Comparisons of Friction Characteristics of a Lightly Loaded Pin Sliding Over Magnetic Disks Coated With Polar and Non-Polar PFPE Lubricants

This paper deals with the measurement of friction force exerted on molecularly thin lubricant film surfaces using a specially arranged pin-on-disk type friction tester. The measurements were carried out by sliding a 1.5-mm-diameter glass ball slider on a rotating disk surface with small loading force. Polar and non-polar PFPE lubricants were dip-coated on magnetic disks covered with diamond-like-carbon (DLC) film. Lubricant film thickness was varied to constitute multiple layered film structures on the DLC surface. To clarify the stratified effect of thin lubricant film on friction, a lightly loading force and a slow rotational speed were selected. The tested results showed that the friction force on non-polar lubricant surfaces increase slightly for mono-layer and multi-layer cases, while the friction force on polar lubricants show steady and gradual increase with increasing loading force. We conclude that friction force at small loading force is dependent intimately on the thickness, molecular weight and end-group functionality.