Self-assembled monolayers of CF3-terminated alkanethiols on gold

The wettability and friction of self-assembled monolayers (SAMs) of termina lly fluorinated alkanethiols, CF3(CH2)(n)SH with n = 9-15, and their nonflu orinated analogs, CH3(CH2)(n)SH with n = 9-15, were examined and compared. Surprisingly, the CF3-terminated monolayers were wetted more by water, glyc erol and N,N-dimethylformamide than were the CH3-terminated SAMs. The termi nally fluorinated films, however, exhibited significantly lower surface ene rgies. The origin of these trends is discussed. The two types of monolayers were also studied by atomic force microscopy (AFM). Compared to the CH3-te rminated SAMs, the fluorinated films revealed an approximately 3-fold incre ase in friction. A new model for the frictional response, which is based on the difference in size between the methyl and trifluoromethyl groups, is p roposed. (C) 1999 Elsevier science B.V. All rights reserved.