The effect of the frictional interfacial interaction of two types of gel lubricants on lubrication mechanisms is investigated. The structure of the two types of gelators, polyhydric gelator (PG) and thiol functionalized polyhydric gelator (FPG), is identical except for one of them having thiol groups. The tribological properties of these gels as lubricants are evaluated for the contacts of steel/steel, steel/aluminum, steel/copper, and steel/alumina ceramic. It is shown that these gels have better friction reduction and antiwear (AW) performance than blank 500SN. Under medium–high pressure, the gel at the interface is liquefied and a growing number of gelator molecules will adsorb onto the metal surface by polar hydroxyl and thiol headgroups. Hydroxylation treatment of sliding pairs can significantly enhance the interfacial absorption interaction and improve tribological properties. Interestingly, FPG gel lubricant exhibits better lubricating and AW properties compared with PG gel under the same test conditions. Quartz crystal microbalance (QCM) measurements suggest that FPG containing the thiol and hydroxyl dual polar groups has better adsorption ability on the contact surface than PG only with hydroxyl groups. FPG gel lubricants therefore form more robust protective films.

Oil removal and collection from spills have been addressed by various techniques, but still remain a challenging topic for practical application because of high cost, low oil absorption capacity, and weak oil keeping stability. To address the challenge, an oil-skimmer composed of 3D printed mesh cap treated with low surface energy materials and commercial vessel has been developed. The good water repellency of the 3D printed mesh realizes high efficient floating oil removal by filtration while the bottom vessel achieves the oil collection by storing the oil directly. Importantly, the collected oil does not escape from the vessel under ambitious stirring or reversion, indicating the skimmer's high potential application under the sea waves or even storm conditions. Taking the advantages of 3D printing in computer-aid design and freeform fabrication, the feasible 3D printing oil-skimmer is believed to be highly promising for the practical oil collection from spills in an on-site design and fabrication manner.

Herein, we systematically investigate the origin of astringent mouthfeel when we eat unripe fruits, drink coffee or tea, from the perspective of lubrication by simulating the dynamic weak interaction on the tongue with model protein (mucoprotein, MP) and polyphenolic compounds (tannic acid, TA). Astringency was due to the protein-mediated lubrication failure when encountering polyphenolic molecules that normally exist, for example in unripe fruits, coffee, tea. The underlying molecular mechanism of oral tribology is widely present in nature and enables us to engineer a tongue-like polyacrylamide composite hydrogel that exhibits high TA sensitivity and to develop a scientific strategy for catching slippery fish using TA-containing gloves. These results provide novel and useful insights into the failure of biological boundary lubrication on soft tissue surface with the adsorbed proteins.

Herein, we describe a simple and robust approach to repeatedly modify surfaces with polymer brushes through surface-initiated atomic transfer radical polymerization (SI-ATRP), based on an initiator-embedded polystyrene sheet that does not rely on specific surface chemistries for initiator immobilization. The surface-grafted polymer brushes can be wiped away to expose fresh underlying initiator that re-initiates polymerization. This strategy provides a facile route for modification of molded or embossed surfaces, with possible applications in the preparation of fluidic devices and polymer-embedded circuits.

Herein, we describe a simple and robust approach to repeatedly modify surfaces with polymer brushes through surface-initiated atomic transfer radical polymerization (SI-ATRP), based on an initiator-embedded polystyrene sheet that does not rely on specific surface chemistries for initiator immobilization. The surface-grafted polymer brushes can be wiped away to expose fresh underlying initiator that re-initiates polymerization. This strategy provides a facile route for modification of molded or embossed surfaces, with possible applications in the preparation of fluidic devices and polymer-embedded circuits.

Herein, we systematically investigate the origin of astringent mouthfeel when we eat unripe fruits, drink coffee or tea, from the perspective of lubrication by simulating the dynamic weak interaction on the tongue with model protein (mucoprotein, MP) and polyphenolic compounds (tannic acid, TA). Astringency was due to the protein-mediated lubrication failure when encountering polyphenolic molecules that normally exist, for example in unripe fruits, coffee, tea. The underlying molecular mechanism of oral tribology is widely present in nature and enables us to engineer a tongue-like polyacrylamide composite hydrogel that exhibits high TA sensitivity and to develop a scientific strategy for catching slippery fish using TA-containing gloves. These results provide novel and useful insights into the failure of biological boundary lubrication on soft tissue surface with the adsorbed proteins.

