Fabrication of AFM‐Compatible Hydrogel Probe to Achieve Hydration Superlubrication in Salt Solutions

Abstract Hydrogels demonstrate effective lubricating properties, but the underlying mechanisms at the nanoscale remain elucidated. In this study, a novel strategy is proposed by fabricating the hydrogel probes compatible with atomic force microscopy (AFM) to establish a superlubrication system based on the hydration interactions. The probe is made of polyethylene glycol diacrylate (PEGDA)‐based hydrogel microspheres, which can achieve an extremely low friction coefficient of 0.0014 when sliding on the mica surface in NaCl solution. The friction coefficients in salt solutions sequence μ(NaCl) < 0.01 < μ(KCl) < μ(LiCl), which contradicts the sequence based on the ion hydration capacity (K ⁺ < Na ⁺ < Li ⁺ ), suggesting that the hydrogel‐based lubrication systems are governed by the interplay between ion hydration lubrication and ions‐polymer interactions simultaneously. The observed superlubrication in NaCl solution is ascribed to the superior hydration capacity of Na ⁺ ions, which forms a stable and smooth hydration layer within the contact zone. This work provides new avenues for AFM‐based hydrogel studies, and also significantly advances the comprehension of hydrogel lubrication mechanisms at the nanoscale