Superlubricity Microcapsules.

Superlubricity, a lubricating state in which the coefficient of friction (COF) is smaller than 0.01, has been achieved at the macroscale in a variety of aqueous solutions and oils, as well as two-dimensional (2D) and carbon materials; nevertheless, it has been rarely realized with polymer composites. In the present work, macroscale superlubricity was achieved with a polymer composite on the basis of the microcapsule technique, which is an effective self-lubricating method for composites by releasing lubricants on demand. Solid submicrometer capsules were used as the basic units of the matrix of a polymer composite, and oil-containing microcapsules were used as lubrication fillers. On the basis of this material design strategy, robust superlubricity with a COF of 0.003-0.009 was achieved in a wide temperature range (0-200 °C) under atmospheric conditions, and it could be kept for a sliding distance of over 500 m. It has been found that the trace oil released from the microcapsules at the sliding interface favored the formation of a hydrodynamic film and a boundary tribo-film with an ultralow shear strength. This work provided a novel method to achieve superlubricity with polymer composites and potentially expanded the engineering application of superlubricity.