The spreading behaviour of perfluoropolyether droplets on solid surfaces

The spread of perfluoropolyether （PFPE） droplets on solid surfaces has been measured from the top-down view through a microscope system. Effects of substrates, molecular weight and end-group functionality on spreading of the PFPE droplets have been studied experimentally and the results were compared with those by molecular dynamics （MD） simulations. Silicon wafer and diamond-like carbon （DLC） substrates were used to study the effect of substrates on spreading. Two types of PFPE, Z-dol and Z-tetraol, with the same chain structure and various molecular weights （2000 and 4000 g/mol） were employed in experiments. Effect of molecular weight has been investigated through comparing the spreading of Z-dol 2000 and Z-dol 4000, and it is found that the increase of molecular weight will decrease the mobility of PFPE. Comparison between spreading of Z-dol and Z-tetraol of the same molecular weight proved that functional end group plays a significant role on the spreading of PFPE, which confirmed the MD simulation results.

Theoretical Investigation on Hyperfine Structures of Perfluoropolyether Radicals

The geometries of CF3OCF2, CF3OCFCF3 and CF3OCF2CF2 radicals were investigated by density functional theory（DFT） method. The calculated results indicate that all the three radicals have pyramidal shapes at their centers, and the aC is one top of the pyramids. Based on the DFT optimized geometries, the hyperfine coupling constants（hfec＇s） of the 19F atoms of the three radicals were calculated by B3LYP, MP2（full） and QCISD（full） methods. The calculated values agree with the experimental values, especially for the a values of Fa, the a values are 125.6× 10 -4, 104.2× 10 - 4, and 83.2×10 -4 T of CF3OCF2, CF3OCFCF3 and CF3OCF2CF2, respectively. These results better explain the experimental observation.

An efficient approach for the treatment of radioactive waste perfluoropolyether lubricants via a synergistic effect of thermal catalysis and immobilization

Perfluoropolyether(PFPE)lubricants are a kind of high-molecular polymer with many excellent properties.However,the use of PFPEs in the nuclear industry can lead to partial decomposition and carrying radionuclides,resulting in a large amount of radioactive waste PFPE lubricants annually.Moreover,radioactive waste PFPE lubricants are difficult to be effectively treated due to their high stability,the risk of possible leakage of radionuclides,and hypertoxic fluorine-containing by-products.In this study,without any precedent,a strategy of Mn O_(2)-catalyzed decomposition and Na_(2)CO_(3)-immobilized conversion was proposed for PFPE lubricant decomposition and fluorine immobilization simultaneously based on the Lewis acid-base and oxygen vacancies concept.A high fluorine conversion efficiency of 95.4%was achieved.Meanwhile,the mechanism of decomposition suggested that Mn O_(2)mainly provided Lewis acid sites and attacked the(basic)fluorine or oxygen atoms in PFPE molecules.The decomposition of PFPE chains was proceed down and volatile fluorine-containing gas was released by partial electron transfer,intramolecular disproportionation reaction,and unzipping fashion.Subsequently,gas by-products could be further oxidized and then immobilized into fluoride salts by carbonate solid absorbents.Overall,this study provides a simple,safe,and potentially practical strategy for the harmless conversion of refractory fluorinated organic wastes,especially perfluoropolymers.

Thermo-mechanical and tribological properties of SU-8/h-BN composite with SN150/perfluoropolyether filler

In this study, SU-8 and its composites are fabricated by blending 10 wt.% hexagonal boron nitride(h-BN) fillers with/without lubricants, such as 10 wt.% base oil(SN150) and 20 wt.% perfluoropolyether(PFPE). The thickness of SU-8 and its composites coating is fabricated in the range ~100–105 μm. Further, SU-8 and its composites are characterized by a 3D optical profilometer, atomic force microscopy, scanning electron microscopy, a thermal gravimetric analyzer, a goniometer, a hardness tester, and an optical microscope. Under a tribology test performed at different normal loads of 2, 4, and 6 N and at a constant sliding speed of 0.28 m/s, the reduction in the initial and steady-state coefficient of friction is obtained to be ~0.08 and ~0.098, respectively, in comparison to SU-8(~0.42 and ~0.75), and the wear resistance is enhanced by more than 103 times that of pure SU-8. Moreover, the thermal stability is improved by ~80–120 ℃, and the hardness and elastic modulus by ~3 and ~2 times that of pure SU-8, respectively. The SU-8 composite reinforced with 10 wt.% h-BN and 20 wt.% PFPE demonstrated the best thermo-mechanical and tribological properties with a nano-textured surface of high hydrophobicity.

Preparation and Rheological Properties of Vacuum Lubricating Grease

A kind of vacuum lubricating grease was prepared by using perfluoropolyether as base oil,perfluorinated polymer as thickener,and self-made additives.The colloidal stability of the grease was greatly improved by introducing a colloidal structure modifier.The rheological properties of the self-made grease(SMG),such as viscosity versus time,thixotropy,etc.,were studied by a rheometer at different temperatures and were compared with those of foreign brand grease(FBG).The results show that the performance of SMG reached the level of similar FBG,and some properties such as mechanical stability,colloidal stability,extreme pressure and antiwear properties were better.It can be used for long life lubrication of moving parts in a vacuum environment.

