The tribology of two potential additive molecules for aluminium has been studied in the self assembled monolayer state at low loads (10 -9-10-2 N) and in dispersion state in n-hexadecane at high load (60 N). The two additive molecules are 1H, 1H, 2H, 2H- perfluorooctyltrichlorosilane (FOTS), which has a rigid rod-like helical structure and octadecyltrichlorosilane (OTS), which has a zigzag backbone configuration. The adhesion, friction and wear performance have been investigated. Molecular conformational order and stiffness were found to play major roles in frictional dissipation and wear resistance, recorded in a nanotribometer and a pin-on-disc machine, while for very low load measurements (LFM), adhesion was found to have a significant role on friction along with molecular entropy. © 2005 Published by Elsevier Ltd.