Structures, Vibrations, and Force Fields of Dithiophosphate Wear Inhibitors from ab Initio Quantum Chemistry

Abstract

Zinc dithiophosphates (ZnDTPs) are ubiquitous lubricating oil additives in today's passenger car motor oils, providing the important functions of wear and oxidation inhibition. However, the molecular-level mechanism by which these materials reduce wear is not understood. As a first step in developing an understanding of this mechanism, we used ab initio quantum chemical methods to examine the structures, vibrations, and energetics of these systems. The results show that the two phosphorus-sulfur bonds of the dithiophosphate of ZnDTPs are equiValent and have character intermediate between single and double bonds. This contrasts with the paradigm of one double bond (PdS) and one single bond (P-S) often used. Vibrational studies of DTP systems lead to a strong IR transition at about 650 cm -1 and a weak transition at about 530 cm -1 . We find modes in good agreement with experiment, where the high-frequency mode is antisymmetric PS stretch (not PdS), while the lower mode is symmetric PS stretch (not P-S). On the basis of the ab initio calculation results, we used the biased Hessian method to develop a vibrationally accurate force field (FF) for ZnDTPs. This FF can be used to examine the binding of DTPs to metal and metal oxide surfaces.

New Phosphorus Compounds K[pcl3(x)] (X= Scn, Cn): Preparation and DFT and Spectroscopic Studies

“…The frequencies (wave numbers) must be correlated with the results of FTIR spectroscopy. The calculated and experimental vibrational spectra correlated well [40][41] . The calculated wave number (frequency) scale was often slightly too high due to the poor modelling of the orbitals and their interactions with the surroundings.…”

The MS-Q Force Field for Clay Minerals: Application to Oil Production

“…The molecular dynamics of oil and water phase flow over chemically modified clay surfaces can form the basis for a rational design of hydrodynamic surface modifiers in the same way that the modeling of organic additives on metal surfaces has helped the discovery of novel metal wear inhibitors. 27,28 Clays in nature are usually covered with other minerals and organic substances, organic-cementing agents, consisting of proteinaeceous and humic materials, 32 C 6 -C 30 methyl esters of aliphatic and aromatic acids, and methoxy derivatives of phenols and phenolic acids. 33 In real reservoir applications, these compounds must be taken into account.…”

First principles multiscale modeling of physico-chemical aspects of tribology

“…The primary objective of the study is to enhance our understanding on how lubricants behave when they past engine surfaces and to assist in designing engine surfaces with reduced engine wear . [65][66][67] The model of the present study builds upon our previous static studies of iron-oxide surfaces covered by a self-assembled monolayer (SAM) of adsorbed wear inhibitors (``brush''). 68 A lubricant film, namely liquid hexadecane, is sandwiched between two such protected ironoxide surfaces.…”

“…The derivation and the parameters for this FF were described elsewhere. [65][66] The results presented below are from four different simulation runs: 1) R = iPr, v = 1 A/ps, and H ~45 A; 2) R = iBu, v = 1 A/ps, and H ~45 A; 3) R = Ph, v = 1 A/ps, and H ~43 A; 4) R = iPr,v = 0.5A/ps, and H ~20 A. Model system parameters are given in Table 2.…”