Modelling of spreading process: effect from hydrogen bonds

Lubricant spreading on solid substrates has drawn considerable attention not only for the microscopic wetting theory but also for the dramatic application in head-disk interface of magnetic storage drive systems. Molecular dynamic simulation based on a coarse-grained bead-spring model has been used to study such a spreading process. The spreading profiles indicate that the hydrogen bonds among lubricant molecules and the hydrogen bonds between lubricant molecules and polar atoms of solid substrates will complicate the spreading process in a tremendous degree. The hydrogen bonds among lubricant molecules will strengthen the lubricant combination intensity, which may hinder most molecules from flowing down to the substrates and diffusing along the substrates. And the hydrogen bonds between lubricant molecules and polar atoms of solid substrates will confine the lubricant molecules around polar atoms, which may hinder the molecules from diffusing along the substrates and cause precursor film to vanish.

Molecular dynamic simulation of lubricant spreading： effect from the substrate and endbead

Molecular dynamic simulations based on a coarse-gralned, bead-spring model are adopted to investigate the spreading of both nonfunctional and functional perfluoropolyether （PFPE） on solid substrates. For nonfunctional PFPE, the spreading generally exhibits a smooth profile with a precursor film. The spreading profiles on different substrates are compared, which indicate that the bead-substrate interaction has a significant effect on the spreading behaviour, especially on the formation of the precursor film. For functional PFPE, the spreading generally exhibits a complicated terraced profile. The spreading profiles with different endbeads are compared, which indicate that the endbead-substrate interaction and the endbead-endbead interaction, especially the latter, have a significant effect on the spreading behaviour.

A Fluorinated,Ion-Conducting and Adaptive Supramolecular Polymer Protective Layer for Stabilizing Lithium Metal Anodes

Perfluoropolyether(PFPE)is a promising material for protective coatings on Li metal anodes due to its chemical inertness and minimal swelling in electrolytes.However,a conventional PFPE coating with poor ionic conductivity and mechanical stability is still not satisfactory for long-term cycling of Li anodes.Here,we design and synthesize an adaptive and high-conductivity supramolecular polymer(PFPE-EG-I).This polymer is constructed from PFPE chains,ethylene glycol(EG)segments,and hydrogen-bonding moieties derived from isophoronediisocyanate,serving as a multifaceted artificial solid electrolyte interphase(SEI).The incorporated EG segments enhance the Li+conductivity of the SEI,and the hydrogen-bonding units introduce a dynamic self-adaptive behavior to the polymer matrix.A solution-processed PFPE-EG-I coating is demonstrated to promote uniform Li deposition and mitigate side reactions between Li and the electrolyte.Consequently,this leads to enhanced coulombic efficiency and prolonged cycle longevity in lithium metal batteries(LMBs).The innovative design of this multifunctional artificial SEI offers a promising avenue for the realization of dendrite-free Li anodes,paving the way for the advancement of high-performance LMBs.

Development of a Completely New PFOS Alternative with Lower Surface Tension for Minimizing the Environmental Burden

Improving the technical performance of related industrial products is an efficient strategy to reducing the application quantities and environmental burden for toxic chemicals.A novel polyfluoroalkyl surfactant potassium 1,1,2,2,3,3,4,4-octafluoro-4-(perfluorobutoxy)butane-1-sulfonate(F404)was synthesized by a commercializable route.It had a surface tension(γ)of 18.2 mN/m at the critical micelle concentration(CMC,1.04 g/L),significantly lower than that of perfluorooctane sulfonate(PFOS,ca.33.0 mN/m,0.72 g/L),and exhibited remarkable suppression of chromium-fog at a dose half that of PFOS.The half maximal inhibitory concentration(IC_(50))values in HepG2 cells and the lethal concentration of 50%(LC_(50))in zebrafish embryos after 72 hpf indicated a lower toxicity for F404 in comparison to PFOS.In a UV/sulphite system,89.3%of F404 were decomposed after 3 h,representing a defluorination efficiency of 43%.The cleavage of the ether C—O bond during the decomposition would be expected to form a short chain·C_(4)F_(9) as the position of the ether C—O in the F404 fluorocarbon chains is C4—O5.The ether unit is introduced in the perfluoroalkyl chain to improve water solubility,biocompatibility and degradation,thereby minimizing the environmental burden.

Electron transfer dominated triboelectrification at the hydrophobic/slippery substrate-water interfaces

Triboelectric nanogenerator(TENG)based on triboelectrification has attracted wide attention due to its effective utilization of green energy sources such as marine energy.However,researches about liquid-liquid triboelectrification are still scanty as solid-liquid triboelectrification has been widely studied.Herein,this work focuses on the hydrophobic/slippery substrate-water interfacial triboelectrification based on the solid friction materials of polytetrafluoroethylene(PTFE)nanoparticles.The hydrophobic/slippery substrate-water interfacial triboelectrification are studied by assembling PTFE coated Al sheets and perfluoropolyether(PFPE)infused PTFE coated Al sheets(formed the slippery lubricant-infused surfaces(SLIPSs))as the friction electrode,and water as liquid friction materials,respectively.The results show that the hydrophobic TENG output performances improved as the PTFE nanoparticles cumulating,and the SLIPSs TENG output performances increased with the thinner PFPE thickness.Both the triboelectrification behavior of hydrophobic/SLIPSs TENG assembled in this work are dominated by the electron transfer.Thanks to the introduction of SLIPSs,the SLIPSs TENG exhibits superior stability and durability than the hydrophobic TENG.The investigation of hydrophobic/slippery substrate-water interfacial triboelectrification contributes to optimize the TENG performances,and expands the application in harsh environments including low temperature and high humidity on the ocean.