Friction Force Microscopy Study of the Langmuir-Blodgett Films with Different Molecular Structures

The microscopic frictional properties of Langmuir-Blodgett (LB) films were investigated with a friction force microscope (FFM). At first, the microscopic frictional properties of LB films with different molecular structures were investigated. It is found that the friction coefficient of a tilt LB film are smaller than that of Ba arachidate. It is suggested that the friction coefficient of the LB film which alkyl chains are tilted with a large limiting area is smaller than that of the LB film with a small limiting area. Second, molecular level friction properties of behenic acid LB films were investigated. The molecular resolution image of the friction force is obtained. It is found that the FFM image shows the two dimensional regularity and the period of the regularity is 0.48 nm and 0.52 nm respectively. The period of the regularity in the FFM image is in fair agreement with that of the atomic force microscope (AFM) image. The molecular simulation of the friction force is carried out using local density functional method for LB film model system. It is found that the period of the regularity of the lateral force is consistent with that of the potential energy. This indicates that the calculated results support the experimental results.