PFPE Lubricant Research Articles

A Numerical Simulation of PFPE Lubricant Kinetics in HAMR Air Bearing

This report investigates the kinetics of lubricant molecules in the HAMR air bearing to understand the initiation and growth of PFPE contamination on the head surface. The collisions with the air bearing induce three forces—drag, thermophoresis, and lift. Of these, we find that lift forces are negligible. Then, a sensitivity analysis of the remaining two forces reveals the conditions where they dominate. Further, a hybrid simulation strategy is utilized to track their movements. The results show that the contaminations (smear) highly depend on the interplay between the thermophoresis and drag forces. We then explain the mechanism of the formation of the various observed patterns. Finally, we offer some recommendations to exploit the air bearing to contain smear on the head.

Study on the Adsorption and Thermal Diffusion of D-4OH Lubricant on Amorphous Carbon Film by Reactive MD Simulation for HAMR

Heat-assisted magnetic recording (HAMR) is an innovative type of storage technology. The PFPE lubricants can improve the friction properties of the HAMR head-disk interface (HDI) in the writing and reading processes. The adsorption and thermal diffusion processes of three D-4OH lubricants with polar functional end groups on amorphous carbon (a-C) film are investigated by reactive molecular dynamics simulation. The potential energy, atomic distribution, radial distribution function (RDF), bonds’ number, atomic migration vector, and atomic shear strain are analyzed both in the relaxation and heating processes. The H atoms of polar functional end groups of D-4OH are bonded with a-C unsaturated carbon atoms via the secondary bonds. The main chains of D-4OH lubricants are adsorbed by a-C film via van der Waals forces. Laser heating helps to enhance the adsorption performance of lubricant on an a-C surface at a low temperature. The thermal diffusion of the lubricant makes the lubricant form a more stable conformation on the surface of the a-C film. Increasing the amount of −OH can improve the adsorption of PFPE lubricant on the a-C film.

Study on the Thermal Decomposition of D-4OH PFPE Lubricant by Reactive Molecular Dynamic Simulation for HAMR

Heat-assisted magnetic recording (HAMR) is one of the ways of ultrahigh density storage technology. The pulsed laser in the HAMR head heats the nano-region of the disk to Curie temperature. The laser heating causes the decomposition of the PFPE lubricant, which indirectly leads to the failure of head-disk interface (HDI). The reactive molecular dynamics (MDs) simulations are performed to research the thermal decomposition of single and multiple D-4OH lubricants. The effect of three different heating rates on the thermal decomposition process of a single D-4OH lubricant is investigated. The decomposition processes of single and multi-D-4OH molecular chains are the same: the functional end groups degrade first and then the main chain. These results are useful for the optimization of PFPE lubricants for HAMR disks.

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 MnO2-catalyzed decomposition and Na2CO3-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 MnO2 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.

Accelerated Thermo-Catalytic Degradation of Perfluoropolyether (PFPE) Lubricants for Space Applications

Perfluoropolyethers (PFPE) are a class of frequently used lubricants in space applications due to their high stability under demanding conditions. However, they are susceptible to aging, with the aging mechanism being dependent on the specific material combination and storage condition. A Lewis-acid-induced thermo-catalytic degradation mechanism is of concern, for example, under steel-on-steel sliding contact, and can be relevant for long-term storage (LTS). Accelerated aging experiments were performed on Fomblin® Z25 and Krytox™ 143AC to investigate thermal stability under the influence of iron(III) fluoride (FeF3) at elevated temperatures (180 °C, 200 °C, and 220 °C) up to a total duration of 2000 h. The degradation effects were monitored via selected analysis techniques: mass loss of the samples due to degradation and subsequent evaporation during aging, FTIR spectroscopy to investigate changes to the chemical structure, dynamic viscosity measurements for the investigation of a potential impact due to changes in molecular mass, and a ball-on-disc tribological test setup to obtain friction behavior of the aged lubricants. Distinct differences between the two types of PFPE lubricants regarding stability to thermo-catalytic degradation were found. Fomblin® Z25 was highly affected by the presence of FeF3 within the selected aging conditions, exhibiting high mass loss, a significant drop in dynamic viscosity, and an increased coefficient of friction due to degradation reactions.

Molecular Dynamics Study of Mechanochemical Reactions of PFPE Lubricant Films in the Presence of Water and Oxygen

Molecular Dynamics Study of Mechanochemical Reactions of PFPE Lubricant Films in the Presence of Water and Oxygen

Effects of SiO2 Contaminant on Thermo-Mechanical/Chemical Properties and Lubricity of PFPE Lubricants

Using the molecular dynamics (MD) simulations with ReaxFF potential, two different types of PFPE lubricants (Ztetraol and ZTMD) are prepared on a-C film, and SiO2 particles are adsorbed onto the lubricants at room temperature. From the simulation results, it is observed that the adsorbed SiO2 particles increase the stiffness of PFPE lubricants leading to less airshear displacement. Since Ztetraol has higher mobility with lower viscosity than ZTMD, the adsorbed SiO2 particles penetrate deeper into the Ztetraol lubricants. Accordingly, the effect of SiO2 on the airshear displacement is more obvious to Ztetraol than ZTMD. In addition, the adsorbed SiO2 particles increase the friction force and the amount of lubricant pick-up during the sliding contact with a nanosized a-C tip.

