Rheology of lubricant basestocks: A molecular dynamics study of C30 isomers

Abstract

Rheological and structural studies of liquid decane, hexadecane, and tetracosane under planar elongational flow using nonequilibrium molecular-dynamics simulations Concentration effects on lubrication rheology for polymer solution in molecularly thin film using molecular dynamics J. Appl. Phys. 95, 8450 (2004); 10.1063/1.1751629 Molecular dynamics study of the nano-rheology of n-dodecane confined between planar surfaces Rheological, thermodynamic, and structural studies of linear and branched alkanes under shearWe have performed extensive equilibrium and nonequilibrium molecular dynamics ͑EMD and NEMD͒ simulations of three isomers of C 30 H 62 at temperatures of 311 and 372 K employing a united atom model. Using the rotational relaxation time calculated from the EMD simulation, the Rouse model predicts a zero-shear viscosity for n-triacontane within 16% of the value determined by NEMD. Compared to experiment, NEMD and the united atom model underpredict the kinematic viscosities of n-triacontane and 9-n-octyldocosane but accurately predict the values for squalane ͑within 15%͒. In addition, the predicted values of the kinematic viscosity index for both 9-n-octyldocosane and squalane are in quantitative agreement with experiment and represent the first such predictions by molecular simulation. This same general potential model and computational approach can be used to predict this important lubricant property for potential lubricants prior to their synthesis, offering the possibility of simulation-guided lubricant design.

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

“…However, UA force-fields have been shown to lead to dramatic viscosity under-prediction for linear, long-chain alkanes (≈ 50% for n-hexadecane [10]) compared to experiment. For alkanes with multiple short branches, UA force-fields can give reasonably accurate viscosity results (≈ 15% for squalane [79]), but for those with fewer, longer branches they are less accurate (≈ 50% for 9-n-octyldocosane).…”

“…In 2000, Moore et al [79] performed bulk NEMD simulations on three C 30 isomers using a UA forcefield [117]. They found that, while the viscosity of the linear (48%) and single-branched (36%) isomers were significantly underpredicted, viscosity prediction for squalane (15%), which contains multiple short methyl branches along its backbone, was more accurate [79].…”

“…They found that, while the viscosity of the linear (48%) and single-branched (36%) isomers were significantly underpredicted, viscosity prediction for squalane (15%), which contains multiple short methyl branches along its backbone, was more accurate [79]. They also analysed the viscosity at different temperatures to calculate the VI, which was in excellent agreement with experiment for all of the isomers (≈ 10%) [79]. McCabe et al [118] performed similar simulations to calculate the VN of 9-octylheptadecane, 9-octyldocosane, and squalane using a UA force-field [117].…”

New Experimental Data and Reference Models for the Viscosity and Density of Squalane

“…[43][44][45][46][47][48][49][50][51][52] In cases where an existing experimental data set was repeated (or it appeared that the same point was not re-measured) in subsequent articles, only the original data set was included in the regression data set: 64 , where there was a very limited data set available for the development of a reference model, the abundance of experimental data for squalane made it unnecessary to include molecular simulations in this work. 37,[65][66][67][68][69][70][71][72][73] Two points from Whitmore et al (1966) 8 were not included due to the inability of converting kinematic viscosities of sub-cooled squalane (219 and 233) K.…”

Molecular dynamics simulations of the surface tension of n-hexane, n-decane and n-hexadecane

“…In these studies the models have been tested via a comparison with the experimental vapour±liquid coexistence curve. Subsequently, these models have been further validated via a comparison of the simulated and experimental di usion coe cients [7] and viscosities [8,9]. Less attention has been given to the surface tension.…”