS2) components as nickel-catchers (Ni-catchers). On the one hand, the hydration layer of zwitterionic hydrogel can efficiently inhibit bacteria adhesion and reduce nickel ions leakage from NiTi corrosion. On the other hand, Ni-catchers can capture leaked nickel ions from NiTi alloy actively by chelation reaction. Therefore, this strategy shows great capabilities in resisting bacteria adhesion and capturing nickel ions, providing the potential possibility for the detection of nickel ion leakage for implantable biomedical materials and devices.

Marine antifouling coatings with surface topographies triggered by phase segregation.

Marine biofouling is a ubiquitous and longstanding challenge that causes both economic and environmental problems. To address this, several antifouling strategies have been proposed, such as the release of biocidal compounds or surface chemical/physical design. Here we report a coating with surface structures (chemical heterogeneity) triggered by phase segregation, which endues the good antifouling properties, alongside robust mechanical properties, low underwater oil adhesion, and excellent optical transparency. This is achieved by arranging the hydrophobic and hydrophilic components to control the assembly and phase separation under the cross-linking and localized swelling process. The structure designs are based on the poly(ethylene glycols) (PEG), zwitterions, and hydrophobic components, which may lower the entropic and enthalpic driving forces for the adsorption of the marine organisms. Our approach could provide an effective way of manufacturing novel coating with amphiphilic micro/nanodomains structure, particularly for the marine industry. And we also showed that the coatings were stable under different temperatures and shear environments. To illustrate the applicability of such a robust coating in marine biofouling, we demonstrated significantly reduced algal adhesion and barnacle attachment in the sea (p < 0.01). We envision that this work will provide great potential for the application in antifouling marine coatings.

Microchannel and Nanofiber Array Morphology Enhanced Rapid Superspreading on Animals' Corneas.

The dynamic spreading phenomenon of liquids is vital for both understanding wetting mechanisms and visual reaction time-related applications. However, how to control and accelerate the spreading process is still an enormous challenge. Here, a unique microchannel and nanofiber array morphology enhanced rapid superspreading (RSS) effect on animals' corneas with a superspreading time (ST) of 830 ms is found, and the respective roles of the nanofiber array and the microchannel in the RSS effect are explicitly demonstrated. Specifically, the superspreading is induced by in-/out-of-plane nanocapillary forces among the nanofiber array; the microchannel is responsible for tremendously speeding up the superspreading process. Inspired by the RSS strategy, not only is an RSS surface fabricated with an ST of only 450 ms, which is, respectively, more than 26 and 1.8 times faster than conventional superamphiphilic surfaces and animal's corneas and can be applied as RSS surfaces on video monitors to record clear videos, but also it is demonstrated that the RSS effect has tremendous potential as advanced ophthalmic material surfaces to enhance its biocompatibility for clear vision.

Improved Ion Transport in Hydrogel-Based Nanofluidics for Osmotic Energy Conversion.

In nature, ultrafast signal transfer based on ion transport, which is the foundation of biological processes, commonly works in a hydrogel-water mixed mechanism. Inspired by organisms' hydrogel-based system, we introduce hydrogel into nanofluidics to prepare a hydrogel hybrid membrane. The introduction of a space charged hydrogel improves the ion selectivity evidently. Also, a power generator based on the hydrogel hybrid membrane shows an excellent energy conversion property; a maximum power density up to 11.72 W/m2 is achieved at a 500-fold salinity gradient. Furthermore, the membrane shows excellent mechanical properties. These values are achievable, which indicates our membrane's huge potential applications in osmotic energy conversion.

Bioinspired Hydrogel-Polymer Hybrids with a Tough and Antifatigue Interface via One-Step Polymerization.

Hydrogel hybrids are one of the key factors in life activities and biomimetic science; however, their development and utilization are critically impeded by their inadequate adhesive strength and intricate process. In nature, barnacles can stick to a variety of solid surfaces firmly (adhesive strength above 300 kPa) using a hydrophobic interface, which inspires us to firmly combine hydrogels and polymers through introducing an adhesive layer. By spreading a hydrophobic liquid membrane directly, tough combination of a hydrogel and a polymer substrate could be achieved after one-step polymerization. The fracture energy of the hydrogel attached to the surface of polyvinyl chloride was up to 1200 J m-2 and the tensile strength reached 1.21 MPa. Furthermore, the adhesion samples with this method exhibit an antifatigue performance, having withstood large bends and twists. It should be pointed out that this approach can also be applied to a variety of complicated surfaces. This work may expand the application range of hydrogels and provides an inspiration for hydrogel adhesion.

