Liwen Mu

Superamphiphobic and Electroactive Nanocomposite toward Self-Cleaning, Antiwear, and Anticorrosion Coatings

Multifunctional coatings are in urgent demand in emerging fields. In this work, nanocomposite coatings with extraordinary self-cleaning, antiwear, and anticorrosion properties were prepared on aluminum substrate by a facile spraying technique. Core-shell structured polyaniline/functionalized carbon nanotubes (PANI/fCNTs) composite and nanosized silica were synergistically integrated into ethylene tetrafluoroethylene (ETFE) matrix to construct lotus-leaf-like structures, and 1H,1H,2H,2H- perfluorooctyltriethoxysilane (POTS) was used to decrease the surface energy. The composite coating with 6 wt % PANI/fCNTs possesses superamphiphobic property, with contact angles of 167°, 163°, and 159° toward water, glycerol, and ethylene glycol, respectively. This coating demonstrates stable nonwetting performance over a wide temperature range (<400 °C), as well as outstanding self-cleaning ability to prevent contamination by sludge, concentrated H2SO4, and ethylene glycol. Superamphiphobic surface property could be maintained even after 45 000 times abrasion or bending test for 30 times. The coating displayed strong adhesive ability (grade 1 according to the GB/T9286) on the etched aluminum plate. The superamphiphobic surface could be retained after immersion in 1 mol/L HCl and 3.5 wt % NaCl solutions for 60 and 90 d, respectively. It should be noted that this coating reveals significantly improved anticorrosion performance as compared to the bare ETFE coating and ETFE composite coating without PANI/fCNTs. Such coatings with integrated functionalities offer promising self-cleaning and anticorrosion applications under erosive/abrasive environment.

Facile synthesis of mesoporous carbon nanocomposites from natural biomass for efficient dye adsorption and selective heavy metal removal

Mesoporous carbon with embedded iron carbide nanoparticles was successfully synthesized via a facile impregnation–carbonization method. A green biomass resource, cotton fabric, was used as a carbon precursor and an iron precursor was implanted to create mesopores through a catalytic graphitization reaction. The pore structure of the nanocomposites can be tuned by adjusting the iron precursor loadings and the embedded iron carbide nanoparticles serve as an active component for magnetic separation after adsorption. The microstructure of the nanocomposites was carefully investigated by various characterization techniques including electron microscopy, X-ray diffraction, surface analyzer, magnetic property analyzer and etc. The newly created mesopores are demonstrated as a critical component to enhance the adsorption capacity of organic dyes and embedded iron carbide nanoparticles are responsible for the selective removal of heavy metal ions (Zn2+, Cu2+, Ni2+, Cr6+ and Pb2+). Isotherm adsorption, kinetic study at three different temperatures (25, 45 and 65 °C) and cycling retention tests were performed to understand the adsorptive behavior of the nanocomposites with organic dyes (methylene blue and methyl orange). Together with the preferable removal of more toxic heavy metal species (Cr6+ and Pb2+), these mesoporous nanocomposites show promising applications in pollutant removal from water. The facile material preparation allows convenient scale-up manufacturing with low cost and minimum environmental impact.

Comparative Study of Tribological Properties of Different Fibers Reinforced PTFE/PEEK Composites at Elevated Temperatures

The friction and wear properties of PTFE/PEEK composites filled with potassium titanate whisker (PTW) or short carbon fiber (CF) at elevated temperatures (160, 180, 200, 220, and 240°C), different loads (100 and 200 N), and various sliding velocities (0.7 and 1.4 m/s) were investigated in this article. The results show that the friction coefficient of PTW/PTFE/PEEK composites is more stable and 30% lower than that of CF/PTFE/PEEK composites at various sliding conditions. Moreover, it is found that the wear rate of PTW-filled PTFE/PEEK composites is only 10 to 40% that of CF/PTFE/PEEK composites. The wear rate of PTW/PTFE/PEEK composites is only 20% of CF/PTFE/PEEK composites at 200 N, 1.4 m/s, and 240°C. Scanning electron microscopy (SEM) study reveals that PTW can reduce the adhesive wear of PTFE/PEEK composites.

Non-corrosive green lubricants: strengthened lignin–[choline][amino acid] ionic liquids interaction via reciprocal hydrogen bonding

A series of novel green lubricants with dissolved lignin in [choline][amino acid] ([CH][AA]) ionic liquids (ILs) have been synthesized in this work. The effect of lignin on the thermal and tribological properties of the lignin/[CH][AA] lubricants was systematically investigated by means of thermogravimetric analysis, differential scanning calorimetry, and a friction and wear tester. The lignin in [CH][AA] has been demonstrated to be an effective additive to improve thermal stability, reduce the wear rates and stabilize the friction coefficients of lignin/[CH][AA] lubricants. Density function theory calculations on the electronic structure of [CH][AA] ILs reveal the atomic natural charge of ILs and their hydrogen bonding capability with lignin. Moreover, these green lubricants show excellent anti-corrosive properties against commercial aluminum and iron boards. The strong physical adsorption of [CH][AA] ILs onto the steel surface and the reciprocal hydrogen bonding between [CH][AA] ILs and lignin synergistically contribute to the enhanced lubrication film strength and thus the tribological properties of these new lubricants. This work provides a new perspective on utilizing complete bio-products in advanced tribological lubrication systems. In addition, this will open a new application venue for lignin to improve product value in lignocellulosic biomass utilization.

