Study On The Preparation Of Imidazoline Surfactants-Modified Nanomaterials And Tribological Properties Of The Related Materials

Due to the excellent decontaminating, bubbling and emulsifying properties, verylow toxicity and good biological degradation, imidazoline-type surfactants have beenwidely used in industrial fields, such as domestic chemical engineering, textile, dying,corrosion inhibition and industrial surface washing, etc. However, people have ignoredto extend their application in other fields so far. Imidazoline-type surfactants are ofspecial molecular structure, in which the long slim hydrophobic chain segment iscomposed of long chain alkyl, while the hydrophilic chain segment with larger volumeis made up of imidazoline ring and the heteroatoms S, N and O located at the sidechain. The special amphiphilic properties make the molecular structure ofimidazoline-type surfactants similar to that of block copolymer, which are of specialsurface/interface properties in selective solvents. Thus, the excellent surface-modifyingeffects of this kind of surfactants in the preparation of nanomaterials are worthexpecting. However, no researches on this aspect have been reported home and abroad.Much more attention has been paid to the preparation and application ofnanomaterials due to their special optic, electrical, photochemical, electrochemical,mechanical and catalytic properties. However, in many fields such as nanotribologyand bioelectrochemical analysis, the poor oil-solubility, dispersion and stability ofnanomaterials in organic media limit their application, and their excellent propertiescan't be exerted completely. Surface-modification with organic surfactants is aneffective way to improve the application effects of nanomaterials. Because of thespecial amphiphilic properties, the imidazoline-type surfactants are very suitable forthe surface-modification of nanomaterials, acting as the surface-modifying agent, dispersing and stabilizing agent and morphology-controlling agent, which is ofsignificant sense in expanding the application of nanomaterials.The synthesis processes of nanomaterials are very important for their application,and it still remains a great challenge to develop a facile, convenient, low-energy andenvironment-friendly route. In this paper, with imidazoline-type surfactants assurface-modifying agents, several methods are exploited to synthesize nanomaterials,especially the room temperature route to the fabrication of nanomaterials with specialmorphologies, which is significant to the manufacture production of nanomaterials in alarge scale. The as-prepared surface-modified MoS₂ micro-sized solid spheres andnano-sized hollow spheres, as well as the surface-modified ZnS hollow spheres are ofexcellent tribological properties in liquid paraffin, base oil 500 SN and medium-loadgear oil GL-4.The purpose of this paper is, the imidazoline-type surfactants with specialmolecular structure are firstly synthesized and characterized, and their interracialproperties are studied systematically; then the as-synthesized imidazoline surfactantsare applied into the preparation of nanomaterials to modify their surface; finally, thetribological properties of the as-prepared surface-modified MoS₂ and ZnS products arestudied as oil additives in lubricating oils, and the action mechanism of the imidazolinesurfactants-modified nanomateirals during the friction process are also investigated soas to provide a new route to the fabrication of practical and effective lubrication oiladditives, which is of active sense to expand the application of surface-modifiednanomaterials in industrial lubrication field.The main contents of this paper are as follows:(1) Four imidazoline-type surfactants quaternary ammonium salts of 2-undecyl(heptadecyl)-1-dithioureido-ethyl-imidazoline (SUDEI/SHDEI) and di (2-undecyl(heptadecyl)-1-formyl aminoethyl imidazoline) hexanediamine (SUAEIHDI/SHAEIHDI) were synthesized and characterized by the measurements of FT-IR,GC-MS and NMR, and their interracial properties were also studied systematically.The critical micelle concentration (CMC) values were obtained and the micellizationthermodynamic functions were calculated as well. The effects of the hydrophobicchain length, temperature and polarity of solvents on the surface properties were alsodiscussed. The Langmuir Monolayer Adsorption Model was employed to explain theinterfacial properties of the four obtained imidazoline-type surfactants.(2) With 7 g/L SUDEI as surface-modifying agent, Na₂MoO₄·2H₂O as Mo source, aminothiourea as S source and N₂H₄·H₂O as reducing agent, MoS₂ solid spheres withsize of 0.5～2μm were synthesized via a solvothermal route at 190℃for 24 h in themixed medium of ethanol-water (1:1, v/v). XRD, TEM, SEM, HRTEM and XPSmeasurements were used to characterize the MoS₂ products, and the effects of varioussurfactants type and concentration, reaction time and solvent on the morphologies ofMoS₂ products were discussed. The formation mechanism of MoS₂ solid sphericalstructure was investigated as well.