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Lubricants for the Disk Drive Industry
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
The vapor pressure of perfluoropolyether lubricants must be sufficiently low to prevent evaporation from the disk. The following method was developed to measure the vapor pressure. A model was derived to calculate the vapor pressure from the measured Zdol molecular weight distribution and evaporation rate. Molecular weight distributions were measured by gel permeation chromatography (GPC), as described in Karis, Marchon, and Hopper, et al. 2002). The vapor pressure of discrete molecular masses was calculated from the evaporation rate measured by isothermal thermogravimetric analysis (TGA) with a stagnant film diffusion model as in Karis and Nagaraj (2000). Polymers such as Zdol differ from the low molecular weight synthetic hydrocarbon oils in that polymers comprise a variety of different molecular weights. The molecular weight distribution must be considered in modeling the evaporation of polymers.
Hydrophobic Modifications of Membranes with Improved Anti-Wetting Resistance
Published in Kang-Jia Lu, Tai-Shung Chung, Membrane Distillation, 2019
Various hydrophobic polymeric materials have been applied for surface coating on MD membranes, such as silicon rubber, styrene-butadiene, perfluoropolyether, and Teflon (Jin et al., 2008; Jung et al., 2016; Lu et al., 2016; Sanguineti et al., 2013; Shaulsky et al., 2017; Yang et al., 2011a). Jin et al. prepared a poly(phthalazinone ether sulfone ketone) (PPESK) hollow fiber membrane and coated its surface by silicone rubber and sol-gel polytrifluoropropylsiloxane. The contact angle and LEP of the resultant membrane increased to 100° and 0.12 MPa, respectively, while the permeation flux reduced remarkably if the silicone rubber solution had a high coating concentration (Jin et al., 2008). A hydrophilic polyamide (PA) membrane was also successfully coated with hydrophobic styrene-butadiene rubber and exhibited a LEP over 1.3 bar (Jung et al., 2016). Yang and coworkers modified the PVDF membrane surface with perfluoropolyether and obtained a membrane with a water contact angle of 115° and a LEP value of 3.9 bar (Yang et al., 2011b). Solvay has filed a patent to coat a perfluoropolyether polymer (Fluorolink) on the surface of polyethersulfone, regenerated cellulose, and PVDF membranes. The water contact angles and LEP of these three types of membranes exceeded 125° and 2.2 bar, respectively (Sanguineti et al., 2013). Lu et al. coated Teflon AF 2400 on a PVDF tri-bore hollow fiber by dip coating. The water contact angle of the resultant membrane increased from 105° to 150°, while the LEP value jumped from 0.58 bar to 1.4 bar (Lu et al., 2016).
Nature and Prospective Applications of Ultra-Smooth Anti-Ice Coatings in Wind Turbines
Published in Ranjusha Rajagopalan, Avinash Balakrishnan, Innovations in Engineered Porous Materials for Energy Generation and Storage Applications, 2018
Hitesh Nanda, P.N.V. Harinath, Sachin Bramhe, Thanu Subramanian, Deepu Surendran, Vinayak Sabane, M.B. Nagaprakash, Rishikesh Karande, Alok Singh, Avinash Balakrishnan
The suitability of the oils mentioned in Table 1 is definite as to the fact that they are colourless, non-flammable, non-reactive and have longer life. The polymer chain of perfluoropolyether is saturated with carbon (22 per cent by weight), fluorine (69 per cent by weight) and oxygen atoms (9 per cent by weight), as seen from the chemical structure in Fig. 8 (DuPont 2011).
Effects of UHMWPE Filler on the Tribological and Mechanical Properties of Biocompatible Epoxies
Published in Tribology Transactions, 2020
Kalathil A. Arshad, Jaswant K. Hirwani, Sujeet K. Sinha
Among epoxies, a new epoxy-based material that is being studied is SU-8 (each molecule has eight epoxy rings). It is a negative photoresist material that is ultraviolet curable and has properties such as mechanical strength, elastic modulus, friction, and wear similar to those of normal epoxies (Katiyar, et al. (20)). A number of studies have been carried out to improve the tribological properties of SU-8 (Katiyar, et al. (9); Tay, et al. (21); Saravanan, et al. (22)). Inclusion of a liquid lubricant, 5 wt% perfluoropolyether, in SU-8 provided excellent results by reducing the COF to 0.03, which was 0.82 for pure SU-8 and 0.39 for SU-8 with 5 wt% carbon nanotubes (Saravanan, et al. (22)). These improvements also accompanied an increase in the wear life by four orders of magnitude as well as improvements in the modulus and hardness compared to pure SU-8. The tribological properties of SU-8 have also been improved by adding graphite and talc powders (Katiyar, et al. (9)). Thus, it is important to study SU-8 and its UHMWPE composites for a thorough comparison with normal epoxies for future applications.
Laboratory evaluation and numerical simulation study on profile modification performance of gel-nitrogen-foam for low permeability formation under fracturing
Published in Particulate Science and Technology, 2020
Fuzhen Chen, Jianwei Gu, Xue Yao
Fluorine oil (perfluoropolyether) was used to replace traditional crude oil as experimental oil. There is an enhanced oil recovery capacity study by nuclear magnetic resonance (NMR) which uses the resonance of hydrogen in formation water. Fluorine oil does not contain hydrogen and will not affect the NMR test. The density of fluorine oil (perfluoropolyether) is 1.87g/ml and the viscosity at 20 °C is 18.43 mPa·s. It has steady chemical property and will not react with fluid and formation mineral during experiment process.
Tribological Behavior of Rice Bran Ceramics in a Vacuum Environment
Published in Tribology Transactions, 2018
Takeshi Yamaguchi, Kei Shibata, Kazuo Hokkirigawa
Rice bran (RB) ceramics are carbon-based porous materials with an amorphous carbon structure; they are prepared by carbonizing a mixture of defatted rice bran and phenolic resin (Hokkirigawa, et al. (1); Yamaguchi and Hokkirigawa (2)). Because RB ceramics exhibit low friction and high wear resistance under dry conditions (Hokkirigawa, et al. (1); Yamaguchi and Hokkirigawa (2); Hokkirigawa (3)) and under water lubrication (Hokkirigawa, et al. (4)), they are used in several tribological applications such as linear sliding-type guide bearings (Yamaguchi and Hokkirigawa (2); Hokkirigawa, et al. (5)). Recently, Yamaguchi et al. (6) investigated the effect of temperature on the friction and wear of RB ceramics under dry conditions and found that the RB ceramics provided a low friction coefficient (<0.05) at 200°C when sliding against an alumina ball. Their results suggest that RB ceramic linear guide bearings can be used at elevated temperatures. In addition to their use under high-temperature conditions, linear sliding bearings are sometimes used under vacuum conditions without lubrication. In a vacuum environment, normal fluid lubricants such as oil cannot be used due to the evaporation rate. Thus, solid lubricants (e.g., MoS2, WS2, soft metals, polytetrafluoroethylene, and polyimide) are generally used. Further, we have observed recently that synthetic oils with low vapor pressure (e.g., perfluoropolyether and multiply alkylated cyclopetane) are also being used (Suzuki (7)). However, there are a few bulk materials that exhibit low friction and wear under vacuum conditions. Therefore, we observe that RB ceramics could be a suitable candidate as a dry sliding bearing material in a vacuum environment if they demonstrate low friction and wear in vacuum conditions. However, whether RB ceramics exhibit a low friction coefficient and a sufficiently low wear rate under vacuum conditions is unclear.