The economic and safety issues caused by ice accretion have become more and more serious. Except for traditional ways of anti-icing, such as spraying agents, mechanical/thermal removal, etc., more economic approaches are urgently required. This work demonstrates the conceptual feasibility of using a self-lubricated photothermal coating for both anti-icing and deicing function. The coating is generally water repellent and infiltrated with hydrocarbon or perfluorocarbon oils as the lubricant to endow a liquid interface for preventing ice accumulation and minimizing the adhesion of ice on surfaces once it is formed. Fe₃O₄ nanoparticles are added to the film to afford high efficiency photothermal effect under near-infrared irradiation for rapidly melting the accumulated ice. The conceptual strategy can be easily implemented as a facile method to fabricate analogous sprayed coatings. It represents a major advance to tackle the challenging icing issue that is normally seen as a disaster in everyday life.

Nature has successfully combined soft matter and hydration lubrication to achieve ultralow friction even at relatively high contact pressure (e.g., articular cartilage). Inspired by this, hydrogels are used to mimic natural aqueous lubricating systems. However, hydrogels usually cannot bear high load because of solvation in water environments and are, therefore, not adopted in real applications. Here, a novel composite surface of ordered hydrogel nanofiber arrays confined in anodic aluminum oxide (AAO) nanoporous template based on a soft/hard combination strategy is developed. The synergy between the soft hydrogel fibers, which provide excellent aqueous lubrication, and the hard phase AAO, which gives high load bearing capacity, is shown to be capable of attaining very low coeffcient of friction (<0.01) under heavy load (contact pressures ≈2 MPa). Interestingly, the composite synthetic material is very stable, cannot be peeled off during sliding, and exhibits desirable regenerative (self-healing) properties, which can assure long-term resistance to wear. Moreover, the crosslinked polymethylacrylic acid hydrogels are shown to be able to promptly switch between high friction (>0.3) and superlubrication (≈10⁻³) when their state is changed from contracted to swollen by means of acidic and basic actuation. The mechanisms governing ultralow and tunable friction are theoretically explained via an in-depth study of the chemomechanical interactions responsible for the behavior of these substrate-infiltrated hydrogels. These findings open a promising route for the design of ultra-slippery and smart surface/interface materials.

This review outlines the up-to-date research progress on controllable interfacial friction on both solid/solid and solid/liquid surfaces. Environment-sensitive materials at a frictional interface react to certain external stimuli and provoke changes in surface chemistry, interfacial charge, and/or topography, which then cause a change in the coefficient of friction. The external stimuli might be solvent, electrolyte, pH, temperature, light, electric potential, and magnetic field etc. In a similar way, controllable fluid–solid friction (i.e., boundary slippage versus non-slippage) can also be achieved by reversibly generating a gas lubricating layer at the interface or by changing the fluid–solid adhesion via physicochemical methods. The author comments are presented and outlooks proposed.

Diamond-like carbon (DLC) film has emerged as a promising material for biomedical applications, but its low tribological properties in air could not be adapted in water and biological fluids. Herein, mussel-inspired catechol adhesive is presented to functionalize DLC film and then polymer brushes are grafted by surface initiated atom transfer radical polymerization (SI-ATRP) to mimic excellent biological lubrication of articular cartilage. Macroscopic tribological evaluation demonstrates low and stable friction coefficient of polymer brushe modified DLC film in water and biological fluids when sliding with a soft polydimethylsiloxane (PDMS) hemisphere, owing to viscous fluid-like boundary lubricant film being formed by high hydration of polymer chains. The strong adhesive capability of catechol anchors also prevents polymer chains being sheared off from the substrate during friction tests. The friction responsiveness of PSPMA brushes is observed in electrolyte solution due to the conformation change of polymer chains. The successful functionalization of DLC with polymer brushes affords DLC film excellent biological lubrication and thus will broaden the scope of its applications in biomedical field.

Effects of atomic oxygen (AO) and ultraviolet (UV) on a polymer film with surface energy of 8.0 mJ m⁻² derived from poly(1H,1H-perfluorooctyl methylacrylate) were investigated by contact angle measurements, X-ray photoelectron spectroscopy, and atomic force microscope. The film was exposed to AO with a flux of 6.73 × 10¹⁵ atoms cm⁻² s⁻¹ and UV with intensity of 15.8 mW cm⁻² at wavelength of 200–450 nm, respectively. It is found that AO and UV irradiation resulted in the reduction of film thickness, change of wettability, and increase of surface energy, and AO exhibited more serious effects than UV on the fluorinated polymer film. Reduced rate of thickness of the film was almost proportional to the AO exposure time. After exposed to AO and UV irradiation, the surface energy of the film increased to 17.3 mJ m⁻² and 11.0 mJ m⁻², respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011