Ultralow Tribological Properties of Polymer Composites Containing [BMIm]PF₆‐Loaded Multilayer Wall Microcapsule

Abstract

polymer bulk materials or coating. Upon damaging the self-lubricating materials by friction, the embedded microcapsules simultaneously rupture, release the lubricant, form the transfer film, and then lubricate the wear surface. Therefore, selflubricating microcapsules must possess several features, such as excellent thermal stability, high encapsulation efficiency, and good lubricating properties.Various lubricants have been microencapsulated, including lubricant oil, [4][5][6][7] paraffin, wax, [8][9][10][11] diisocyanate, [12,13] and ionic liquid. [14][15][16] In addition to reducing friction and wear, lubricating oils are required to cool the rubbing surfaces that are heated due to friction. Thermooxidative stability of lubricants is essential to minimize degradation during service and storage. Lubricating oils may vaporize and sometimes may catch fire due to friction heat. Therefore, less volatile and nonflammable liquids are desirable for lubricants. [17] Compared with some common lubricants, ionic liquids have high thermal stabilities (the thermal degradation temperature is usually higher than 350 °C) and low volatility and non-flammability. These excellent properties make them more suitable as high-performance lubricants. [18][19][20][21] Nevertheless, when the wrapped core material is an ionic liquid, the encapsulation efficiency is lower because the high viscosity and bipolar nature of the ionic liquid make them difficult to disperse in a continuous phase during microencapsulation. [22][23][24][25] Recently, we have prepared ionic liquid [BMIm] PF 6 -loaded polyurea (PU) microcapsules with >70 wt% encapsulation efficiency by optimizing a Pickering emulsion and interface polymerization method. The Pickering emulsion was stabilized by lignin solid particles instead of molecular surfactants and some inorganic particles, and we found that the lignin exhibited excellent emulsifying properties for ionic liquid. [26] However, the smooth outer surface of PU microcapsules prevents them from forming a good interface with the resin matrix when they are used to prepared composites. In order to improve the thermal stability, mechanical properties, long-term stability at room temperature of microcapsules, and then to make these microcapsules were satisfy the requirements of the processing of polymeric composites under high temperatures and large shear stress conditions, Self-Lubricating CompositesMultilayer wall microcapsules efficiently loaded with a lubricant (ionic liquid [BMIm]PF 6 ) are successfully synthesized via a combination of interfacial and in situ polymerization reactions based on lignin nanoparticle-stabilized Pickering emulsion templates. The resulting microcapsules are spherical in shape, with an ideal structure of a rough outer surface and a smooth inner surface. The mean diameter and wall thickness of the resultant microcapsules are 52 ± 18 µm and 3-6 µm. The core fraction is ≈71.29 wt%. Compared with the pure epoxy resin, the friction coefficient of self-lubricating composites decreases by 83.6% (fr...

The tribological behaviors of core‐shell n‐octadecane@TiO2/epoxy composites

“…Furthermore, n-octadecane@TiO 2 / epoxy had a narrower wear track at 4 N, 2 cm/s, which means that the composites had a good load capacity. It is presumed that the released n-octadecane core prevent direct contact between the composites and the counterface [51,52] . The "healing" phenomenon also could be seen in the worn area after high speed (2 N, 4 cm/s) reciprocating sliding, a plenty of closed or filled cracks were distributed all over the wear tracks, which were the result of repairing by mixture of crushed n-octadecane @ TiO 2 .…”

Effects of nickel shell microcapsules and short fibers on polyamide 6‐matrix composites: Thermal, surface wetting, mechanical, and tribological properties

“…The performance of microcapsules usually undergoes material-level tests at the laboratory level, and the matrix materials used mostly are EP resins, which are easy to form and cure. [23][24][25][26][27][28] Nonetheless, no further reports have mentioned their engineering applications. In fact, the application of microcapsules in engineering needs to consider more than lubricating effects, it is also necessary to consider high temperature resistance of microcapsules, thermal stability, and mechanical properties of prepared composites, dimensional stability, loadcarrying capacity, and service performance of the prepared parts.…”

A Novel Finding of Tribological and Mechanical Linking to Micro‐Convex Texture on Hydrophilic Composites Surface under Water‐Lubricating Conditions

“…[7,8] However, since the water viscosity is only ≈1/10 of the oil, which makes it impossible to form a stable water film between the waterlubricated bearing and bushing in the process of ship operation, especially under special conditions, such as start-up, shutdown, low speed, heavy load, etc., they are often in the state of boundary lubrication or even dry friction, and the tribological properties are greatly reduced. [9][10][11] In this case, it is quite easy to cause frictional self-excited vibration and produce tremor and a whistling sound repeatedly for a long time, which will seriously affect the safety and service life of underwater vehicles. [12,13] Therefore, improving the tribological properties of the water-lubricated bearing materials is of great significance to ensure the ship's performance and promote the development of the ship field.…”