Silver-modified polydopamine-coated silica core-shell nanospheres as functional additives for lubricants and shear thickening fluids

The limited effectiveness of conventional nano-additives in carrier liquids has prompted research into multicapable, sustainable, and intelligent application systems. Herein, multifunctional SiO2-PDA@Ag nanoparticles were synthesized by dotting silver (Ag) nanoparticles on polydopamine (PDA)-coated SiO2 nanospheres (SiO2-PDA). The base oil (PAO) containing these synthetic nanoparticles showed excellent lubricity under high contact pressure, and the mechanism was analyzed. The addition of SiO2-PDA@Ag modified with Ag nanoparticles showed better tribological performances compared to PAO and base oils with starting nanomaterials. A concentration of 3 wt% SiO2-PDA@Ag provided the most effective performance. Furthermore, multi-phase STFs were developed by incorporating SiO2-PDA@Ag particles into SiO2-based STFs, significantly enhancing the shear thickening effect. Compared to the pure SiO2-based STF, the peak viscosity of the multi-phase STF increased by about 89.36 %. Notably, the multi-phase STF exhibited higher stress under squeeze, which facilitates the development of high-performance STF devices in extrusion mode. This enhancement is attributed to the nanocore-shell structure of SiO2-PDA@Ag, which effectively prevents the agglomeration of dispersed phase particles in organic carrier medium. The results of this work provide a promising additive nanoparticle in the field of smart materials and lubricants.