Control of adhesion is a crucial aspect in the design of microelectromechanical and nanoelectromechanical devices. To understand the dependence of adhesion on nanometer-scale surface roughness, a roughness gradient has been employed. Monomodal roughness gradients were fabricated by means of silica nanoparticles (diameter ∼12 nm) to produce substrates with varying nanoparticle density. Pull-off force measurements on the gradients were performed using (polyethylene) colloidal-probe microscopy under perfluorodecalin, in order to restrict interactions to van der Waals forces. The influence of normal load on pull-off forces was studied and the measured forces compared with existing Hamaker-approximation-based models. We observe that adhesion force reaches a minimum value at an optimum particle density on the gradient sample, where the mean particle spacing becomes comparable with the diameter of the contact area with the polyethylene sphere. We also observe that the effect on adhesion of increasing the normal load depends on the roughness of the surface.

No abstract

No abstract

No abstract

Variation in sliding velocity—both in magnitude and direction—during a meshing cycle, the load distribution among the pairs of teeth, and the accuracy with which teeth are cut are some of the factors that make the mathematical analysis of friction in gear teeth extremely difficult. Of these, sliding velocity, which is responsible for the formation of an oil film between the teeth, plays an important role, and any attempt to determine the friction coefficients must take account of changes in sliding velocity. In this note an expression has been developed, considering the variation in sliding velocity, for power loss in terms of the coefficient of friction and gear parameters. The experimental results are compared with those obtained by other methods.