Effect of surface patterning on the adhesive friction

Tribological properties play an important role in many applications that require low adhesion or non sticking surfaces; therefore, understanding the effect of the surface morphology on adhesion can allow for improved surfaces to be created. In the last 10 years, researchers have paid attention to the impact of the surface roughness on the tribological behaviour. As a result the idea of surface pattering or texturing has emerged as a mean of controlling the friction and adhesion between contacting surfaces. In this study, the effect of the different surface patterns with specifically selected parameters, such as the pattern size, and pattern density on the adhesion force which is measured by Atomic Force Microscope (AFM) is thoroughly investigated. First, micro laser dimples of different diameters' (D's) of 5, 10 and 20 μm are fabricated on air hardened tool steel samples using High quality-high power CuBr vapour laser. The distance (L), between the centers of two neighbouring circular dimples, were set to different values of 5, 10, 20, 40 and 80 μm. The AFM tip is modified so that the effect of the patterning on the adhesive force can be captured. A customized micro fabricated polystyrene particle of 120 μm in diameter is used as a tip attachment to the end of calibrated silicon nitride cantilever. The pull-off force versus displacement curves are recorded and used to estimate the average adhesion force for each surface pattern. It has been observed that selected surface patterns significantly decrease the adhesive forces compared to a flat surface. The ratio D/L, which represents the pattern density or the complement of the contact area establishes a well-defined trend of decrease of the adhesion force as D/L increases.