Frictional Properties of the Ultra-thin Films Constructed with Fluorocarbon Rods

We have investigated the frictional properties of the Langmuir-Blodgett (LB) films by lateral force microscope. The LB films were prepared with the amphiphiles having fluorocarbon or hydrocarbon tails. The frictional behavior was discussed as a function of the terminal atom of hydrophobic end and the size of the hydrophilic groups. The films prepared with F-terminated amphiphiles showed friction force lower than those prepared with corresponding H-terminated amphiphiles. The monolayers of the fluorinated diols gave higher friction at lower normal load. When the normal load was less than 10 nN, large hydrophilic head of diol increases the free volume around the hydrophobic chain. The large free volume accelerates energy dissipation within the monolayer, which enlarges the friction at lower load.