The effect of branching on slip and rheological properties of lubricants in molecular dynamics simulation of Couette shear flow

Molecularly thin liquid films of alkane in extreme conditions in a thin film lubrication regime have been investigated. To get an insight into the effects of molecular architecture in the behaviour of these thin lubricant films we have studied six different molecules, mainly isomers Of C-30. In this work the effect of branching on rheological properties and behaviour of lubricant film is examined. Our study shows viscosity and normal stress effects depend on the degree of branching. Dynamics of the molecules and their orientation are also affected by the degree of branching. A weaker layering near the wall is observed for branched molecules. Slip between the wall and lubricant film also was larger for branched molecules. Branched molecules had less tendency to change their orientation under the flow. The results obtained here could be helpful in designing new lubricants at the molecular level. (C) 2002 Published by Elsevier Science Ltd.