The dependence of friction and adhesion forces on normal load is investigated on surfaces with stochastically arranged, identical nano-scale structures. A nanoparticle roughness gradient, with particle diameter 12 nm, is prepared to mimic a multiple-asperity surface.Adhesion and friction measurements were conducted, along the roughness gradient, by means of polyethylene colloid-probe atomic force microscopy under perfluorodecalin. The results show that the adhesion force is proportional to the number of particles in contact and the measured friction is proportional to the observed adhesion. An abrupt increase in adhesion and friction values is observed when the colloid sphere touches the supporting substrate under low-particle-density conditions. A nonlinear dependence of friction with load is observed when the adhesion is high (high particle density).  However at low particle densities, lower adhesion result in linear dependence of friction with load . Our result shows that the obtained friction forces for rough surfaces are proportional to real area of contact, where Areal is the product of the number of particles that come in contact with the contact area between the colloidal sphere and each nanoparticle. Contact mechanics are applied and a transition from a JKR to a DMT model is seen as the particle density decreases along the gradient.

Relation between adhesion, friction, and surface roughness

244th National Meeting (2012)

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