The oleylamine (OA)-modified carbon nanoparticles (CPs-OA) with particle sizes of 25–35 nm were synthesized by a facile one-pot pyrolysis method. As the OA molecules were covalently attached on the surfaces of CPs-OA, the CPs-OA exhibited good dispersibility in polyalphaolefin (PAO). Then the tribological behaviors of CPs-OA as the lubricating additives of PAO were investigated in detail. Under the four-ball mode and the load of 392 N, the CPs-OA showed the best friction-reducing and antiwear properties at the optimal concentration of 1.0 wt%. Specifically, in comparison with that of pure PAO, the mean friction coefficient and mean wear scar diameter of the 1.0 wt% CPs-OA/PAO suspension reduced by 47 and 30%, respectively. The friction-reducing and antiwear capabilities of CPs-OA strengthened with increasing load from 200 to 392 N and increasing test time from 240 to 480 min. In addition, the CPs-OA-based additives could work for a long time without weakening the lubrication capability. The synergistic effect of tribofilm, including PAO molecules and the CPs-OA layer, might account for the outstanding friction-reducing and antiwear capabilities of CPs-OA-based additives under boundary lubrication.

Ionic liquid (1-aminopropyl-3-methyl-imidazolium bromide) capped carbon dots (CDs-Br), with a mean particle size of 1.73 nm and poor crystallinity, have been successfully synthesized by a one-pot pyrolysis method. The CDs-NTf2 were obtained from the CDs-Br by an anion exchange reaction between Br− and N(CF3SO2)2− (NTf2−). The NTf2− endowed the CDs-NTf2 with wonderful dispersion stability in poly(ethylene glycol) (PEG). The tribological performances of CDs-NTf2 as the lubricant additive for PEG were investigated in detail using a four-ball model by altering the concentration of CDs-NTf2, the test load and the duration. The results demonstrated that these CD-NTf2-based additives exhibited excellent friction-reducing and antiwear properties. In particular, the friction coefficient and wear scar diameter (WSD) of lower balls lubricated by PEG under 392 N correspondingly reduced by 70% and 33% when 0.3 wt% of CDs-NTf2 was introduced. The WSD reduction further increased by 45% when the test load was increased to 600 N. Moreover, the CD-NTf2-based additives could work for a long time without weakening the lubrication capabilities. The lubricating mechanism of CD-NTf2-based additives has also been proposed and illustrated that the synergistic lubricating effect of CDs-NTf2, including film lubrication of IL groups and nano-lubrication of carbon cores such as rolling, mending and polishing effects, might account for their outstanding tribological behaviors. The above results indicate that CDs are expected to be utilized as a kind of designable and high-performance lubricant additive and find wide applications in machinery and equipment.

A series of tertiary amide-based gemini surfactants, 2,2′-(1,4-phenylenebis(oxy))bis(N-(3-(dimethylamino)propyl)alkylamide), abbreviated as Cm–A–Cm (m = 8; 10; 12; 14), were synthesized. The surface property and aggregation behaviors of the Cm–A–Cm aqueous solutions were studied in detail. The Cm–A–Cm exhibited high and pH-regulated surface activity at the air/water interface; i.e., the critical micelle concentration was 5.6 × 10−6 mol L−1 at pH = 2.50 when m = 14 and was further regulated to 1.8 × 10−6 mol L−1 by altering the pH to 6.50. When the pH was tuned from 2.0 to 12.0, the appearance of the C12–A–C12 aqueous solution (35 mM) underwent 5 states: transparent water-like solution, viscous fluid, gel-like fluid, turbid liquid and dispersion system with white precipitate. The results of rheology, cryogenic transmission electron microscopy, and dynamic light scattering characterization revealed that the transition from water-like to viscous or gel-like liquid was actually due to aggregate microstructure transition from spherical to worm-like micelles. This transition was completely reversible between pH = 2.50 and 6.81, tuned by adding HCl and NaOH solutions for at least 4 cycles. Similar micellar transitions regulated by pH were also found for m = 8 and 10, whereas only worm-like micelles were formed for m = 14 at both acidic and nearly neutral conditions. Finally, a reasonable mechanism of aggregate behavior transition was proposed from the viewpoint of the molecular states, molecular structures, and the intra- and inter-molecular interactions.

By mixing an aqueous solution of tertiary amine, N,N-dimethylethanolamine (DMEA), with naphthenic acid (RCOOH) derived from heavy oil, a CO2 switchable zwitterionic surfactant (RCOO−DMEAH+) aqueous system was constructed. The CO2 switchability of this zwitterionic surfactant was confirmed by visual inspection, pH measurements, and conductivity tests, i.e., the RCOO−DMEAH+ decomposed into RCOOH, DMEAH+ and HCO3− after bubbling CO2 through but switched back to its original state by subsequent bubbling N2 through at 80 °C to remove the CO2. The interfacial tension tests of heavy oil in DMEA aqueous solutions indicated that the solution containing 0.5 wt% of DMEA and 0.2 wt% of NaCl resulted in the lowest interfacial tension. The O/W emulsion formed when aqueous solutions of DMEA were used to emulsify heavy oil exhibited the best performance when the oil/water volume ratio, DMEA concentration, and NaCl concentration were 65:35, 0.5 and 0.2 wt%, respectively. The feasibility of pipeline transport of the O/W heavy oil emulsion was evaluated. The results illustrated that the demulsification of the O/W emulsion after transport could be easily realized by bubbling CO2 through. Although demulsification efficiency still needs to be improved, the recycling of the aqueous phase after demulsification by removal of CO2 looks promising.

Ionic liquid (1-aminopropyl-3-methyl-imidazolium bromide) capped carbon dots (CDs-Br), with a mean particle size of 1.73 nm and poor crystallinity, have been successfully synthesized by a one-pot pyrolysis method. The CDs-NTf2 were obtained from the CDs-Br by an anion exchange reaction between Br− and N(CF3SO2)2− (NTf2−). The NTf2− endowed the CDs-NTf2 with wonderful dispersion stability in poly(ethylene glycol) (PEG). The tribological performances of CDs-NTf2 as the lubricant additive for PEG were investigated in detail using a four-ball model by altering the concentration of CDs-NTf2, the test load and the duration. The results demonstrated that these CD-NTf2-based additives exhibited excellent friction-reducing and antiwear properties. In particular, the friction coefficient and wear scar diameter (WSD) of lower balls lubricated by PEG under 392 N correspondingly reduced by 70% and 33% when 0.3 wt% of CDs-NTf2 was introduced. The WSD reduction further increased by 45% when the test load was increased to 600 N. Moreover, the CD-NTf2-based additives could work for a long time without weakening the lubrication capabilities. The lubricating mechanism of CD-NTf2-based additives has also been proposed and illustrated that the synergistic lubricating effect of CDs-NTf2, including film lubrication of IL groups and nano-lubrication of carbon cores such as rolling, mending and polishing effects, might account for their outstanding tribological behaviors. The above results indicate that CDs are expected to be utilized as a kind of designable and high-performance lubricant additive and find wide applications in machinery and equipment.