Expedited Phonon Transfer in Interfacially Constrained Polymer Chain along Self-Organized Amino Acid Crystals

In this work, poly(vinyl alcohol) (PVA)/amino acid (AA) composites were prepared by a self-organized crystallization process. Five different AAs (cysteine, aspartic acid, glutamic acid, ornithine, and lysine) were selected based on their similar functional groups but different molecular structures. The different PVA-AA interactions in the five PVA/AA composites lead to two crystal patterns, i.e., continuous network (cysteine and lysine) and discrete particles (glutamic acid, ornithine, and aspartic acid). Scanning thermal microscopy is then applied to map the distribution of thermal conduction in these composites. It is found that the interface surrounding the crystals plays a dominating role in phonon transport where the polymer chains are greatly restrained by the interfacial confinement effect. Continuous crystal network builds up a continuous interface that facilitates phonon transfer while phonon scattering occurs in discrete crystalline structures. Significantly improved thermal conductivity of ∼0.7 W/m·K is observed in PVA/cysteine composite with AA loading of 8.4 wt %, which corresponds to a 170% enhancement as compared to pure PVA. The strong PVA-AA molecular interaction and self-organized crystal structure are considered the major reasons for the unique interface property and superior thermal conductivity.

Superhydrophobic polyaniline hollow spheres with mesoporous brain-like convex-fold shell textures

Novel hollow nano/microspheres of polyaniline (PANI) with mesoporous brain-like convex-fold shell structures were prepared via a new micelle-mediated phase transfer method, using perfluorooctanoic acid (PFOA)/aniline as a soft template. These self-assembled hollow spheres possess high specific surface areas (835.7 m2 g−1), and uniform particle morphology with narrowly distributed particle size can be controlled by adjusting the PFOA/aniline molar ratio and polymerization time. The conductive emeraldine state of PANI is also confirmed by FT-IR spectroscopy, UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry. In particular, these PANI spheres exhibit superhydrophobicity and high oleophobicity simultaneously, with contact angles of 165 ± 0.9°, 134 ± 0.8°, 131 ± 0.9° and 125 ± 0.7° towards water, glycerin, ethylene glycol and corn oil, respectively. Furthermore, the mechanisms of PANI structural evolution are proposed involving the formation, phase transfer and self-reassembly process of PFOA/aniline spherical micelles.

Ionic Grease Lubricants: Protic [Triethanolamine][Oleic Acid] and Aprotic [Choline][Oleic Acid].

Ionic liquid lubricants or lubricant additives have been studied intensively over past decades. However, ionic grease serving as lubricant has rarely been investigated so far. In this work, novel protic [triethanolamine][oleic acid] and aprotic [choline][oleic acid] ionic greases are successfully synthesized. These ionic greases can be directly used as lubricants without adding thickeners or other additives. Their distinct thermal and rheological properties are investigated and are well-correlated to their tribological properties. It is revealed that aprotic ionic grease shows superior temperature- and pressure-tolerant lubrication properties over those of protic ionic grease. The lubrication mechanism is studied, and it reveals that strong physical adsorption of ionic grease onto friction surface plays a dominating role for promoted lubrication instead of tribo-chemical film formation.

Grafting heteroelement-rich groups on graphene oxide: Tuning polarity and molecular interaction with bio-ionic liquid for enhanced lubrication

Two different heteroelement-rich molecules have been successfully grafted on graphene oxide (GO) sheets which were then used as lubricant additives in bio-ionic liquid. The grafting was processed with reactions between GO sheets and synthesized heteroelement-rich molecules (Imidazol-1-yl phosphonic dichloride and 1H-1,2,4-triazol-1-yl phosphonic dichloride, respectively). The modified GO (m-GO) was added into [Choline][Proline] ([CH][P]) bio-ionic liquid, and has been demonstrated effective additive in promoting lubrication. Different characterization techniques have been utilized to study the reaction between GO and the two modifiers. The effect of molecular structure of the modifiers on the rheological and tribological properties of m-GO/[CH][P] lubricants was systematically investigated. Both theoretical calculation and experimental results demonstrated that the introduced heteroelement-rich groups are beneficial to increase the robustness of lubrication film by intensified hydrogen bonding and enhance the lubricant/friction surface adhesion by increased polarity of the m-GO. As a result, the interfacial lubrication could be significantly improved by these newly developed m-GO/[CH][P] lubricants.

Confined molecular motion across liquid/liquid interfaces in a triphasic reaction towards free-standing conductive polymer tube arrays

A “water/oil/water” triphasic reaction system was employed to control diffusion and reaction at separate “water/oil” and “oil/water” interfaces. The former controls the reactant feed rate and the latter determines the reaction rate. By the synergistic integration of diffusion and reaction in one reactor, freestanding tubular-arrayed polymer thin films were successfully fabricated. Molecular dynamics simulation was performed to understand the reactant diffusion across the two interfaces.

Self-Lubricating polytetrafluoroethylene/polyimide blends reinforced with zinc oxide nanoparticles

ZnO nanoparticle reinforced polytetrafluoroethylene/polyimide (PTFE/PI) nanocomposites were prepared and their corresponding tribological and mechanical properties were studied in this work. The influences of ZnO loading, sliding load, and velocity on the tribological properties of ZnO/PTFE/PI nanocomposites were systematically investigated. Results reveal that nanocomposites reinforced with 3 wt% ZnO exhibit the optimal tribological and mechanical properties. Specifically, the wear loss decreased by 20% after incorporating 3 wt% ZnO compared to unfilled PTFE/PI. Meanwhile, the impact strength, tensile strength, and elongation-at-break of 3wt% ZnO/PTFE/PI nanocomposite are enhanced by 85, 5, and 10% compared to pure PTFE/PI blend. Microstructure investigation reveals that ZnO nanoparticles facilitate the formation of continuous, uniform, and smooth transfer film and thus reduce the adhesive wear of PTFE/PI.