The challenges of developing ionic liquids as tribological lubricants for thin film media

Ionic liquids (ILs) could be promising candidates for heat-assisted magnetic recording media due to their extraordinary properties such as considerably thinner monolayer (ML) thickness and extremely good thermal stability. In this paper, the physical properties and mechanism clearance of some novel fluorinated ILs were investigated through several analytical technologies including contact angle, FTIR, XPS, AFM, TGA and Candela OSA. Although the ML thickness of the ionic lubricants was confirmed only 50 – 60 % of that of conventional PFPEs, their evaporation performance as two-dimension lubricant nanofilm is significantly inferior to conventional PFPEs. In addition, the greater surface energy of ILs vs conventional PFPE lubricants, resulting in their poor mechanical clearance. The findings here reveal critical challenges in the developing of ionic lubricants for thin film magnetic media and may serve as guidance for the future design of ILs as media lubricants.

Reactive Molecular Dynamics Study of Effect of Water and Oxygen Molecules on Decomposition of PFPE Lubricant Films in Heat-Assisted Magnetic Recording

Reactive Molecular Dynamics Study of Effect of Water and Oxygen Molecules on Decomposition of PFPE Lubricant Films in Heat-Assisted Magnetic Recording

Comparison study on surface and thermo-chemical properties of PFPE lubricants on DLC film through MD simulations

Molecular dynamics simulations are performed using four types of PFPE lubricants (Zdol, Ztetraol, TA-30, and ZTMD) to investigate their spreadability, airshear behavior, surface contamination, and friction. The more functional end groups in PFPE lubricants the less spreadability on DLC surface, which agrees with the experimental results. The airshear simulation shows that the tangential shear movement of lubricants reduces as the number and the polar strength of functional end group increases. The higher temperature, the more shear displacement due to the increasing mobility. In HDI contact simulations, the PFPE lubricant with more and stronger functional end groups results in higher friction force and less head contamination by lubricant transfer. The higher temperature, the more head contamination but lower friction force.

Supramolecular PFPE gel lubricant with anti-creep capability under irradiation conditions at high vacuum

Perfluoropolyether (PFPE) remains a highly desirable synthetic fluid for industries like aerospace and special machinery lubricants owing to its excellent chemical constancy, radiation and corrosion resistance, lubricating properties. However, like most phenomenal substances, even PFPE exhibits some shortcomings like low surface tension, which produces creeping and leakage from friction interface while in use. This manuscript reports a new method to rectify the creeping demonstrated by the PFPE lubricant, which is deemed to utilize the confinement effect of the supramolecular gel. A novel fluorine-functionalized gelator (BHD) which can gelatinize PFPE, was successfully synthesized. The results of molecular dynamics and experiment reveal that BHD compound self-assembles into spherical by interactions among the gelators and PFPE. The event of thermocapillary migration and creep behavior of the PFPE gel lubricants acting on the steel, while employing temperature gradients and exposure to the irradiation of Atomic Oxygen (AO) and Ultraviolet (UV) for 4 h was thoroughly investigated. The results reveal that the gelation of PFPE oils minimizes the thermocapillary migration of PFPE and averts the creeping from occurring at the sliding interface. The tribological representations of supramolecular gels ensure excellent lubricity and anti-wear performances under some critical environments, including ranging from high to low temperatures and irradiation in vacuum conditions. Furthermore, the supramolecular gels register that the PFPE oils are slow-release lubricants enabled by their complicated reassembling network, manifesting stronger anti-irradiation properties. These deductions make a strong case for this gel lubricant to replace PFPE lubricants administered for the lubrication of aerospace machinery components.

Design novel three-dimensional network nanostructure for lubricant infused on titanium alloys towards long-term anti-fouling

Titanium alloys, recognized as a marine material with great potential, are currently facing serious biofouling problems, which greatly limits its application range. To improve the antifouling performance of titanium alloys, three unique surface of three-dimensional network, grass-like and linear nanostructures were obtained on titanium alloys via hydrothermal treatment in this work. Further, slippery liquid-infused porous surfaces (SLIPSs) were fabricated on titanium alloys via infusing PFPE lubricant into these nanostructures. Water contact angles and sliding angles of SLIPSs were measured to evaluate the effect of nanostructures on the stability of PFPE lubricant layer. Anti-fouling capability of SLIPSs were investigated by quantifying the cells of chlorella and phaeodactylum tricornutum (P. tricornutum)adhered to titanium alloys. The results shows that all the SLIPSs exhibited remarkable inhibition capacity for the settlement of chlorella and P. tricornutum. Among them, the SLIPS with three-dimensional network nanostructure displayed the longest-term anti-fouling performance, and its reduction rate of P. tricornutum and chlorella reaching 77.2 % and 84.5 % after being cultivated for 21 days, respectively, indicating that there existed a positive correlation between the stability of lubricant layer in the artificial seawater and the antifouling effect.

