Ultralow friction polymer composites incorporated with monodispersed oil microcapsules
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Ultralow friction polymer composites incorporated with monodispersed oil microcapsules Lin ZHANG1, Guoxin XIE1,*, Shuai WU1, Shiguang PENG1, Xiaoqing ZHANG2, Dan GUO1, Shizhu WEN1, Jianbin LUO1,* 1
State Key Laboratory of Tribology, Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
2
School of Materials Science and Mechanical Engineering, Beijing Technology and Business University, Beijing 100048, China
Received: 15 April 2019 / Revised: 18 June 2019 / Accepted: 01 July 2019
© The author(s) 2019. Abstract: Ultralow friction polymer composites were prepared by adding oil-loaded microcapsules into epoxy (EP) resin. Mono-dispersed polystyrene (PS)/poly alpha olefin (PAO) microcapsules with a diameter of ~2 μm and a shell thickness of ~30 nm were prepared by solvent evaporation method in an oil-in-water emulsion. The lubrication behaviors of the EP resin composites with oil-loaded microcapsules have been investigated under different loads and sliding speeds. As compared with the pure EP resin, the friction coefficient of the composite could be reduced to 4% (from 0.71 to 0.028) and the wear rate could be decreased up to two orders of magnitude. It was demonstrated that the released PAO oil from the microcapsules during the friction process produced a boundary lubricating film, which could prevent the direct contact of two rubbing surfaces, and thus leading to an extremely low friction coefficient and wear rate. Moreover, the composites with microcapsules could achieve comparable lubrication properties to the case under the external lubrication condition, while the former case could effectively minimize the lubricant leakage and improve the lubrication efficiency. Keywords: polymer composite; microcapsules; solvent evaporation; ultralow friction; boundary lubrication
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Introduction
In recent years, microcontainers, e.g., hollow microspheres, microcapsules, porous microspheres, and metal-organic frameworks (MOFs), with the ability to carry versatile core materials have attracted great interest for their variety of applications [1−6]. Representatively, the microcontainers encapsulated liquids can be employed to develop a new family of selflubricating materials, because traditional external lubrication that lubricants are directly added into the interface of two rubbing surfaces could have some limitations under certain conditions. As compared with external lubrication, the release of liquid lubricants from microcontainers to the interface occurs when triggered by the friction processes (load or temperature), which could prevent lubricant leakage, and thus
increasing the durability of the effective lubrication process [7−10]. Recently, epoxy (EP) resin composites incorporated with MOFs microcontainers have been prepared and the improved lubricating performance of the composites was associated with the lubricating film produced by the chemical reaction between the released oleylamine from the capsules and the matrix [5]. Another type of
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