Vanishing Friction: Progress toward Mechanistic Understanding and Potential Engineering Applications

Friction and wear collectively account for nearly a quarter of the world's energy consumption, resulting in over eight Gigatons of CO2 emissions annually. With increasing mobility and industrial activity, the adverse effects of friction and wear on energy, the environment, the global economy, and sustainability will undoubtedly intensify. Unless we reverse this unsustainable trend, our planet could face a major ecological and environmental catastrophe. Fortunately, significant strides have been made in reducing friction to almost undetectable levels, with friction coefficients below 0.001. These remarkable achievements have resulted from numerous collaborative efforts and global initiatives focused on developing novel materials, surfaces, and interfaces that exhibit minimal or near zero friction, even at macro or engineering scales. This paper provides a comprehensive overview of the factors that contribute to and hinder superlubric sliding conditions, examining the impact of both intrinsic and extrinsic factors that are integral parts of the test conditions and environments. Drawing from recent analytical, experimental, and computational findings, underlying mechanisms most responsible for superlubricity are also discussed. The paper discusses recent mechanistic studies on highly ordered 2D materials, such as graphene, MoS2, h-BN, MXene, etc., and thin solid coatings such as diamond-like carbon or DLCs, as well as liquids, and discusses their potential for the development of large-scale mechanical systems. These exciting advancements pave the way for designing and producing next-generation engineering systems that can minimize friction in practical applications, thus conserving energy, enhancing durability, and protecting the environment for a sustainable future.