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Molecular spectroscopic studies of the effect of base oils on additive—additive interactions
Author(s) -
Sarpal A. S.,
Bansal V.,
Sastry M. I. S.,
Mukherjee S.,
Kapur G. S.
Publication year - 2003
Publication title -
lubrication science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.632
H-Index - 36
eISSN - 1557-6833
pISSN - 0954-0075
DOI - 10.1002/ls.3010160103
Subject(s) - chemistry , base (topology) , monomer , solvation , zinc , infrared spectroscopy , solvent , polar , base oil , nmr spectra database , organic chemistry , methanol , polymer chemistry , spectral line , polymer , materials science , scanning electron microscope , mathematical analysis , physics , mathematics , astronomy , composite material
The effect of different types of base oil of API Groups I to V, such as mineral based (solvent refined, hydrofinished, hydro‐cracked/ wax isomerised) and synthetic based (polyalphaolefin and ester), on the interaction of zinc dialkyldithiophosphate (ZDDP) with polyisobutylene succinimide (PIBS) has been studied by variable‐temperature (VT) IR and 31 P NMR spectro‐scopic techniques. Since ZDDPs are known to exist in monomeric and polymeric forms and as neutral and basic salts, and their functioning is temperature dependent, the structural changes observed in the NMR and IR spectra of the ZDDP—PIBS system in different base oils have been addressed with this in mind. The strength and composition of ZDDP—PIBS complexes has been explained in terms of the degree of solvation provided by the medium (base oil) in which they are present, and thermodynamic parameters ΔH and ΔS estimated from the VT IR spectra. The results indicate that the complexes are stronger and stable in polar base oils, such as from Groups I and V. The equilibrium shifts towards the neutral form of ZDDP in polar base oils. The results have been substantiated by correlating the variation in the shift and width of IR and 31 P NMR signals to the stability of the complexes and low values of ΔH and ΔS. Polar solvents, such as methanol and tetrahydro‐furan, also favour the formation of the neutral form of ZDDP and stronger complexes between PIBS and ZDDP, in a manner similar to that observed for polar base oils.