| When the size of devices decreases to micro scale, as a result of the large surface area to volume ratio, tribological issues such as adhesion, friction and wear would be the major reasons led to the reduction of the performances and the operating lifetimes of micro electromechanical systems(MEMS) devices. Hydrophobic/superhydrophobic surfaces which were thought to be solving the friction, wear and adhesion problems of MEMS for their lower surface free energy. Silicon and its compounds are the main materials for MEMS, while with the development of metals in applications of MEMS devices, the corrosion should be considered for the high chemical activity of the metals. When studying the effect of hydrophobic/superhydrophobic surfaces on the tribological properties of metals, it is of great importance to research the corrosion properties of metals for increasing the operating lifetimes of MEMS devices.Based on the hydrophobic modification of surfaces, this paper focus on fabricating of hydrophobic/superhydrophobic surfaces on the MEMS materials, like conditional single crystal silicon, new-typed Nd Fe B and potential magnesium alloy via polymer plating, selfassembling, electroplating and electroless deposition, and exploring the relations between wettability and corrosion/friction performance. The main conclusions are as follows:(1) A composite film was prepared by combining electroless deposition and polymer plating. Electroless Ni-P film was fabricated on silicon substrate first and then the composite film Ni-P-ATP was obtained. The contact angle of distilled water increased to 119.7° compared to 23.2° for the substrate and 67.9° for Ni-P film. Besides, the surface free energy for Ni-P-ATP decreased to 10.16 m J/m2, which is much lower than 38.12 m J/m2 for Ni-P film and 67.46 m J/m2 for Si substrate. At the nano scale, the adhesion force was effectively reduced from 36.21 n N for the substrate to 18.93 n N for Ni-P film and 8.23 n N for Ni-P-ATP film. The friction tests under mili-Newton loads show that Ni-P-ATP film has a lowest friction coefficient value about 0.12, while the friction coefficient for the substrate was 0.51 and for the Ni-P film was 0.22. Under a lower constant load of 50 m N and 100 m N, the ATP film illustrated good wear resistance. However, when the applied load increased to 200 m N, the ATP film was remained stable to about 55 cycles and then completely destroyed about 145 sliding cycles.(2) An organic film with thickness of 27.6 nm was successfully deposited on sintered Nd Fe B substrate surface by polymer plating of ATP. The contact angle of distilled water increased to 122.5° compared to 43.9° for the substrate, and the surface free energy was reduced to 6.91 m J/m2 compared to 59.2 m J/m2 for the substrate. The dynamic potential polarization in 0.1 mol/L Na Cl solution suggested that the corrosion potential(Ecorr) positively increases from-930.9 m V of the substrate to-804.3 m V of the ATP film. The corrosion current density(Icorr) of the superhydrophobic surfaces is 19.7 μA/cm2 while the value is 4.9 μA/cm2 for the ATP film, and the potential efficiency is 75.13%. The friction test at the applied load of 100 m N suggested that the friction coefficient for the substrate was 0.75 and reduced to 0.20 for the ATP film. ATP film could remain stable for 130 s, and then the film began to abscise and was completely destroyed about 180 s.(3) A composite film TES-ATP was prepared on sintered Nd Fe B substrate by selfassembling of TES and polymer plating of ATP. The contact angle of distilled water for TESATP was 123.5° compared to about 0° for hydroxylated substrate. The surface free energy of TES-ATP decreased to 10.19 m J/m2 from 73.13 m J/m2 for the substrate. The friction test at the applied load of 100 m N suggested that the friction coefficient was effectively reduced from 0.71 for substrate to 0.22 for TES and 0.12 for TES-ATP. In addition, the wear life for the TES, ATP film and TES-ATP was 15 s, 130 s and 180 s respectively. The wear life for TESATP composite film is more than the sum of TES and ATP film. The composite film possessed a good lubrication effect.(4) Two different organic compounds with a same terminal group octadecyl are used for the preparation of two kinds of hydrophobic organic films on the surface of Mg-Mn-Ce alloy by polymer plating and self-assembling technology, respectively. The polymer plated film was short as STN film and self-assembled film was short as OTS film. The contact angle of distilled water increased from 55.0° for the substrate to 132.4° for STN film and 135.7° for OTS film. The surface free energy of STN and OTS film decreased from 51.83 m J/m2 for the substrate to 30.81 and 30.14 m J/m2, respectively. At the nano scale, the adhesion force was effectively reduced from 12.35 n N for the substrate to 5.76 n N for STN film and 4.12 n N for OTS film. The friction force was effectively reduced from 19.82 n N for the substrate to 7.30 n N for STN film and 6.23 n N for OTS film and the friction coefficient was reduced from 0.454 for the substrate to 0.094 for STN film and 0.128 for OTS film.(5) A rapid one-step method was developed to fabricate a superhydrophobic surface on the cathode(Mg-Mn-Ce magnesium alloy) by a simple electrodeposition process in an ethanol solution containing cerium nitrate hexahydrate and myristic acid. The time to obtain the superhydrophobic property can be as short as 1 min. The obtained surface is composed of cerium myristate with a hierarchical micro-nanoscaled-particles structure and has a maximum contact angle of 159.8° and sliding angle less than 2°. The as-prepared surface shows good mechanical stability and chemical stability. Besides, the superhydrophobic surface shows an excellent performance of corrosion resistance when immersed in the corrosive aqueous solutions(3.5 wt.% Na Cl, Na2SO4, Na Cl O3 and Na NO3). |
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