N-doped carbon dots based nano-composite coatings with ultra-low coefficient of friction and superior corrosion resistance

Carbon dots (CDs) are widely recognized for their superior adsorption and film-forming capabilities on metallic surfaces, making them effective as liquid lubricant additives and corrosion inhibitors. However, their applications in solid lubricating and organic anti-corrosion coatings have been less reported. In this study, nitrogen-doped CDs (N-CDs) with a polymer‒carbon core hybrid structure are synthesized via the facile aldol condensation of acetaldehyde and urea. The incorporation of these N-CDs as additives into waterborne epoxy (WEP) coatings enhances interfacial compatibility, resulting in remarkable improvements in lubricating performance and corrosion resistance. Compared to the pure WEP coating, the N-CDs based nano-composite coating (WEP(PDMS)@N-CDs) (PDMS = polydimethylsiloxane) demonstrates a dramatic reduction in the coefficient of friction from 0.760 to 0.049, representing a 93.6% decrease. Additionally, the WEP(PDMS)@N-CDs coating exhibits exceptional corrosion resistance, as evidenced by a stable low-frequency impedance modulus of |z|_0.01Hz = 3.5×10⁷ Ω·cm². These improvements are primarily attributed to the abundant polymer branched chains on the N-CDs surface, which effectively increase the cross-linking density of the WEP polymer. The resulting WEP(PDMS)@N-CDs coating not only facilitates dynamic repair during friction but also enhances the barrier effect of the coating, leading to significantly improved wear and corrosion resistance.