Dihexylamine

Diethylamine, dibutylamine, dihexylamine, carbon disulfide, and silver nitrate (99.8%) were purchased from Sigma-Aldrich Trading Company Limited (Shanghai, China). Polyamic acid with a solid content of 38.0% was obtained from Beijing Sino-rich Technology Company Limited (Beijing, China). The mixed solvent of N,N-dimethylformamide and N-methylpyrrolidone (volume ratio 1:1) was used as the co-dispersion medium of the paint. All chemicals were directly used as-received. AISI-1045 steel block (19.00 mm × 12.00 mm × 12.00 mm, Rockwellhardness (HRC) 28–32, E = 210 GPa) was used as the substrate, and AISI-52100 bearing steel ball (Φ 6 mm, HRC 58–61, E = 208 GPa, Ra = 0.02 μm) was used as the counterpart.

Sodium lignosulfonate (STARLIG^®®Na98S, industrial grade) in the form of yellow powder was supplied by Lignostar International BV (Hague, the Netherlands). Chloroform (analytical grade), thionyl chloride (reagent grade), phosphorus pentachloride (reagent grade), sodium hydroxide (analytical grade), and dihexylamine (97%) were purchased from Sigma-Aldrich (Darmstadt, Germany). Hydrochloric acid of analytical purity (35–38 wt%) was purchased from Chempur (Piekary Śląskie, Poland). All of the chemicals were used as received.