Surface-Functionalized Ti3C2Tx MXene as a Kind of Efficient Lubricating Additive for Supramolecular Gel

Versatile MXene Gels Assisted by Brief and Low-Strength Centrifugation

Due to the mutual repulsion between their hydrophilic surface terminations and the high surface energy facilitating their random restacking, 2D MXene nanosheets usually cannot self-assemble into 3D macroscopic gels with various applications in the absence of proper linking agents. In this work, a rapid spontaneous gelation of Ti3C2Tx MXene with a very low dispersion concentration of 0.5 mg mL-1 into multifunctional architectures under moderate centrifugation is illustrated. The as-prepared MXene gels exhibit reconfigurable internal structures and tunable rheological, tribological, electrochemical, infrared-emissive and photothermal-conversion properties based on the pH-induced changes in the surface chemistry of Ti3C2Tx nanosheets. By adopting a gel with optimized pH value, high lubrication, exceptional specific capacitances (~ 635 and ~ 408 F g-1 at 5 and 100 mV s-1, respectively), long-term capacitance retention (~ 96.7% after 10,000 cycles) and high-precision screen- or extrusion-printing into different high-resolution anticounterfeiting patterns can be achieved, thus displaying extensive potential applications in the fields of semi-solid lubrication, controllable devices, supercapacitors, information encryption and infrared camouflaging.

Supramolecular gelator functionalized liquid metal nanodroplets as lubricant additive for friction reduction and anti-wear

In this work, dopamine n-butenylamide (DBA) modified GLM nanodroplets were prepared via directional ultrasound of bulk liquid metal in ethanol aqueous solution as well as DBA self-assembly, followed by grafting with urea-based gelators via radical polymerization to obtain GLM-based supramolecular gelators (Gelator@GLM). The grafting gelators can impart their good compatibility between the GLM nanodroplets and the base oil, so that the Gelator@GLM nanodroplets can be dispersed in the base oil uniformly and stably for more than 3 weeks. Meanwhile, the tribological properties of Gelator@GLM nanodroplets was significantly enhanced, with a reduction of coefficient of friction (COF) and the wear volume of 41.18% and 92.13%, respectively, when compared with the base oil. Furthermore, Gelator@GLM additives exhibited stable lubrication performance even under variable temperature and frequency conditions. The synergistic effect of GLM nanodroplets and the gels generating a physical adsorption film and a chemically protective film (containing iron and chromium oxides, nitrides and carbides) can be credited with the improved tribological performance.

Supramolecular Soft Material Enabled by Metal Coordination and Hydrogen Bonding: Stretchability, Self-Healing, Impact Resistance, 3D Printing, and Motion Monitoring

Metal coordination can significantly improve the macroscopic performance of many materials by enhancing their dynamic features. In this study, two supramolecular interactions, Fe³⁺ -carboxylic acid coordination, and structural water-induced hydrogen bonding, into an artificial polymer were introduced. Various attractive features, including flexibility and stretchability, are achieved because of the bulk state and dynamic hydrogen bonds of poly(thioctic acid-water) (poly[TA-H]). These unique features are considerably enhanced after the incorporation of Fe³⁺ cations into poly[TA-H] because metal coordination increased the mobility of the poly[TA-H] chains. Thus, the poly(thioctic acid-water-metal) (poly[TA-HM]) copolymer exhibited better flexibility and stretchability. Moreover, notable underwater/low-temperature self-healing capacity is obtained via the synergistic effect of the metal and hydrogen bonding. Most of the impact energy is quickly absorbed by poly[TA-H] or poly[TA-HM] and effectively and rapidly dissipated via reversible debonding/bonding via the interactions between the metal and hydrogen. Macroscopic plastic deformation or structural failure is not observed during high-speed (50-70 m s^-1 ) impact experiments or high-altitude (90 m) falling tests. Furthermore, poly[TA-HM] displayed good thermal molding properties, which enabled its processing via 3D fused deposition modeling printing. Poly[TA-HM] also showed considerable effectiveness for monitoring complicated, dynamic, and irregular biological activities owing to its highly pressure-sensitive nature.