Frozen Tofu-Inspired Porous Oil-Reserved Polymer Composite Coating For Solid–Liquid Dual Lubrication

To solve oil starvation and lubrication failure in low-speed and heavy-load machinery rotation or sliding parts, the application of solid-liquid dual lubricating coatings is very extensive. The design and preparation of porous structures are key concerns, potentially impacting the friction coefficient and temperature rise at the friction interface. In this work, a robust micronano porous polytetrafluoroethylene/polyphenylene sulfide (PTFE/PPS) coating with a thickness of 20-40 μm was readily prepared by freezing the wet film at -10 °C, inspired by frozen tofu. The porosity and average pore diameter of the coating were analyzed to be about 7.4% and 50 μm, respectively. The pore formation mechanism is proposed by modulating the microphase separation of PTFE and PPS components through the synergistic effect of ice crystals as a pore-forming agent and a surfactant as a pore-expanding agent. The oil friction coefficient (μ' ≈ 0.054) was reduced by 65% than that of the dry friction condition (μ ≈ 0.155), and the wear resistance life was greater than 2.57 km/μm. The porous surface and its lipophilicity facilitate the oil to be replenished at the friction interface. This is expected to provide the idea for designing porous polymer coatings to apply in solid-liquid dual lubrication.