The Contribution of Thin PFPE Lubricants to Slider-Disk Spacing. 3. Effect of Main Chain Flexibility

We have investigated the effect of main chain flexibility of a perfluoropolyether lubricant, Zdol 4000, on dynamic slider-disk spacing. The major conclusion of this work is that increasing the Zdol chain flexibility results in a decrease in the dynamic slider-disk spacing. The Zdol main chain flexibility is quantified by ab initio computations of the barriers to internal rotation about C-O and C-C bonds in model structures containing -CF₂O- and -CF₂CF₂O- monomer units. C-O bond rotations for -CF₂O- monomer units bordered by -CF₂O- monomer units are relatively unhindered with a barrier to internal rotation of 1.7 kcal/mol. C-O and C-C bond rotations in -CF₂OCF₂CF₂O- units have barriers to internal rotation of 8 and 5 kcal/mol, respectively. The presence of the C-C bond imparts considerable rigidity to the Zdol chain.