Microscopic friction anisotropy and asymmetry related to the molecular tilt azimuth in a monolayer of glycerol ester

The molecular tilt azimuth in domains of a condensed phase in monolayers of 1-monopalmitoyl-rac-glycerol and 1-monostearoyl-rac-glycerol at the air/water interface exhibits a regular star texture. Lateral-force microscopy has been used to investigate the friction behavior of these monolayers that have been transferred onto silicon substrates. The condensed domains revealed strong friction anisotropies and asymmetries. The angular dependence of these properties correlates well with the tilt azimuth of the alkyl tails in the monolayer.