Hydrophilic/Hydrophobic Heterogeneity Anti-Biofouling Hydrogels with Well-Regulated Rehydration.

Hydrogels, as a representative of soft and biocompatible materials, have been widely used in biosensors, biomedical devices, soft robotics, and the marine industry. However, the ir-recoverability of hydrogels after dehydration, which causes the loss of original mechanical, optical, and wetting properties, has severely restricted their practical applications. At present, this critical challenge of maintaining hydrogels' accurate character has attracted less attention. To address this, here we report a hydrogel based on synergistic effects to achieve both well-regulated rehydration and deswelling properties. The hydrogel after dehydration can quickly restore its original state both on the macro- and microscale. In addition, the hydrogel has excellent mechanical stability after several dehydration-rehydration cycles. All of these properties offer a possibility of water condition endurance and increase the service life. The robust property is attributed to the hydrophilic-hydrophobic and ionic interactions induced by the synergy of hydrophilic/oleophilic heteronetworks. Moreover, zwitterionic segments as hydrophilic network play a vital role in fabricating anti-biofouling hydrogels. The durable and reusable hydrogel may have promising applications for biomedical materials, flexible devices, and the marine industry.

Design of hierarchical comb hydrophilic polymer brush (HCHPB) surfaces inspired by fish mucus for anti-biofouling.

Anti-biofouling surfaces are of high importance owing to their crucial roles in biosensors and biomedical devices, especially in the marine industry. However, traditional anti-biofouling surfaces based on either the release of biocidal compounds or surface peeling will contaminate the environment. The outstanding performances of natural anti-biofouling surfaces motivate the development of new bioinspired antifouling surfaces. Herein, a universal strategy inspired by the special performance of fish skin mucus is proposed for rationally designing anti-biofouling surfaces using grafted hierarchical comb hydrophilic polymer brushes (HCHPBs) on plastics and elastomers. The results show that the plastic substrate surface grafted PAA (polyacrylic acid)-g-PEG (polyethylene glycol) (MW 2000, 6000, and 11 000 Da) exhibits excellent hydrophilic and underwater oleophobic properties, and also shows good performance in terms of lubricity and drag reduction in water, which can be attributed to the HCHPB and the nanostructure on plastic surfaces. In addition, the modified substrate shows superior and long-lasting anti-biofouling properties to resist the adhesion of algae compared to the initial substrate. This comprehensive investigation is of great importance to understand the physicochemical properties of hierarchical comb hydrophilic polymer brushes and the mechanism against the adhesion of marine microorganisms.

Hydrogel with Ultrafast Self-Healing Property Both in Air and Underwater.

Self-healing hydrogels have a great potential application in 3D printing, soft robotics, and tissue engineering. There have been a large number of successful strategies for developing hydrogels that exhibit rapid and autonomous recovery. However, developing a gel with an excellent self-healing performance within several seconds is still an enormous challenge. Here, an ultrafast self-healing hydrogel based on an agarose/PVA double network (DN) is presented. The gel utilizing a dynamic borate bond exhibits 100% cure in strength and elongation after healing for 10 s in air, and this hydrogel shows an excellent self-healing property underwater as well. In addition, the agarose/PVA DN hydrogel exhibits a smart self-healing property for an in situ priority recovery, ensuring that the shape and the function are the same as those of the original one. With the combination of self-healing properties, such a hydrogel could be applied to a board range of areas.

A robust double-network hydrogel with under sea water superoleophobicity fabricated via one-pot, one-step reaction.

A robust double-network (DN) hydrogel fabricated by a one-pot, one-step reaction is reported. The DN hydrogels not only have high mechanical strength and extremely low underwater oil adhesion, but also exhibit excellent characteristics, such as short processing duration, moderate swelling and free shaping. The DN hydrogel is durable in artificial sea water, and its mechanical property can be easily adjusted by adjusting the crosslinking agent concentration. In addition, because a large number of free hydroxyl groups remain in their networks, the mechanical property of the hydrogel can be enhanced and repaired by presenting more glutaraldehyde in the system.