(3) With acidic extractant Cyanex 301 as S source and surface-modifying agentand Na₂MoO₄·2H₂O as Mo source, 2H-MoS₂ hollow spheres with size of 200～300 nmwere synthesized via a solvothermal route at 190℃for 24 h in the mixed medium ofethanol-water (3:1, v/v). Compared with the literature, this approach has theadvantages of low reaction temperature, low cost, mild and easy control of the reactionprocess. Petal-like MoS₂ particles with size of about 20 nm were also obtained via thesimilar way mentioned above in DMF. XRD, TEM, SEM and EDXA measurementswere used to characterize the MoS₂ products, and the effects of extractantconcentration, reaction time and temperature on the morphologies of MoS₂ werediscussed. The formation mechanisms of MoS₂ hollow and petal-like structure wereinvestigated as well.(4) With 0.05 mol/L SUDEI as surface-modifying agent, Pb(Ac)₂·3H₂O as Pbsource and Na₂SeSO₃ as Se source, well-dispersed rectangular PbSe nanocrystal wasprepared via a solvothermal route at 150℃for 12 h. in the mixed medium ofethanol-water (3:1, v/v); with 4 g·L^-1 SUDEI as surface-modifying agent,(K(SbO)C₄H₄O₆.1/2H₂O) as Sb source and Se powder as Se source, rod-like Sb₂Se₃nanocrystal was prepared via a hydrothermal route at 150℃for 24 h. XRD, TEM andXPS measurements were used to characterize the PbSe and Sb₂Se₃ products, and theeffects of various surfactants type and concentration, reaction temperature and mediumon their morphologies were discussed. The formation mechanisms of PbSe and Sb₂Se₃nanocrystals were investigated as well.(5) With 4 g/L SUAEIHDI as surface-modifying agent, Zn(Ac)₂·2H₂O as. Znsource, Se powder as Se source and N₂H₄·H₂O as reducing agent, ZnSe nanosphereswith size of 100-300 nm were synthesized via a hydrothermal route at 150℃for 24 h.XRD, TEM, SEM, FT-IR and UV-vis measurements were used to characterize theZnSe products, and the effects of various surfactants type and concentration, reactiontemperature and solvent on the morphologies of ZnSe were discussed. The formation mechanism of ZnSe spherical structure was investigated as well.(6) With 6 g/L SUDEI as surface-modifying agent, CdCl₂·2.5H₂O as Cd sourceand Na₂SeSO₃ as Se source, well-dispersed CdSe solid spheres with size of 0.5-1μmwere synthesized in water at 90℃for 6 h in air without stirring. XRD, EDXA, TEM,SEM, FT-IR and UV-vis measurements were used to characterize the CdSe products,and the effects of various surfactants type and concentration, reaction time and solventon the morphologies of CdSe were discussed. The formation mechanism of CdSespherical structure was investigated as well. The preliminary electrochemicalproperties indicate that the DNA molecules can be labeled easily on the CdSenanoparticles, and the detection limit of DNA is up to pmol/L.(7) With 6 g/L SUDEI as surface-modifying agent, Zn(Ac)₂·2H₂O as Zn sourceand TAA as S source, well-dispersed ZnS hollow spheres with size of 0.5-1μm weresynthesized in absolute ethanol at room temperature for 24 h in air. XRD, EDXA,TEM, SEM, FT-IR and UV-vis measurements were used to characterize the ZnSproducts, and the effects of various surfactants type and concentration, reaction timeand solvent on the morphologies of ZnS were discussed. The formation mechanism ofZnS hollow spherical structure was investigated as well.(8) With 6 g/L SUDEI as surface-modifying agent, Bi(NO₃)₃·5H₂O as Bi sourceand TAA as S source, well-dispersed urchin-like Bi₂S₃ products with size of 200～400nm were synthesized in DMF at room temperature for 24 h in air. XRD, EDXA, TEM,SEM, FT-IR and UV-vis measurements were used to characterize the Bi₂S₃ products,and the effects of various surfactants type and concentration, reaction time and solventon the morphologies of Bi₂S₃ were discussed. The formation mechanism of Bi₂S₃urchin-like structure was investigated as well.(9) The tribological properties of SUDEI-modified MoS₂ micro-sized solidspheres (SU-MoS₂), Cyanex 301-modified MoS₂ nano-sized hollow spheres(301-MoS₂) and Cyanex 302-modified MoS₂ micro-sized solid spheres (302-MoS₂) inliquid paraffin (LP), base oil 500 SN and medium-load gear oil GL-4 were studied andcompared with those of commercial colloidal MoS₂ (CC-MoS₂). The results show thatthe three self-prepared surface-modified MoS₂ additives are of excellent dispersion andstability, extreme-pressure characteristics and anti-wear and friction-reducingproperties in the three base stocks mention above, which are much better lubricatingmaterials compared with commercial colloidal MoS₂ (CC-MoS₂). Furthermore, thetribological properties of the as-prepared SUDEI-modified ZnS hollow spheres (SU-ZnS) in LP and base oil 500 SN were also studied, indicating that thesurface-modified ZnS hollow spheres are of excellent dispersion and stability,anti-wear and friction-reducing properties in the two base stocks. SEM and XPSmeasurements were used to observe the surfaces of the wear scars and the lubricationmechanisms of the systems lubricated with self-prepared surface-modified MoS₂ andZnS products in the friction process were investigated as well, which could be deducedas the effective surface composite film composed of chemical adsorption film,chemical reaction film and deposition film under boundary lubrication conditions, aswell as the existence of rolling friction.