Green Superlubricity Enabled by Only One Water Droplet on Plant Oil-Infused Surfaces

Abstract

The increase in energy loss due to friction and the use of large amounts of lubricants to improve it are major challenges we face from a global environmental perspective. Pitcher-plant-inspired liquid-infused surfaces (LISs) are emerging superrepellent surfaces against liquids. However, their coefficient of friction (CoF) against solids is higher than that of conventional lubricant surfaces. Herein, we demonstrate superlubricity with a single water droplet placed on a LIS holding oleic acid, a component of plant oil. When a water droplet is placed on the fluid layer, the CoF under reciprocating and rotating friction is 0.012 and 0.0098, respectively. A force in the direction opposite to the loading due to the Laplace pressure on the droplet and an autonomous positional movement of the water accompanied by the optimization of surface energy maintain the fluid-lubrication state and prevent direct contact between the surface and the friction material, resulting in a decrease of the dependence of the CoF on the friction velocity. The key technology here will not only present a novel strategy for preparing LISs against solids but also serve as a step toward a sustainable green strategy for friction reduction and lubrication, which would greatly reduce energy loss and environmental degradation.

Light-Driven Liquid Conveyors: Manipulating Liquid Mobility and Transporting Solids on Demand

“…This force lifted the materials placed on the surface upward because of the Laplace pressure created by the surface tension difference with the air and liquid layer surrounding the droplets (Figure b). In the case of a water droplet, this force can be simply expressed as − where γ wa and γ wl are the interfacial tensions between air and water and between the liquid layer and water, respectively, r is the contact radius of the covered material starting from the center of the droplet, θ A is the contact angle on the covered material, θ B is the contact angle at the surface of the base material, and h is the height of the droplet.…”

Superlubricity of Materials: Progress, Potential, and Challenges

“…The development and application of superlubric systems should consider the environmental impact, resource consumption, and long-term performance. Researchers are exploring sustainable lubricants, eco-friendly coatings, and self-healing materials to address these concerns and ensure that superlubric technologies contribute to a more sustainable future [ 69 , 98 , 100 ]. Another aspect is the lifecycle analysis of superlubric materials and coatings.…”

Study on the Superlubricity Behavior of Ions under External Electric Fields at Steel Interfaces

“…Superlubricity represents a highly promising lubrication regime − characterized by extremely low sliding friction (below 0.01) and nearly negligible wear. Scientists have achieved superlubricity at macroscopic and microscopic scales with various lubrication materials. − Luo’s group achieved macroscopic superlubricity at the interface of engineering steel by using black phosphorus as an additive. The study found that a trilayer frictional film, composed of amorphous carbon, graphene crystals, and phosphorus trioxide, was formed during the friction process.…”