Smear and Decomposition Mechanism of Magnetic Disk PFPE Lubricant Film by Laser Heating in Air and Helium Conditions

Smear and Decomposition Mechanism of Magnetic Disk PFPE Lubricant Film by Laser Heating in Air and Helium Conditions

Laser-induced depletion of ultrathin PFPE lubricants using a quantitative coarse-grained model.

Knowledge of laser-pulsed processing of ultrathin liquids on solid surfaces is of great importance in advancing the understanding of synthesis, characterization and applications of functional nanofilms. In this work, we performed molecular dynamics simulations coupled with a novel quantitative coarse-grained model to study laser-induced local heating and depletion behaviors of Fomblin Z2000 lubricants. It was found that the Fomblin lubricant films experience severe evaporation and thermodiffusion-related degradation under laser heating. The ultrathin lubricants inevitably lose their frictional resistance under extremely high temperatures and thermal gradients (i.e., up to 990K and 65.4K/nm) that are required for FePt media in HAMR systems. The factors that influence the local thermal depletion, such as laser power, spot size, and scanning velocity, were investigated as well. The results clearly show that the laser power has the greatest influence on the relative maximum temperature change and subsequently the severe lubricant film depletion during rapid laser heating, while the spot size and scanning velocity play a relatively weaker role in the laser-induced local thermal instability. The findings in this work are thus believed to provide molecular scale insights into laser-induced local heating and depletion of ultrathin lubricant films from a precise quantitative perspective.

Adsorption characteristics of PFPE lubricants with different main chain structure

Adsorption characteristics of PFPE lubricants with different main chain structure

HDI tribology characteristics of PFPE lubricants with different main-chains on magnetic disks

HDI tribology characteristics of PFPE lubricants with different main-chains on magnetic disks

Transfer Behaviors of PFPE Lubricant from Disk Surface to Slider

The rapid growth in storage areal density of hard disk drive (HDD) forces the flying height of slider has been currently reduced to less than 2 nm. In such a narrow spacing, perfluoropolyether (PFPE) lubricant is easier to transfer from disk surface to slider under fluid force field and heat transfer field, which is found to have a great effect on date storage reliability. Firstly, the lubricant transfer volume expression with respect to lubricant molecular weight is established. Secondly, the finite element models (FEM) of both Tri-pad positive pressure slider and flat slider are developed, and based on this, the PFPE lubricant transfer behaviors in HDD are investigated. Finally, four type unite cells composed of lubricant molecules and air molecules are established by using Materials Studio software, then both dynamic temperature and diffusion coefficients are researched based on molecular dynamics theory. Results show that the PFPE lubricant amount decreases with increasing pitch angles, rotation angles, slider flying height and disk rotation velocity, while it increases when heat source power increases. The diffusion coefficients of ZTMD lubricant is the maximum in the four lubricants we researched, while the temperature change ratio of Z-15 lubricant is the maximum.

Probing fretting performance of DLC and MoS2 films under fluid lubrication

Transition from onefold to synergistic lubrication for solving fretting wear and fatigue problems is of great practical significance, because fluids can regulate fretting regime for minimizing wear, solid films can restrain nucleation and formation of crack. Here synergistic lubrication coatings were prepared using diamond-like carbon (DLC) and molybdenum disulfide (MoS2) films as anti-wear/fatigue layer, and high-performance lubricants (including silicone oil, ionic liquids, multialkylated cyclopentanes and perfluoropolyethers (PFPE)) as flowable lubrication layer. Their fretting performance was evaluated in detail and fretting mechanism was revealed by surface/interface analysis techniques. Results determine the synergistic lubrication coatings with good anti-wear and anti-fatigue abilities, deriving from the synergy of improved yield strength and shear strength, transfer layer and boundary film. Moreover, the fretting regime is pointedly regulated by solid films with different composition and performance, for example, DLC-based lubrication coatings under applied load of 22 N correspond to slip regime, so do as the MoS2-based coatings under 4 N, and PFPE-lubricated MoS2 films display better anti-wear ability than others, while DLC under PFPE lubrication reverses. The choice of optimal scheme depends on the working condition and lubrication state for achieving the requirements of high reliability, high precision, high efficiency, and long lifetime.

Effect of laser heating on the smear behavior of PFPE lubricant films on magnetic disks in air and helium

Effect of laser heating on the smear behavior of PFPE lubricant films on magnetic disks in air and helium

Smear and Decomposition Behaviors of PFPE Lubricant Film on Magnetic Disk by Laser Heating in Air and Helium

Smear and Decomposition Behaviors of PFPE Lubricant Film on Magnetic Disk by Laser Heating in Air and Helium