The role of lubricant molecular shape in microscopic friction
  With the help of a simple two-dimensional model we simulate the tribological properties of a thin lubricant film consisting of linear (chain) molecules in the ordinary soft-lubricant regime. We find that friction generally increases with chain length, in agreement with their larger bulk viscosity. When comparing the tribological properties of molecules which stick bodily to the substrates with others carrying a single sticking termination, we find that the latter generally yield a larger friction than the former. 
Oleg M. Braun, Nicola Manini, Erio Tosatti